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Interactive effects of selected pesticides on the two-spotted spider mite and its fungal pathogen Neozygites floridana
Abstract
Benomyl affected populations of Tetranychus urticae by interfering with the pathogenic fungus, Neozygites floridana. Benomyl delayed but prolonged spider mite outbreaks. Few mites were infected with the pathogen when benomyl was used. Reductions in mite populations treated with fentin hydroxide were associated with a high incidence of N. floridana infection, Benomyl did not affect sporulation of N. floridana but appeared to inhibit conidial germination or growth of the fungus.
Interactions de pesticides selectionnés sur Tetranychus urticae et son champignon pathogène, Neozygites floridana
Le bénomyl a modifié les populations de Tetranychus urticae Koch en interférant avec son champignon pathogène, Neozygites floridana (Weiser & Muma). Le bénomyl retardait mais prolongeait les pullulations de l'acarien. Peu d'acariens étaient infectés par le champignon quand on utilisait du bénomyl. Les réductions des populations d'acariens traitées avec l'hydroxyde de fentine étaient associées à un haut niveau d'infection par N. floridana. Le bénomyl ne modifiait pas la sporulation de N. floridana mais semblait inhiber la germination des conidies ou la croissance du champignon.
... 22 Only a few controlled laboratory studies have been conducted on the effect of pesticides to N. floridana as a natural enemy of T. urticae. 10,23 Some field or semi field studies have been conducted with T. urticae, however, 20,24 and a few with another host species, T. evansi. 25,26 In this study, we tested sulfur-based pesticides in addition to many other synthetic pesticides. ...
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.
... For instance, fi eld studies have frequently shown that N. fl oridana is associated with dramatic declines in the abundance of spider mites. However, the reduction in incidence of infection by N. fl oridana has also been associated with the application of benomyl in fi elds infested with spider mites (Brandenburg and Kennedy 1983 ). These fi ndings demonstrate the importance of understanding pesticide interactions because of their potential in inducing secondary pest outbreaks. ...
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.
... For instance, fi eld studies have frequently shown that N. fl oridana is associated with dramatic declines in the abundance of spider mites. However, the reduction in incidence of infection by N. fl oridana has also been associated with the application of benomyl in fi elds infested with spider mites (Brandenburg and Kennedy 1983 ). These fi ndings demonstrate the importance of understanding pesticide interactions because of their potential in inducing secondary pest outbreaks. ...
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.
... They generally live under the surface of leaves, where they spin protective silk webs, but in severe cases they also appears on the upper surfaces of leaves. The importance of this mite pest is not only due to the direct damage to plants including defoliation, leaf burning and in excessive outbreak, plants may die but also due to indirect damage to plants by decreasing the rate of transpiration and photosynthesis (Brandenburg & Kennedy 1983;Razmjou et al. 2009). ...
An anamorphic entomopathogenic fungus Neozygites sp. belonging to the Family Neozygitaceae was found infecting the tetranychid mites Tetranychus urticae Koch (Acari: Tetranychidae) of French bean (Phaseolus vulgaris L.) for the first time in Eastern Plateau and Hill region of India in the month of October 2011. The report of entomopathogenic fungus could be of help in managing acaricide resistant mites.
... Critically, the fungus does not infect predatory phytoseiid mites in the ® eld (Smitley et al., 1986b). Epizootics of N. Xoridana are delayed and /or suppressed by regular sprays of fungicides (Brandenburg & Kennedy, 1983;Boykin et al., 1984;Smitley et al., 1986b), and farmers have been encouraged to modify their spray programmes appropriately to take full advantage of the fungus (Klubertanz et al., 1991). Although N. Xoridana undoubtedly plays an important role in T. urticae population dynamics, epizootics may occur too late to prevent crop damage on some crops such as maize (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 .
... 1-3). The subsequent increase in mite number was apparently related to the phenology of peanut (Boykin 1983, Margolies & Kennedy 1984 which passed through peak bloom, but was probably conditioned by other factors as well, such as weather and pesticide schedules (Campbell, 1978;Boykin & Campbell, 1982;Brandenburg & Kennedy, 1983). In neither year, however, did mites cause damage which was perceived as being treatable before peanut harvest. ...
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.
... Neozygites floridana (Weiser and Muma) Remaudiére and S. Keller (Zygomycetes: Neozygitaceae) is a fungal pathogen that is an important natural enemy of T. urticae and T. evansi and it is a major mortality factor that causes decline in field populations of T. urticae attacking different crops such as corn (Smitley et al., 1986), peanuts (Boykin et al., 1984), soybean (Klubertanz et al., 1991), lima beans (Brandenburg and Kennedy, 1983), cotton (Carner and Canerday, 1970), strawberry (Klingen and Westrum, 2007) as well as T. evansi attacking tomato (Humber et al., 1981;Duarte et al., 2009). This fungus develops inside spider mites as hyphal bodies, kills its hosts, sporulates and produces primary conidia on conidiophores on the outside of the dead mite when conditions are favorable. ...
In a series of tritrophic-level interaction experiments, the effect of selected host plants of the spider mites, Tetranychus evansi and Tetranychus urticae, on Neozygites floridana was studied by evaluating the attachment of capilliconidia, presence of hyphal bodies in the infected mites, mortality from fungal infection, mummification and sporulation from fungus-killed mite cadavers. Host plants tested for T. evansi were tomato, cherry tomato, eggplant, nightshade, and pepper while host plants tested for T. urticae were strawberry, jack bean, cotton and Gerbera. Oviposition rate of the mites on each plant was determined to infer host plant suitability while host-switching determined antibiosis effect on fungal activity. T. evansi had a high oviposition on eggplant, tomato and nightshade but not on cherry tomato and pepper. T. urticae on jack bean resulted in a higher oviposition than on strawberry, cotton and Gerbera. Attachment of capilliconidia to the T. evansi body, presence of hyphal bodies in infected T. evansi and mortality from fungal infection were significantly higher on pepper, nightshade and tomato. The highest level of T. evansi mummification was observed on tomato. T. evansi cadavers from tomato and eggplant produced more primary conidia than those from cherry tomato, nightshade and pepper. Switching N. floridana infected T. evansi from one of five Solanaceous host plants to tomato had no prominent effect on N. floridana performance. For T. urticae, strawberry and jack bean provided the best N. floridana performance when considering all measured parameters. Strawberry also had the highest primary conidia production. This study shows that performance of N. floridana can vary with host plants and may be an important factor for the development of N. floridana epizootics.
... 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.
... Treatments with fungicide may affect the incidence of fungus disease in populations of spider mites. Brandenburg and Kennedy (1983) observed a lower proportion of spider mites infected by N. floridana in lima bean when benomyl was applied. This fungicide did not affect sporulation of the fungus but seemed to affect conidial germination and growth of the fungus negatively. ...
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.
... For example, application of fungicides has been implicated in the reduction of Neozygites spp. incidence in the Weld resulting in host population increases of mainly aphids and mites (Brandenburg and Kennedy 1983; Boykin et al. 1984; Bower et al. 1995; Klingen and Westrum 2007). Although it might be desirable to conduct Weld experiments to determine the eVect of pesticides on the disease dynamics of the entomopathogenic fungi, Weld experiments are expensive, time consuming, and often not appropriate to identify speciWc factors that aVect the entomopathogenic fungi. ...
The tomato red spider mite, Tetranychus evansi Baker and Pritchard, is an invasive species in Africa causing considerable damage to Solanaceous crops. The fungal pathogen Neozygites floridana Weiser and Muma from Brazil has been considered a potential candidate for introduction into Africa for the control of T. evansi. To be incorporated in the tomato production system, N. floridana has to be compatible with the pesticides used for the control of other pests and diseases. Pesticides used in tomatoes that might affect the fungus were therefore studied by the use of different methods. Two insecticides (Lambda-cyhalothrin and Methomyl), two acaricides (Propargite and Abamectin), and two fungicides (Captan and Mancozeb) were tested in two concentrations: the mean commercial rate (CR) and 50% of the mean commercial rate (CR/2). Fungus-killed mite cadavers or the substrates used for sporulation (leaf discs and coverslips) were either immersed or sprayed with the pesticides before testing their effects on sporulation, germination of primary conidia and infectivity of N. floridana. Direct immersion of cadavers, coverslips or leaf discs into pesticides affected sporulation and germination stronger than the spray tower method, although infectivity of capilliconidia was neither affected by the method of application nor the concentration of the pesticides. The fungicides Captan and Mancozeb resulted in a high reduction in sporulation and germination at both concentrations. Propargite did not inhibit sporulation but affected germination of primary conidia. Methomyl and Abamectin resulted in less effects on N. floridana.
An epizootic of entomophthoraceous fungus, Zoophthora radicans in a population of Empoasca onukii in a tea field,Iruma, Japan, are described. The occurrence of the epizootic was monitored 1 or 2 times in a month, from September to October in 1980 and from April to November in 1981,under insecticide control. No fungicides were applied.The cadavers of adults and nymphs of E.onukii by the fungus were observed on the abaxial surface of tea leaves.Infections of the fungus caused up to 40.7% nymphs mortality in late September, 1980 and 36.2% adults and nymphs mortality in late October, 1981.The cadavers developing resting spores were observed with the cadavers developing conidia in late September, 1980 and in late October,1981.This is the first report of Z.radicans infecting E.onukii in Japan.
Neozygites floridana (Weiser & Muma) Remaudière & Keller and Hirsutella thompsonii Fisher are important fungal pathogens of mites on cassava in Benin. Bioassays were conducted to evaluate the influence of four concentrations (50, 100, 200 and 500 ppm) of a water-dispersible formulation (Gaucho 70 WS) of imidacloprid on the conidial germination of these two fungi. Imidacloprid significantly reduced the germination of primary conidia and formation of infective capilliconidia in N. floridana. In contrast, imidacloprid concentrations of 100 ppm and above increased conidial germination in H. thompsonii. Another bioassay was conducted to evaluate possible synergism between imidacloprid and H. thompsonii in the mortality of the cassava green mite, Mononychellus tanajoa (Bondar). Hirsutella thompsonii alone and in combination with imidacloprid both killed around 95% of the mites after five days. In contrast, the mortality of mites treated with imidacloprid alone was close to that of untreated mites, which was around 30% on the fifth day after treatment.
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.
Fungicidal effects of glyphosate and glyphosate formulations on the entomopathogenic fungi Beauveria bassiana (Balsamo) Vuillemin, Metarhizium anisopliae (Metchnikoff) Sorokin, Nomuraea rileyi (Farlow) Samson, and Neozygites floridana Weiser & Muma were evaluated under laboratory conditions. Media previously inoculated with entomopathogenic fungi were exposed to distilled water, glyphosate (active ingredient), seven glyphosate formulations, and five blank formulations (carrier only). The fungicidal activity was determined by measuring inhibition in mycelial growth in solid media (B. bassiana, M. anisopliae, and N. rileyi), and spore concentration in liquid medium (N. floridana). Glyphosate did not have fungicidal activity against any of the fungi tested. Fungicidal properties of glyphosate formulations varied among fungal species. Neozygites floridana and M. anisopliae were susceptible to all glyphosate formulations. RoundUp Ready-To-Use was consistently the glyphosate formulation with one of the strongest fungicidal properties. Fungicidal activity of some formulations had a synergistic effect with glyphosate. RoundUp Original was the only formulation that did not show any interaction on fungicidal activity between glyphosate and the formulation. The results showed that the four fungi tested are susceptible to various glyphosate formulations when exposed to field concentrations.
RESUMEN Los effectos fungicidas de glyphosato y formulaciones de glyphosato fueron evaluados bajo condiciones de laboratorio en los hongos entomopatógenos Beauveria bassiana (Balsamo) Vuillemin, Metarhizium anisopliae (Metchnikoff) Sorokin, Nomuraea rileyi (Farlow) Samson, y Neozygites floridana Weiser & Muma. Medios de crecimiento previamente inoculados con los hongos entomopatógenos fueron expuestos a agua destilada, glyphosato (ingrediente activo), siete formulaciones de glyphosato, y cinco formulaciones sin ingrediente activo (solamente inertes). La actividad fungicida fue determinada en medios de crecimiento sólidos midiendo el área de crecimiento miceliar inhibido (B. bassiana, M. anisopliae, y N. rileyi), y en el medio de crecimiento líquido determinando la densidad de esporas (N. floridana). Glyphosato no tuvo ninguna actividad fungicida para ninguno de los hongos. Las propiedades fungicidas de las formulaciones de glyphosato diferieron entre las especies de hongos. Neozygites floridana y M. anisopliae fueron susceptibles a todas las formulaciones de glyphosato. RoundUp Ready-To-Use fue consistentemente una de las formulaciones de glyphosato con propiedades fungicidas mas fuertes. La actividad fungicida de varias formulaciones tuvieron un effecto sinérgico con glyphosato. RoundUp Original fue la única formulación que no mostró ninguna interacción en la actividad fungicida entre glyphosato y la formulacion. Los resultados muestran que los cuatro hongos en este estudio son susceptibles a varias de las formulaciones de glyphosato cuando expuestos a concentraciones de campo.
In northeastern North Carolina, outbreaks of Tetranychus urticae Koch on commercial corn and peanut plantings were observed to coincide with flowering and fruiting of the crop host. In greenhouse studies, when equal mite numbers were started on plants in either vegetative or reproductive growth stages, populations increased significantly more after 3–4 weeks on reproductive plants of both corn and peanut. This direct response of mite populations to differences in plant phenology appears to be an important component in the population dynamics of T. urticae. The importance of this effect in understanding mite outbreaks on corn and peanut is discussed, especially in reference to the corn‐peanut agroecosystem in North Carolina.
RÉSUMÉ
Réponse de populations de Tetranychus urticae Koch., aux phenologies du maïs et de l'arachide
Les populations de tétraniques sont souvent associées à la floraison et à la fructification des plantes attaquées. Dans les agrosystèmes maïsarachide du N.E. de la Caroline du Nord, l'augmentation rapide de populations de T. urticae a été observée lors de la maturation des épis mǎles du maïs et du maximum de floraison de l'arachide. Bien que ces observations suggèrent une relation causale avec la phénologie des plantes hǒtes, il est difficile de déterminer dans les conditions de la nature si l'augmentation des populations d'acariens sur les stades reproducteurs des plantes est due à une réponse à la phénologie des cultures ou à une autre cause, comme le passé de la population ou une immigration. Des expériences ont été réalisées dans une serre pour mettre en évidence l'action de la phénologie du maïs et de l'arachide sur les populations d'acariens en maǐtrisant ces autres hypothétiques facteurs. Des effectifs identiques d'acariens femelles ont été libérés sur des plantes à des stades tant végétatifs que reproductifs, et ensuite laissés sans interventions pendant plusieurs semaines, au bout desquelles les effectifs sur chaque plante ont été dénombrés. Sur les deux hǒtes, les populations sur plante à un stade reproducteur avaient augmenté significativement plus que sur les plantes de měme espèce à un stade végétatif. Ces résultats montrent que T. urticae répond directement à des différences entre plantes à un stade végétatif et à un stade reproductif. Cette réponse semble jouer un rǒle important dans la dynamique des populations de T. urticae.
The object of this review paper is to provide a guide to agrochemical research involving organotin compounds which has been performed since 1980. The information is presented in a tabular form and is divided into four main sections as indicated by the title. Each section is then subdivided to cover the various commercial organotin compounds. A final subsection lists investigations involving novel compounds. An additional section covers the effects of organotin agrochemicals on non-target organisms. A table of the contents has been provided to enable ease of reference. Acaricidal, antifeedant, chemosterilant and insecticidal properties are covered here. Fungicidal, bactericidal and herbicidal aspects are covered in Part 1.
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.
Microbial pathogens play a vital role in the natural regulation of many arthropod populations in agricultural systems. Their
importance has been underemphasized compared to parasitoids and predators because fewer specialists work on pathogens, and
pathogens are generally less noticeable than parasitic and predaceous arthropods.
Fungi of the order Entomophthorales (Zygomycota, Zygomycetes) constitute a group of mostly insect pathogenic species, which
attracts attention of insect pathologists because of their high capacity for use in biological control of pest insects. This
work primarily focuses on entomophthoralean species attacking aphids. The Entomophthorales are considered major pathogens
of aphids in nature. In fact, the fungi are the only pathogens that regularly and effectively can affect aphid populations
in natural ecosystems as well as in agroecosystems. Up to now, 33 entomophthoralean species organized into 9 genera have been
recorded in aphid hosts. All fungal species are listed and organised by genus in the work. Descriptions are presented for
all the fungal genera and species, including a nomenclature genesis, a geographical distribution, a host specificity/host
range, a capability of cultivation in vitro, and possible prospects for their use in biological control strategies. A key to identification of the pathogens is provided
as well. A general life cycle outline of the pathogens is followed by fundamental facts on biology and ecology of the fungi
and analysis of primary factors that are involved in the study of epizootiology of infectious diseases in insect populations.
The abiotic and biotic elements of the environment, which interfere in the pathogen-host interactions, are also underlined.
In the last chapter, several examples are reviewed when the Entomophthorales were used against aphids within the four strategies
of biological control, namely classical biological control, inoculation biological control, inundation biological control,
and conservation biological control. The aim of this review is to cover the present status of knowledge about the natural
enemies of aphids and to stimulate an interest of insect pathologists in this group of entomopathogenic fungi.
Scirtothrips dorsalis Hood (Thysanoptera: Thripidae), a polyphagous tiny insect pest, causes a
characteristic upward leaf curl on tender leaves of chilli (Capsicum annuum L.) due to their feeding. Infestation
of S. dorsalis during early cropping period resulted 30-70 % yield loss in dry chilli. All the chilli varieties used
in India and Sri Lanka are affected by the thrips. Chilli grown in irrigated condition was badly affected by this
pest. Indiscriminate use of inorganic insecticides to manage the thrips consumes almost 50 per cent of the total production cost. An attempt was made to find suitable biological agents to reduce the use of inorganic pesticides. On an exploration of naturally existing entomopathogenic fungi, sampling of chilli leaves was done from chilli growing areas of Karnataka, India during January–May 2004. An entomopathogenic fungus, Neozygites floridana (Weiser and Muma) Remaud and Kellar (Zygomycetes: Neozygitaceae) was recorded during April 2004 at Shimoga district of Karnataka, India. First and second larval instars of S. dorsalis were found infected by this fungus and the diseased instars initially expressed a characteristic milky white symptom then the colour turned to pale yellow to light brown and finally became black. Neither pupae nor adults of the S. dorsalis exhibited disease symptoms. Cent percent mortality of first and second larval instars of S. dorsalis was recorded within six days under poly house condition (25±20C and 79 ± 4% RH). An average of 5-7% N. floridana diseased larval thrips was also recorded in the field during this period. The body of the larvae of thrips was filled with large number of primary conidia while examining the diseased larvae under microscope (40x). The primary conidia were 14-22μm in length and 10-11μm in width with a mean of 17.95 x10.37μm. The mean length of capillary tube that entangled conidia was 57.51μm. N. floridana was cultured in Sabouraud medium enriched with 1% yeast extract and potato dextrose agar media however the fungi failed to establish further in either media. The onset of rainfall after a long spell of drought and a sudden increase in the relative humidity from 60 to 79% would have influenced the epizootics of N. floridana on larvae of S. dorsalis during this period. This Zygomycetes fungus, N. floridana is well known to infect mites however the present investigation of infecting on larvae of S. dorsalis suggests using this potent fungus against insect pests. The identity of N. floridana was confirmed by Dr.R.A.Humber, USDA-ARSEF, Ithaca, USA.
The phenomenon of insecticide-induced resurgence of arthropod pests has long been known to occur in response to a reduction in natural enemy populations, releasing the pest population from regulation. However, studies of resurgent populations infrequently examine other mechanisms, although numerous alternative mechanisms such as physiological enhancement of pest fecundity, reduction in herbivore-herbivore competition, changes in pest behaviour, altered host-plant nutrition, or increased attractiveness may also cause, or enhance the probability of, resurgence. Additionally, many studies that have identified natural enemy mortality as the primary cause of resurgence do not document a priori regulation by natural enemies and, therefore, are correlative in nature. In this paper, a universal definition of resurgence is proposed and criteria for determining the occurrence of resurgence are listed. Both of these are essential to rigorous evaluation of this important phenomenon. Alternative mechanisms for resurgence and potential areas of future research are identified. It is argued that insecticide resistance is not a mechanism underlying resurgence; rather, it simply enhances the probability that resurgence may occur. The similarity of resurgence to some insect outbreaks is discussed. In some cases natural outbreaks differ only in the initiating factor. The importance of resurgence management to plant protection is that resurgence is totally contradictory to the intended outcome of insecticidal application. This conflict strengthens the need to identify specifically the causal factors for each case of resurgence in order to manage this detrimental phenomenon effectively.
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.
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.
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.
The two papers presented here were prepared at the request of the Special Committee
of the International Biological Program, as part of a broad program on the ecology
and natural control of spider mites (Tetranychidae) on a worldwide basis.
Part I is a review of the pertinent literature and a discussion of the biology and
ecology of various spider mite enemies, their potential as biological control agents,
and the effects of pesticides on their populations.
Part II reviews the literature pertaining to tetranychid abundance, and the evidence
supporting various hypotheses concerned with their populations. It evaluates the action
of various predators and discusses possible ways of implementing biological control.
A third paper in this series (Part III), by the same authors, will review the literature
and discuss the problem of spider mites from the standpoint of their biology, ecology,
pest status, and their relationship to host plants. This paper is expected to be published
shortly.
Pesticides commonly applied to the foliage of peanuts in North Carolina were evaluated under field conditions for their effect on the twospotted spider mite Tetranychus urticae Koch. Most fungicides caused a higher mite increase than insecticides on NC 2 peanuts. When fungicides and insecticides were tank mixed or applied on alternate weeks, mite outbreaks occurred. These outbreaks were followed by severe injury to the foliage and finally defoliation and yield reductions.
Among the fungicides applied only Du-Ter and Copper Count failed to cause significant mite damage even when combined with an insecticide. Since mites failed to develop on untreated peanuts following six or more mite releases during the season, it was apparent that pesticides predispose peanuts to spider mite buildup and damage.
Numerous pesticides are known to provoke outbreaks of a variety of mites and aphids. Some of the conditions surrounding- these upsets arc reviewed, and the capabilities of 59 different pesticides to induce increases of mites and/or aphids are examined in relation to their individual effects on some of the major natural enemies of mites and aphids. When critical examination is made of the arguments for either of the 2 suspected causes of such pesticide- induced outbreaks, i.e., (a) natural enemy destruction and (b) pest fecundity stimulation, it appears that neither by itself offers a completely adequate explanation. Since one of the methods now commonly used for evaluating natural enemy effectiveness relies on measurement of host increases in insecticidal check plots, this technique may credit the natural enemies with undeserved efficiency if the insecticide stimulates the pest's fecundity. In this first of a series of experimental programs designed to resolve the problem of whether abnormal mite or aphid increases can be generated by pesticidal stimulation of the fecundity of mites or aphids, 59 different materials were examined for their effect on the reproductivity of the two-spotted spider mite, Tetranychus urticae Koch, and the cotton aphid, Aphis gossypii Glover. Following treatment with the different materials, population fold increases of each pest were measured weekly on the potted cotton plants held in the greenhouse and outdoors in the complete absence of natural enemies. The period of retention of toxicity of each material to mites and aphids (or the period during which any stimulation effect might be masked) is presented. Some anomalous conditions of treatment which caused abnormal increases in these tests could be explained by elimination of either pest when competing with the other. Some other abnormal increases of both mites and aphids were found which were difficult to explain other than as a pest-stimulation effect. For these cases no common denominator could be found. A few of the stimulatory responses obtained appeared in- consistent with the recorded performance of the materials in inducing upsets in the field.
Several species of entomophthoraceous fungi have been reported infecting potato-infesting aphids in Maine (Patch 1907, Shands et al. 1962, 1963, 1972), but their impact on the populations has been variable (Shands et al. 1958). Because these fungi have been recorded as causing dramatic reductions in aphid populations, they are potential biological control agents in an integrated pest management system. Their utilization must take into consideration their compatibility with pesticides; on potatoes in Maine, for instance, it would be unreasonable to abandon the use of fungicides against early and late blight (c.a. Alternaria solani [Ellis and Martin] Jones and Grant and Phytophthora infestans [Mont.]dBy). It would be especially important to select a fungicide that would control blights without inhibiting the spread of insect-attacking fungi.
During the summer of 1968, a study was conducted in Alabama to determine the importance of Entomophthora sp. as a natural control factor in field populations of the two-spotted spider mite, Tetranychus urticae Koch. Studies on the distribution of this fungus revealed its presence in 14 of the 15 counties where collections were made. Average infection by Entomophthora was 25%.
Five epizootics of the pathogenic fungus were observed in two-spotted spider mite populations in Lee County, Ala. Each epizootic was characterized by a high degree of infection by Entomophthora accompanied by a rapid decline in mite numbers.
Two applications of the fungicides Benlate®, Du Ter®, and Bravo®, and Benlate in combination with carbaryl were made to soybean. Infection of lepidopterous larvae by the entomogenous fungus Nomuraea rileyi (Farlow) Samson was inhibited to some degree by application of Benlate ®, Du Ter®, and Bravo®. Bravo caused the most inhibition followed by Bentlate and Du Ter respectively. In one instance the combination of Benlate + carbaryl was more disruptive to N. rileyi than either chemical alone. Inhibition was greatest when pesticide application coincided with the early stages of N. rileyi epizootics.
A P-generation of female Tetranychus urticae Koch kept on residues of a 200 ppm spray of carbaryl, 100 ppm DDT, and 25 ppm dioxacarb showed significantly (carbaryl and DDT) higher egg-totals than their untreated controls. With dioxacarb the increase of egg production was marginal in the statistical analysis. The ratio females/males in the F1 was shifted in favor of the females in the broods reared on carbaryl and DDT residues, but not in the case of dioxacarb. This increase in the female proportion is highly significant for carbaryl with the strongest shift and DDT with a lesser one. Adult females of the F1, too, had a significantly higher egg production on carbaryl and DDT than their untreated counterparts. Hormoligosis—stimulation by small quantities of a stressor—is assumed responsible for observed effects, not an improved nutritional basis via an altered physiology of the host plant.
Spray applications of the systemic fungicide benomyl (methyl 1- (butylcarbamoyl) -2-benzimidazolecarbamate), at 0.03% active ingredient depressed hatch of eggs of Tetranychus urticae Koch. Viability was reduced by direct application to the egg or through ingestion of treated plant tissue by gravid females. The toxicant was at sufficient levels in leaves up to 7 days after foliar application to affect significantly viability of eggs from females feeding on treated leaf tissue.
Significant differences in infection rates of the entomogenous fungus, Nomuraea rileyi (Farlow) Samson among populations of Anticarsia gemmatalis (Hübner) in soybean treated with benomyl, benomyl and methyl parathion, and benomyl and carbaryl were observed. Development of N. rileyi was delayed in treated plots for at least 3 weeks. The yield of the check plot was significantly higher than that of the pesticide treated plots.
The fungicides benomyl, chlorothalonil, thiabendazole, and fentin hydroxide were applied alone and in combination with methyl parathion or methomyl to soybeans. Larval population levels of Plathypena scabra (F.), Anticarsia gemmatalis (Hübner), and Pseudoplusia includens (Walker) were monitored as well as selected arthropod predators and the incidence of the fungal entomopathogens Nomuraea rileyi (Farlow) Samson and Entomophthora gammae (Weiser).
Application of fungicides at the recommended rates failed to suppress an epizootic of E. gammae in P. includens populations. The incidence of N. rileyi was suppressed in a low density population of A. gemmatalis. When larval density increased, no difference was detected in the incidence of N. rileyi infection in treated and untreated plots. Differences in predator population levels were not observed in a 1976 P. includens test but generally lower predator populations were noted in the 1977 P. includens-A. gemmatalis test in fungicide and/or insecticide treated plots.
Fentin hydroxide alone and treatments which included methyl parathion or methomyl reduced larval populations of P. scabra and A. gemmatalis. Only treatments containing methomyl reduced larval populations of P. includens. Pseudoplusia includens population resurgence was detected following treatments with benomyl and methyl parathion, chlorothalonil + methyl parathion and fentin hydroxide + methyl parathion. Anticarsia gemmatalis population resurgence followed treatment with fentin hydroxide + methomyl.
Entomophthora sp. killed its host, Tetranychus urticae, in 3.38 days at 25°C and in 11.02 days at 15°C. Development of hyphal bodies within the mite was studied with a light microscope, and a scanning electron microscope was used to examine spore development and structure. A comparison of this fungus with other mite-infecting fungi revealed that it is more closely related to E. floridana than to E. tetranychi, and should be called Entomophthora sp. near floridana until a more detailed study of E. floridana can be made.