Larvae of two ladybirds, Phymatosternus lewisii and Scymnus posticalis (Coleoptera: Coccinellidae), exploiting colonies of the brown citrus aphid Toxoptera citricidus (Homoptera: Aphididae) attended by the ant Pristomyrmex pungens (Hymenoptera: Formicidae)

Abstract

The distribution of two small coccinellids, Phymatosternus lewisii and Scymnus posticalis, across colonies of the aphid Toxoptera citricidus in relation to ant-attendance of the colonies and ant species, behavioral interactions between the coccinellid larvae and ants, and the overlap in the larval distribution of the two coccinellids were examined in a citrus grove in Japan. P. lewisii larvae were found frequently in aphid colonies attended by the ant Pristomyrmex pungens but rarely in colonies attended by another ant, Lasius japonicus, and in ant-excluded colonies. A number of S. posticalis larvae were also recorded in P. pungens-attended colonies and some larvae in ant-excluded colonies. A few P. lewisii adults were noted only in P. pungens-attended colonies, whereas some S. posticalis adults were observed in ant-excluded colonies. In most encounters, P. pungens workers tapped P. lewisii larvae with their antennae but showed no aggressive behavior; otherwise, P. pungens workers ignored the larvae. P. pungens exhibited the same behavior when encountering S. posticalis larvae. The proportion of P. pungens-attended aphid colonies where the larvae of both coccinellids occurred did not significantly differ from the probability of both coccinellids occurring in the same colonies given their random distribution across the colonies. Thus, larvae of the two coccinellids exploited aphid colonies attended by a particular ant, P. pungens, and the larval distribution of the two species may be independent of each species.