Marking mosquitoes in their natural larval sites using ²H-enriched water: a promising approach for tracking over extended temporal and spatial scales

Abstract

1. Background.

Tracking mosquitoes using current methods of mark-release-recapture are limited to small spatial and temporal scales exposing major gaps in understanding long-range movements and extended survival. Novel approaches to track mosquitoes may yield fresh insights into their biology which improves intervention activities to reduce disease transmission.

Stable isotope enrichment of natural mosquito breeding sites allows large-scale marking of wild mosquitoes absent human handling. Mosquito larvae that develop in ²H-enriched water are expected to be detectable for over four months using tissue mass-fraction ²H measurements, providing opportunities for long-term mark-capture studies on a large scale.

2. Approach.

A laboratory study followed by a field experiment of mosquito larval habitat ²H-enrichment was conducted in Mali, to evaluate potential labeling of wild mosquitoes. Twelve natural larval sites were enriched using [ ²H]-Deuterium-oxide (D ₂O, 99%). Enrichment level was maintained by supplementation following dilution by rains. Availability of ²H to mosquito larvae was enhanced by locally collected and cultured microorganisms (i.e. protozoa, algae and bacteria) reared in deuterated water, and provided as larval diet. Putative natural predators were removed from the larval sites and first instar larvae Anopheles gambiae s.l. larvae were added every other day. Emergence traps enabled collection of eclosing adults. Adult mosquitoes were kept at laboratory conditions for analysis of label attrition with age.

3. Results.

Deuterium enrichment of wild mosquitoes above background levels (maximum = 143.1 ppm) became apparent 5–6 days after initial exposure, after which ²H values increased steadily until ~24 days later (to a mean of approx. 220 ppm). Anopheles and Culex mosquitoes showed significantly different ²H values (211 and 194.2 ppm respectively). Both genera exhibited exponential label attrition ( e ^(-x)) amounting to 21.6% by day 30 post emergence, after which attrition rate continuously decreased. Males of both taxa exhibited a higher mean ²H value compared to females.

4. Conclusions.

Deuterium-oxide proved useful in marking mosquitoes in their natural larval sites and although costly, may prove valuable for studies of mosquitoes and other aquatic insects. Based on our field study, we provide a protocol for marking mosquito larval sites using deuterium-oxide.