Oviposition attraction and repellency of Aedes aegypti (Diptera: Culicidae) to waters from conspecific larvae subjected to crowding, confinement, starvation, or infection.

As the biomass of Aedes aegypti (L.) larvae increased in relation to the volume of rearing waters, oviposition attraction of these waters to conspecific, gravid females first rose to a peak and then declined. Further increases in biomass rendered waters strongly repellent. Comparable responses were elicited by a decrease in the volume of rearing waters or an increase in the relative size or number of mosquito larvae. Low volumes of water reduced oviposition attraction and increased repellency, whereas larger volumes increased attraction. Excessively large volumes diluted attraction to neutrality. Constraints imposed by the physical dimensions of the larval environment which interfered with the normal postural movements and behaviors of the larvae also induced repellency, independent of rearing volume. Titration of repellent waters revealed that infection with the digenean Plagiorchis elegans (Rudolphi) generated the most powerful repellent effect, whereas crowding or starvation induced significantly weaker responses. At no time did dilution of repellent waters restore attractive properties. Repellents, even at minute concentrations, overrode attractants. The density-dependent action of oviposition attractants and repellents may help to maintain larval populations near optimal levels through their influence on recruitment. Oviposition repellency induced by sublethal infections with P. elegans may maintain population levels below the carrying capacity of the environment. Persistence of oviposition attraction and repellency varied inversely with temperature. The magnitude of the repellent effect induced by larvae appears to be a good indicator of their probability of survival and may be of selective significance. Repellency may deflect ovipositing females away from sites close to human habitation and may lead to new, and perhaps more effective, method, to control mosquitoes and the diseases they transmit.

Serum composition of Aedes aegypti (Diptera: Culicidae) larvae and the production of an oviposition repellent are influenced by infection with the entomopathogenic digenean Plagiorchis elegans (Trematoda: Plagiorchiidae), starvation, and crowding.

Subjecting Aedes aegypti (L.) larvae to conditions that induced the production of oviposition repellency also reduced their wet and dry weights and the concentration of total serum carbohydrates, amino acids, and proteins. Thus, infection with metacercariae of the entomopathogenic digenean Plagiorchis elegans (Rudolphi), starvation for 7 d, or crowding for 2 d reduced larval dry weights by as much as 32, 20, and 23%, respectively, and wet weights by 20, 14, and 11%, respectively. Total serum carbohydrates declined by as much as 36, 21, and 29% for infected, starved, and crowded larvae, respectively, amino acids by 39, 48, and 44%, and protein concentrations by 72, 63, and 62%, respectively. Repellency dilution titers were correlated inversely with movement of the mouth parts and gut. Incubation of infected, starved, and crowded larvae in 0.01 g/liter glucose greatly reduced the level of repellency of their waters, whereas adding glucose to repellent waters had only minor effects. Results indicate that the induction of repellency is associated strongly with nutritional depletion effects.

Oviposition responses of Aedes aegypti and Ae. atropalpus (Diptera: Culicidae) females to waters from conspecific and heterospecific normal larvae and from larvae infected with Plagiorchis elegans (Trematoda: Plagiorchiidae).

Ovipositing Aedes aegypti (L.) females were attracted to waters in which uninfected Aedes atropalpus (Coquillett) larvae had been reared, but were repelled by waters from larvae of either species infected with the entomopathogenic digenean Plagiorchis elegans (Rudolphi). In contrast, Ae. atropalpus females were attracted to or repelled by waters from conspecific uninfected and infected larvae, respectively, but did not respond to corresponding waters from Ae. aegypti larvae. The sensitivity of ovipositing females of both species to repellents and attractants is discussed in terms of possible selective pressures exerted by unstable breeding environments.