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

Abstract

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). © 2019 Society of Chemical Industry

The Effect of Cover Crops on the Biodiversity and Abundance of Ground-Dwelling Arthropods in a Mediterranean Pear Orchard

“…In the case of pear trees, there is some evidence of a positive effect of ground covers on beneficial fauna [64,97,101]. In the present study, some of the ground-dwelling arthropods influenced by the plant cover, namely, ants and spiders, are key species for the assemblage of arthropods in pear orchards in the Mediterranean area [51][52][53]. Therefore, increasing the herbaceous vegetation in pear orchards is expected to have an impact on the population dynamics of the species in the canopy of the trees.…”

“…The samples were collected on 24 April, 13 May, 28 May and 11 June 2019. This period was chosen both because it is favourable for the development of the cover and because it is characterised by a high activity of insects and spiders [51,52]. The summer months in southern Spain are very arid, and plant covers dry out.…”

“…The summer months in southern Spain are very arid, and plant covers dry out. The plots were sampled every two weeks because it was known from previous studies that the density of insects changes very little between two consecutive weeks [51,52].…”

“…Pest control in pear orchards has traditionally relied on chemicals, but due to the restriction in the application of insecticides and the development of resistances, integrated pest management (IPM) has become the most-sustainable alternative [46][47][48]. Pear orchards with limited use of pesticides can be inhabited by a rich community of arthropods, which includes many natural enemies such as anthocorids, mirids, ants, and spiders that contribute to the regulation of the populations of herbivorous species [49][50][51][52][53]. In some parts of the Mediterranean area, ants (namely, Lasius grandis Forel, Hymenoptera: Formicidae) have been reported to be the key predator for the control of the pear psyllid [52,53].…”

“…Pear orchards with limited use of pesticides can be inhabited by a rich community of arthropods, which includes many natural enemies such as anthocorids, mirids, ants, and spiders that contribute to the regulation of the populations of herbivorous species [49][50][51][52][53]. In some parts of the Mediterranean area, ants (namely, Lasius grandis Forel, Hymenoptera: Formicidae) have been reported to be the key predator for the control of the pear psyllid [52,53]. This ant species spends the main part of its life cycle in the soil or on the soil surface; thus, its abundance and foraging activity may be greatly influenced by agricultural practices that modify soil conditions.…”