Lethal and Sub-Lethal Effects of Organic-Production-Approved Insecticides and Fungicides on the Predator Macrolophus pygmaeus (Rambur) (Hemiptera: Miridae)

SIMPLE SUMMARY: Macrolophus pygmaeus is an important natural enemy of major tomato insect pests; however, its beneficial role may be negatively impacted by insecticides and fungicides. Studies on lethal and sub-lethal effects of widely used insecticides and fungicides on this predator are limited. This predator may slightly, partially or fully consume its prey, and this study examined the effects of pesticides on each of these predatory behaviors as a means of identifying in more detail the influences of pesticides on the activity of this predator. The effects of paraffin oil, copper hydroxide, copper oxychloride, wettable sulfur, Beauveria bassiana and deltamethrin, as a toxic reference treatment, were examined. The results showed that copper hydroxide and B. bassiana may cause significant adverse effects on the survival of M. pygmaeus depending on their application. In addition, the sub-lethal effects on the predatory behavior of M. pygmaeus, as shown by variation in the percentages of prey slightly, partially and fully consumed, were differentiated among the pesticides. The importance of the results for defining best practices in IPM and new approaches in studying sub-lethal effects on M. pygmaeus and other hemipteran predators are discussed. ABSTRACT: In this study, the effects of paraffin oil, copper hydroxide, copper oxychloride, wettable sulfur, Beauveria bassiana and deltamethrin, as a toxic reference treatment, on the survival and predation rate of M. pygmaeus were investigated. In each treatment, the prey were classified as slightly, partially or fully consumed. The mortality rate after contact exposure was high (66.6%) when nymphs were treated with copper hydroxide but much lower after residual exposure (6.6%). B. bassiana caused 53.3% and 46.6% mortality via contact and residual exposure, respectively. The total prey consumption was significantly lower in the pyrethroid reference treatment control and B. bassiana treatments. The highest percentage of slightly consumed prey was recorded in the toxic reference and B. bassiana treatments, that of partially consumed prey in the copper hydroxide treatment and, finally, that of fully consumed prey in the paraffin oil treatment. Therefore, assessing the sub-lethal effects by separating the prey killed into slightly, partially and fully consumed is a sensitive approach to detect impacts which otherwise may remain unnoticed. The results provide information for the most appropriate use of M. pygmaeus in IPM programs and introduce more sensitive approaches in the detection of side-effects of pesticides on M. pygmaeus and other hemipteran predators.