The gecko: an environmentally friendly biological agent for mosquito control

Laboratory experiments with Aedes aegypti mosquitoes investigated the effects of light, mosquito density and physiological state on predation rates by the Australian gecko Gehydra dubia and the exotic Asian house gecko Hemidactylus frenatus. For both gecko species a positive correlation was demonstrated between prey density and the predation rate. Using Ae.aegypti males and unfed females as prey in a terrarium (0.054 m3), consumption rates reached 76-108/day for G.dubia and 63-109/day for H.frenatus, with significantly more female mosquitoes than males being eaten in most experiments. Comparing dark with semi-illuminated conditions no consistent contrast of predation rate was demonstrated. Gehyra dubia predation rates on various Australian mosquito species were compared in an experimental room (32 m3) for 24 h exposure with photoperiod L:D 12:12 h Five photophilic species (Aedes vigilax, Anopheles annulipes, Coquillettidia xanthogaster, Culex annulirostris, Cx sitiens) suffered 78-100% predation, compared with only 33-53% predation of four non-photophilic species: Aedes aegypti, Ae.notoscriptus, Ae.vittiger and Cx quinquefasciatus. This demonstrates the potential benefit of domestication for geckoes that learn to hunt at light. When offered a mixture of unfed, freshly blood-fed and gravid females of Ae.aegypti in an illuminated terrarium, both gecko species consumed significantly more unfed than fed or gravid female mosquitoes, presumably because the latter rested whereas the former foraged more actively. H.frenatus consumed significantly more mosquitoes of all categories than did G.dubia per 24 h: unfeds 5.1 +/- 0.1% v. 4.5 +/- 0.5%, blood-feds 4.5 +/- 0.3% v. 4.0 +/- 0.5% and gravids 4.8 +/- 0.4% v. 3.9 +/- 0.5%. Possible relevance of these results to competitive displacement of G.dubia by H.frenatus is discussed.