Submitted to: Entomologia Experimentalis et Applicata
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 25, 2002
Publication Date: N/A
Interpretive Summary: Commercial agriculture continues to rely heavily on chemical pesticides for insect pest control, despite problems with environmental contamination, worker exposure, and residues in agricultural products. Nucleopolyhedroviruses (NPVs) are naturally occurring viruses, each of which infects only a certain few species of insects or other arthropods. They are promising alternatives to pesticides for many important pests, especially caterpillars. However, NPVs work much slower than most chemical insecticides; they require from several days to a few weeks to kill insects, depending on the virus and insect involved. During the time between when a virus is sprayed and when the insects die, considerable damage to the crop can occur. NPVs are thus usually applied when insects are small, so that they will be killed before they are large enough to do significant damage. However, little specific information exists on exactly how small the insects must be when treated with NPVs in order for damage to be prevented. Our results show that NPV applied to lima beans against second or third instar corn earworms prevented nearly all damage; NPV applied against fourth instars prevented most, but not all, damage. This finding should allow growers to better time NPV applications, and thus obtain better results. The development of effective and economical use patterns for NPVs in practical insect pest management programs should thus increase. This can, in turn, reduce the use of chemical pesticides and problems of contamination, worker exposure, and residues.
Larvae of the corn earworm, Helicoverpa zea (Boddie) were caged as second, third, or fourth instars on lima bean (Phaseolus lunatus L.) plants in the field with or without treatment of the foliage with the H. zea nucleopolyhedrovirus. The virus treatment prevented over 90% of damage to pods and beans if larvae were second or third instars when placed in the cages. Damage to pods and beans was reduced by 73 and 86%, respectively, when the larvae were fourth instars. When insects survived to the end of the test (which occurred only on control plants), damage was not affected by the stadium of the larva when it was placed on the plant, indicating that most damage was done by fourth or later instars. Treatments should thus be applied before insects reach the fourth instar. These results may also be applicable to other crops attacked by the corn earworm, including tomato and soybean.