Study of the overwintering ecology of the hazelnut pest, Palomena prasina (L.) (Hemiptera: Pentatomidae) in a perspective of Integrated Pest Management

Palomena prasina, the green shield bug (GSB), is widely distributed in the Eurosiberian region. In the Southwest of France, it is considered as a serious pest of hazelnuts, its feeding punctures lead to blank hazelnuts and kernel necrosis, causing heavy losses in commercial orchards. To date, no Integrated Pest Management strategy is available to control P. prasina. Control strategies often focus on the pests' spring–summer ecology, when they are in the field or in the vicinity of crops. However, the abundance of pest populations in crops is also related to their autumn‐winter ecology. The present work focussed on the autumn‐winter ecology of P. prasina to identify new opportunities for this pest suppression. We investigate (i) where P. prasina overwinters, (ii) if it aggregates in its overwintering sites and (iii) if it mates while overwintering. Samples were collected over a 2‐year period in different ecosystems (forests, hedges, orchards), in human‐made structures and habitats (litter, bushes/trees, dead trees). The reproductive status of GBS individuals was monitored in winter, and in spring when they emerged from overwintering sites. Our results show that 97% P. prasina adults overwinter in the leaf litter of orchards and natural ecosystems and that 70% overwinter individually. The abundance of GSB in those sites is negatively correlated with litter temperature and positively correlated with humidity levels. Furthermore, adults only mate after leaving their overwintering site. Finally, unexpectedly, there was an important number of overwintering adults hosting endoparasitoids (32%). The fact that GSB overwinters alone in the leaf litter means controlling its populations by destroying the overwintering sites is not a solution. All the same, our results point out some promising lines of research for developing methods to control P. prasina. First, the emergence traps, in particular the cone traps, proved efficient for collecting emerging adults and could be considered for monitoring. Moreover, our observations suggest the existence of long‐range mating signals that could be exploited for trapping. Last but not least, the important number of overwintering parasitised adults is a potential biocontrol avenue.