A Pugnacious ant (Anoplolepis custodiens) confounds ant assemblage responses to bush encroachment

Habitat structure is a key determinant of variation in biodiversity. The effects of increased vertical and horizontal vegetation structure can result in marked shifts in animal communities. This is particularly true for ants in response to woody thickening, with predicted negative impacts on ant diversity. We used pitfall traps to study the response of epigeic ants in two co-occurring dominant habitats (closed and open) of an African savanna biome experiencing extensive woody thickening. Although species richness was higher in open habitats, evenness was significantly lower. Thickening explained significant amounts of variation in ant composition, but site-specific characteristics and seasonality were more important. These site-specific characteristics were largely linked to Anoplolepis custodiens, a species that were locally abundant in open habitats with clayey soils, where they often accounted for more than 90% of all ant activity. As A. custodiens also responds positively to disturbance, indiscriminate bush clearing could lead to knock on effects associated with the numerical and behavioural dominance of this species.

Hexadecanol and hexadecyl formate in the venom gland of formicine ants

The venom apparatus of workers of five representative species of formicine ant, Anoplolepis custodiens , Camponotus vagus, Formica polyctena, Lasius niger and Polyrhachis gagates , have all been shown to contain a mixture of hexadecanol, its formate and acetate, unaccompanied by homologous compounds. These compounds are not found in venom or in the venom reservoir but in the convoluted gland. It is suggested that the gland is lined with hexadecanol and its esters to protect the tissue from the corrosive venom.

The pugnacious ant, Anoplolepis custodiens (Hymenoptera: Formicidae), and its beneficial effect on coconut production in Tanzania

In a field of six hectares, the number of palms foraged by Anoplolepis custodiens (Smith) increased from January to December 1988 from 32 to 85% and the ant activity scores (0–3 system) from 0.5 to 2.0. During the same time, the population of the coconut bug, Pseudotheraptus wayi Brown (Heteroptera: Coreidae) as well as the damage it caused, decreased significantly. A significant relationship between low percentages of damaged nutlets and high ant scores of the palms could be established. The nut set of ant foraged palms was 2–3 times higher than that of comparable palms in an immediately adjacent field free of A. custodiens. Palms with high A. custodiens scores had invariably high scores of the coconut aphid, Cerataphis variabilis Hille Ris Lambers (Homoptera: Aphididae). The performance of the palms was not visibly affected by the aphids.

Interrelationship between an entomogenous fungus and two ant-homopteran (Hymenoptera: Formicidae-Hemiptera: Pseudococcidae & Aphididae) mutualisms on guava trees

On guava trees at Nelspruit, South Africa, there was a mutualism between the ant Anoplolepis custodiens (F. Sm.) and the mealybug Planococcus citri (Risso), which raised the population levels of both. When ants were excluded from half the trees, their overall population level also dropped by half. Further, they moved their nests to be as near as possible to their main food source, the honeydew of the mealybugs. When deprived of their ant mutualists, the mealybugs were heavily preyed on by coccinellids such as the ant–intolerant Exochomus flavipes (Thnb.) and the ant–tolerant Scymnus spp. Later, the mealybugs were almost totally eliminated by the primary entomogenous fungus Cladosporium sp. near C. oxysporum. The coccinellids, now without food, were forced to abandon the trees. In contrast, in trees where ants were allowed to continue their normal activity, the epizootic among the mealybugs was delayed by 14 days. This limitation by the ants of disease allowed a basal but fragmented mealybug population to survive. As the mealybugs declined, the ants switched to attending the aphid Aphis gossypii Glov. Fifteen days after the epizootic struck the ant–attended mealybug population, it began to devastate the aphid population. With both mealybugs and aphids at a low level, the ant population declined. However, the ant–homopteran mutualisms, although severely hit by the epizootic, nevertheless remained intact.

The Relationship between certain Ant Species with particular Reference to Biological Control of the Coreid, Theraptus sp.

In the coastal region of British East Africa three ant species, Anoplolepis custodiens, A. longipes and Pheidole punctulata may destroy the ant Oecophylla longinoda which is a valuable predator on the coconut pest Theraptus sp. (Coreidae). The three first-named species do not prey on Theraptus, which may severely damage palms occupied by them.Nesting habits of the three ant species and their behaviour towards O. longinoda and certain other insects are described.O. longinoda has been exterminated in the limited areas occupied by the two Anoplolepis species. P. punctulata is widespread and is usually common in areas occupied by O. longinoda and is also present, though relatively less common, in A. longipes areas.The distribution of the Anoplolepis species, particularly A. custodiens, is correlated with sandy soils bearing a sparse ground vegetation. Where there are heavy soils or a thick ground vegetation of grasses and creepers the Anoplolepis species are absent and O. longinoda is usually present. It is suggested that the Anoplolepis species are limited by the relatively low temperature of soils shaded from sunlight by thick vegetation.