Evaluation of Insecticides for Lygus Bug Control and Their Effect on Predators and Pollinators

Abstract

A laboratory method involving the use of caged carrot seed heads was evolved to study the effectiveness of new insecticides and insecticidal combinations for lygus bug control. These laboratory tests showed that DDT or toxaphene combined with Dipterex or malathion resulted in quicker lygus bug mortality and lasted for a longer period of time than each insecticide did when used alone. Malathion and Dipterex alone resulted in satisfactory lygus bug control, but they were not as long lasting as DDT. Bayer 19639, Thiodan, demeton, endrin, and a combination of DDT-Trithion were identified as new treatments of potential value against this pest by means of the laboratory tests. Replicated plots and aircraft applications in fields of seed carrots showed that DDT was satisfactory for lygus bug control in this area. DDT did not appreciably reduce numbers of honeybees or cause a buildup of red spiders. Dipterex and malathion resulted in satisfactory lygus bug control, caused no spider mite buildup, but did not last as long as DDT and were of no ad- vantage for use on the carrot seed crop. Under the conditions of these experiments, DDT-Dipterex was the only new treatment indicated as a possible substitute for DDT or toxaphene for lygus bug control. This combination treatment significantly increased mortality over that of DDT, did not induce a buildup of spider mites, or reduce numbers of honeybees. The toxaphene-Dipterex combination was also significantly more toxic to lygus bugs than DDT. However, this combination, as well as toxaphene-malathion and DDT-malathion combinations, caused a spider mite buildup; and they were highly toxic to the predaceous insects present in carrots grown for seed. Data from field trials on carrot seed crops showed that it was advisable to evaluate new treatments in terms of their effect on beneficial insects as well as on the lygus bugs.