March 2010. A caterpillar infesting coconuts on Vilamendhoo island resort, south Ari atoll, Maldives. The identity and control were requested.
It is most likely the oil palm slug caterpillar, Darna furva Wileman (Lepidoptera: Limacodidae), found infesting oil palm in Thailand. A similar species, Darna trima (Moore), has been reported from Malaysia infesting oil palm as well. Both can attack coconut and a few other palms.
Control could be done by light traps using black light and Bt spray. Synthetic chemicals such as carbaryl (Sevin 85%WP), trichlorfon (Dipetrex 95%WP), deltamethrin (Decis 3% EC), etc., could be used
A number of natural enemies consisting of several hymenopterous larval and pupal parasitoids and hemipterous predatory bugs have been observed to keep this slug caterpillar under control in Thailand.
It was also said that the same caterpillar caused problems on Sun Island in Ari Atoll, in 2006. The resort used pesticides to control it then, but only after many of the coconut palms were damaged. A few months after the attack, and the application of insecticides, there was no sign of the caterpillars, but many moths were found in the garden lights, and there were several pupal cases. There was no indication of any natural enemies, but there has been no recurrence of the pest since, it appears.
The same caterpillar is also a pest in India, defoliating coconuts causing severe yield losses. During 2000-2002, there was a report of 27% (?yield loss) in the first year after attack followed by 17% in the second year after control measures were instigated. Beauveria bassiana was tried using spore concentrations ranging from 1000 to 10000 spores per ml and found effective, and on par with chemical insecticides like quinalphos and lambda cyhalothrin.