The effects of foraging ants on arboreal insect herbivores in an undisturbed woodland savanna

Abstract

ABSTRACT. A comparison was made of the insect fauna on paired Terminalia sericea, Burkea africana and Ochna pulchra trees; one tree in each pair was treated with Formex® to exclude ants from the canopy, and the other was designated the control. Treatment with Formex banding to exclude ants did not influence plant phenology. Pyrethrum knockdown samples from control trees had generally more insect individuals and insect species than samples from trees where ants were excluded. Formex‐treated trees had significantly less homopterous individuals and species than the control trees. With the exception of ants and Homoptera, there was no difference in the insect guild composition and dominance ranking of various insect taxa, sampled by pyrethrum knockdown, between the control and Formex‐treated trees. T.sericea had significantly greater populations of both sessile and mobile Homoptera on the control trees than on the Formex‐treated trees. A similar trend could be seen on B.africana. There were significantly more sessile homopterans on the control trees of O.pulchra than on the Formex‐treated trees. Low numbers of mobile Homoptera were recorded on both control and Formex‐treated O.pulchra trees, and numbers on control trees were fewer in comparison to numbers of mobile Homoptera on control T.sericea and B.africana trees. It is concluded that the ants have similar effects on the insect communities of trees in a natural, undisturbed savanna as has been demonstrated on trees in agro‐ecosystems, and on plants that are structurally adapted for mutualistic associations with ants. Although slight, leaf damage by some leaf‐feeding insects was greater on trees where ants had been excluded than on control trees that supported foraging ant populations.

Spiders associated with Psychotria carthagenensis Jacquin. (Rubiaceae): vegetative branches versus inflorescences, and the influence of Crematogaster sp. (Hymenoptera, Formicidae), in South-Pantanal, Brazil

“…Halaj et al (1997) also found a strong interaction between spiders and ants, with spider displacement by ants. The reduction of spiders by the ants represents a contrast with other studies, which show a null or a positive correlation between spider and ant numbers (Grant and Moran, 1986;Karhu, 1998). In the case of P. carthagenensis, there is an indication of a negative effect, because ants may displace both the spiders and their potential prey.…”

Plant‐attracted ants affect arthropod community structure but not necessarily herbivory

“…Thus, the presence of wrong ant species may result in costs rather than benefits to the plant. Such a negative impact of ants on potentially beneficial arthropods was shown by some studies (Halaj et al ., 1997; James et al ., 1999), but not by others (Grant & Moran, 1986; Karhu, 1998; Floren & Otto, 2002).…”

A note on manna feeding by ants (Hymenoptera: Formicidae)

“…That sugary secretions other than those from extrafloral nectaries could be an important mechanism aiding plant protection by ants was first proposed by Scott (1980). The findings of Skinner and Whittaker (1981), Fowler and MacGarvin (1985), Grant and Moran (1986) and Mackay (1991) suggest that when plants do not provide external sources of nourishment for foraging ants then the reduction in herbivore numbers and/or herbivore damage through ant predation is minimal. This relationship appears to change markedly when external sources of carbohydrate are present on plant surfaces.…”