Three formulations of malathion, were each aerially applied at three different doses to cotton fields near Carlsbad New Mexico for evaluation against boll weevil. An extensive bioassay utilizing field collected cotton leaves and laboratory reared weevils and field estimates of feeding and oviposition damage were used to compare the individual activity levels among the different treatments. Mortalities resulting from weevils exposed to treated and untreated leaves were compared. Feeding and oviposition damage was compared between treated and untreated plots. Mortality data resulting from all treatments for residual ages of 0, 2, 4, 6, 8, 10, 12 and 14 days are shown. Feeding and oviposition damage data are reported generally for all treatments at 4 and 8 days after application.

All three doses of the standard Fyfanon ULV formulation demonstrated significant activity for two days after treatment. The traditional 0.93 lb AI/acre dose produced 100% mortality compared to 7% mortality in untreated populations on day 0. At 4 days after treatment, the 0.93 lb AI/acre dose produced 25% mortality compared to 11% in the untreated populations which was not statistically different in this study.

The two highest doses of the Cheminova CS formulation produced significant activity for 4 days after treatment. The 0.93 lb AI/acre dose produced 85% mortality compared to 48% mortality in untreated populations on day 4. At 6 days after treatment, both the 0.93 lb AI/acre dose and untreated populations demonstrated 11% mortality.

All three doses of the 3M MEC formulation demonstrated significant activity for 14 days after treatment. At 14 days after treatment, the 0.93 lb AI/acre, 0.77 lb AI/acre and 0.62 lb AI/acre doses produced 32%, 33% and 41% mortality respectively, compared to 6% mortality in the untreated population.

In this study, the 3M MEC formulation demonstrated significant activity for 12 days longer than the standard Fyfanon ULV treatment. When coupled with the data gathered in 1999, where the 0.77 lb AI/acre Cheminova CS formulation produced significant activity at 12 days after treatment, our data strongly suggest that activity for two weeks after treatment may be achieved with an encapsulated formulation of malathion. Such improvement in treatment effectiveness could substantially reduce overall pesticide load, application costs and logistics for boll weevil programs.