The management of aphids and other nest inhabitants by the ant Lasius flavus (F.)

Abstract

An area of rough pastureland has been sampled regularly for Lasius flavus and other soil animals for three years. The density of ants found in these nests agrees well with estimates of other workers using mature nests from undisturbed sites. The abundance of ants in the surface 10cm of the nest was correlated with twenty biotic and abiotic measurements to see which factors most heavily influenced ant captures. It was found that the model: Ant = 17494 x larval brood dry biomass (g) activity + 10654 x adult reproductives dry biomass (g) + 0.1 x base area of nest mound (sq.cm) + c could predict the trends in ant activity with high accuracy (0.0001 < p < 0.002).The relationship of subterranean aphids to ants was also investigated. Generally there were positive associations between Lasius flavus and regularly tended root aphids; but species which show obligatory host alternation e.g. Anoecia corni and aphids which are not ant tended e.g. Aploneura lentisci show marked negative associations with Lasius flavus. During periods of high larval biomass, the number of adult aphids was practically unchanged, although many first instar aphids vanished from the nest, presumably due to predation. Only when the alate ants emerged were aphid numbers drastically reduced. This was attributed to the feeding up of the new queens, which subsequently fast until the development of their first brood. Despite the fluctuation of aphid numbers, no deliberate form of regulation by ants could be shown. The distribution of aphids within the nest was studied and clump sizes for aphid species were calculated. These varied with sub-family, and showed that for most of the year different species intermingled within the nest, not forming separate mosaics. At high aphid density however, it was found that different aphid species became most abundant in certain parts of the nest; those most heavily sclerotized/waxy still possessing rudimentary siphuncles, furthest from the nest centre, and those without siphuncles and some with legs adapted for ant 'communication' near the centre of the nest. This is related to the degree of ant attendance towards each aphid.