Investigation Of Earwigs As A Biological Control Agent Of Tirathaba Mundella (Lepidoptera: Pyralidae)

Abstract

Infestation of developing oil palm bunches by Tirathaba mundella is common in most young plantings in South East Asia, especially in extensive new development areas. In severe infestations, abortion of fruit bunches has been recorded. Further, the pest may cause fruitlet to fall prematurely, or to develop with a hollow centre instead of a kernel. Such losses can be of economic significance. In the past, control has been achieved by application of insecticides. Tirathaba is subject to a number of insect natural enemies, earwigs that are commonly found in bunches. The present study has noted a correlation between caterpillar and earwig numbers per bunch, R² = 0,5. It is reasonable to assume that the earwigs are predatory on Tirathaba and play a part in their regulation at low numbers, even though cause and effect may be difficult to prove. A trial showed a negative correlation between earwigs numbers and percentage of palms positive for signs of Tirathaba incidence, and a positive correlation of earwigs to Tirathaba numbers in infested bunches. An investigation into introducing earwigs to young palms indicated that the decline in Tirathaba numbers with increasing palm age can be speeded up, and, by implication, that the decline itself may be due to earwigs. Removal of developing bunches around six to twelve months before opening up for commercial harvesting (“castration” or “ablation”) is sometimes practised. Generally, the intention is to remove bunches that are failing in association with Tirathaba presence. A trial indicated that this does break the Tirathaba cycle of re-infestation, but did not suggest a major effect on bunch fruit set characteristics, by the time of harvesting.