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The infectivity of the pea aphid, Acyrthosiphon pisum, by the aphid-specific entomophthoralean fungus, Pandora neoaphidis, was studied in environmental chambers using computer simulated late-season temperature and photoperiod patterns and an excised fava bean leaf system. A complementary log-log (CLL) time–dose–mortality model was used to model time–dose trends in infectivity of A. pisum by P. neoaphidis as a function of time and dose, and calculate the LC[sub 50]. The likelihood ratio test based on the CLL model was used to test for differences in levels of aphid infectivity by P. neoaphidis over different photoperiod regimes. Differences in the LC[sub 50] values from CLL modelling over different time periods were found among the two regimes of 11- and 16-h photophases at a constant temperature of 20°C, and two regimes at daily fluctuating temperatures from 5.4 to 18.9°C (with half-hourly changes of 0.56°C the mean temperature was 12.12°C). The LC[sub 50] for the same time period was lower under the higher temperature conditions than under lower fluctuating temperature conditions. The likelihood test ratio statistics showed no significant difference in the slope parameter for three out of four treatments (two from the constant temperature of 20°C, and one from 5.4 to 18.9°C, irrespective of photophase conditions). This suggests that different temperatures and photophases may change the temporal characteristics of P. neoaphidis, and result in higher or lower infectivity to the pea aphid at certain dosage levels. However, changes in the photoperiod appear to be less important for the infectivity of P. neoaphidis to pea aphid than changes in temperature. [ABSTRACT FROM AUTHOR]

Beauveria bassiana (Balsamo) Vuillemin, Metarhizium anisopliae (Metschnikoff) Sorokin var. anisopliae, Fusarium sp. near F. solani (Martius) Appel & Wollenweber, Cordyceps sp., Penicillium sp. and Aspergillus sp. were isolated from pest June beetles, Phyllophaga spp., in southern Quebec. The pathogenicity of the Hyphomycetes for Phyllophaga grubs was assessed by contact with sporulating fungal cultures. Grubs were moderately to highly susceptible to the fungi. Mortality was higher with B. bassiana (Bb) and M. anisopliae (Ma) than with other Hyphomycetes. The muscardines were also bioassayed against grubs using various administrative routes (oral, topical, injection and soil application). Both Bb and Ma were weakly to not infectious when injected or force-fed to the grubs. Topical application of spore suspensions induced green muscardine mycosis in 64% of second and 52% of third instar grubs, but mortality was lower with Bb (39 and 28%). Soil application of relatively low spore rates of Ma gave respectively 82 and 97% control of second and third instar grubs, but a 10-fold higher spore rate of Bb achieved only 24% control of second instars. White grubs were also susceptible to Ma applied to the soil of field plots under natural environmental conditions. The LC50 value for the fungus was ca. 1.0 × 10-12 spores ha-1 of soil. Metarhizium anisopliae is considered as a promising biocontrol agent of Phyllophaga spp. Zusammenfassung Z.um Auftreten von Pilzen in natürlichen Populationen von Phyllophaga spp. und zur Empfindlichkeit von Phyllophaga anxia (LeConte) (Col., Scarabaeidae) gegenüber Beauveria bassiana und Metarhizium anisopliae (Deuteromycotina) Beauveria bassiana (Balsamo) Vuillemin, Metarhizium anisopliae (Metschnikoff) Sorokin var. anisopliae, Fusarium sp. nahe F. solani (Martius) Appel & Wollenweber, Cordyceps sp., Penicillium sp. und Aspergillus sp. konnten aus Junikäfern, Phyllophaga spp. im südlichen Quebec isoliert werden. Die Pathogenität dieser Pilze für Phyllophaga-Larven wurde durch Kontaktinfektion mit sporulierenden Pilzkulturen getestet. Die Larven erwiesen sich als leicht bis hochempfindlich. Bei der Infektion mit B. bassiana (Bb) und M. anisopliae (Ma) ergaben sich höhere Mortalitätswerte als bei anderen Hyphomycetes. Daneben wurden auch andere Infektionswege getestet: oral, topikal, Injektion und Bodenbehandlung. Sowohl Bb als auch Ma waren nur schwach bis nicht infektiös, wenn sie den Larven injiziert oder per Zwangsfütterung verabreicht wurden. Die topikale Applikation der Sporensuspension verursachte bei 64% der L2 und bei 52% der L3-Larven eine Mykose, aber die Mortalitätsrate war geringer (39 bzw. 28%). Die Bodenapplikation einer relativ geringen Sporenkonzentration von Ma führte bei L2-Larven zu 82% und bei L3-Larven zu 97% Mortalität, dagegen konnte bei einer 10x höheren Bb-Konzentration nur eine 24%ige Mortalität der L2-Larven beobachtet werden. Weiße Larven erwiesen sich gleichfalls als empfindlich gegenüber Ma, wenn der Pilz unter natürlichen Umweltbedingungen im Freiland getestet wurde. Der LC50-Wert betrug ca. 1 × 1012 Sporen pro ha Bodenfläche. Metarhizium anisopliae kann in der biologischen Bekämpfung von Phyllophaga spp. als sehr vielversprechend betrachtet werden. [ABSTRACT FROM AUTHOR]

Laboratory bioassays were conducted to determine the effect of host plant on mycosis in two geographically distinct populations of early 2nd-instar nymphs of Bemisia argentifolii Bellows & Perring from the entomopathogenic fungi Beauveria bassiana (Balsamo) Vuillemin and Paecilomyces fumosoroseus (Wize) Brown & Smith. Mycosis in B. argentifolii nymphs varied according to the host plant on which the nymphs were reared but not according to the population. Both populations of whiteflies reared on cotton were consistently significantly less susceptible to infection by either fungus than when reared on melon. We hypothesized that the cotton plant produced a fungal inhibitor that may confer protection on whiteflies feeding (and possibly sequestering) upon it. Germination of conidia of both fungi was strongly inhibited (below 12% germination) on the cuticle of nymphs reared on cotton but was over 95% on the cuticle of nymphs reared on melon. We further hypothesized that the terpenoid gossypol, produced by many cultivars of cotton, might have been involved in antibiosis. Gossypol mixed with Noble agar at five concentrations was tested for its effects on germination of conidia of both fungi. P. fumosoroseus was highly tolerant of gossypol, even at the relatively high concentration of 1000 ppm, while B. bassiana tolerated gossypol at concentrations up to 500 ppm and strong inhibition only occurred in presence of gossypol at 1000 ppm. Our in vivo findings on cotton and on the insect's cuticle pointed at a potential host plant-mediated antibiosis. The in vitro tolerance of P. fumosoroseus and partial tolerance of B. bassiana to gossypol disagreed with our in vivo data. Gossypol concentrations higher than 1000 ppm might have increased the sensitivity of the fungi in our in vitro tests. Sequestered gossypol (and/or other cotton plant allelochemicals) by B. argentifolii nymphs would explain, at least partially, the insect's defense against the pathogens.

Experiments were conducted to determine the effects of whitefly parasitoids on the cuticular lipid composition of the silverleaf whitefly, Bemisia argentifolii Bellows and Perring [=sweetpotato whitefly, Bemisia tabaci (Gennadius), Biotype B] nymphs. The cuticular lipids of B. argentifolii nymphs that had been attacked by parasitic wasps, either Eretmocerus mundus Mercet or Encarsia pergandiella Howard, were characterized by capillary gas chromatography and CGC-mass spectrometry and the results compared with the cuticular lipids of unparasitized nymphs. Previous studies with B. argentifolii nymphs had shown that wax esters were the major components of the cuticular lipids with lesser amounts of hydrocarbons, long-chain aldehydes, and long-chain alcohols. No appreciable changes in lipid composition were observed for the cuticular lipids of E. pergandiella-parasitized nymphs as compared to unparasitized controls. However, the cuticular lipids from nymphs parasitized by E. mundus contained measurable quantities of two additional components in their hydrocarbon fraction. Analyses and comparisons with an authentic standard indicated that the two hydrocarbons were the even-numbered chain length methyl-branched alkanes, 2-methyltriacontane and 2-methyldotriacontane. The occurrences and possible functions of 2-methylalkanes as cuticular lipid components of insects are discussed and specifically, in regard to host recognition, acceptance, and discrimination by parasitoids. Published 2000 Wiley-Liss, Inc.