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Introduction
Coconut palm (Cocos nucifera Linn.) is a perennial oil seed crop with high commercial value. This palm has a pivotal role in domestic, industrial, constructional, medicinal and religious purposes. The leaf-eating caterpillar Opisina arenosella Walker (Lepidoptera: Oecophoridae) is the most important lepidopteran pest of coconut palm in India, Sri Lanka and Myanmar (Rao, 1924; Jayaratnam, 1941; Alam, 1962; CIE, 1966; Cock and Perera, 1987).
Opisina arenosella attacks coconut palms during its growth phase from seedling stage to maturity.The caterpillars weave silken webs reinforced with leaf bits and excreta on the lower surface of leaflets and devour the chlorophyll-containing abaxial leaf surface tissues, causing dryness of leaf. Severe damage results in drying of the outer and middle whorl of leaves, reduction in rate of production of flower spikes, increased premature nut fall and retarded growth (Lever, 1969). Damage to the leaves renders them unsuitable for thatching and for other purposes. The pest infests coconut palms throughout the year and the maximum pest population is observed in the field during summer. The pest population periodically assumes epizootic proportions on coconut palms in coastal and backwater tracts in South India. In severe outbreaks, all the fronds are affected and the plantation presents a burnt appearance. Information on the yield loss in coconut due to this pest attack is very meagre. Assessment of crop loss is essential for a realistic planning for research and developmental policies. Hence the present study was undertaken to quantify the crop loss in terms of nut yield due to infestation by O. arenosella.
Materials and methods
The investigation was carried out in Kannur District of Kerala State, India (11°86[variant prime]N and 75°22[variant prime]E), where a severe outbreak of the pest occurred on coconut palms during 2002. The plantations are rainfed coconut monocrop with West Coast Tall variety falling under the age group of 30-35 years. During 2002, 150 palms infested with O. arenosella were selected from the severely infested area and were labelled for observations. Observations were recorded on total number of leaves and pest-infested leaves. Pest incidence symptom in more than 10% leaflets/leaf is considered as infested leaf. The bunch-wise number of nuts available on the crown from fully opened inflorescence to the last...