Cannibalism and Necrophagy Promote a Resource Loop and Benefit Larval Development in Insects of Temporary Waters

Abstract

Temporary aquatic habitats are contingent on the allochthonous inputs of plant and animal detritus, whose quality and availability can significantly affect the species developing in these habitats. Although animal detritus (i.e., invertebrate carcasses) is a high-quality food, it is an unpredictable and variable resource. On the contrary, conspecific individuals (dead or alive) are a nutritionally high-quality food source that is always available. In this context, conspecifics consumption, by cannibalism or necrophagy, can be a good strategy to overcome nutrient limitation and allow individual maintenance and development. Here, we tested this hypothesis by using the tiger mosquito Aedes albopictus. By carrying out laboratory and semi-field experiments, we first estimated the relative rate of cannibalism and necrophagy, under different larval densities. Then, we analyzed the effects of cannibalism and necrophagy on larval survival and adult yield. Consistent with our hypothesis, we found that cannibalism and necrophagy occurred under all experimental conditions, and that conspecific consumption had positive effects on individual development, as it significantly increased the rate of adult emergence and larval survival. Interestingly, about 50% of the initial cohort was consumed by conspecifics, suggesting that cannibalism and necrophagy can drive an important resources loop in temporary aquatic habitats.

Keywords: Aedes albopictus; cannibalism; ephemeral habitat; larval development; mosquito ecology; mosquito vectors.

Figure 1

Rate of conspecifics’ consumption in Aedes albopictus. Panel (A) represents the percentage of cannibalism, conspecific necrophagy and remaining carcasses observed at each tested density and life-stage in laboratory experiments. Panel (B) represents the percentage of cannibalism, conspecific necrophagy and remaining carcasses observed at each tested density and life-stage in semi-field experiments. For each density, the percentage of emerged adults is also shown.

Figure 2

Effects of conspecifics’ consumption on larval development and adult yield in Aedes albopictus. The proportion of larvae that reached the pupal and adult stages and the proportion of pupae that developed to adult stage observed in each group are shown; “NC” group: no larval consumption occurred; “CAN” group: cannibalism occurred; “NEC” group: necrophagy occurred. Significant differences among groups were tested using 2 × 2 contingency tables. Equal letters mean no significant differences (chi-square tests, p > 0.05).

Figure 3

Kaplan–Meier survival curves. The Aedes albopictus larvae were grouped into three groups: the “NC” group (blue): no larval consumption occurred; “CAN” group (red): cannibalism occurred; “NEC” group (green): necrophagy occurred. The horizontal axis (x-axis) represents time (expressed in days), and the vertical axis (y-axis) shows the survival probability. At time zero, the survival probability is 1.0 (or 100% of the individuals are alive). The dotted lines show the median survival.