Interspecific Differences in Feeding Behavior and Survival Under Food-Limited Conditions for Larval Aedes albopictus and Aedes aegypti (Diptera: Culicidae)

Abstract

Aedes albopictus has replaced Aedes aegypti in much of the latter species' historic range within the United States. The leading hypothesis for this displacement is exclusion via resource competition; however, the proximate mechanism producing a competitive advantage for A. albopictus over A. aegypti has not been identified. We performed laboratory experiments to test the hypotheses that these species differ in feeding behavior, and that these differences result in differences in survival when resources are scarce. Differences in feeding behavior were assessed in three environments with food (growing microorganisms) available: 1) in fluid only; 2) on leaf surfaces only; 3) or both in fluid and on leaf surfaces. We determined behavior of larvae in these environments, recording their positions (bottom, wall, leaf, top, or middle) and activities (browsing, filtering, resting, or thrashing) using instantaneous scan censuses. A. albopictus spent significantly more time at leaf surfaces, whereas A. aegypti spent more time engaging in nonfeeding activities. Both species showed a significant shift in foraging activity toward leaves when leaves were available. In a second experiment, we recorded survivorship for individuals raised in two treatment combinations: whole or half 17-mm disks of live oak leaves, with or without direct access to the leaf surface (controlled using nylon mesh, which allowed movement of microscopic organisms, but prevented mosquito larva movement between container sides). After 31 d, survivorship of A. albopictus was significantly greater than that of A. aegypti regardless of treatments. Moreover, A. albopictus showed significantly greater survivorship compared with A. aegypti when deprived of access to leaf surfaces and in whole leaf disk treatments, suggesting superior resource-harvesting ability for A. albopictus. Our experiments suggest that differences in foraging behavior contribute to the competitive advantage of A. albopictus over A. aegypti that has been observed in North America.

Fig. 1

Bivariate means (±SE) for PC1 and PC4, which made the greatest contributions to multivariate differences among three food environments (Table 3). Activities and positions most closely associated with large positive or large negative PC scores are indicated parallel to each axis. All multivariate differences among all pairs of food environments were significant (Bonferroni adjustment, experiment-wise α = 0.05).

Fig. 2

Bivariate means (±SE) for PC3 and PC4, which made the greatest contributions to multivariate differences between species. Activities and positions most closely associated with large positive or large negative PC scores are indicated parallel to each axis.

Fig. 3

Survivorship curves for A. albopictus and A. aegypti larvae (proportions alive ± 95% confidence interval).

Fig. 4

Survivorship curves for A. albopictus (AA) and A. aegypti (AE) larvae in leaf size treatments (proportions ± 95% confidence interval). Whole leaf is a single 17-mm live oak leaf disk; half leaf is one-half of a 17-mm live oak leaf disk. No mortality occurred before d 8. Within each treatment combination, early points indicating 100% survivorship are not shown.

Fig. 5

Survivorship curves for A. albopictus (AA) and A. aegypti (AE) larvae in leaf access treatments (proportions ± 95% confidence interval). Access indicates the leaf was on the same side of a mesh divider as the mosquito. No access indicates that the leaf was on the opposite side of a mesh divider as the mosquito. No mortality occurred before d 8. Within each treatment combination, early points indicating 100% survivorship are not shown.