Coconut (Cocos nucifera L.) is a major crop in tropical Asia. The coconut mite, Aceria guerreronis Keifer, was recently introduced to Sri Lanka and southern India where it is causing considerable damage to that crop. The objective of this study was to identify the phytoseiid mites in the main coconut growing areas where the pest has been reported in Sri Lanka and to determine plants on which phytoseiid predators of A. guerreronis could be found. Twenty species were found in a survey conducted in July 2003, 3 of which are new to science and are here described. They are Euseius ceylonicus Moraes and Lopes, n. sp., Euseius pauciventripilis Moraes and Lopes, n. sp. and Phytoseius calopogonium Moraes and Lopes, n. sp.. Five species were found on coconut plants, 3 of which, Amblyseius largoensis (Muma), Neoseiulus baraki (Athias-Henriot) and Neoseiulus paspalivorus (DeLeon), on fruits, in association with A. guerreronis. In addition to coconut, A. largoensis was found on 11 plant species, whereas N. baraki was also found on 2 plant species; N. paspalivorus was found only on coconut. The latter 2 phytoseiids were by far the most numerous in association with A. guerreronis.

Distribution patterns and numerical variability of the coconut mite Aceria guerreronis Keifer (Acari: Eriophyidae) and its predator Neoseiulus aff. paspalivorus DeLeon (Phytoseiidae) on the nuts of 3- to 7-month-old bunches of coconut palms were studied at two sites in Sri Lanka. At the two sites, coconut mites were present on 88 and 75% of the nuts but no more than three-quarters of those nuts showed damage symptoms. N. aff. paspalivorus was found more on mature nuts than on immature nuts. Spatial and temporal distribution of coconut mites and predatory mites differed significantly. The mean number of coconut mites per nut increased until 5-month-old bunches and declined thereafter. The densities of predatory mites followed a similar trend but peaked 1 month later. Variability in the numbers of mites among palms and bunches of the same age was great, but was relatively low on 6-month-old bunches. The results indicate that assessment of infestation levels by damage symptoms alone is not reliable. Sampling of coconut and/or predatory mite numbers could be improved by using several nuts of 6-month-old bunches. The effect of predatory mites on coconut mites over time suggests that N. aff. paspalivorus could be a prospective biological control agent of A. guerreronis.

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