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Observations and experiments on Triplosporium floridanum (Entomophthorales) attacking spider mites in Israel
Abstract
The fungus Triplosporium floridanum is common in various regions of Israel, attacking green and red forms of the two-spotted spider mite, Tetranychus telarius sensu lato. No resting spores have been found in this species in Israel.With dried, mummified, infected mites from the field, kept in vials for 6 weeks at 4°C, sporulation of associated T. floridanum was effected in moist chambers; after the dried mummies had been held for another 9.5 months at room temperature, the number of mites showing sporulating fungi in moist chambers remained very high. The fungus sporulated within an extremely wide temperature range, 4–37°C. Primary conidia were produced in less than a day at 6, 18, 27, 30, and 37°C, and anadhesive spores at 18, 27, and 30°C. After 2 days, anadhesive spores formed at 6°C as well. Heaviest sporulation occurred at 27† and 30°C. The longevity of the normal-appearing hyphal bodies within the mites after prolonged desiccation is considered to be a possible mechanism for tiding the fungus over periods during which the host is rare in the field.
... Resting spores are formed late season (October to November) in populations of T. urticae in Alabama USA (Carner, 1976), but in North Carolina the fungus is thought to pass the winter in mummies or by infection cycling (Brandenburg & Kennedy, 1981). Resting spores were not found in T. urticae in Israel (Kenneth et al., 1972), but they were found in diseased M. tanajoa in Brazil (Delalibera et al., 1992). They may remain associated with mite cadavers (Dick et al., 1992), but the cadavers that contain them are fragile and easily ruptured (Carner, 1976), in which case they could become redistributed over plant material or onto the soil. ...
... DiVerent isolates of N. Xoridana may be adapted to local temperature conditions. For example, the optimal temperature range for the formation of primary conidia is 18± 23ë C for isolates from Brazil (Oduor et al., 1996b), 16± 21ë C for isolates from the southern USA (Smitley et al., 1986a), while an isolate from Israel was able to produce primary conidia at 37ë C (Kenneth et al., 1972). Oduor et al. (1995b;1996a) observed that the production of primary conidia of a Brazilian strain of N. Xoridana on M. tanajoa was inhibited above 23ë C, and the germination of primary conidia and capilliconidia was curtailed above 28ë C, but mites died rapidly at 33ë C once infection had taken place. ...
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 .
... This fungus was also pathogenic to the citrus red mite, Panonychus ulmi (Kock), and the six-spotted mite, Eotetranychus sexmaculatus (Riley), but the rates of infection were much lower than for Texas citrus mite (Selhime and Muma 1966). Since its description, N. floridana has been reported in several countries infecting many species of mites in the family Tetranychidae (Kenneth et al 1972, Nemoto et al 1975, Keller 1991, Mietkiewski et al 2000. ...
The fungal pathogen Neozygites tanajoae Delalibera Jr., Humber & Hajek sp. nov. (Zygomycetes: Entomophthorales) is being used in Africa as a biological control agent against the introduced cassava green mite (CGM), Mononychellus tanajoa (Bondar) (Acari: Tetranychidae). This fungus is specific to CGM and has been referred to as N. floridana (Weiser & Muma) Remaud. & Keller, a common pathogen of many tetranychid mites. In the present study N. tanajoae is investigated at the morphological and molecular levels and physiological attributes of N. tanajoae and N. floridana are compared. Morphological observations of N. tanajoae isolates generally correspond to N. floridana and to other mite pathogenic species of Neozygites. However, this fungus readily can be distinguished from N. floridana based on 18S rDNA sequences, host ranges, nutritional requirements for growth in vitro, tolerances to cold (4 C) and abilities to withstand specific cryopreservation techniques. N. tanajoae isolates from Brazil and Africa have identical 18S rDNA sequences but they presented 5.7 and 9.94% pairwise distance from N. floridana isolates. N. tanajoae proved to differ sufficiently from other mite-pathogenic fungi referred to as N. floridana to justify the description of a new species.
... Hasta el presente fueron descritas cuatro especies (Balazy, 1993). La especie N. floridana fue descrita por Weiser & Muma (1966) como patógena del ácaro Eutetranychus banksi, en Florida, Estados Unidos, desde entonces fue citada en Israel (Kenneth et al., 1972), Japón (Nemoto et al., 1975), Suiza (Keller, 1991) floridana, sin embargo a través de estudios moleculares y otros complementarios, como rango de hospedadores, requerimientos nutricionales, crecimiento in vitro y tolerancia al frío (4º C) determinaron la separación de ambas especies. La clasificación tradicional de especies del género Neozygites ha estado fundamentada en caracteres morfológicos, principalmente tamaño de la espora y hospedador, sin embargo la ocurrencia de un complejo de especies es común en los Entomophthorales (Hajek et al., 2003). ...
First record of Neozygites sp. (Zygomycota: Entomophthorales), pathogen of Tetranychus urticae (Acari: Tetranychidae) in Argentina. In this paper, the presence of the fungi Neozygites cf. floridana (Zygomycota: Zygomycetes: Entomophthorales), as pathogen of the mite Tetranychus urticae (Acari: Tetranychidae), is recorded for first time in Argentina. Samplings were carried out in La Plata, on tomato, pepper, egg-plant, and other horticultural crops. Microscopic slides and mites infected were placed in the Herbarium of the Institute of Botany C. Spegazzini and in the Herbarium of CEPAVE. This work contributes to further expand the distribution and the host range of Neozygites as well as the information of entomopathogenic fungi in Argentina.
... Entomopathogenic fungi generally pass the period before epizootics either at low prevalence (enzootic) levels in the living hosts in the stage of hyphal bodies or as resting spores in dead hosts. The latter strategy aids the fungus in surviving through unfavourable seasons (Sawyer, 1931;Kenneth et al., 1972;Wilding, 1973;Nemoto and Aoki, 1975;Carner, 1976). Some fungi form conidia in young immature stages of their hosts and resting spores in older ones, which may be an attempt to increase survival (Wilding and Lauckner, 1974;Newman and Carner, 1975;Shimazu, 1979;Shimazu and Soper, 1986). ...
The survival of Neozygites cf. floridana (Weiser and Muma) as dry hyphal bodies in mummified cassava green mites, Mononychellus tanajoa (Bondar), at 5.0% RH in the dark was affected by storage temperature. Survival of the fungus in mummies kept at 241.0C could be demonstrated for 6–7 months. When stored at 4C, the fungus sporulated from 90% of the mummies liberating an average of 186.9 primary conidia per mummy even after a storage period of 16 months, when the experiment was terminated. The temperature, humidity and light condition significantly affected the viability of primary conidia. The percent viability across all factors dropped from 98.4% after 0 h (beginning of the experiment) to 23.4% after a 1 h exposure to the conditions tested. Lower temperatures maintained higher viabilities with 86.3% of the conidia surviving after 18 h at 18C, whereas almost all conidia died after 12 h at 33C. Conidia survived less than 1 h when exposed to SDs (saturation deficit) of 2.0 mm Hg or higher at any tested temperature.
... 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). ...
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.
... This fungus was also pathogenic to the citrus red mite, Panonychus ulmi (Kock), and the six-spotted mite, Eotetranychus sexmaculatus (Riley), but the rates of infection were much lower than for Texas citrus mite (Selhime and Muma 1966). Since its description, N. floridana has been reported in several countries infecting many species of mites in the family Tetranychidae (Kenneth et al 1972, Nemoto et al 1975, Keller 1991, Mietkiewski et al 2000. ...
The fungal pathogen Neozygites tanajoae Delalibera Jr., Humber & Hajek sp. nov. (Zygomycetes: Entomophthorales) is being used in Africa as a biological control agent against the introduced cassava green mite (CGM), Mononychellus tanajoa (Bondar) (Acari: Tetranychidae). This fungus is specific to CGM and has been referred to as N. floridana (Weiser & Muma) Remaud. & Keller, a common pathogen of many tetranychid mites. In the present study N. tanajoae is investigated at the morphological and molecular levels and physiological attributes of N. tanajoae and N. floridana are compared. Morphological observations of N. tanajoae isolates generally correspond to N. floridana and to other mite pathogenic species of Neozygites. However, this fungus readily can be distinguished from N. floridana based on 18S rDNA sequences, host ranges, nutritional requirements for growth in vitro, tolerances to cold (4 C) and abilities to withstand specific cryopreservation techniques. N. tanajoae isolates from Brazil and Africa have identical 18S rDNA sequences but they presented 5.7 and 9.94% pairwise distance from N. floridana isolates. N. tanajoae proved to differ sufficiently from other mite-pathogenic fungi referred to as N. floridana to justify the description of a new species.
... for instance were reported to sporulate between 5 °C and 25 °C (Wilding, 1971), and N. floridana between 10 °C and 26 °C (Smitley et al., 1986). The optimum sporulation temperature in this study of 25 °C and 29 °C is comparable to the optimum temperature of 27–30 °C reported by Kenneth et al. (1972) on N. floridana, but is higher than 18–23 °C reported by Oduor et al. (1995) . However, these reports refer to different tetranychid mite hosts, to Tetranychus urticae Koch and Mononychellus tanajoa Bondar, respectively. ...
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.
... Neozygites tetranychi also might be N. Xoridana (Balazy 1993). In the past, N. Xoridana was called Triplosporium Xoridana (Kenneth et al. 1972), Triplosporium sp. (Humber et al. 1981), and Entomophthora Xoridana (Nemoto et al. 1975). ...
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.
... Our study demonstrated that 80% or more of the cadavers sporulated from 4 of the 6 tested storage periods, which was substantially higher than that reported for the related species N. floridana, a pathogen of cassava green mites [Mononychellus tanajoa (Bondar) (Acari: Tetranychidae)] which, when stored at 5% RH and 4 °C, resulted in approximately 50% sporulation after 16 months storage ( Oduor et al., 1995). Kenneth et al. (1972) observed that N. floridana survived as hyphal bodies within spider mite cadavers [Tetranynchus urticae Koch (Acari: Tetranychidae)] for 11 months under dry conditions, most of the time at room temperature, although neither the exact temperature nor RH were recorded. When the mites were subsequently moistened sporulation of the fungus was noted as ''remaining very high.'' ...
Neozygites fresenii-infected Aphis gossypii cadavers, containing dormant hyphal bodies of N. fresenii, were stored in 4 ml glass vials at -14 degrees C in a standard consumer-type refrigerator/freezer for 1, 21, 30, 43, 51, and 68 months to determine the effect of storage on fungal survival. When the cadavers were removed from the freezer and placed in 25+/-1 degrees C, 100% relative humidity, and 12:12 (L:D) conditions, N. fresenii survival, as shown by fungal sporulation from the cadavers, was high at all storage periods. The average percentage of cadavers from which the fungus sporulated were 93, 47, 100, 100, 80, and 60% from 1, 21, 30, 43, 51, and 68 months storage periods, respectively. The number of primary conidia discharged from each sporulating cadaver was estimated using a scale of 1 (low, ca. 1000 primary conidia), 2 (medium, ca. 2000 primary conidia) and 3 (high, ca. 3000 primary conidia). The median scores for the number of primary conidia produced per sporulating cadaver were 3, 2, 3, 3, 2.5, and 1 for 1, 21, 30, 43, 51, and 68 months, respectively. Therefore, except for the longest storage period, most cadavers produced medium to high numbers of primary conidia. Mean germination of primary conidia produced from N. fresenii-infected-aphid cadavers from each time period varied significantly from 66.3 to 86.1% in the 21 and 43 months categories, respectively. Infectivity of capilliconidia, produced from frozen N. fresenii, to live healthy cotton aphids varied significantly from 16.7 to 68.7% from cadavers stored 68 months and 1 month, respectively. Overall N. fresenii survived well in dried frozen cotton aphid cadavers for up to 6 years with little reduction in sporulation, numbers of spores produced, germination of primary conidia, or infectivity.
... In live mounts of mites made from fields where resting sporefilled cadavers were found in abundance, none were found in live mounts. Other studies of N. floridana have found resting spores to be rare or absent (Carner and Canerday, 1968;Humber et al., 1981;Kenneth et al., 1972;Ramaseshiah, 1971;Weiser and Muma, 1966). It may be in some of these cases that the structures were simply not observed, so it is suggested that this possibility be considered. ...
Survival of pathogens during long periods of unfavorable conditions can be critical to their ecology and to their use in biological control. In northeastern Brazil, the mite pathogen Neozygites floridana must survive hot and dry conditions between wet seasons when it infects the cassava green mite Mononychellus tanajoa. We report on large numbers of mite cadavers bearing resting spores towards the end of epizootics in mid-1995. High within-leaf variability indicated that local factors may be important in determining resting spore formation. These spores remain in the host cadaver on a leaf until the cadaver breaks up, whereupon the spores fall freely to the soil, there to remain dormant. Laboratory simulation of field conditions led to ca. 25% of mycosed individuals bearing resting spores. Mummies (without resting spores) kept in hot and dry conditions showed little or no viability within 2 months, implying no role for survival over extended dry periods. It is proposed that resting spores form the principal means by which this pathogen survives the dry season in the study area. This has implications for its introduction to new areas in classical biological control.
A fungal pathogen was observed to decimate natural populations of Banks grass mite, Oligonychus pratensis, and twospotted spider mite, Tetranychus urticae, on field corn and grain sorghum in the western Great Plains of the United States. The fungus was reared on O. pratensis in the laboratory to study its biology and morphology. Additional observations of the fungus were made on naturally infected O. pratensis and T. urticae collected in Kansas and Texas fields. The morphology of the pathogen most closely resembles that described for Neozygites adjarica. Resting spores were commonly produced, even at late summer field temperatures, and they were smooth and globose to pyriform. Rhizoids were also commonly present and were found only in cadavers that contained resting spores. This is the first description of this pathogen in O. pratensis.
An entomophthoraceous fungus, Entomophthora floridana, attacked the Sugi spider mite, Oligonychus hondoensis, in a plantation of Japanese cedar, Cryptomeria japonica, in the Kyushu District of Japan. The fungus infected mainly the adult mite. It formed primary conidia and two types of secondary conidia. The mites were infected by one of the secondary types of conidia (anadhesive spores). Only resting spores occurred in the dead mummified mites during winter. © 1975, JAPANESE SOCIETY OF APPLIED ENTOMOLOGY AND ZOOLOGY. All rights reserved.
The surface structure and the function of conidium and anadhesive spore of Entomophthora (Triplosporium) floridana attacking Sugi spider mite were studied by scanning electron microscopy (SEM). Anadhesive spore showed corrugated surface and attaching sac which adhered to body surface of the mite. The conidium had textured surface which differed from smooth surface of Carner's E. sp. near floridana. Flattened conidium supported vertically anadhesive spore on slender capillary tube. Anadhesive spore was considered as an aerial organ for attachment. Resting spores which filled mites had smooth surface. © 1979, JAPANESE SOCIETY OF APPLIED ENTOMOLOGY AND ZOOLOGY. All rights reserved.
Phytophagous mites of the genus Tetranychus are commonly found attacking ornamentals in production plants and indoor landscapings. The control of those pest organisms is normally done by means of chemical pesticides. Problems of pest resistance and side effects of those products' use have led growers to look for alternative pest control methods. Biological control has been practiced on such ornamental crops as roses, chrysanthemum and different tropical foliage crops, by using almost exclusively the predatory phytoseiid mite Phytoseiulus persimilis Athias-Henriot. This predator is sold commercially by a number of suppliers in different countries. Other species of predators as well as species of pathogens have not been sufficiently studied. More extensive use of biological control depends upon further explorations of prospective species of predators and pathogens, probably waiting to be discovered in poorly studied areas around the world.
The prolong survival of cultures of Entomophthora coronata (COST.) Kevork. 〔=Conidiobolus coronatus (Cost.) Tyrrell. and MacLeod〕, E. virulenta Hall and Dunn, E. thaxteriana(Petch) Hall and Bell, and E. sphaerosperma Fres. under air-tight condition appeared to be dependent on the hyphae, some of which were knobby and might become chlamydo-spores. The conidia were very short lived, and the resting spores produced by E. virulenta also did not survive for long periods. The conidia survived longer at 5°C than at room temperatures. Under air-tight condition, the metabolic activity of the fungus was reduced as indicated by the production of only a few small conidia and narrow hyphae. As air became available more conidia were produced, the hyphae increased in size, became vacuolated, fragmented, and then collapsed and disintegrated. © 1974, JAPANESE SOCIETY OF APPLIED ENTOMOLOGY AND ZOOLOGY. All rights reserved.
Keller, S. (1997). The genus Neozygites (Zygomycetes, Entomophthorales) with special reference to species found in tropical regions. - Sydowia 49(2): 118-146. Several collections of mites (Acari: Tetranychidae, Phytoseiidae), mealybugs (Homoptera: Pseudococcidae) and aphids (Homoptera: Aphididae, Lachnidae) infected with Entomophthorales mainly from West Africa, South America and the Philippines were examined. All fungi found on Tetranychidae including the green cassava mite, Mononychellus tanajoa, were assigned to N. floridana. Species found on the phytoseiid Euseius citrifolius were identified as N. acaricida comb. nov. and N. cf. acaridis, respectively. All material from mealybugs (Rastrococcus invadens and Coccidohystrix insolita) was identified as N. fumosa. An emended description of this species is given. The fungi from Aphis craccivora and A. fabae were identified as N. fresenii. A new species, N. cinarae attacking the lachnid Cinara pilicornis, is described. The life-cycles of N. floridana and N. fresenii are described and compared. A key to all known species and a short characterisation is provided.
A fungal pathogen was observed to decimate natural populations of Banks grass mite, Oligonychus pratensis, and twospotted spider mite, Tetranychus urticae, on field corn and grain sorghum in the western Great Plains of the United States. The fungus was reared on O. pratensis in the laboratory to study its biology and morphology. Additional observations of the fungus were made on naturally infected O. pratensis and T. urticae collected in Kansas and Texas fields. The morphology of the pathogen most closely resembles that described for Neozygites adjarica. Resting spores were commonly produced, even at late summer field temperatures, and they were smooth and globose to pyriform. Rhizoids were also commonly present and were found only in cadavers that contained resting spores. This is the first description of this pathogen in O. pratensis.
A novel piece of equipment, the sporulation monitor, is described for the comparison of conidia production from mycelia receiving diVerent formulation and storage treatments. This equipment was used to compare the viability of Zoophthora radicans mycelial samples treated either with 10% maltose solution or with distilled water before drying and storage for 0-12 weeks at 4oC. Freshly dried maltose-treated mycelial mat samples produced significantly more conidia for a significantly longer time than distilled water-treated mat samples of the same age. Very few conidia were produced from mats in either treatment after storage for 4 weeks or longer. There were great diVerences in conidia production from mycelial mat samples produced in diVerent fermenter runs. These results are discussed in relation to the potential for the use of dried mycelia in biological control programmes.
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.
Laboratory-produced sclerotia (mummified cadavers of Heliothis virescens) and conidia of Nomuraea rileyi were held under field conditions from October 30, 1974 to August 8, 1975. Conidia were infectious after being held on the surface of the soil and in a glass vial for 138 and 209 days, respectively. Cadavers held on the surface of the soil began sporulating after 47 days. Infectious conidia were found on these cadavers for the entire sampling period (281 days). Infectious conidia were also present on cadavers buried 10 cm in the soil on the first sampling period (14 days) and last recorded at 194 days. N. rileyi was found to survive through the last sampling period (281 days) as was evident from the sporulation which occurred when the cadavers were placed at 27°C under laboratory conditions.
Entomophthora aphidis survived for at least 32 weeks at 0°C and 20 or 50% RH and E. thaxteriana for at least 16 weeks at 10°C and 20 or 50% RH in mummified infected pea aphids, Acyrthosiphon pisum. The fungi produced infective conidia when the aphids were moistened. This probably explains the survival of Entomophthora species infecting aphids during short periods when the weather is unsuitable for conidial discharge and host infection.
Fungal pathogens are capable of causing sensational levels of mortality in insect populations. As early as about 1000 AD, sericulturists in Asia reported Beauveria bassiana infections in silkworms (Steinhaus, 1956). The “germ theory of disease,” the concept that microbes can cause disease, was first experimentally proven by Agostino Bassi in 1834 working with B. bassiana and silkworms. From the late 1800s through 1925, research on the potential use of fungi for insect control was conducted. In recent years, largely due to our present knowledge of the hazards and inefficiencies of dependence on synthetic chemical pesticides for insect control, interest in developing fungal pathogens for control purposes has increased dramatically (Roberts and Hajek, 1992; Vandenberg, 1993). Although abundant research on use of entomopathogenic fungi for control has been conducted, there are major gaps in our understanding of the basic ecology of these fungal species, in part due to the complexity of host/pathogen/environment interactions and the diversity of host/pathogen systems to be studied. Lack of successful control in some systems and difficulties in adapting some species for typical control practices has promoted a shift in research emphasis. At present, some research efforts are directed toward understanding the factors leading to fungal infection in insects in order to investigate the potential for manipulating these systems to enhance levels of infection and promote development of epizootics (disease outbreaks).
Tetranychus urticae Koch was found on feral host plants during the winter months. Individual mites collected in January with the physical appearance of being in diapause laid eggs immediately when placed on excised lima bean leaves at 27°C and 16-h photoperiod. A pathogeruc fungus, Entomophthora floridana Weiser and Muma, was found in a viable state throughout the winter. Laboratory studies indicated that the fungus can maintain itself at low winter temperatures common to eastern North Carolina. Infection of twospotted spider mites and fungal development, although significantly reduced from that measured at higher temperatures, occurred at 5°C.
Isolates of Pandora neoaphidis (Remaudière & Hennebert) Humber from field collections in Kentucky (KY)and North Carolina (NC) were subjected to various temperature and humidity regimes to evaluate sporulation plasticity. Greatest conidial production occurred at 10-25°C and 100% RH or in free water. No conidia were produced at 30°C or below 98% RH. The optimal temperahlre for in vitro growth of the 2 isolates on modified egg-milk-agar media was 15°C. The NC isolate was more virulent than the KYisolate against tobacco aphid, Myzus nicotianae Blackman, collected from the Lexington, KY, site. Alatae were more susceptible to P. neoaphidis th:rn apterae when exposed to the same source of inoculum at 23°C, 100% RH, and a photoperiod of 16:8 (L:D) h. Conidia produced in vitro by both isolates, when showered onto tobacco leaf disks, were infectious to M. nicotianae for at least 35 h at 100% RH and 23°C.
Preliminary investigations have shown the presence of pathogenic fungi in natural populations of the cassava green spider mites. Among others, Entomopthora sp. and Hirsutella sp. were isolated from dead mites sampled from the field. Laboratory bioassays have given mite mortality of up to 60%, indicating the possibility of utilizing some of these pathogens in mite control. Tests with Beauveria bassiana, isolated from lepidopteran pests, have also shown that the mite is susceptible to this fungus.RésuméDes études préliminaires ont montré, la présence de champignons pathogènes, dans des populations naturelles d'acariens (verts) du manioc. Entre autres, Entomopthora sp. et Hirsutella sp. ont été isolés des échantillons d'acariens (verts) morts prélevés sur le terrain. Des études en laboratoire ont montré un taux de mortalité allant jusqu'à 60%; ce qui suggère la possibilité de l'utilisation de certains champignons pathogènes, dans le contrôle d'acariens. Des tests réalisés avec Beauverua bassiana isolé des Lépidoptères ravageurs ont également montré que l'acarien (vert) est sensible à ce champignon.
Persistence of conidia of an isolate of Erynia radicans (Syn. Zoophthora radicans) was investigated in relation to the meteorological conditions which occurred during autumn-winter of 1990–91 in the coastal plain in Israel. Capilljconidia shielded from the sun, placed on the abaxial surface of leaves of Plumeria acuminata, persisted for 24 h to at least 120 h. Exposed capilliconidia, placed on the adaxial surface of the same leaves, died within 24 h. Almost all the primary conidia shielded from the sun (placed on the abaxial surface of the same leaves) died within a single day. Conidial viability was expressed in subsequent germination on an agar medium.
Capilliconidial persistence was closely related to the daily air temperatures, expressed as cumulative day-degrees. Differences in relative humidity had no substantial effect on capilliconidial mortality. At daytime temperatures of ≤ 20°C, mortality after 24 h incubation was lowest (≤ 34%) and the persistence duration, longest (at least 120 h). Increases in daytime temperature up to 24°C for a few hours increased mortality (37–57% after 24 h incubation) and shortened the persistence duration (72–120 h). Exposure to 24–29°C during daytime greatly increased mortality (65–58% after 24 h) and further shortened the persistence duration (24–48 h). Daytime temperatures of > 29°C were lethal to all capilliconidia within 24 h. Temperature had a profound effect on capilliconidial persistence also under controlled environmental conditions. The significance of capiliiconidial persistence is discussed in relation to activity of the fungus in its natural environment.
Survival of primary conidia and capilliconidia of isolate 3186 of Erynia radicans was compared at 50, 90, and 100% relative humidity (RH), 20°, 25°, and 30°C, and incubation periods of 24, 48, and 72 hr, in darkness. The capilliconidia invariably survived better than the primary conidia, especially at the unsaturated atmospheres, as expressed in subsequent germination on agar medium. At 50% RH and 20°C, 19% of capilliconidia still survived after 5 weeks, compared to almost none of the primary conidia after only 1 week. Addition of light (white, fluorescent) to a low RH treatment significantly reduced capilliconidial survival. The capilliconidia of three additional isolates of E. radicans, and of an isolate each of Erynia phalloides and Neozygites fresenii, also survived at 50% RH and 20°C in darkness for a week (32–76.3% germination), but almost none of their primary conidia survived (max 0.3% germination). For Erynia phytonomi, lower temperatures, 10° and 16°C, were required for survival of 9 and 16% of the capilliconidia at 50% RH in darkness for a week, while almost none of their primary conidia survived this treatment. The importance of this phenomenon to capilliconidia-forming fungi in their natural environment is discussed.
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.
The survival of three isolates of Zoophthora radicans (NW 250, NW 253 & NW 182) as hyphal bodies in dried larvae of Plutella xylostella stored at 4, 10 and 20°C and 20% R.H was determined. After storage at 20°C, the production of conidia by all isolates was unaffected after 2 weeks but diminished increasingly after 4 and 8 weeks and was entirely lost after 16 weeks. By comparison conidium production at 10°C was unaffected after 16 weeks (isolates NW 250 and NW 182) and, 24 weeks (NW 253) of storage though it declined rapidly in all isolates thereafter. At 4°C many conidia were produced by all isolates even after 34 weeks of storage. These results are consistent with work on other entomophthoralean fungi in dried cadavers suggesting that this may be a common survival strategy in these fungi. NW 250, 253 and 182 were isolated from P. xylostella in Malaysia and Taiwan, where conditions allow the host to remain active throughout the year. None produced resting spores in vivo or in vitro but as hosts are always available the ability to survive short dry periods is probably more important than long-term survival for which resting spores are most adapted.
Tests were conducted on the hostspecificity of a Brazilian isolate of thefungus Neozygites floridana, a potentialbiological control agent for the cassava greenmite, Mononychellus tanajoa, in Africa.Five insect and two mite species, mostly fromthe cassava agroecosystem, were evaluated forsusceptibility to N. floridana, namelyEuseius concordis, E. citrifolius, Phenacoccus herreni, Stethorus sp., Aleurothrixus aepim, Apoanagyrusdiversicornis, and Bombyx mori.Individuals of each species were exposed tocapilliconidia (the infective stage of thefungus). None of the tested individuals wasfound with hyphal bodies (the vegetative stageof the fungus), whereas 73 to 94% of thecassava green mites in the controls becameinfected. Non-germinated capilliconidia were,however, found attached to several individualsin most species. N. floridana appears tobe safe for exportation. Further evaluation ofits performance against M. tanajoa inAfrica is therefore desirable.
Infections ofTetranychus evansi
Baker & Pritchard byTriplosporium sp. were observed on tomatoes from April through June of 1979 in Petrolina (Pernambuco), Brazil. Apparently, the pathogenic
effect of the fungus together with the direct effect of the rain are important factors in reducing mite populations. The morphological
characteristics of this species are described and compared with those of other mite-infectingTriplosporium spp. The taxonomic status of this fungus on the specific and generic levels is discussed.
Dans les conditions de Petrolina (Pernambouc), Brésil, on a observé sur des plants de tomate, chezTetranychus evansi
Baker & Pritchard un taux élevé d'infection causée par unTriplosporium sp. Ces observations correspondent à la période Avril–Juin 1979. Elles permettent de conclure que selon toute vraisemblance,
l'action pathogène du champignon et l'effet direct de la pluie jouent un rôle important dans la diminution des populations
d'acariens. Les caractères morphologiques de cette espèce sont décrits et comparés avec ceux des autres espèces deTriplosporium qui affectent les acariens. La position spécifique et générique de ce champignon est discutée.
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.
Species of entomophthoraceous fungi attacking insects and mites are very well represented in Israel. In the last decade, 22
species ofEntomophthora sensu stricto, Triplosporium, Zoophthora, Conidiobolus, and others under the designationEntomophthora sensu lato, have been identified, of which three are new species:Entomophthora turbinata, Zoophthora erinacea andZ. orientalis. Fiftyfour host-pathogen combinations hitherto not recorded in Israel are listed, of which 19 insect species are new hosts
of entomophthoraceous species anywhere.
The seasonal occurrence of entomophthoralean host-pathogen combinations and of conidialvs. resting spore production in Israel is presented and discussed. The data recorded during 1968–1979 concern the following species
and their recorded hosts:Conidiobolus apiculatus, C. coronatus, C. osmodes, C. thromboides, andConidiobolus spp.;Entomophthora planchoniana;Neozygites fresenii; Erynia erinacea, E. neoaphidis, E. nouryi, E. occidentalis, E. phalloides,
E. phytonomi andE. radicans.
The fungusEntomophthora culicis (Braun) Fies. 1858 was found in Israel for the first time in 1976 on insects of the order Diptera on grapefruit.
Dentre 45 isolados de Hyphomycetes testados, oito de Beauveria bassiana e quatro de Metarhizium anisopliae causaram em Tetranychus urticae, mortalidades superiores a 80 e 90%, respectivamente, cinco dias após a inoculação na concentração de 5x107 conídios/mL. Hirsutella sp. atingiu 73% de mortalidade na concentração de 1,7x107 conídios/mL. Entre 80 a 100% dos cadáveres de ácaros colonizados pelos isolados de B. bassiana e M. anisopliae apresentavam, internamente, cristais de cálcio. Conídio aéreo, blastósporo e célula de levedura de cinco isolados B. bassiana foram patogênicos a esta praga. Diferenças significativas (P đ 0,05) para CL50 e coeficiente angular entre os isolados e entre as estruturas infectivas foram observadas. Os valores da CL50 variaram de 4,95x106 a 8,21x107 estruturas infectivas/mL. Não houve diferença significativa entre as estruturas infectivas para os dois parâmetros avaliados, contudo, houve diferenças significativas para a CL50 entre as estruturas infectivas em um mesmo isolado de B. bassiana. Três formulações de fungicidas, 24 de inseticidas e/ou acaricidas foram compatíveis com B. bassiana, sendo formulados com as seguintes moléculas: propamocarb hidrocloreto, enxofre, abamectin, acefato, acetamiprid, betacyflutrin, bifentrina, ciromazina, deltametrina, diafentiuron, diflubenzuron, dimetoato, fenpropatrina, fenpyroximate, fenvalerate, imidacloprid, metamidofós, propargite, tebufenozide e triclorfon. Houve grande varia. (Continuação) reduziu de 1,8 para 0,1 ácaro/folha. Na cultura do morango (Fragaria spp.) a eficiência de B. bassiana foi inferior ao crisântemo, com densidade média de ácaros ao longo de 21 dias de avaliação para as concentrações 1x108 e 5x107 conídios/mL de 13 ácaros/folíolo, contra 43 ácaros/folíolo nas parcelas não tratadas. As variedades de morango Campinas e Princesa Isabel foram as que apresentaram as menores densidades do ácaro, contudo, não houve evidência de que estas variedades interferiram na eficiência de controle da praga por B. bassiana. Assim, M. anisopliae, B. bassiana e Hirsutella sp. foram os fungos mais promissores para serem formulados como micoacaricidas para o controle de T. urticae. Tese (Doutorado).
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.
Infections by insect-pathogenic fungi of the order Entomophthorales in two adult black fly populations were studied in the Réserve Faunique du Saint-Maurice (Quebec). Entomophaga near limoniae infected Simulium verecundum/rostratum in June whereas Erynia curvispora predominantly parasitized Simulium decorum from the 2nd week of July to September and Erynia conica attacked the Simulium venustum complex, Simulium verecundum/rostratum, and the Simulium vittatum complex from May to September. The fungi did not infect the adult stage of Prosimulium species. Possible evidence of host specificity for Erynia conica is discussed.
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.
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.
Recently, Selhime and Muma (1966) studied the biology of an entomophthoraceous fungus attacking the Texas citrus mite, Eutetranychus banksi (McGregor). This study and a series of earlier publications including Fisher (1954), Muma (1955 and 1958) and Muma et al. (1961) have indicated the unusual frequency of the fungus in the field and its potential importance in the biological control of the Texas Citrus mite. This fungus, described in the present paper, is not the only Entomophthora known to infect Acarina. Petch (1940) described Entomophthorct acaricida from Halotydems destructor Tucker and later, Petch (1944) described E. acaridis from other infected Acarina. Recently, Batko (1965) recorded Conidiobolus brefeldianus Couch from Tyrophagus perniciosus Zachvatkin and other tyroglyphid mites. METHODS
A pathogenic fungus, Entomophthora fresenii Nowakowski, was found attacking the two-spotted spider mite, Tetranychus urticae Koch, and the carmine spider mite, T. telarius (L.), at several locations in Alabama. The following structures of the fungus were observed: hyphal bodies which are the vegetative phase that proliferates in the hemocoel of the mite; conidia which are forcibly ejected from the body of the dead mite; secondary spores which are formed by germination of the conidia; tertiary spores; quaternary spores. The secondary spores appear to be the infective units of the fungus.
Parasitism of spider mites by the fungus in the field varied with the location and collection date and ranged from an average of 30.9% in collections from Lee County (Loachapoka) to 86.4% in those from Cullman County (Cullman). Up to 88% of the live mites collected from fields where epizootics of the fungus were observed succumbed to mycosis within 2 days after collection.
It appears that this fungus may play a role in the regulation of populations of some species of spider mites on cotton.