Effects of Acibenzolar-S-methyl on the Probing Behaviour and Mortality of Cacopsylla pyri on Pear Plants

SIMPLE SUMMARY: Acibenzolar-S-methyl is an analogue of salicylic acid, and it is known as a plant elicitor able to induce plant endogenous defences against plant pathogens. Recently, it has been shown to also affect phloem-feeder pests, even though the mechanism is still unclear. Pear psylla (Cacopsylla pyri) is a serious threat for pear production in Europe, and its control is usually based on the use of chemical insecticides. The development of novel innovative control approaches is becoming more and more important, especially in integrated pest management. The present work investigated the possible indirect influence of acibenzolar-S-methyl, through the expression of pear Pathogenesis-Related protein (PR) coding genes, on the probing behaviour and on the survival of C. pyri nymphs and adults feeding on pear potted plants. The minor effects observed on the pest would suggest that acibenzolar-S-methyl cannot be used against psyllas, but it might be recommended on pear orchards in the primary control of other targets such as fire blight disease. ABSTRACT: European pear psylla, Cacopsylla pyri, is one of the worst pests of pear in Europe. We investigated whether acibenzolar-S-methyl (ASM) application on pear plants might affect the behaviour in C. pyri. The elicitor was applied on pear potted plants, and after 48 h, we confirmed the ASM-mediated induction of several Pathogenesis-Related protein (PR) coding genes. At the same time, an in-depth analysis was performed on the probing behaviour of adults and nymphs of C. pyri on ASM-treated pear plants by the EPG-DC system, as well as the assessment of young nymphs’ survival 7 days after the ASM application. The elicitor application weakly interfered with C. pyri nymphs probing behaviour and survival, while it did not affect adult stages. These data confirm previous observations obtained on C. pyricola and suggest that the elicitor does not represent a viable tool in the control of pear psylla species, especially if used alone, but it might be used in integrated management strategies focused on other plant pathogens such as Erwinia amylovora.