Chemical nature and persistence of the oviposition deterring pheromone in the tracks of the larvae of the two spot ladybird, Adalia bipunctata (Coleoptera : Coccinellidae)

Aphidophagous ladybirds are reluctant to oviposit in patches of prey where conspecific larvae are present. This is adaptive as larval cannibalism is a major threat to egg survival. Ladybirds avoid laying eggs in such patches by responding to a species specific oviposition deterring pheromone present in the tracks of larvae. This study revealed that the oviposition deterring pheromone consists of a mixture of alkanes of which n-pentacosane is the major component (15.1%). These alkanes are likely to spread easily on the hydrophobic cuticle of plants and so leave a large signal. In addition, they are not quickly oxidized and therefore provide a long lasting signal. The latter was confirmed by the observation that 10 day old tracks still deterred oviposition.