Predatory Potential of Nymphal Odonates on Aedes aegypti Developing in Freshwater and Brackish Water Habitats

Abstract

Aedes aegypti, the primary vector of dengue, undergoes preimaginal development in brackish water (BW). However, dengue vector control exclusively targets freshwater (FW) habitats. The present study evaluated the predatory efficacy of nymphal odonates that can develop in both FW and BW. Nymphs of three damselfly and three dragonfly species from FW and BW habitats were identified and acclimatized to FW (<0.5 gL^-1 salt) and BW (10 gL^-1 salt) mesocosm conditions. The experiment was repeated nine times with nine different individual predators per species under both salinity conditions. One hundred L3 Ae. aegypti from FW and BW laboratory colonies were introduced to determine the predatory rate (PR) and clearance rate (CR) after 24, 48, and 72 h, and one hundred L3 larvae were introduced every 24 h. The dragonfly nymph Hydrobasileus croceus and the damselfly nymph Paracercion hieroglyphicum showed the highest PR and CR under both rearing conditions at all times. However, damselfly and dragonfly nymphs significantly (p < 0.05) differed in their CR under both FW and BW conditions. Thus, all six odonate species have predatory potential and this suggests that they could be used as biological control agents to eliminate preimaginal stages of Ae. aegypti developing in both FW and BW habitats.

Keywords: Sri Lanka; biological control; clearance rate of predator; dengue vector control; predatory rate.

Figure 1

Geographical maps showing (A) the location of Sri Lanka on the Indian subcontinent, (B) the location of Jaffna, Sri Lanka, in the Indian ocean, and (C) the Jaffna district with major lagoons in northern Sri Lanka. Odonates were collected at the Jaffna city limits, and ponds where the sampling of predators was undertaken are marked as round solid red points. (D,E) show sampling at Irupalai and Allaipiddy ponds, respectively. (F) shows the experimental mesocosm set up.

Figure 2

Dendrogram of the cluster analysis of the odonates in terms of the Aedes larval consumption patterns, where the numbers from 1–4 represent the different clusters and organisms represent the clusters DG—dragonfly and DS—damselfly. DG1: Pantala flavescens, DG2: Hydrobasileus croceus, DG3: Brachydiplax sobrina, DS1: Ceriagrion coromandelianum, DS2: Paracercion hieroglyphicum, and DS3: Paracercion v-nigrum.