Studies on the ecology of Oncopera intricata Walker (Lepidoptera: Hepialidae). 3. Survival of the eggs under field conditions.

Abstract

The survival of the eggs of Oncopeva intricata Walker was investigated under field conditions in 1961 and 1963. Egg batches were placed under pasture cover and sampled at intervals during the incubation period. Predators destroyed over 90% of the eggs after 46 days in 1961 and about 85% of the eggs after 43 days in 1963. Some of the predation was by a seed-harvesting ant, Pheidole sp., which removed complete egg batches within 2-3 weeks. The remainder was due to a slower predation of the eggs in situ by general predators in the pasture sward. The egg batches were subject to desiccation in both years due to the low rainfall and of those eggs that survived predation for 46 days in 1961 the mean percentage hatching was 13% while in 1963 after 43 days it was 26%. In 1961 the viability of the eggs surviving predation was at a minimum after 30 days of exposure after which there was an increase. This suggests that in that experiment, after the eggs had been exposed for 30 days, predators were destroying proportionately more of the eggs that would not have hatched due to the effects of weather.