|Ramirez Ii, Ricardo|
Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/13/2008
Publication Date: 12/30/2008
Citation: Ramirez II, R., Henderson, D.R., Riga, K., Lacey, L.A., Snyder, W.E. 2008. Harmful Effects of Mustard Bio-fumigants on Entomopathogenic Nematodes. Biological Control 48:147.154. Interpretive Summary: Plant parasitic nematodes and the Colorado potato beetle are significant pests of potato in the principal potato production areas of Washington, Oregon and Idaho and other regions where potato is grown. The traditional means of control of these pests is the use of broad-spectrum chemical fumigants and insecticides. Researchers wishing to develop a biorationale approach to pest control have investigated the use of non-chemical means of control. These include bio-fumigant mustards that are tilled into the soil for nematode control and insect–specific nematodes for control of insect pests. Researchers at Washington State University in Pullman and Prosser, WA, and at the USDA-ARS Research Laboratory in Wapato, WA investigated the compatibility of these two methods. Most of the insect-specific nematodes are negatively affected by most of the mustard bio-fumigants. However some cultivars of mustard and at least one species of insect-specific nematode appear to have a degree of compatibility. The use of bio-fumigant mustards for control of plant parasitic nematodes and insect-specific nematodes for control of the Colorado potato beetle and other insect pests provide alternatives to conventional chemical pesticides and may play significant roles in sustainable agriculture. The senior author and his major professor (W. Snyder) have had this manuscript reviewed by at least two colleagues in the WSU Department of Entomology in Pullman and at the IAREC, in Prosser.
Technical Abstract: Green manures, particularly mustards tilled into the soil preceding potato crops act as bio-fumigants that are toxic to plant parasitic nematodes, providing an alternative to synthetic soil fumigants. It is not known if mustard green manures also kill beneficial entomopathogenic nematodes (EPNs) that control of pest insects. We found that rates of entomopathogen infection were lower in fields where mustard bio-fumigants were applied, compared to controls. In laboratory bioassays we then tested if extracts from two mustard cultivars (Brassica juncea) that differ in glucosinolate levels disrupted the abilities of a diverse group of EPN species to infect insect hosts. We used wax moth larvae as hosts, and included multiple EPN spp. in the genera Steinernema and Heterorhabditis. EPN infection rates were lower in laboratory arenas receiving mustard extracts than the control (water), and lower still when EPNs were exposed to extracts from plants with high versus low glucosinolate levels. One EPN species, Steinernema feltiae, appeared relatively unaffected by exposure to mustard extracts. Steinernema species generally exhibited higher infection rates than did Heterorhabditis species. However, there was no evidence that the susceptibility to the negative effects of mustard extracts differed on average between the two EPN genera. Together, our results suggest that the use of mustard bio-fumigants for the control of plant parasitic nematodes has the potential to interfere with the biocontrol of insect pests using entomopathogens. Thus, it may be challenging to combine these two approaches in integrated pest management programs.