Aphid infestation promotes survival of a seed predator: observations and experiments on a tritrophic community module

Abstract

We investigated whether aphid presence and abundance influence the survival of an endophagous predispersal seed predator of the same host plant. We studied a terrestrial community module consisting of one plant (Laburnum anagyroides) and four insect species/groups (an aphid, Aphis cytisorum, a pre-dispersal seed predator bruchid, Bruchidius villosus, aphid-attending ant species, and parasitoids of the bruchid). Two complementary investigations were carried out in parallel: (a) a plant-aphid-ant complex was experimentally manipulated by excluding aphids, ants, or both for 5 years to assess their impacts on the seed predator's survival and parasitism rate; and (b) different aphid infestation levels on randomly selected infructescences were correlated with plant traits, nutrient allocation pattern, and variables of seed predator's survival, such as the number of eggs laid and adults emerged influenced by parasitoid activity, for 7 years. We found that ants did not affect bruchid oviposition negatively, but egg-parasitism was significantly decreased by their presence. Plant traits, such as the number of seeds and seed mass, as well as seed predator performance were negatively affected by heavy aphid infestation. Seed predator -infested seeds had no effect on the mass of remaining seeds in the pods. This study suggests that aphids were nevertheless promoting bruchid abundance and survival, depending on their infestation rate.

From dispersal to predation: A global synthesis of ant–seed interactions

“…Our data build upon the prior work in other plant systems that have shown a continuous range of variation in the outcome of species interactions that vary by habitats or the taxonomic identities of the participants. Mycorrhizae are more likely to be detrimental in simplified systems and ant bodyguards are less likely to work for the plant's benefit when herbivory is minimal or incentives are offered by a competitor (Johnson et al., ; Renault, Buffa, & Delfino, ; Szentesi & Schmera, ). These contexts may be determined not only by nutritional requirements but also in terms habitat and the relative proportion of certain resources made available by the plants present (Dejean, Bourgoin, & Gibernau, ; Sanders & Gordon, ).…”

“…Our data build upon the prior work in other plant systems that have shown a continuous range of variation in the outcome of species interactions that vary by habitats or the taxonomic identities of the participants. Mycorrhizae are more likely to be detrimental in simplified systems and ant bodyguards are less likely to work for the plant's benefit when herbivory is minimal or incentives are offered by a competitor (Johnson et al, 1997;Renault, Buffa, & Delfino, 2005;Szentesi & Schmera, 2011).…”