Tightness of the Perianth of Cococuts in Relation to Infestation by Coconut Mites

Abstract

The coconut mite, Aceria guerreronis Keifer (Acari: Eriophyidae) is an economic pest of coconuts, Cocos nucifera L., in many countries of the Americas and Africa where these palms are grown (Mariau 1986). Damage occurs when the mites congregate and feed on the meristematic tissue of the coconut, which is the area of the coconut surface that is normally protected by the inner whorl of the perianth (Fig. 1). The tissue growing from beneath the perianth at a point near a coconut mite colony becomes first chlorotic and then crackledand cork-like. Eventually, half or more of the exposed surface of the coconut may be damaged. Coconut mite damage reduces the production of copra, causing losses of up to 30% (Hernandez-Roque 1977). Adult coconut mites are 36-52 ,um thick (Keifer 1965), thus are able to penetrate very minute spaces. There is general agreement in results from several localities [Mariau & Julia (1970) in Ivory Coast, Hall & Espinosa-Becerril (1981) in Mexico, and Moore & Alexander (1987) in St. Lucia] that coconut mites do not infest the meristematic zones of unfertilized female coconut flowers or fruits of less than a few weeks old. According to detailed observations on 'Malayan dwarf' coconuts (Moore & Alexander 1987), coconut mite populations built up rapidly and peaked on coconuts of about 3 to 6 months old. Populations declined on older fruits. Generally, it appeared that fruits of 1 to 4 months old were the most susceptible to attack. The above authors suggested that the perianths of younger coconuts were tightly appressed and thus protected the meristematic zone, but became looser as the coconut developed. Populations declined on larger coconuts, and were virtually absent from coconuts of about 20 cm in length. They suspected that conditions for coconut mites became unfavorable as coconuts matured. We conducted similar sampling and observations at Cabo Rojo, Puerto Rico, and Miami, Florida, and observed a similar relationship between the stages of development of coconuts and coconut mite infestation (unpublished). Moore (1986) reported that the arrangement of the tepals of the inner whorl of the perianth of young coconuts affected the pattern of coconut mite attack, thus providing further evidence that physical access space is important for coconut mite invasion and subsequent population development. We attempted to determine whether the perianth protects the meristematic zone during young stages of growth of the coconut. A test using marking ink was conducted to determine whether the tepals of smaller coconuts are more tightly appressed to the fruit surface than those of larger coconuts. It was found empirically that a marking ink, Volger's Indelible Ink? (Philadelphia, Pennsylvania), penetrated beneath the perianth of most older coconuts and dried to the surface. Coconuts were pruned from 5 'Golden Malayan Dwarf coconut palms. Ten coconuts were in each of the following length classes: 2-3 cm, 7-9 cm, and 11-13 cm, corresponding to developmental stages of approximately the first, fourth and sixth months, respectively.