Ant-psyllid mutualism affects predation of Diaphorina citri by lady beetle larvae and abundance of psyllid natural enemies

Ants can be involved in mutualistic relationships with honeydew producing hemipterans in which ants provide protection against their natural enemies, and, in return, hemipterans reward ants with honeydew. Such mutualism may affect population regulation of hemipterans by third trophic level predators. However, current knowledge regarding the effects of this food-for-protection mutualism of ants with Asian citrus psyllid, Diaphorina citri, in Florida, USA is limited. Two treatments were established in replicated small plots under field conditions in a citrus (var. Valencia) grove: (1) ants present, and (2) ants absent by exclusion with a tangle-trap sticky barrier deployed on the base of trees. Lower abundance of Coccinellidae, Araneae, and Eulophidae and corresponding higher abundance of D. citri were recorded in trees with ants compared to that recorded in trees without ants as measured by direct visual observations and stem tap sampling. In addition, ant-beetle behavioral interactions were directly investigated with three species of ants [Solenopsis invicta Buren, Dorymyrmex bureni (Trager), and Brachymyrmex obscurior Forei]. Predation of D. citri nymphs by ladybeetle larvae was reduced on leaf flushes infested with S. invicta as compared with leaves without ants and this species caused significant direct mortality to larval beetles. Our results support the hypothesis that predation of D. citri by natural enemies may be reduced in citrus groves colonized by S. invicta than in those where ant populations are suppressed. Furthermore, our results indicate that S. invicta aggressively protect D. citri nymphs on leaves from otherwise effective potential predators, such as Harmonia axyridis.