Intraspecific genetic variation in arthropods is often studied in the context of evolution and ecology. Such knowledge, however, can also be very usefully applied to biological pest control. Selection of genotypes with optimal trait values may be a powerful tool to develop more effective biocontrol agents. Although it has repeatedly been proposed, this approach is still hardly applied in the current commercial development of arthropod agents for pest control. In this perspective study, we call to take advantage of the increasing knowledge on the genetics underlying intraspecific variation to improve biological control agents. We argue that it is timely now because at present both the need and the technical possibilities for implementation exist, as there is (1) increased economic importance of biocontrol, (2) reduced availability of exotic biocontrol agents due to stricter legislation, and (3) increased availability of genetic information on non-model species. We present a step-by-step approach towards the exploitation of intraspecific genetic variation for biocontrol, outline that knowledge of the underlying genetic mechanisms is essential for success, and indicate how new molecular techniques can facilitate this. Finally, we exemplify this procedure by two case studies, one focussing on a target trait -offspring sex ratio -across species of hymenopteran parasitoids, and the other on a target species -the two-spot ladybird beetle -where wing length and body colouration can be optimized for aphid control. With this overview, we aim to inspire scientific researchers and biocontrol agent producers to start collaborating on the use of genetic variation for the improvement of natural enemies.

Summary7-spot ladybirds secrete alkaloid (coccinelline)-rich fluid (reflex blood) from leg joints as a defence mechanism against predators. A technique is described that enables the collection and accurate quantification of reflex blood produced, and the amount of coccinelline therein. Coccinelline was found distributed throughout the body, although concentrated in the reflex blood. Reflex blood was collected from a large set of beetles at several time points. Significant variation was found among beetles in the amount of reflex blood produced (for males and for females corrected for body weight) and the coccinelline concentration of the reflex blood. The results are discussed in relation to automimicry and the maintenance of variation through energy trade-offs. The relationships between tendency to aggregate, ability to reflex bleed and the possession of aposematic coloration are also considered.

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The £ea beetle Phyllotreta nemorum L. (Coleoptera: Chrysomelidae: Alticinae) is polymorphic for its ability to use Barbarea vulgaris R. Br. (Brassicaceae) as a host plant. The genetic factors in£uencing this ability show both sex-linked and autosomal inheritance. Evidence was found for the presence of major genes such as those found in earlier studies, but also of genes with a smaller e¡ect which have not previously been found. Although the ability to survive on B. vulgaris exists in most populations in eastern Denmark, it is usually at a low frequency. Beetles collected on B. vulgaris, however, usually produced larvae that survived on this plant. The inheritance and the abundance of the ability to use B. vulgaris are discussed in the context of the evolution of the interaction between P. nemorum and its atypical host plant.