Resistance of Diabrotica virgifera virgifera to several insecticides
In Nebraska (US), as in many parts of the western Corn Belt, continuous maize is widely grown and subject to serious damage caused by Diabrotica virgifera virgifera (EPPO A2 quarantine pest). Insecticides are often applied: soil insecticides at planting or first cultivation against larvae; foliar applications to reduce adult populations and therefore egg-laying. In Nebraska, application of soil insecticides at planting time were initially used in the late 1940s. Organochlorine insecticides (BHC, aldrin, heptachlor) were commonly used by 1954. Ineffective control was first observed in 1959, in south-central Nebraska. By 1963, high levels of resistance to aldrin had been reported. The resistant insects rapidly spread and, by 1980, they were present in most of the Corn Belt. Even today, populations of D. virgifera virgifera are still resistant to organochlorine compounds, although these have not been used for many years. From 1970s to early 1990s, carbamates and organophosphorus compounds (e.g. carbaryl, methyl parathion) have been used in Nebraska and provided good larval and adult control. During the last 5 years, reports of insecticide failure have increased in parts of Nebraska where spray programmes have been used for many years. Laboratory studies were done on the susceptibility of adults (collected in selected areas in Nebraska) to 3 insecticides (methyl parathion, carbaryl, bifenthrin). It was found that these field populations showed differences in susceptibility for each insecticide. Relative differences in LD50 values between the most tolerant and susceptible populations were 16.4 and 9.4 fold for methyl parathion and carbaryl, respectively. For bifenthrin, there were less differences (up to 4-fold difference in LD50 values). Bioassays done on F1 colonies showed that these susceptibility traits are heritable. Populations with the highest LD50 values were found in 2 areas where adult management programmes have been extensively applied and treatment failures had commonly been reported. The authors concluded that the current management practices have led to significant levels of resistance to methyl parathion or carbaryl (or both) in certain areas of Nebraska.
Sources
Meinke, L.J.; Siegfried, B.D.; Wright, R.J.; Chandler, L.D. (1998) Adult susceptibility of Nebraska Western corn rootworm (Coleoptera: Chrysomelidae) populations to selected insecticides.
Journal of Economic Entomology, 91(3), 594-600.