The impact of ant mutualistic and antagonistic interactions on the population dynamics of sap-sucking hemipterans in pear orchards

BACKGROUND Ants are known to establish antagonistic and mutualistic interactions with honeydew-producing hemipterans, depending on the species involved and the ecological context. The aim of this work was to infer the role that such interactions play in the population dynamics of psyllids and aphids in pear orchards. Interactions were inferred from field data and periodical sampling along a 4-year study, and from interaction assays performed under controlled conditions. RESULTS A decline in the abundance of the pear psyllid (Cacopsylla pyri L.), parallel to an increase in the abundance of aphids, was registered over 4 years. Ants were the dominant species, representing about 90% of the predators, followed by spiders and predatory hemipterans (namely Pilophorus gallicus Remane). Ant abundance increased over the 4 years, matching the population dynamics of aphids. Evidence of mutualistic and antagonistic interactions were found for ant-aphid and ant-psyllid, respectively: (i) ant-aphid abundances on pear trees were positively correlated, and ants reduced predation on aphids by generalist predators, and (ii) ant-psyllid abundances were negatively correlated, ants have a negative effect on the psyllid population growth rates, and ants were found to prey on the psyllid. CONCLUSIONS Because of their high abundance in comparison with other predators and the mutualistic-antagonistic relationships with aphids-psyllids, ants are considered to be the principal force behind the decline of pear psyllid populations and the increase in aphid numbers. In summary, ants contribute positively to biological control by the suppresion of pests (i.e. the psyllid) which are more damaging than those they protect (i.e. aphids). (c) 2019 Society of Chemical Industry