Side effects of inscticides in tomato crops on the predatory mirids Macrolophus basicornis and Nesidiocoris tenuis

Abstract

The South American tomato pinworm, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is probably the main tomato pest in several countries around the world. Caterpillars of this species feed on all aerial parts of tomato plants and can cause up to 100% yield loss if not controlled. Chemical control with synthetic insecticides is the main tactic employed in most of the cases, however there are several problems associated with this practice, such as selection of T. absoluta resistant populations. For this reason, other control measures should be adopted to reduce T. absoluta populations. The biological control with predatory hemipterans is a well succeeded strategy in several Europeans countries, most frequently with the mirid Nesidiocoris tenuis (Reuter) (Hemiptera: Miridae). In Brazil the species Macrolophus basicornis (Stal) (Hemiptera: Miridae) is being studied, and was observed that it can prey upon T. absoluta eggs and small larvae. However, for these species effectively exerce their biological control, insecticides must be employed carefully. Therefore, the main objectives of this study were: (I) evaluate lethal and sublethal effects of insecticides recommended to control T. absoluta in Brazil on M. basicornis, (II) determinate sublethal concentrations of insecticides and plant essential oils to N. tenuis, and (III) evaluate the effect of sublethal concentrations (LC1, LC10, LC30) of insecticides and plant essential oils on N. tenuis fecundity and orientation. In the experiments of the present thesis the predators M. basicornis and N. tenuis were exposed to insecticide compounds in laboratory conditions. Nymphs of the South American species (M. basicornis) were exposed to full doses of insecticides considered safe to natural enemies (teflubenzuron, methoxifenozide and chlorantraniliprole), plus a positive control (abamectin) by residual contact on tomato leafles. Only abamectin caused high nymph mortality, however the other compounds caused sublethal effects, such as reduction in adult size and increase of development time, although adult survival and progeny were not affected. Among them, chlorantraniliprole was considered the safest insecticide for M. basicornis. For the European species (N. tenuis), adult females were directly treated with sublethal concentrations of three neurotoxic insecticides (lambda-cyhalothrin, chlorpyrifos and spinosad) and four plant essential oils encapsulated in nanoemulsions (anice, lavender, garlic and fennel). First, a concentration-mortality relation was stablished for all compounds and N. tenuis females, with this was possible to estimate sublethal concentrations. Nesidiocoris tenuis females were exposed to three sublethal concentrations of each compound (LC1, LC10 and LC30) and their effect was assessed on their fecundity and orientation. The fecundity of females was affected by sublethal concentrations of the compounds. Moreover, some of the compounds, even in very low concentrations, affected the orientation insects and also the response time to make a choice. The insecticides and essential oils must be used carefully.