Tarnished and Alfalfa Plant Bugs in Alfalfa: Population Suppression with ULV Malathion

ULV malathion (9.7 oz AI/acre) was applied to a 16 mi2 area in August 1968, 1969, and 1970 for western corn rootworm, Diabrotica virgifera LeConte, adult control. Nontarget insects in alfalfa, also treated, were monitored. Tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), was reduced 89–98%. Survival of eggs and adult migration resulted in rapid reinfestation of the treated area in 1969 and 1970; adult migration alone was important in 1968. Alfalfa plant bug, Adelphocoris lineolatus (Goeze), was reduced 96–98%. Repopulation following the 1969 and 1970 treatments was by development from eggs surviving the treatment. The 1969 treatment resulted in lower populations in the treated area through 3 generations the following year. Migration appeared to be a factor in repopulation only following the 1968 treatment, which failed to reduce the 1st generation the next year. Timing of alfalfa harvest during nymphal development is equally effective in population suppression