Host Plant Nutrition and Outbreaks of the Coconut Caterpillar, Opisina arenosella Walker in Sri Lanka

Abstract

The coconut caterpillar, Opisina arenosella, causes locally serious outbreaks with severedefoliation to coconut palms and subsequent loss of yield. However, there appears to be anatural resistance in the host plant to 0. arenosella attack, for infestations are confined tomature and senescing fronds and even within a heavily attacked plantation a few palms mayremain unattacked or only slightly damaged. Also previous work had indicated that potassiumdeficiency benefited O. arenosella. Therefore experiments were carried out to examine thepossible role in host resistance of major plant nutrients and also of certain amino acids.Comparisons were made between plantations with a history of frequent outbreaks('attacked') and those that had never been attacked ('unattacked'). The results showed thatthere were no significant differences between mean amounts of foliar potassium, nitrogen,phosphorus, calcium and magnesium at 'attacked' and 'unattacked' sites. However, thesesamples were taken at the end of unusually long dry seasons when differences in potassiumwould be expected to be relatively small because uptake is limited from dry soil. Potassiumlevels were highest in the youngest fronds which are those not normally attacked whereaspeak amounts of nitrogen occurred in those fronds which are most susceptible to attack. Alsoamounts of 'amide' were notably higher at 'unattacked' sites.It was concluded that further work was required on the relationship between major plantnutrients and levels of attack by 0. arenosella, particularly in relation to changes in nutrientconcentrations which occur at different times of the year. Thus, palms may be moresusceptible to pest attack during critical periods which need to be defined in order to optimisecontrol strategies.