Aphid-tending Ants Research Articles

Larval behavior of predacious sister-species: orientation, molting site, and survival in Chrysopa

Field and laboratory studies compared two features of larval behavior in a pair of predacious sisterspecies of green lacewings: one (Chrysopa slossonae) a specialist on a single species of colonial aphids (the woolly alder aphid) that occur on branches and trunks of alder trees, the other (C. quadripunctata) a general aphid feeder whose primary prey is dispersed on foliage of diverse types of trees. First, a few hours after hatching, larvae of the two species develop significantly different phototactic responses; the differences correspond well with the spatial distributions of their prey. Most C. slossonae exhibited negative phototaxis, a response that helps move hatchlings inward on alder trees toward the woolly alder aphid colonies, whereas most C. quadripunctata hatchlings showed positive orientation to light, a response that tends to keep them in tree canopies with their prey. Second, in greenhouse experiments, a significantly greater proportion of C. slossonae larvae (second instars) molted within woolly alder aphid colonies and remained with the aphids than did C. quadripunctata larvae. These differences indicate that the specialist larvae have evolved a high degree of behavioral fidelity to their prey. However, larvae (second instars) of the two species that were released near ant-tended woolly alder aphid colonies in the field had similar recovery (= survival) rates. Consequently, natural selection may not act on behavioral traits that influence larval fidelity to prey during the late second and early third instars.

Aphid-ant interaction reduces chrysomelid herbivory in a cottonwood hybrid zone.

In a cottonwood (Populus) hybrid zone, Chaitophorus aphids attract aphid-tending ants which subsequently reduce herbivory by the leaf-feeding beetle, Chrysomela confluens. Observations and experimental manipulations of aphids and beetle larvae on immature cottonwood trees demonstrated that: 1) via their recruitment of ants, aphids reduced numbers of beetle eggs and larvae on the host; 2) these interactions occurred within a few days of the host being colonized by aphids; and 3) although aphid colonies were ephemeral, their presence resulted in a 2-fold reduction in beetle herbivory. The aphid-ant interaction is most important in the hybrid zone where 93% of the beetle population is concentrated (for reasons unrelated to aphids and ants). Because beetle defoliation of immature trees is high (ca. 25%), the indirect effect of aphids in reducing herbivory is likely more beneficial to trees in the hybrid zone than in adjacent pure zones where beetle herbivory is virtually absent. Tree genotype likely affects the impact of the aphid-ant interaction on trees within the hybrid zone, since levels of herbivory differ between sympatric Fremont and hybrid cottonwoods.

Response of Aphid-Tending Ants to a Repellent Produced by Wasps (Hymenoptera: Formicidae, Vespidae)

Predation by ants on wasp brood is responsible for the evolution of an ant repellent produced by social wasps in the genus Polistes . The active component of the repellent, methyl palmitate, and its methyl ester homolog, methyl myristate, were tested against four ant species tending aphids. All four ant species were repelled, but the degree of repellency varied. Two hypotheses were tested to account for the differential repellency among ant species: repellency is a negative function of body size, and differences in social modes of foraging correlate with differences in repellency. The latter hypothesis was supported, in that ant species lacking plasticity in their foraging strategy and relying on trail odors are repelled much more extensively than ants using a variety of cues for locating food. It is hypothesized that wasps evolved their chemical defense in response to selection pressure from trail-following ants.

Intra- and interspecific competition for mutualists: ants as a limited and limiting resource for aphids

We present two years of experimental and descriptive data which support the hypothesis that fireweed aphids (Aphis varians) compete with intra-and interspecific aphid neighbors for the services of ant mutualists (Formica fusca and F. cinerea). Specifically, we have shown that ants are a Limited and Limiting resource for a tended aphid species. First, the presence of heavily aphid-infested fireweed shoots significantly reduced the number of ants tending neighboring conspecific populations on fireweed. Second, the presence of ant-tended aphids (Cinara sp.) on Engelmann spruce significantly reduced the number of ants tending neighboring aphid populations on fireweed. Third, the number of ants, and not just the presence of ants, had a significant effect on the fitness of fireweed aphids. Aphid populations tended by three or more F. cinerea exhibited significantly higher probabilities of persisting and growing through time than colonies tended by one or two ants. Aphid populations tended by F. fusca had a significantly higher probability of growing when tended by three or more ants only if they had declined in size during the previous week.

Distribution and Dynamics of Aphid (Homoptera: Drepanosiphidae) Populations onBetula pendulain Northern California

Three species of autoecious aphids, Callipterinella calliptera (Hartig), Euceraphis betulae (Koch), and Betulaphis brevipilosa Borner, commonly occur on European white birch trees, Betula pendula Roth, in northern California. Populations were sampled from 1981 through 1984 at two sites. Within-tree populations of all three species were more abundant in the lower and middle vertical thirds of tree canopies. Optimal sample sizes were estimated for individual trees as well as tree populations, given variable mean aphid densities, sampling reliability levels, and sampling costs. An aesthetic injury level for honeydew production was estimated. At both sites, all species exhibited spring and fall peaks with a summer decline in numbers. Callipterinella calliptera and B. brevipilosa populations increased during late summer while feeding on mature leaves. Euceraphis betulae preferred developing and senescing leaves and was reproductively inactive during summer. At the warmer inland site, C. calliptera and E. betulae were present only early in spring and late in fall and B. brevipilosa populations were virtually absent. Natural enemies associated with these aphids did not prevent the development of large populations, although coccinellids and syrphids demonstrated numerical responses. The only ant-tended aphid species, C. calliptera, developed the largest populations of all three aphid species.