No abstract

Worldwide biological-control research has shown that the fungal entomopathogen Metarhizium anisopliae (Metschnikoff) is an alternative to chemical insecticides for controlling grasshoppers and locusts. The pathogenicity of two recently discovered isolates of M. anisopliae var. anisopliae Driver and Milner from Canadian soil to the key grasshopper pest Melanoplus bivittatus (Say) and the yellow mealworm, Tenebrio molitor L., was determined by means of laboratory bioassays. Insects were fed a single dose of 105 conidia suspended in sunflower oil on food (a standard-size lettuce wafer). Subsequent feeding activity, movement, and mortality were assessed daily. The isolates were equally pathogenic, and similar in pathogenicity to the industry standard, Green Guard (M. anisopliae var. acridum Driver and Milner). Treatment with the three isolates resulted in 50% grasshopper mortality in 5–6 days and 90% mortality in 6–7 days.

A genetic variant of the entomopathogenic fungus Metarhizium anisopliae var. anisopliae, isolated from a soil in Alberta, Canada, from a location with a history of severe grasshopper infestations, was evaluated for pathogenicity in bioassays of living grasshoppers. Mortality in treated individuals drawn from a laboratory colony was 99% (LT 50 = 6.7 days, LT 90 = 9.6 days) at 12 days postinoculation compared to 100% (LT 50 = 4.1 days, LT 90 = 5.8 days) mortality at 8 days in insects exposed to a commercial isolate of M. anisopliae var. acridum (IMI 330189). Experimental infection of field-collected grasshoppers under laboratory conditions with the native isolate of M. anisopliae var. anisopliae resulted in 100% (LT 50 = 4.4 days, LT 90 = 5.4 days) mortality attained within 7 days compared to 100% (LT 50 = 4.7 days, LT 90 = 6.3 days) mortality in 9 days in insects treated with M. anisopliae var. acridum. Amplification of fungal genomic DNA from the indigenous isolate with primers for the specific detection of M. anisopliae var. anisopliae produced a product almost 300 bp larger than expected based on previously known isolates. This is the first demonstration of a highly virulent, indigenous non-chemical control agent of grasshoppers in North America.