Asymmetric oviposition behaviour and the influence of larval competition in the two pyralid moths Ephestia kuehniella and Plodia interpunctella

Larvae of the two phycitid moths Ephestia kuehniella and Plodia interpunctella (Lepidoptera: Pyralidae) emit a secretion from their mandibular glands which affects oviposition behaviour of both species. The response elicited in females of the two species was however very different. Females of E. kuehniella were deterred by high densities of larvae, while low densities did not affect oviposition choice when compared with an uninfested substrate. In P. interpunctella low larval densities stimulated oviposition, while high densities did nor affect oviposition behaviour when compared with an uninfested substrate. In a choice between equal larval densities of the two species, E. kuehniella females laid only a small proportion of eggs on patches where conspecific larvae had been present. P. interpunctella females did, on the other hand, not differentiate between patches with larvae of the two species during oviposition. The effect of intra- and interspecific larval competition on adult weight and larval development time was studied in both species. E. kuehniella showed lower weight and longer development time at higher densities of conspecifics. When subjected to competition with P. interpunctella, E. kuehniella showed higher weight and shorter development time than when competing with conspecifics. P. interpunctella showed no significant differences in weight or development time between the different densities with intraspecific competition. How-ever, a longer development time was observed with interspecific competitors, while no change in weight occurred. Factors influencing the oviposition choice and competition patterns observed in E. kuehniella and P. interpunctella are discussed.