Effect of simulated heat waves on the behaviour of two mirid predators

Extreme climatic events, including heat waves with high-temperature peaks during the day, are expected to occur more often in many parts of the world due to climate change and may exert negative effects on existing biological control strategies. To assess the effects of high-temperature peaks on two commonly used, and naturally co-occurring mirid predators, adults and nymphs of Nesidiocoris tenuis and Macrolophus pygmaeus were exposed either to constant 25 degrees C or daily mean temperatures of 25 degrees C with cycles rising up to 30 or 40 degrees C. Preferred location of the two mirid species on different strata of tomato plants was investigated when they were exposed to the different temperature regimens alone or combined. Activity of mirids under the different temperature regimens was continuously monitored for 48 h using a Drosophila Activity Monitor system. Finally, the efficacy of the mirids preying on Tuta absoluta eggs was measured at the different temperature regimens in a Petri dish assay. Heat waves reaching 30 and 40 degrees C in some instances affected the location of the mirids either when they were on the plant alone or under competition conditions. Locomotory activity of M. pygmaeus in the 40 degrees C treatment was strongly reduced, whereas it remained high in N. tenuis. Effects of temperature peaks on prey consumption were visible in M. pygmaeus nymphs, N. tenuis females and males of both species. We suggest that the different responses of the two species to high-temperature peaks may reduce their competition and support sustained control when both species are present simultaneously. Moreover, both species were found to be less susceptible to heat peaks when compared to previously reported results for their prey T. absoluta.