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Relationship of Neozygites floridana (Entomophthorales: Entomophthoraceae) to Twospotted Spider Mite (Acari: Tetranychidae) Populations in Field Corn
Abstract
Abrupt declines in populations of Tetranychus urticae Koch are frequently associated with epizootics of the pathogen Neozygiles floridana Weiser and Muma. Use of benomyl and chlorothalonil to exclude the fungal pathogen from twospotted spider mite populations in field corn plots did not prevent this population decline. Environmental monitoring revealed that periods of cooler tempertures and high relative humidity (>90%) prevailed for ca. 40 h before a noticeable increase in the incidence of the pathogen. A small percentage (2.7) of the spider mites that dispersed from the corn on wind currents were infected with the pathogen and transported it to new host sites.
... These mites usually overwinter in grasses located in and around cornfields (Holtzer et al. 1984). In the spring and early summer these mites disperse into cornfields, often with the aid of wind currents (Brandenburg and Kennedy 1982, Margolies 1987). Late in the summer, especially under hot, dry conditions, spider mite populations can reach damaging levels where they can reduce corn yield if infestations occur during the tasseling and grain filling stages (Ehler 1974). ...
... Both the twospotted spider mite and the Banks grass mite have been widely documented to use passive aerial dispersal to move from one location to another. This method of dispersal plays a key role in the spider mite's persistence and pest status in agricultural systems (Brandenburg and Kennedy 1982, Margolies and Kennedy 1985, Margolies 1987). As previously documented, the predatory mite Neoseiulus sp. is a well-documented predator of the twospotted spider mite and the Banks grass mite on the western Great Plains (Messenger et al. 2000). ...
... These mites usually overwinter in winter annual grasses located in and around cornfields (Holtzer et al. 1984). In the spring and early summer these mites disperse into cornfields, often with the aid of wind currents (Brandenburg and Kennedy 1982, Margolies 1987). Late in the summer, especially under hot, dry conditions, spider mite populations can reach damaging levels where they can affect corn yield if infestations occur during the tasseling and grain filling stages (Ehler 1974). ...
This study evaluated whether using a cover crop with corn would increase the threat from spider mites in western Kansas because cover crops may serve as a winter host. This study also evaluated whether a cover crop could affect corn rootworm and other ground dwelling arthropods in the cornfield. In the first study, downy brome, Bromus tectorum L., was used as the winter cover crop. There were two trials repeated for three years each. Each trial included: two amounts of irrigation, downy brome, and herbicide to control weeds. In the first trial there were no significant differences in corn rootworm, Diabrotica virgifera LeConte, damage across treatments, because there were no differences in brome residue across the treatments. In the second trial, corn rootworm damage was significantly more in plots with higher amounts of downy brome residue. There were no differences in numbers of spider mites: Banks grass mites, Oligonychus pratensis (Banks) or twospotted spider mites, Tetranychus urticae Koch, across treatments. Spider mite populations appeared to be suppressed by the predatory mite Neoseiulus spp., which also overwintered in the cover crop. Corn rootworm samples taken from a no-till irrigation experiment were variable among irrigation treatments but indicated a trend for rootworm damage to increase with increasing irrigation. In the second study, winter wheat, Triticum aestivum L., was used as the winter cover crop. There were three trials repeated for three years each. Each trial included two amounts of irrigation and winter wheat and three amounts of herbicide to control weeds. Upon completion of the agronomy trials, the plots were split into two subplots and one was tilled. Pitfall traps were installed to capture ground dwelling arthropods: (Coleoptera: Carabidae), wolf spiders (Araneae: Lycosidae) and crickets (Orthoptera: Gryllidae). Four carabid genera were more common under no-till conditions. One was more common in tilled plots. Five carabid genera were more common in plots with a history of high weed densities. Two carabid genera were more numerous in plots with the history of a cover crop. Crickets were more common under no-till conditions. Wolf spiders were more common in no tillage with a history of a cover crop. Master of Science Masters Department of Entomology Larry L. Buschman, Lawrent Buschman
... A decade later, N. fl oridana was found causing epizootics in North Eastern Brazil on the red spider mite, Tetranychus evansi Baker and Pritchard on tomato (Humber et al. 1981 ). Other reports on the occurrence of N. fl oridana in spider mites included Oligonychus hondoensis Ehara on cedar in Japan (Brandenburg and Kennedy 1982 ) and Mononychellus tanajoa (Bondar) on cassava in Venezuela (Agudelo-Silva 1986 ), Kenya (Bartkowski et al. 1988 ) and Brazil (Delalibera et al. 1992 ). ...
... Natural epizootics are very common especially in spider mite populations during hot humid conditions (Humber et al. 1981 ;Brandenburg and Kennedy 1982 ). Dependence on the natural epizootics of entomophthoralean fungi and diffi culties to predict their occurrences makes them less reliable management strategy, however, in some systems (or countries) where natural epizootics are common, they still play a signifi cant role. ...
An overview of infectious microorganisms associated with pest mites is presented. Many mites are major impediments to the production of food crops either in open fields or under protected environments such as greenhouses and plastic tunnels. Reliance on chemical acaricides for management of these mites is of serious concern due to the development of resistance in mite populations, environmental disturbance and effect on human health. Several pathogens play an important role in the regulation of pest mite populations through natural epizootics. The majority of these are fungi, but other pathogens include viruses, bacteria, protozoa, and nematodes. Several successful examples of pathogens that have been produced in vitro for the control of pest mites are presented. Interaction of the pathogens with beneficial arthropods such as predatory mites is also important for implementing biological control. Prospects for the application of acaropathogens in the management of mites in various agricultural systems are discussed.
... A decade later, N. fl oridana was found causing epizootics in North Eastern Brazil on the red spider mite, Tetranychus evansi Baker and Pritchard on tomato (Humber et al. 1981 ). Other reports on the occurrence of N. fl oridana in spider mites included Oligonychus hondoensis Ehara on cedar in Japan (Brandenburg and Kennedy 1982 ) and Mononychellus tanajoa (Bondar) on cassava in Venezuela (Agudelo-Silva 1986 ), Kenya (Bartkowski et al. 1988 ) and Brazil (Delalibera et al. 1992 ). ...
... Natural epizootics are very common especially in spider mite populations during hot humid conditions (Humber et al. 1981 ;Brandenburg and Kennedy 1982 ). Dependence on the natural epizootics of entomophthoralean fungi and diffi culties to predict their occurrences makes them less reliable management strategy, however, in some systems (or countries) where natural epizootics are common, they still play a signifi cant role. ...
The Mesostigmata is a large mite order corresponding to about 20 % of all known mite species. These are found in different habitats, but are most abundant and diverse in the soil. Several mesostigmatid groups have been little studied, especially for not being abundant or for being difficult to handle, especially those living in the soil. Knowledge about the diversity of soil mites is still very small in most of the world. Considering just the number of described mesostigmatid species (let aside the number of undescribed species), the number of biological and ecological studies is very limited. Available studies most often are restricted to the evaluation of the ability of particular species to feed on pre-determined food sources. A few have received some attention, among which two superfamilies of the infraorder Gamasina, Rhodacaroidea (in the hyporder Dermanyssiae) and Parasitoidea (in the hyporder Parasitiae). This chapter comprises the biological and ecological information regarding the Mesostigmata.
... In the southern states of the USA, the factors leading to outbreaks of N. Xoridana in spider mites on ® eld crops are being determined. Disease outbreaks are periodic and are triggered by a drop in the maximum daily temperature to below 29ë C and an elevation in humidity, usually caused by rain (Brandenburg & Kennedy, 1982). Epizootics usually start in mid summer and cause declines in mite populations in mid-August to September. ...
... In North Carolina, RH in excess of 90% for ca. 40 h (minimum 5 h per day) was required for fungalinduced population decline of T. urticae on maize (Brandenburg & Kennedy, 1982;Smitley et al., 1986b), but leaf wetness was not required for fungal activity (Smitley et al., 1986a). Although high humidity is necessary to trigger epizootics, some infection can also occur during dry periods if capilliconidia have already been formed (Dick & Buschman, 1995). ...
Mites and ticks are susceptible to pathogenic fungi, and there are opportunities to exploit these micro-organisms for biological control. We have collated records of 58 species of fungi infecting at least 73 species of Acari, either naturally or in experiments. Fungal pathogens have been reported to kill representatives of all three orders of the Actinotrichida (the Astigmata, Oribatida and Prostigmata) and the Ixodida and Mesostigmata in the Anactinotrichida. Most reports concern infections in the Prostigmata, particularly in the families Tetranychidae and Eriophyidae. Two species of Acari-specific pathogens - Hirsutella thompsonii and Neozygites floridana - are important natural regulators of pestiferous eriophyoid and tetranychid mites respectively. Research has been done to understand the factors leading to epizootics of these fungi and to conserve and enhance natural pest control. Hirsutella thompsonii was also developed as the commercial product Mycar for the control of eriophyoid mites on citrus, but was withdrawn from sale in the 1980s, despite some promising effects in the field. Beauveria bassiana , Metarhizium anisopliae, Paecilomyces farinosus, Paecilomyces fumosoroseus and Verticillium lecanii infect ixodid ticks in nature, and B. bassiana and M. anisopliae are being studied as biological control agents of cattle ticks in Africa and South America. Beauveria bassiana also has potential as a mycopesticide of the two-spotted spider mite, Tetranychus urticae . There is scope to develop fungal biocontrol agents against a range of acarine pests, both as stand-alone treatments and for use in integrated pest management. Further research is required to clarify the taxonomic status of fungal pathogens of Acari, to study their ecosystem function, and to develop efficient mass production systems for species of Hirsutella and Neozygites .
... e the fungus completes colonization of the host. At the late stage of Neozygites infection, the dead mite is filled with fungal hyphal bodies and becomes mummified. The fungus actively discharges the conidia from the host when conditions are favorable. The favorable conditions are usually mild temperatures and high humidity (Oduor et al., 1996a,b). Brandenburg and Kennedy (1982) observed that epizootics of N. floridana on Tetranychus urticae populations in field corn were preceded by 2 days of high relative humidity and mild temperatures . Other authors also associated the production of primary and secondary conidia of N. floridana with relative humidity close to 100% (Selhime and Muma, 1966; Saba, 1974; Carner ...
... Wekesa et al. (2008) verified under laboratory study that Captan has a negative effect on the sporulation and germination of N. floridana and may reduce transmission and epizootic development. The direct effect of pesticides on natural epizootics has also been reported (Brandenburg and Kennedy, 1982; Boykin et al., 1984). It was not possible to identify the source of initial foci of N. floridana . ...
The tomato red spider mite, Tetranychus evansi (Acari: Tetranychidae) was recently introduced in Africa and Europe, where there is an increasing interest in using natural enemies to control this pest on solanaceous crops. Two promising candidates for the control of T. evansi were identified in South America, the fungal pathogen, Neozygites floridana and the predatory mite Phytoseiulus longipes. In this study, population dynamics of T. evansi and its natural enemies together with the influence of environmental conditions on these organisms were evaluated during four crop cycles in the field and in a protected environment on nightshade and tomato plants with and without application of chemical pesticides. N. floridana was the only natural enemy found associated with T. evansi in the four crop cycles under protected environment but only in the last crop cycle in the field. In the treatments where the fungus appeared, reduction of mite populations was drastic. N. floridana appeared in tomato plants even when the population density of T. evansi was relatively low (less than 10 mites/3.14cm2 of leaf area) and even at this low population density, the fungus maintained infection rates greater than 50%. The application of pesticides directly affected the fungus by delaying epizootic initiation and contributing to lower infection rates than unsprayed treatments. Rainfalls did not have an apparent impact on mite populations. These results indicate that the pathogenic fungus, N. floridana can play a significant role in the population dynamics of T. evansi, especially under protected environment, and has the potential to control this pest in classical biological control programs.
... A fungal pathogen, Neozygites sp. has been reported to cause epizootics in this pest in South America (Agudelo-Silva, 1986; Delalibera et aL, 1992). Since Entomophthora ( = Triplosporium = Neozygites) spp. was reported to attack Eutetranychus banksi (Weiser and Muma, 1966), its association with various tetranychid mites has been the subject of widespread research (Selhime and Muma, 1966;Carner and Canerday, 1968;Kenneth et al., 1972;Nemoto and Aoki, 1975;Carner, 1976;Brandenburg and Kennedy, 1982;Smitley et al., 1986;Klubertanz et al., 1991;Mietkiewski et al., 1993). Epizootics of this fungus have been observed to occur during periods of high atmospheric moisture (> 90% RH) and temperatures below 30°C (Carner and Canerday, 1968;Humber et al., 1981;Brandenburg and Kennedy, 1982;Smitley et al., 1986). ...
... Since Entomophthora ( = Triplosporium = Neozygites) spp. was reported to attack Eutetranychus banksi (Weiser and Muma, 1966), its association with various tetranychid mites has been the subject of widespread research (Selhime and Muma, 1966;Carner and Canerday, 1968;Kenneth et al., 1972;Nemoto and Aoki, 1975;Carner, 1976;Brandenburg and Kennedy, 1982;Smitley et al., 1986;Klubertanz et al., 1991;Mietkiewski et al., 1993). Epizootics of this fungus have been observed to occur during periods of high atmospheric moisture (> 90% RH) and temperatures below 30°C (Carner and Canerday, 1968;Humber et al., 1981;Brandenburg and Kennedy, 1982;Smitley et al., 1986). These observations suggest that prevailing atmospheric conditions affect the development of the fungal pathogen. ...
The effect of temperature, humidity and photoperiod on the development of Neozygites cf. floridana (Weiser and Muma) in the cassava green mite, Mononychellus tanajoa (Bondar) was studied in the laboratory. Dead infected mites began to appear 2.5 days after inoculation. At 33 and 28C peak mortalities were higher and occurred earlier (after 2.5 days), than at 23 and 18C. Mean LT50 (time for half the infected mites to die) decreased with increasing temperature as follows: 3.9, 3.0, 2.9 and 2.5 days at 18, 23, 28 and 33C, respectively. When placed under conditions of high relative humidity for a period of 24 h, the percentage of dead infected mites from which the fungus sporulated was highest at 28C (51.4%) and lowest at 33C (6.5%). The development of the fungus inside the mite was not significantly affected by ambient humidity or photoperiod. No significant interactions between tested factors were found.
... have worldwide distributions and are often responsible for wide-scale epizootics (Fuxa, 1987). Although natural epizootics are well documented (Brandenburg & Kennedy, 1982;Ríos-Velasco et al., 2010;Moura-Mascarin et al., 2016), the inherent biological processes involved in the interactions between the fungal pathogen and the insect pest are not completely understood. In their natural state, in which epizootics are produced, some soil EF like Metarhizium sp. could act as a multisporic organism rather than a monosporic isolate. ...
Currently only monosporic strains from several entomopathogenic fungi have been selected and used for mass production and bioinsecticide manufacturing worldwide. The main reasons for the use of single spore instead of multispore strains are the attenuated
virulence and the contaminants of the same species. In this study, different polisporic isolates and their monosporic combinations were tested against Tenebrio molitor (L.) larvae as an insect model. Isolates were obtained from arid soils. Four Metarhizium sp. (Metschn.)
multisporic isolates (CEP413, CEP589, CEP590 and CEP591) were selected for bioassays. Trials were performed to evaluate mortality on three treatments, Full Polisporic (FP), Partial Polisporic (PP) and Pure Monosporic (PM). Cumulative mortality was measured at day 4 post
infection. Sporulation percentage was assessed at day 6 post infection. The highest mortality was found at FP treatment (94%), the lowest mortality at day 4 was found at PM-CEP413 (32%). At day 6 the sporulation percentage was higher on FP (94%) and it was different
from the rest of the treatments. To elucidate different polisporic and monosporic combinations to improve their effectiveness, may help to expand the use of bioinsecticides based on entomopathogenic fungi.
... The optimum conditions for entomopathogenic fungi are temperatures between 20 and 30ºC and high relative humidity. However, despite these climatic constraints, Neozygites epizootics occur (Roberts andCampbell 1977, Brandenburg andKennedy 1982). Field studies have shown that the entomopathogenic fungus Neozygites floridana is associated with dramatic declines in the abundance of Tetranychus urticae, and in North Carolina they appear all summer, regardless of environmental conditions or mite densities (Carner andCanerday 1970, Boykin et al. 1984). ...
The woolly poplar aphid, Phloeomyzus passerinii, causes severe damage to poplars in Southern Europe and Asia, where outbreaks of this pest can lead to massive mortality of trees in mature stands. In Chile, this aphid was reported for the first time in 1997 in plantations of Populus nigra. During April 2016 and again in March 2017 (autumn season), several mycosed individuals were found attached to the poplars’ twigs. The fungus was identified as a Neozygites species by its characteristic morphology with subglobose primary conidia, 19.8 ± 0.4 × 16.1 ± 0.4 μm, with a small, flat papilla, produced on the surface of cadavers, and capilliconidia that are almond shaped but rarely observed, 21.7 ± 0.8 × 14.4 ± 0.6 μm. The resting spores were subglobose, 26.3 ± 0.5 × 21.2 ± 0.5 μm, black in mass, with a thick more or less smooth-surfaced wall, and formed inside the aphid. Neozygites comprises a relatively homogeneous group of species exclusively pathogenic to arthropods. Their narrow host ranges make them potentially valuable biocontrol agents. This is the first report worldwide of any Neozygites on P. passerinii.
... The optimum conditions for entomopathogenic fungi are temperatures between 20 and 30ºC and high relative humidity. However, despite these climatic constraints, Neozygites epizootics occur (Roberts andCampbell 1977, Brandenburg andKennedy 1982). Field studies have shown that the entomopathogenic fungus Neozygites floridana is associated with dramatic declines in the abundance of Tetranychus urticae, and in North Carolina they appear all summer, regardless of environmental conditions or mite densities (Carner andCanerday 1970, Boykin et al. 1984). ...
... have worldwide distributions and are often responsible for wide-scale epizootics (Fuxa, 1987). Although natural epizootics are well documented (Brandenburg & Kennedy, 1982;Ríos-Velasco et al., 2010;Moura-Mascarin et al., 2016), the inherent biological processes involved in the interactions between the fungal pathogen and the insect pest are not completely understood. In their natural state, in which epizootics are produced, some soil EF like Metarhizium sp. could act as a multisporic organism rather than a monosporic isolate. ...
https://doi.org/10.25085/rsea.763406 Currently only monosporic strains from several entomopathogenic fungi have been selected and used for mass production and bioinsecticide manufacturing worldwide. The main reasons for the use of single spore instead of multispore strains are the attenuated virulence and the "contaminants" of the same species. In this study, different polisporic isolates and their monosporic combinations were tested against Tenebrio molitor (L.) larvae as an insect model. Isolates were obtained from arid soils. Four Metarhizium sp. (Metschn.) multisporic isolates (CEP413, CEP589, CEP590 and CEP591) were selected for bioassays. Trials were performed to evaluate mortality on three treatments, Full Polisporic (FP), Partial Polisporic (PP) and Pure Monosporic (PM). Cumulative mortality was measured at day 4 post infection. Sporulation percentage was assessed at day 6 post infection. The highest mortality was found at FP treatment (94%), the lowest mortality at day 4 was found at PM-CEP413 (32%). At day 6 the sporulation percentage was higher on FP (94%) and it was different from the rest of the treatments. To elucidate different polisporic and monosporic combinations to improve their effectiveness, may help to expand the use of bioinsecticides based on entomopathogenic fungi.
... Neozi/gitcs sp. epizootics can build up rapidly in two-spotted spider mite populations when humidity is high (Brandenburg & Kennedy, 1982;Klubertanz et al., 1991). Another fungus, Verticillium sp., which caused H. destructor mortality in the laboratory (Ridsdill-Smith & Gaull, 1995), was not found attacking mites in pastures. ...
Seasonal occurrence and abundance of redlegged earth mite, Halotydeus destructor (Tucker), was measured by weekly sampling in grazed annual pastures near Keysbrook (1990–1992) and Narrogin (1991–1992) in southwestern Australia. Mites were active for 27 weeks from the late autumn (May) to mid-spring (October), completing three generations at approximately 8 week intervals. The summer is spent as diapause eggs in the cadavers of adult female mites. In 1991 and 1992, active H. destructor was on average twice as abundant at Keysbrook (mean 11,300 mites/m2), as at Narrogin (mean 6400 mites/m2). Three times more eggs were laid at Keysbrook than Narrogin (mean 8500 and 2900 eggs/m2 respectively). Rainfall at Keysbrook was twice that at Narrogin, and temperatures were higher. We suggest that the rate of oviposition was less at Narrogin, probably because of resource limitation. The mature adult sex ratio was female biased, but was lower at Keysbrook (0.669) than at Narrogin (0.813). Neozygites acaridis, a fungal disease, was detected in less than 4% of the population, mainly in adult mites in late spring. Rainfall and temperatures were lower in the spring of 1992 than 1991 at both sites. Pasture was grazed considerably shorter in the spring of 1992, and numbers of H. destructor were lower, but numbers of eggs laid in the two years were similar. We suggest that active mite mortality was greater in spring of 1992, probably due to lower relative humidity. There were fewer adult mites in spring, and fewer diapausing eggs in summer at both sites in 1992 (36,600 diapause eggs/m2) than in 1991 (148,000 diapause eggs/m2). It is proposed that controlling mites in spring should lead to lower numbers of diapause eggs in summer and of mites emerging in autumn.
... In 1981 and 1982 this decline was coincident with a period of rainy weather, and many mites appeared to be infected with a fungal pathogen, Neozygites floridana Weiser & Muma, during and immediately following the population decline. Brandenburg & Kennedy (1982b) and Smitley (personal communication) have found that epizootics caused by this pathogen, which can rapidly reduce mite populations, are typically associated with periods of wet weather. It is likely that an epizootic of N. floridana rather than dispersal was responsible for the observed declines in mite populations on corn in 1981 and 1982, given the low aerial trap catches, the incidence of rain, and the concommitant appearance of fungus-infected mites. ...
A 3 year study of spider mites in a corn-peanut agroecosystem indicated that the persistance and pest status of mite populations depended on dispersal among a succession of temporarily suitable cultivated and non-cultivated hosts. In the spring, mites crawled from overwintering sites in vegetation along field margins into both peanut and corn fields, but became established only in corn. Initiation of aerial dispersal from corn was coincident with and appeared dependent upon mites moving to the top of the corn canopy, where they were exposed to the wind. Mites were first observed in peanut immediately following the onset of aerial dispersal from corn, and these aerial dispersers were the primary source of subsequent mite infestations in peanut. As populations grew in peanut, mites dispersed into vegetation along peanut field margins and became the nucleus of populations which persisted over the winter. This pattern of host utilization was reinitiated in the spring if corn was planted adjacent to infested field borders. This pattern commonly occurs since corn is planted following peanut in the predominant crop rotation sequence in this area.
Déplacements de Tetranychus urticae Koch parmi ses hôtes dans un système agricole avec maïs et arachide
Des populations d'acariens ont été étudiées pendant 3 ans sur maïs, arachide et végétation spontanée, dans 7 fermes commerciales de Chowan Co., Caroline du Nord. Les déplacements d'acariens parmi ces plantes ont été notés en fonction de la croissance de la population et de la phénologie des hôtes. Un schéma cohérent de croissance de la population d'acariens et de leurs mouvements en découle, dont seule la taille change suivant les fermes et les années. Les acariens provenant de populations hivernantes sur la végétation spontanée bordant les champs migrèrent dans les champs cultivés adjacents quelle qu'en soit la nature de la culture. Cependant, à cette époque, les populations d'acariens ne s'établissaient que dans le maïs. Dans le maïs, les acariens se répandirent à travers le champ et se multiplièrent sur des pieds particuliers jusqu'à ce qu'ils eussent atteint le sommet de la canopée du maïs. Les premiers acariens transportés par le vent ont été capturés la semaine suivant la première apparition d'acariens au sommet de la canopée du maïs et aussitôt après la découverte des premiers acariens dans les arachides voisines. Ceci suggère que les acariens dispersés par le vent sont à l'origine des contaminations ultérieures des arachides voisines. Plus tard dans la saison, les acariens se dispersèrent à partir de l'arachide vers les sites d'hibernation dans la végétation spontanée poussant autour du champ d'arachide. Puisque des champs semés en arachides sont généralement semés en maïs l'année suivante, les acariens se dispersant au printemps depuis les sites d'hibernation rencontrèrent souvent du maïs qu'ils colonisèrent. Ce cycle répétitif d'utilisation de l'hôte et de dispersion est considéré comme fortement responsable de la pérennité des acariens et de leur danger potentiel dans les agroécosystèmes à maïs-arachide, caractéristiques du canton de Chowan (N.C.).
Les problèmes potentiels posés par les acariens sur arachide ont paru être liés à l'intensité de l'attaque d'acariens sur le maïs voisin, qui sert de réservoir pour les populations d'acariens. Ceci suggère que le contrôle des populations d'acariens sur maïs peut être une stratégie viable pour limiter les infestations ultérieures sur arachide et, en dernier lieu, les populations hivernantes.
... If these males are carriers of the fungus they may promote its spread by increasing the contact rate with healthy mites. Whether the spread of the fungus is promoted by the dispersal of infected females or males is not known, but it is a distinct possibility as shown by the observation of Brandenburg and Kennedy (1982) that some of the two-spotted spider mites (Tetranychus urticae Koch) migrating between corn plants were infected with N. floridana. Whether this leads to maximal transmission, remains to be investigated, but under this assumption our model reflects the most favourable conditions for a fungal epidemic and, hence, may overestimate the capacity of the fungus to suppress the local host population. ...
The fungus, Neozygitis cf. floridana is parasitic on the cassava green mite, Mononychellus tanajoa (Bondar) (Acari: Tetranychidae)
in South America and may be considered for classical biological control of cassava green mites in Africa, where cassava is
an important subsistence crop, cassava green mites are an imported pest and specific natural enemies are lacking. Spider mites
generally have a viscous structure of local populations, a trait that would normally hamper the spread of a fungus that is
transmitted by the contact of susceptible hosts with the halo of capilliconidia surrounding an infectious host. However, if
infected mites search and settle to produce capilliconidia on sites where they are surrounded by susceptible mites before
becoming infectious, then the conditions for maximal transmission in a viscous host population are met. Because the ratio
between spider mites and the leaf area they occupy is constant, parasite-induced host searching behaviour leads to a constant
per capita transmission rate. Hence, the transmission rate only depends on the number of infectious hosts. These assumptions
on parasite-induced host search and constant host density lead to a simple, analytically tractable model that can be used
to estimate the maximal capacity of the fungus to decimate local populations of the cassava green mite. By estimating the
parameters of this model (host density, per capita transmission rate and duration of infected and infectious state) it was
shown that the fungal pathogen can reduce the population growth of M. tanajoa, but cannot drive local mite populations to
extinction. Only when the initial ratio of infectious to susceptible mites exceeds unity or the effective growth rate of the
mite population is sufficiently reduced by other factors than the fungus (e.g. lower food quality of the host plant, dislodgement
and death by rain and wind and predation), will the fungal pathogen be capable of decimating the cassava green mite population.
Under realistic field conditions, where all of these growth-reducing factors are likely to operate, there may well be room
for effective control by the parasitic fungus.
... The only fungal pathogen that has been frequently found causing natural mortality in spider mites is Neozygites floridana Weiser and Muma (Entomophthorales). N. floridana is a virulent fungus which causes regular epizootics in populations of spider mites in various crops (Humber et al., 1981; Brandenburg and Kennedy, 1983; Carner and Canerday, 1970 ) and its potential to control spider mites has already been demonstrated (Brandenburg and Kennedy, 1982; Wekesa et al., 2007). The isolates of this fungus can be collected as mycosed cadavers of mites during epizootics and used as primary inocula for in vivo production under laboratory 0022-2011/$ -see front matter Crown Copyright Ó 2009 Published by Elsevier Inc. ...
The fungal pathogen Neozygites floridana Weiser and Muma has been evaluated as a classical biological candidate for introduction into Africa against the invasive tomato red spider mite Tetranychus evansi Baker and Pritchard. In this study, the effect of temperature on sporulation, germination and virulence of three isolates of N. floridana collected from T. evansi in three climatically distinct regions of Brazil and Argentina was determined. Six constant temperatures of 13 degrees C, 17 degrees C, 21 degrees C, 25 degrees C, 29 degrees C and 33 degrees C were tested for their effect on the ability of the three fungal isolates to sporulate, germinate and kill the mites. Six alternating-temperature regimes of 17-13 degrees C, 21-13 degrees C, 29-13 degrees C, 33-13 degrees C, 33-23 degrees C, 33-28 degrees C under a 12h photophase were also tested to estimate virulence of the three isolates against T. evansi. The Vipos isolate discharged more conidia than isolates from Recife or Piracicaba at all temperatures and sporulation was strongly temperature dependent. Optimal sporulation rates were observed at 25 degrees C while optimal germination rates were observed at 25 degrees C and 29 degrees C. At 29 degrees C, the shortest mean survival time of T. evansi (3.16 days, 95% CI of 3.05-3.27) was observed for the isolate from Vipos, while the longest LT(50) (3.47 days, 95% CI 3.34-3.59) was observed for the isolate from Piracicaba. Mortality of mites increased as the differences between alternating day and night temperatures increased from 8 degrees C (21-13 degrees C), to 10 degrees C (33-23 degrees C), to 16 degrees C (29-13 degrees C), with smallest and highest temperature differences of 4 degrees C (17-13 degrees C) and 20 degrees C (33-13 degrees C), both producing low mortalities. The overall results suggest that the Vipos isolate is better adapted to a wider range of temperatures than the other isolates tested.
... N. floridana has been reported infecting populations of the twospotted spider mite, Tetranychus urticae Koch, worldwide (Brandenburg and Kennedy, 1982;Boykin et al., 1984;Nordengen and Klingen, 2006). Because of the economic importance of T. urticae in many horticultural crops (Jeppson et al., 1975) and the fact that it has developed resistance to several pesticides, most of the investigations with N. floridana aimed to evaluate the potential of this fungus as a biological alternative to control T. urticae. ...
Neozygites floridana (Weiser & Muma) (Zygomycetes: Entomophthorales) has been reported infecting naturally at least 18 species of tetranychids worldwide. However, the host range of N. floridana is unknown. Epizootics caused by this pathogen to tetranychid populations indicate that N. floridana has the potential to be used as a biological control agent. However, the virulence and specificity of species and strains of Neozygites need to be assessed in the laboratory to reveal its potential as a biological control agent. N. floridana isolates are currently been investigated in Brazil as biological control agents against the tomato red mite, Tetranychus evansi Baker & Pritchard, and the two-spotted spider mite, Tetranychus urticae Koch. The pathogenicity of five strains of N. floridana obtained from T. urticae, T. evansi and T. ludeni Zacher was assessed against populations of Mononychellus tanajoa (Bondar), Schizotetranychus sacharum Flechtmann & Baker, Tetranychus abacae Baker & Pritchard and Tetranychus armipenis Flechtmann & Baker, in addition to the species from which the fungus was obtained. Mummified mites were placed on leaf discs of the host plant of each tetranychid to promote fungal sporulation, and after 24h the mites were transferred to the leaf discs. Contamination, infection and mummification were evaluated daily for seven days after confinement. Each isolate was pathogenic to three or four out of the six spider mite species tested. However, except for isolate ESALQ1421, all isolates caused higher levels of infection and significant mummification only to the tetranychid species from which they were collected. None of the isolates was pathogenic to S. sacharum and only one isolate infected T. abacae. Alternative hosts may be important for N. floridana survival in tropical regions where resting spores are rarely found.
... Suppression and reduction of the infection level of N. Xoridana in T. urticae populations by the fungicide benomyl (a benzimidazole) have been reported in bean and corn Welds ( Kennedy 1982, 1983 ). Other fungicides, such as chlorothalonil, mancozeb and maneb also reduced the infection level of N. Xoridana in T. urticae populations infesting corn and peanut Welds (Brandenburg and Kennedy 1982; Boykin et al. 1984; Smitley et al. 1986). Klingen and Westrum (2007) compared the eVect of diVerent pesticides (fungicides, insecticides, acaricides and molluscicides) used in strawberry plantation on N. Xoridana. ...
The spider mites Tetranychus urticae Koch and Tetranychus evansi Baker and Pritchard are important pests of horticultural crops. They are infected by entomopathogenic fungi naturally or experimentally. Fungal pathogens known to cause high infection in spider mite populations belong to the order Entomophthorales and include Neozygites spp. Studies are being carried out to develop some of these fungi as mycoacaricides, as stand-alone control measures in an inundative strategy to replace the synthetic acaricides currently in use or as a component of integrated mite management. Although emphasis has been put on inundative releases, entomopathogenic fungi can also be used in classical, conservation and augmentative biological control. Permanent establishment of an exotic agent in a new area of introduction may be possible in the case of spider mites. Conservation biological control can be achieved by identifying strategies to promote any natural enemies already present within crop ecosystems, based on a thorough understanding of their biology, ecology and behaviour. Further research should focus on development of efficient mass production systems, formulation, and delivery systems of fungal pathogens.
... Neozygites floridana has subsequently been observed on several species of spider mites on various agricultural crops. For example, it was reported on T. tumidus on cotton (Saba, 1971), on T. evansi on tomato in Brazil (Humber et al., 1981), on T. ludeni on bean in India (Rameseshiah, 1971) on Oligonychus hondoensis on cedar in Japan (Nemoto and Aoki, 1975), on T. urticae on field corn in North Carolina, USA (Brandenburg and Kennedy, 1982) and on the cassava green mite, Mononychellus tanajoa, in Venezuela (Agudela-Silva, 1986) and in Brazil (Delalibera et al., 1992). Some of these reports concern only observations without details on the effect that the fungus may cause to spider mite populations. ...
An overview is given of studies on diseases of mites. Knowledge of diseases of mites is still fragmentary but in recent years more attention has been paid to acaropathogens, often because of the economic importance of many mite species. Most research on mite pathogens concerns studies on fungal pathogens of eriophyoids and spider mites especially. These fungi often play an important role in the regulation of natural mite populations and are sometimes able to decimate populations of phytophagous mites. Studies are being conducted to develop some of these fungi as commercial acaricides. Few bacteria have been reported as pathogens of the Acari but in recent years research has been concentrated on intracellular organisms such as Wolbachia that may cause distorted sex ratios in offspring and incompatibility between populations. The role of these organisms in natural populations of spider mites is in particular discussed. The effect of Bacillus thuringiensis on mites is also treated in this review, although its mode of action in arthropods is mainly due to the presence of toxins and it is, therefore, not considered to be a pathogen in the true sense of the word. Microsporidia have been observed in several mite species especially in oribatid mites, although other groups of mites may also be affected. In recent years, Microsporidia infections in Phytoseiidae have received considerable attention, as they are often found in mass rearings of beneficial arthropods. They affect the efficacy of these predators as biological control agent of insect and mite pests. Microsporidia do not seem to have potential for biological control of mites.
This is my Dissertation of PhD. It has been reviewed by Dr John R Ruberson of Department of Entomology, University of Nebraska, Lincoln, Nebraska, USA, and by Dr. Kenneth Ostlie of Department of Entomology, University of Minnesota, St. Paul, Minnesota, USA. The dissertation is not published yet.
Background
The beneficial fungus Neozygites floridana kills the two-spotted spider mite Tetranychus urticae, which is a serious polyphagous plant pest worldwide. Outbreaks of spider mites in strawberry and soybean have been associated with pesticide applications. Pesticides may affect N. floridana, and, consequently, the natural control of T. urticae. N. floridana is a fungus difficult to grow in artificial media; for these reasons, very few studies have been conducted with this fungus, especially regarding the impact of pesticides. The aim of this study was to conduct a laboratory experiment to evaluate the effect of pesticides used in strawberry and soybean crops on N. floridana.
Results
Among the pesticides used in strawberry, the fungicides sulfur and cyprodinil + fludioxonil completely inhibited both the sporulation and conidia germination of N. floridana. The fungicide fluazinam affected N. floridana drastically. The application of the fungicide tebuconazole and the insecticides fenpropathrin and abamectin resulted in a less pronounced negative effect on N. floridana. Except for epoxiconazole and cyproconazole, all tested fungicides used in soybean resulted in a complete inhibition of N. floridana. Among the three insecticides used in soybean, lambda-cyhalothrin and deltamethrin resulted in a significant inhibition of N. floridana.
Conclusion
The insecticides abamectin / lambda-cyhalothrin at half concentrations and fenpropathrin / permethrin and the fungicide tebuconazole at the recommended concentrations resulted in the lowest impact on N. floridana. The sulfur fungicides, cyprodinil + fludioxonil, azoxystrobin, azoxystrobin + cyproconazole, trifloxystrobin + tebuconazole and pyraclostrobin + epoxiconazole negatively affected N. floridana.
The two-spotted spider mite, Tetranychus urticae Koch is a major pest that feeds on >1,100 plant species. Many perennial crops including hop (Humulus lupulus) are routinely plagued by T. urticae infestations. Hop is a specialty crop in Pacific Northwest states, where 99% of all U.S. hops are produced. To suppress T. urticae, growers often apply various acaricides. Unfortunately T. urticae has been documented to quickly develop resistance to these acaricides which directly cause control failures. Here, we investigated resistance ratios and distribution of multiple resistance-associated mutations in field collected T. urticae samples compared with a susceptible population. Our research revealed that a mutation in the cytochrome b gene (G126S) in 35% tested T. urticae populations and a mutation in the voltage-gated sodium channel gene (F1538I) in 66.7% populations may contribute resistance to bifenazate and bifenthrin, respectively. No mutations were detected in Glutamate-gated chloride channel subunits tested, suggesting target site insensitivity may not be important in our hop T. urticae resistance to abamectin. However, P450-mediated detoxification was observed and is a putative mechanism for abamectin resistance. Molecular mechanisms of T. urticae chemical adaptation in hopyards is imperative new information that will help growers develop effective and sustainable management strategies.
Surveys were made in southwestern Kansas to identify and establish relative abundances of predaceous arthropod species associated with the Banks grass mite (BGM). Oligonychus pratensis (Banks), in field corn and in the surrounding vegetation. A two-year experiment also was done to determine whether the release in the spring of commercially produced predatory mites (Acari: Phytoseiidae) in grasses adjacent to corn field borders would enhance BGM suppression over that in corn fields where no predators were released. In 1996, the release of Neoseiulus fallacis (Garman), Neoseiulus californicus (McGregor), and Galandromus occidentalis Nesbitt in roughly equal proportions at a ratio of 1 predator per 24 BGM did not significantly reduce pest mites compared to control fields. Releases in 1997 of only N. californicus at a 1:1 predator to prey ratio also did not have a significant impact on BGM populations. Berlese samples in corn and in alternate hosts 2 weeks after release failed to recover N. californicus or G. occidentalis in experimental fields, and neither predator occurred naturally in control (nonrelease) fields. Neoseiulus fallacis was recovered in both release and control fields in 1996 and 1997, but could not be distinguished from native populations. In addition to N. fallacis, four other species of naturally occurring phytoseiids were collected: Neoseiulus comitatus (DeLeon), Neoseiulus setulus (Fox), Proprioseiopsis ovatus Garman, and Amblyseiella setosa Muma. All five phytoseiids were recovered in corn and in alternate host vegetation. However, N. fallacis was the most abundant phytoseiid in corn and its population densities were significantly correlated with BGM populations. The insidious flower bug. Orius insidiosus Say (Hemiptera: Anthocoridae), was also a relatively abundant predator in corn, but its populations were not significantly correlated with those of the BGM. Several other species of predators suspected to attack BGM are reported.
The entomopathogenic fungus Beauveria bassiana (Balsamo) as control agent of European red mite, Panonychus ulmi Koch, citrus rust mite Phyllocoptruta oleivora (Ashmed), and two-spotted spider mite Tetranychus urticae Koch was investigated. Fungal spore suspensions at 2×106 and 2×108 spores/ml were applied to P. ulmi and Ph. oleivora. Mite mortality increased with an increase in spore concentration and exposure time; 14 days after treatment with 2×106 and 2×108 spores/ml, average mortality was 62.5 and 83.3% for P. ulmi, and 82.6 and 91.7% for Ph. oleivora, respectively. Spore suspension (2×108) was applied to citrus fruits and leaves to control citrus rust mite under field conditions. Seven days after spraying fruits and leaves, respectively, reduction of the mite population was 74.9 and 72.5%, and after 14 days 83.8 and 85.8%. Spore suspension (2×106) was also applied to cotton plants (cultivars Giza 70, 45, and 83) in the field, to control T. urticae. Spider mites on Giza 45 were more susceptible to fungus treatment than on the other two cultivars; 14 days after treatment, the mite population was reduced by 67.9, 78.4, and 66.5% on Giza 70, 45, and 83, respectively.
Neozygites parvispora was isolated from Tbrips tabaci infesting leek plants. In vitro cultivation of two isolates was achieved using supplemented Grace's insect tissue culture medium complemented with fetal bovine serum (FBS) and pre-treated lepidopteran hemolymph. This medium composition enabled exponential cell growth as rod-shaped hyphal bodies with a length over diameter ratio of 4.5-5.0. Both FBS and hemolymph were mandatory for sustained growth. The growth requirements indicate the presence of one or several growth factors in both the hemolymph and FBS. Absence of FBS resulted in growth arrest with subsequent cell lysis. Omission of hemolymph led to rounding and size decrease of the hyphal bodies, some of which formed septated germ tubes in a later stage. Eventually, cell death occurred under such conditions. Hyphal bodies from in vitro culture were capable of capilliconidia formation after entrapment in alginate pellets. This suggests the requirement of a liquid/air interface, which triggers primary sporulation and subsequent capilliconidium formation.
Primary and secondary conidia of Neozygites floridana were produced in the greatest numbers at 15° to 26°C and at 100% RH. No conidia were produced at 32°C or at or below 85% RH. When twospotted spider mites, Tetranychus urticae, were released on bean leaves previously infested with capilliconidia, temperature had little effect on the incidence of infection (RH was held at 90–95%). In a similar test at 30% RH, no mites became infected at any temperature. Apparently RH is more important than temperature in determining the longevity of previously established capilliconidia. Infected mites maintained at 10°, 20°, 30°, and 37°C died within 15, 5, 4, and 7 days, respectively. Epizootics of N. floridana were induced in the greenhouse by 14-hr periods of approximately 100% RH per day, but not by 30 min of simulated rain when the water was applied without an associated period of 100% RH.
An overview is given of diseases in mites, caused by infectious microorganisms. Many pathogens play an important role in the
regulation of natural populations of mite populations and are for this reason subject of research on the feasibility to develop
such pathogens to biological control agents. Several examples are given of successful application of pathogens for the control
of mite pests, but also failures are discussed. Most studies concern fungal pathogens of tetranychids and eriophyids; some
of these fungi are possible candidates for biological control agent of species of noxious mites. An interesting group of pathogens
form the intracellular symbionts: bacteria that may cause unusual effects in their hosts, such as parthenogenesis, feminization,
male killing and incompatibilities. This group of bacteria is present in many invertebrates species and are presently widely
studied as new molecular techniques have become available that make detection of such symbionts possible. Attention is also
given to quality control of beneficial mites that are being used in integrated control programs. Beneficial mites, as e.g.
predatory mites, may also be infected by microorganisms (bacteria, viruses, microsporidia), resulting in poor performance
of the predator. Prospects for the application of pathogens in IPM systems are discussed.
In field plots in which populations of predaceous species were suppressed using carbaryl, populations of the twospotted spider mite, Tetranychus urticae Koch, on field corn declined in association with aerial dispersal of the mites or with epizootics of the entomogenous fungus, Neozygites floridana Weiser & Muma. The relative importance of these two factors varied from year to year depending on environmental conditions. When moist weather conditions induced epizootics of N. floridana before corn plants became heavily infested with mites, the pathogen appeared to be the major factor causing mite population declines. When dry weather conditions allowed mite populations to expand unchecked until corn plants became entirely infested, mite aerial dispersal was the major factor associated with mite population declines. In every field in which there was an epizootic of N. floridana, routine applications of the fungicide maneb delayed epizootics and reduced or delayed the impact of the pathogen on mite populations. The total number of Neozygites-infected mites produced in maneb-treated plots throughout the test period was significantly greater than that in untreated plots when epizootics were initiated during periods of mite population growth. Fewer total infected mites were produced in maneb-treated plots compared to untreated plots when epizootics were initiated during periods of mite population decline.
Influence du champignon entomophage, Neozygites floridana, sur le déclin dans des champs de maïs des populations de l'acarien, Tetranychus urticae
Dans des parcelles de maïs dont les populations d'espèces prédatrices avaient été éliminées par du carbaryl, des populations de T. urticae ont régressé en fonction de la dispersion aérienne des acariens ou d'épizooties provoquées par N. floridana. L'importance relative de ces deux causes varie d'année suivant les conditions écologiques. Le pathogène paraissait la principale cause de déclin des populations quand le temps humide a induit les épizooties par N. floridana avant que le maïs n'ait été largement contaminé par les acariens. Quand le temps sec a permis aux populations d'acariens de se développer sans frein jusqu'à contamination totale du maïs, la dispersion aérienne des acariens était la principale cause de déclin des populations d'acariens. Dans tous les champs où il y avait eu épizootie de N. floridana, des traitements de routine avec le fongicide meneb ont retardé les épizooties et réduit ou retardé l'impact du pathogène sur les populations d'acariens. Pendant toute la période d'étude, le nombre total d'acariens infestés par Neozygites était significativement plus élevé dans les parcelles traitées au maneb que dans les parcelles non traitées, lorsque les épizooties étaient provoquées pendant la période de croissance des populations d'acariens. Quand les épizooties ont été déclenchées pendant la période de déclin des populations d'acariens, un nombre plus faible d'acariens infestés était observé dans les parcelles traitées au maneb que dans les parcelles sans traitement.
Neozygites floridana is an important natural enemy of the two-spotted spider mite, Tetranychus urticae. Pesticides used in strawberries that might affect the conservation and enhancement of this beneficial fungus were therefore studied. This was done in a laboratory study by letting non-inoculated (healthy) mites and mites inoculated with N. floridana feed on strawberry leaf disks treated with one of the following pesticides: the fungicides tolylfluanid, fenhexamid or cyprodinil + fludioxonil or the acaricide/insecticide/molluscicide methiocarb. The effect of these pesticides on mortality and egg production of T. urticae and on the killing capacity and sporulation of N. floridana were determined. Tolylfluanid increased the mortality of non-inoculated mites (75.3%) compared to the non-inoculated control (27.5%). Methiocarb also killed non-inoculated mites. Fenhexamid did not have any effect on the mortality of non-inoculated mites (19.2%), neither had cyprodinil + fludioxonil (19.1%). Tolylfluanid did not reduce the mortality of mites inoculated with N. floridana (89.3%) compared to the inoculated control (80.0%). Neither did methiocarb, it rather increased the mortality of inoculated mites (93.2%). Fenhexamid did, however, reduce the mortality of inoculated mites (66.7%). The same was true for cyprodinil + fludioxonil (48.7%). In addition, cyprodinil + fludioxonil increased the time to death of inoculated mites (6.69 days) compared to the control (6.10 days), and inhibited sporulation of N. floridana (7.9% sporulation) compared to the control (42.4% sporulation). Tolylfluanid also reduced sporulation of N. floridana (15.5% sporulation). Results from this study indicate that the use of the fungicides tested will potentially reduce the survival and efficacy of the natural enemy N. floridana in the field.
We studied the effects of downy brome, Bromus tectorum L., winter cover crop on several corn, Zea mays L., pests in the summer crop after the cover crop. An experiment was conducted that consisted of two trials with two levels of irrigation, two levels of weed control, and two levels of downy brome. Corn was grown three consecutive years after the downy brome grown during the winter. Banks grass mites, Oligonychus pratensis (Banks), twospotted spider mites, Tetranychus urticae Koch, and predatory mites from the genus Neoseiulus were present in downy brome at the beginning of the growing season. They moved into corn, but their numbers did not differ significantly across the treatments. Larval western corn rootworm, Diabrotica virgifera virgifera LeConte, feeding on corn roots was evaluated the second and third years of corn, production. Irrigation and herbicide treatments had no significant effects on rootworm injury levels. In one trial, rootworm injury ratings were significantly greater in treatments with a history of high versus low brome, but this effect was not significant in the other trial. Rootworm injury seemed to be similar across plots with different surface soil moistures. This suggests that the use of a winter cover crop such as downy brome will not have a major negative impact the arthropods studied.
The production and germination of primary conidia of Neozygites floridana as affected by temperature, humidity, and photoperiod was studied in the laboratory. All tested factors significantly affected the two processes studied. Production increased with increasing temperature between 13 and 23°C, with means of 35.5 and 55.4 conidia, respectively, discharged from each mummified mite cadaver. No conidia were produced at 28 or 33°C. Conidial production dropped significantly from 96.1/mummy in a moisture-saturated environment [saturation deficit (SD) 0] to 33.9/mummy at SD 0.2. Very few conidia were produced at SD 0.7 (0.6/mummy) and none at SD 1.2. Significantly fewer conidia were produced under continuous light (11.2/mummy) than under continuous darkness (40.1/mummy) or 12L:12D (46.7/mummy) photoperiods. Between 82 and 100% of the conidia produced under 12L:12D photoperiod were released in the dark phase. Germination of primary conidia started within 2 hr and increased with decreasing temperature between 13 and 28°C. Percentage germination of 20.1% at 13°C and 17.6% at 18°C was significantly higher than 11.2% at 28°C. There was no germination at 33°C. High humidities (>95%) were necessary to effect germination. Germination at SD 0 (27.2%) and 0.2 (23.4%) was significantly higher than at SD 0.7 (0.4%), where germination began after 6 hr and was observed only at 13, 18, and 23°C. No germination was observed at SD 1.2. There was no germination among conidia maintained under continuous light.
Annual cropping systems consist of a shifting mosaic of habitats that vary through time in their availability and suitability to insect pests. Agroecosystem instability results from changes that occur within a season with crop planting, development, and harvest. Further instability results from continuous alterations in biotic and abiotic insect life system components and from agricultural inputs. Changes to agroecosystems occur across seasons with changing agricultural practices, changing cropping patterns, and technological innovations. Much of this instability is a result of events unconnected with pest management. The abilities of polyphagous pest species to move among and utilize different habitat patches in response to changes in suitability enable the pests to exploit unstable cropping systems. These pest characteristics determine the location and timing of damaging populations. Habitat suitability is influenced by plant species and cultivar, crop phenology, and agricultural inputs. Pest movement is affected by a suite of intrinsic factors, such as population age structure and mobility, and extrinsic factors, including weather systems and habitat distribution. The life systems of three selected polyphagous pests are presented to demonstrate how an understanding of such systems in agricultural ecosystems improves our ability to predict and hence manage these populations.
Entomophthorales pathogenic to insects and mites often cause epizootics in their host populations, but some have been difficult to culture in vitro and, therefore, to develop as biopesticides. Grace's insect cell culture medium supplemented with lactalbumin hydrolysate and yeastolate has allowed growth of several species which until recently were referred to as obligate parasites. The research reported here was designed to evaluate the effects of the salts, vitamins and amino acids used to prepare the insect cell culture medium on in vitro growth of Batkoa sp. and Furia sp., pathogens of the spittlebug pests of pasture and sugar-cane in Brazil, and Neozygites floridana, a pathogen of several mite species. Also, several sources of carbon and nitrogen were examined. Batkoa sp., Furia sp. and N. floridana were similar concerning their growth patterns in a basic medium with added salts, vitamins and amino acids, as well as with a combination of all three compoments. The addition of salts to the basic medium of sugars plus lactalbumen hydrolysate and yeastolate caused a significant increase in biomass production of the three fungal species. The addition of vitamins and amino acids had less effect. Batkoa sp., Furia sp. and N. floridana are similar in growth patterns in media with various sources of carbon, but different in media with different sources of nitrogen. The production of the three fungal species is significantly higher in medium containing 2.66% glucose than in medium with 2.66% sucrose. The addition of 0.1% monossacarides to media containing 2.66% sucrose did not significantly increase biomass production.
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