OVIPOSITION CHOICE BY THE ONOPORDUM-CAPITULUM WEEVIL LARINUS-LATUS (COLEOPTERA, CURCULIONIDAE) AND ITS EFFECT ON THE SURVIVAL OF IMMATURE STAGES

Female Larinus latus lay eggs into the capitula of their Onopordum spp . host plants from the onset of capitulum development until the comple tion of flowering. This tight linkage between insect life-history and plant development optimised larval survival, apart from some initial a synchrony between the readiness of the females to oviposit and the sui tability of the very small capitula to physically support eggs. Eggs w ere laid on bracts and stems of capitula or directly in the florets, w hen these became available. Both the location of the egg and time of o viposition influenced mortality factors such as egg and larval parasit ism, egg desiccation and larval establishment. Overall, survival of eg gs laid later in the season into florets was higher, although the adul ts that emerged were smaller. The change in choice of oviposition site that occurs at the onset of flowering, not only favours survival, but ensures more efficient resource use by the larvae. This occurs becaus e sequential flowering of Onopordum spp. drives a sequential ovipositi on pattern and spreads the egg load more evenly over the available cap itula, reversing a trend earlier in the season to clump eggs that were laid directly on the bracts. Other potential constraints, such as cap itulum size, absolute egg density and previous egg-laying do not play a major role in determining the oviposition pattern of L. latus. Larva l survival was positively correlated with capitulum size and not stron gly influenced by egg density. Competition for resources only appeared to play a role in smaller capitula, and manifested itself in a reduct ion in the size of emerging adults rather than the death of immatures. In the absence of strong interspecific competition, the oviposition b ehavior of L. latus has become geared to maximising resource use for l arvae (i.e. its own potential competitiveness) rather than minimising interactions with other members of the capitulum endophage guild.