By Lukasz Stelinski
Ants can be involved in mutualistic relationships with honeydew-producing hemipterans. 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 (ACP, Diaphorina citri) in Florida is limited. Therefore, two treatments were established in replicated plots under field conditions in a Valencia grove. In one treatment, ants were present. In the other treatment, ants were absent by exclusion with a tangle-trap sticky barrier deployed on the base of trees.
Lower abundance of ladybeetles, spiders and Tamarixia parasitoids and corresponding higher abundance of ACP, were recorded in trees with ants compared to that recorded in trees without ants. Measurements were conducted via direct visual observations and by stem tap sampling.
In addition, ant-beetle behavioral interactions were directly investigated with three species of ants (Solenopsis invicta, Dorymyrmex bureni and Brachymyrmex obscurior). Predation of ACP nymphs by ladybeetle larvae was reduced on leaf flushes infested with S. invicta fire ants as compared to leaves without ants. This species caused significant direct mortality to larval beetles.
Study results support the hypothesis that predation of ACP by natural enemies may be reduced in citrus groves colonized by S. invicta fire ants compared to those where ant populations are suppressed. Furthermore, results indicate that fire ants aggressively protect ACP nymphs on leaves from otherwise effective potential predators, such as ladybeetles. Collectively, these results indicate that fire ant suppression in citrus may improve biological control of ACP.
Lukasz L. Stelinski is a professor at the University of Florida Institute of Food and Agricultural Sciences Citrus Research and Education Center in Lake Alfred.
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