Boll weevil is the major cotton pest in Brazil, and insecticides are widely recommended against it. We determined the susceptibility of boll weevil to insecticides either in single or in mixture ready-to-use formulations, which are registered to spray cotton fields under the hypothesis that mixtures are more toxic to the target pest. Concentration-mortality curves were determined to adult species, simultaneously through dried residues and ingestion. Ten insecticide formulations were studied with five in mixture (lambda-cyhalothrin + thiamethoxam, lambda-cyhalothrin + chlorantraniliprole, thiamethoxam + chlorantraniliprole, and fenitrothion + esfenvalerate) and their five respective single formulations. Cotton leaf discs and cotyledons were dipped into insecticide dilutions prepared by diluting the commercial products into distilled water. Adult mortality was assessed 48 hours after caging adults on treated and untreated materials. The LC50s-concentrations varied from 0.004 to 0.114 g a.i./L, with a relative potency between single and mixture ones, varying from 1.37- to 29.59-fold. Furthermore, lambda-cyhalothrin and thiamethoxam in single formulation were the most toxic insecticides to boll weevil. Among insecticide mixtures, only lambda-cyhalothrin + chlorantraniliprole resulted in a synergic effect; whereas the remaining mixtures showed an antagonistic effect. Therefore, except for the mixture of lambda-cyhalothrin + chlorantraniliprole, the remaining mixtures did not enhance toxicity against the boll weevil and should be recommended only when aimed at different purposes.
Predator species under field conditions can face different and variable densities of prey species. This work evaluated the functional response of the neotropical lady beetle Eriopis connexa(Coleoptera: Coccinellidae) subjected to different densities of the aphids Brevicoryne brassicaeand Aphis craccivora(Hemiptera: Aphididae). Thus, predation rates were analyzed of fourth-instar larvae and one-day old adults of the lady beetle preying upon the aphids at constant densities of 20, 40, 50, 60, and 70 aphids with 15 repetitions per density. The aphids were offered on 5 cm leaf discs of each plant host. The handling times and attack rates were 0.03 h-1and 0.27 h-1for larvae and 0.03 h-1and 0.15 h-1for adults fed B. brassicae and 0.59 h-1and 0.35 h-1for larvae and 0.70 h-1and 0.95 h-1for adults fed A. craccivora, respectively. Both larva and adult lady beetles increasedpredation rate as a function of prey density offered, with an estimated maximum number of prey consumed of 30.3 and 31.6 B. brassicae and 36.3 and 34.6 of A. craccivora by larva and adult lady beetles at the highest prey density, respectively. In conclusion, larvae and adults of E. connexaexhibited a type II functional response.
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