Oviposition preference of Culex pipiens molestus and C. tritaeniorhynchus summorosus onto the waters conditioned by the egg rafts or the larvae

Abstract

The effects of waters conditioned by the egg rafts or the larvae of Culex pipiens molestus and C. tritaeniorhynchus summorosus on their intraspecific oviposition preference were investigated. Preference was shown to the water on which egg rafts of the same species had been floated for one day at 20℃ over tap water in C. p. molestus, but not in C. tritaeniorhynchus. When the number of egg rafts was over ten in water conditioning, the oviposition females of C. p. molestus discriminated between the conditioned water and tap water. C. tritaeniorhynchus was reluctant to choose the water which had contained the 1st-instar larvae for only one hour at 25℃, but this effect was trivial with the water in which the 4th-instar larvae had been held. However, the oviposition females of C. p. molestus showed a significant preference to the water which had contained the over thirty 4th-instar larvae in 200ml for one hour at 25℃. Even if two 4th-instar larvae had been contained per pot for one day, but not one hour, the water was selected by C. p. molestus. However, no clear discrimination was made by C. p. molestus between tap water and the water which had contained the 1st-instar larvae for one hour at 25℃. The water in which larvae were reared from the 1st-instar to pupation at 25℃ was preferred for oviposition over tap water in both species. This difference in the experimental results for C. tritaeniorhynchus may be attributed to the food present in the microbiota rich, larvae-rearing water. The interpretation of these results was made in connection with the larval adaptability to the density and the ecological characteristics of larval habitat in each species.