Biological control of insect pests in clover seed crops

Long-term pest management is crucial in sustainable agriculture, assuring that both ecological and economical aspects are taken into account. In organic farming it would be of particular interest to use odour-based control methods, involving manipulation of the chemical signals used by the target species when searching for a mate or suitable host plant. Such pest control has the advantage that non-toxic chemicals are used, with minimal negative impact on beneficial insects, such as pollinators and natural enemies of the pest insects, which could result in higher and more stable yields.

Production of clover seed is fundamental within the agricultural sector, as clover is used in leys to produce animal fodder and as green manure. The latter is particularly important on organically managed farms where the use of inorganic fertilizers is prohibited. The clover seed yield in Sweden is very variable between farms and between years, which results in negative economical consequences for seed producers, such as unpredictable production, increased storage costs and seed shortage. The reason for the unpredictable seed yield is not fully understood, but it is confirmed that seed-eating pest insects, predominantly Apion weevils, can cause yield losses of more than 50%. These weevils are traditionally controlled by pyrethroid insecticides with limited success, while no established control measure exists within the organic sector. Pest management in clover seed production would thus be particularly well favoured by developing odour-based strategies to control these weevils, which is the end goal of this project.

The aims of the research are to identify pheromones and host plant volatiles for several species of seed-eating weevils, and to use these compounds to develop environmentally friendly methods for monitoring and control of weevil populations in clover seed fields. A first step in this process has been to analyse which host plant volatiles the weevils can detect with their antennae. The species A. flavipes, which is a major pest in white clover seed fields, has been used as model in this screening, where single olfactory sensory neurones were stimulated with compounds reported to be present in white and red clover. The analysis showed that A. flavipes is equipped with very selective olfactory sensory neurones, which only respond to one or a few chemically related compounds. Responses were elicited to 21 of the 28 compounds tested, indicating that the species has a well-equipped olfactory system for detection of host volatiles.