First report on semiochemical spacing in larvae of predators

Our research revealed repellent effects of larval tracks on conspecific larvae in aphidophagous coccinellids. Searching behaviour of insects was monitored in double choice tests with the assistance of automatic video tracking system EthoVision. Larvae of the coccinellid Cycloneda limbifer Say (Coleoptera: Coccinellidae) effectively differentiated clean substrates from substrates with fresh tracks of conspecific first instars. Fourth instars walked significantly further and stayed longer on clean substrates than on those with tracks of first instars. These results indicate the presence of a deterring pheromone in tracks of larvae. The mode of action of repellent secretion of larvae is complementary to previously described semiochemical-mediated egg-spacing mechanism in coccinellids. Grown up coccinellid larvae may disperse away from potentially less suitable aphid colonies and thus contribute to a decline of the rate of cannibalism, especially of immobile prepupae and pupae. Active semiochemical spacing of larval predators is likely to adjust the distribution of voracious larvae to dynamic changes in prey-predator ratio. We suggest that the occurrence of immature heterospecific competitors in an aphid colony might be for some species even more hazardous than the presence of conspecific larvae. Thus, interspecific effects of larval tracks on active spacing of aphidophagous coccinellids deserve further attention.

In: Růžička Z., Zemek R. (2007) Deterrent effects of larval tracks on conspecific larvae in Cycloneda limbifer. DOI 10.1007/s10526-007-9109-x BioControl.