Crematogaster sp. B

Crematogaster sp. B

This ant species is restricted to Grey Mangrove Avicennia marina where it nests in cavities in the branches in all parts of the tree. The ants are not capable of excavating the cavities themselves, instead being dependent on holes tunneled by weevils ( De Baar 1993). So the nest sites and the extension of the cavities are limited by the abundance of the beetles.

The nest structure of this species was examined by Nielsen (1997b) and (Nielsen unpublished) on A. marina trees in the outer part of the mangrove in Darwin Harbor, where the nests are inundated during most of the tides. The single tree investigated contained at least three separate colonies, and each colony consisted of several separate compartments/nests, each with an entrance less than two mm in diameter. The distribution of two colonies were identified and all compartments marked in the month of November. Each branch with a colony was removed from the tree and the branches were cut into pieces each containing one nest. In the laboratory, the branches were frozen and later split vertically in two parts. The length and volume of the nest was estimated and the contents sorted, counted, and the biomass determined. The data collected are presented in Table 2A and 2B:

In each colony the egg laying queens with numerous eggs were in one chamber, and larvae and pupae were found in most of the other chambers. The most conspicuous insect in many of the chambers were the large - up to 9 mm - long pink coccids, Alecanopsis mirus , which often occupied the whole surface of the cavity to which they were strongly attached as adults ( Fig. 5). Only the first instar nymph is mobile and capable of moving around in the nest. The coccids feed on the plant’s sap and produce honeydew, which is probably the main source of energy for the ants. The biomass of the coccids is a substantial part of the total biomass in the nest, and in one nest amounted to 240 mg per ml nest cavity ( Table 2B) (Nielsen unpublished data).

In order to demonstrate that cavities in the tree were limiting the size of the colonies, two kinds of additional spaces were provided on an A. marina tree with a colony of Crematogaster sp. B . One type was an 8 mm hole in the branch of the mangrove tree with a stopper with a 2 mm hole. The second type of artificial nest was formed in the same way using a small branch from another tree and attached it to the tree with colony.

After 10 days, 7 nests were occupied by ants and three of them also contained first instar coccids (Nielsen unpublished data)