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 predatio n rates by the Australian gecko Gehydra dubia and the exotic Asian hou se gecko Hemidactylus frenatus. For both gecko species a positive corr elation was demonstrated between prey density and the predation rate. Using Ae.aegypti males and unfed females as prey in a terrarium (0.054 m(3)), 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 we re compared in an experimental room (32 m(3)) for 24h exposure with ph otoperiod L:D 12:12 h. Five photophilic species (Aedes vigilax, Anophe les annulipes, Coquillettidia xanthogaster, Culex annulirostris, Cx si tiens) 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 ben efit of domestication for geckoes that learn to hunt at light. When of fered a mixture of unfed, freshly blood-fed and gravid females of Ae.a egypti in an illuminated terrarium, both gecko species consumed signif icantly more unfed than fed or gravid female mosquitoes, presumably be cause the latter rested wheras the former foraged more actively. H.fre natus consumed significantly more mosquitoes of all categories than di d G.dubia per 24h: 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%. Possib le relevance of these results to competetive displacement of G.dubia b y H.frenatus is discussed.