Biological control of locusts and grasshoppers.

Control of grasshoppers and locusts has traditionally relied on synthetic insecticides, and for emergency situations this is unlikely to change. However, a growing awareness of the environmental issues associated with acridid control as well as the high costs of emergency control are expanding the demand for biological control. In particular, preventive, integrated control strategies with early interventions will reduce the financial and environmental costs associated with large-scale plague treatments. The recent development of effective oil formulations of Metarhizium anisopliae spores in Africa, Australia, and Brazil opens new possibilities for environmentally safe control operations. Metarhizium biopesticide kills 70%-90% of treated locusts within 14-20 days, with no measurable impact on nontarget organisms. An integrated pest management strategy, with an emphasis on the use of Metarhizium, that incorporates rational use of chemical pesticides with biological options such as the microsporidian Nosema locustae and the hymenopteran egg parasitoids Scelio spp., has become a realistic option.

Effect of temperature on vegetative growth among isolates of Metarhizium anisopliae and M. flavoviride.

Effects of temperature on vegetative growth on a semi-synthetic medium of 22 isolates of Metarhizium anisopliae and 14 isolates of M. flavoviride were determined. The majority of isolates of both species grew between 11 and 32 degrees C; several isolates grew at 8 and 37 degrees C. None of the isolates grew at 40 degrees C. Relative growth rate, calculated from the maximum growth rate for each isolate, was significantly affected by temperature and isolate, with significant isolate * temperature interactions. The maximum absolute growth rates among the isolates ranged from 2.5 mm to 5.9 mm/day. Optimal temperatures were generally between 25 and 32 degrees C with several isolates exhibiting optimal growth at temperatures as high as 32 degrees C. Overall, relative growth rates were greater in isolates of M. anisopliae than M. flavoviride at temperatures of 25 degrees C or lower; conversely mean relative growth rates were greater in M. flavoviride than M. anisopliae at temperatures higher than 25 degrees C. However, the two most cold tolerant isolates at 8 degrees C were M. flavoviride and the three most heat tolerant at 35 degrees C were M. anisopliae. Since temperature growth responses varied considerably between isolates, strain selection according to thermal tolerance may be warranted when choosing a strain for development as a microbial control agent.

Variability in susceptibility to simulated sunlight of conidia among isolates of entomopathogenic Hyphomycetes.

The influence of simulated sunlight on survival of conidia of 4 species of entomopathogenic Hyphomycetes was investigated. Conidia from 65 isolates ofBeauveria bassiana, 23 ofMetarhizium anisopliae, 14 ofMetarhizium flavoviride and 33 isolates ofPaecilomyces fumosoroseus were irradiated by artificial sunlight (295 to 1,100 nm at an ultraviolet-B irradiance of 0.3 W m(-2)) for 0, 1, 2, 4 and 8 h. Survival was estimated by comparing the number of colony forming units (CFU) produced by conidia exposed to irradiation to the number of CFUs produced by an unexposed control. Survival decreased with increased exposure to simulated sunlight; exposure for 2 h or more was detrimental to all isolates tested. Overall, isolates ofM. flavoviride were the most resistant to irradiation followed byB. bassiana andM. anisopliae. Conidia ofP. fumosoroseus were most susceptible. In addition to the large interspecies differences in susceptibility to irradiation, there was also an intraspecies variation indicating that strain selection to irradiation tolerance may be important in the development of microbial control agents where increased persistence in an insolated environment is desirable.

Growth of nuclear polyhedrosis virus in larvae of the cabbage moth, Mamestra brassicae L.

Growth of nuclear polyhedrosis virus (NPV) in 5 larval instars of cabbage moth, Mamestra brassicae, has been quantified using 2 methods. Numbers of polyhedra were estimated by light microscope counts while concentrations of virus protein antigen were estimated using ELISA. Virus growth was rapid initially but slowed during its later stages, although ELISA protein concentrations decreased once a peak had been reached. There was a linear correlation between polyhedral counts and virus protein during the initial growth phase. Maximum polyhedral production ranged from 2 x 107 (first instar) to 3.4 x 109 (fifth instar) and could be correlated directly to increasing larval weight. Using ELisa, virus antigen was detectable at least 24 hours before polyhedra were observed under the light microscope. Productivity ratios ranged from 83,500 in the first instar to 1352 in the fifth instar.