Foliar persistence and residual activity of four insecticides of different mode of action on the predator Engytatus varians (Hemiptera: Miridae).

A greenhouse study was conducted to investigate the degradation kinetics of spinosad, flufenoxuron, dimethoate and imidacloprid in tomato (Solanum lycopersicum L.) foliage and their residual toxicity on Engytatus varians (Distant) (Hemiptera: Miridae), a predator of the tomato psyllid Bactericera cockerelli (Sulcer) (Hemiptera: Triozidae). Insecticides were sprayed at 100% and 50% of their maximum field-registered concentrations (MFRC). Starting 6 h after spraying, leaf samples were taken every 10 d for 40 d and analyzed while E. varians adults were exposed to treated leaves to evaluate residual toxicity. Immediately after application at 100% MFRC, the residue concentrations were 73.34 µg g-1 spinosyn A and 59.2 µg g-1 spinosyn D, 9.21 µg g-1 flufenoxuron, 71.49 µg g-1 dimethoate and 31.74 µg g-1 imidacloprid. At 50% MFRC, initial residue concentrations were between 75% and 90% those at 100% MFRC. The estimated half-life (DT50) of spinosyns A and D, flufenoxuron, and dimethoate was between 34 and 40 d, while that of imidacloprid was 112 d. Flufenoxuron caused no mortality, while mortality due to spinosad was less than 10%, and only during the first 10 d. Mortality caused by either imidacloprid or dimethoate was around 100% up to 10 d after application, then decreased to around 30% after 40 d. Dimethoate toxicity was approximately proportional to residue concentration, while for imidacloprid there was an apparent threshold around 15 µg g-1. These results can be used to establish periods harmless for release of E. varians in the control of B. cockerelli on tomato crops under greenhouse conditions.

Lethal and Sublethal Effects on Tamarixia triozae (Hymenoptera: Eulophidae), an Ectoparasitoid of Bactericera cockerelli (Hemiptera: Triozidae), of Three Insecticides Used on Solanaceous Crops.

Lethal and sublethal effects of refined soybean oil, imidacloprid, and abamectin on Tamarixia triozae (Burks; Hymenoptera: Eulophidae) were assessed after exposure of the eggs, larvae, and pupae of this parasitoid to three concentrations of these active substances: the LC50 for fourth-instar Bactericera cockerelli (Sulc.; Hemiptera: Triozidae) and 50% and 100% of the minimum field-registered concentration (MiFRC). Soybean oil caused 26-61% mortality in T. triozae eggs and 6-19% in larvae; mortality in both eggs and larvae was ≤19% for imidacloprid and 4-100% for abamectin. All three compounds caused <18% mortality of T. triozae pupae, with the exception of the abamectin 50% (47%) and 100% (72%) MiFRC. The mortality of larvae and pupae derived from treated eggs was ≤39% for all three insecticides, and that of pupae derived from treated larvae was ≤10%. In general, emergence of adults developed from treated eggs, larvae, and pupae was affected more by abamectin than by the other treatments. The proportion of females derived from all three development stages was not affected by treatment with the compounds, except when the parasitoid was treated as larvae with the soybean oil 100 and 50% MiFRC (66 and 68%, respectively) or when treated as pupae with the imidacloprid LC50 and 100% MiFRC (~60%). Female longevity was generally higher than that of males. The use of imidacloprid, soybean oil, and abamectin in combination with T. triozae for pest control may be effective when the parasitoid is in the pupal stage because this stage is less susceptible than other immature stages.