Status of coconut mite Aceria guerreronis and biological control research in Sri Lanka

Abstract

The coconut mite, Aceria guerreronis (Acari: Eriophyidae), invaded Sri Lanka in 1997, and subsequently spread in many areas infesting 17% of the total coconut extent by 2005. It is more prevalent in the dry zone than in the intermediate and wet zones. Within each year, populations fluctuated with high peaks in June-August and relatively low levels in November-February. Neoseiulus baraki and N. paspalivorus (Phytoseiidae) are the most common predatory mites found beneath the bracts of infested coconuts; N. baraki is found in higher proportions in drier areas, N. paspalivorus in wet and intermediate areas, occasionally in cooler pockets of the dry areas. Populations of N. baraki constantly increased in the period 2000-2005 and their fluctuating numbers followed a pattern similar to that of coconut mite. This strong interrelationship suggests that N. baraki is a prospective candidate for control of coconut mites. Its use involves mass breeding and field release techniques. It turned out that N. baraki could be mass-reared in laboratory arenas on Tyrophagus putrescentiae (Acari: Acaridae). Mass releases of lab-reared N. baraki increased its numbers and reduced coconut mite numbers in the field, up to a period of 4-6 weeks after release. Also the use of the entomopathogenic fungus Hirsutella thompsonii was explored. The most effective isolate persisted for up to 16 weeks on the nuts. Over 90% of the nuts had low numbers of live coconut mites up to 4 weeks after treatment. The trials indicate that either biological control agent lacks the ability to suppress the coconut mite for a longer period. Hence, frequent applications of these natural enemies and/or interventions by use of low toxic chemicals may be required for sustainable control. Directions in biological control research of coconut mite are discussed.