A Betalight Trap for Mosquito Larvae1

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Abstract
A light trap for collecting mosquito larvae by night consists of a cylindrical biscuit tin with a strip-light on the inside of the lid, and an opening in the base through which larvae can pass towards the light. The trap is placed horizontally in the breeding water partially submerged by support on wires or floats. The subdued luminance of the Betalight is derived from the action of tritium gas on a phosphor coating lining the glass tube of the light. They are safe, unaffected by immersion in water, produce no heat, and last for several years. In laboratory tests with 50 or 100 larvae in aquarium tanks in a dark room, control traps (without a light) caught 8%–15% of larvae. Catches with a white Betalight ranged from 45%–85% for Culex pipiens molestus, C. p. fatigans and Aedes togoi, 24%–35% for Anopheles labranchiae atroparvus, but few Aedes aegypti were taken. With green, blue or red Betalights catches were from 74%–96% with Culex and Ae. togoi. Results suggest a diel rhythm in larval activity. Overnight catches in natural breeding places, in Sarawak, gave catches with Betalights of 15 to 95 larvae of Culex spp., including C. tritaeniorhynchus, from ditches compared with 0 to 2 larvae in control traps, and a 6-fold increase (230 larvae, 78 pupae) over control catches, of C. mimulus in forest pools. Possibilities for the trap as a larval sampling device and some factors to consider in its use are noted.

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