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Interspecific Competition and Frequency Changes Among Ants in Solomon Islands Coconut Plantations

1971; Wiley; Volume: 8; Issue: 2 Linguagem: Inglês

10.2307/2402874

1365-2664

Penelope Greenslade,

Insect and Pesticide Research

Four ant species are important in the control of Amblypelta cocophaga China (Hemiptera, Coreidae), which causes premature fall of coconuts in the Solomon Islands in the southwest Pacific (Phillips 1956; Brown 1959a). The ants inhabit palms and two of the species, Oecophylla smaragdina (F.), and Anoplolepis longipes (Jerdon), afford protection from Amblypelta attack while the other pair, Iridomyrmex cordatus Fr. Smith (= L myrmecodiae Emery), and Pheidole megacephala (F.), do not. Over the last 40 years there have been fluctuations in the relative abundance of these ant species in plantations on the North coast of Guadalcanal and since 1948 there are fairly detailed records of their frequencies. These show a complex series of replacements among the species. Hitherto there have been no adequate explanations to account for the changes in frequency which have occurred although they are a major factor influencing copra yields. Understanding them is the first step towards controlling ant populations so that beneficial species predominate. Now, with the perspective of 20 years' data it is possible to explain some of these frequency changes. Dealing with unique past events any explanations are necessarily tentative but they allow anticipation of further changes. They are therefore capable of being tested and improved upon. The ants compete for occupancy of coconut palms which, with the surrounding ground, provide sites for nests and feeding territories. In order to understand the population changes of these ants an account of competition between them is necessary. Evidence is presented of an apparent cycle in colonies of Oecophylla smaragdina. The bionomics of the four ant species are described elsewhere (Greenslade 1964 and in prep.). 0. smaragdina and Iridomyrmex cordatus are native to the Solomon Islands and are arboreal. Pheidole megacephala and Anoplolepis longipes are primarily groundnesting and have been introduced into the Islands. Oecophylla smaragdina has discrete colonies with a single queen, while the other species occur in continuous populations with many queens. 0. smaragdina is diurnal and is well adapted to the Solomon Islands climate, while Iridomyrmex cordatus and Pheidole megacephala are less resistant to low daytime humidities and are mainly nocturnal. Maximum foraging activity normally occurs at dusk in Anoplolepis longipes, since it is limited in the day by low humidity and at night by low temperature. All four species of ant appear to have no important enemies, except each other.