Conspecific and allospecific larval extracts entice mosquitoes to lay eggs and may be used in attract-and-kill control strategy

Abstract

One of the strategies of integrated vector management is to lure gravid mosquitoes for surveillance purposes or to entice them to lay eggs in water containing toxins that kill the offspring (attract-and-kill or trap-and-kill). Typically, the major challenge of this approach is the development of a lure that stimulates oviposition plus a toxin with no deterrent effect. Bacillus thuringiensis var. israelensis (Bti) satisfies the latter criterion, but lures for these autocidal gravid traps are sorely needed. We observed that gravid Aedes aegypti, Ae. albopictus, and Culex quinquefasciatus laid significantly more eggs in cups with extracts from 4th-stage larvae (4 L) of the same or different species. No activity was found when 4 L were extracted with hexane, diethyl ether, methanol, or butanol, but activity was observed with dimethyl sulfoxide extracts. Larval extracts contained both oviposition stimulant(s)/attractant(s) and deterrent(s), which partitioned in the water and hexane phases, respectively. Lyophilized larval extracts were active after a month, but activity was reduced by keeping the sample at 4 °C. In the tested range of 0.1 to 1 larvae-equivalent per milliliter, oviposition activity increased in a dose-dependent manner. In field experiments, Ae. aegpti laid significantly more eggs in traps loaded with larval extracts plus Bti than in control traps with water plus Bti.

Behavioural and antennal responses of Aedes aegypti (l.) (Diptera: Culicidae) gravid females to chemical cues from conspecific larvae

“…The data presented here confirm the positive influence of conspecific immature stages on the oviposition of gravid Ae . aegypti females, as already observed in literature [ 16 – 20 ]. The presence of larval-associated signals within a breeding site may notify gravid females about suitable conditions that can ensure the proper development of their progeny.…”

“…For instance, some plant extracts have been found to affect gravid females at long distance [ 13 ], and their association with signals from immature mosquito conspecifics may also increase the influence on females when they seek or land on potential oviposition sites, as well as improve the specificity to the targeted organisms. In an ovitrap-based system, the association of attractants with biocide agents may improve the efficiency of vector control, as demonstrated with an association of caproic acid and Temephos [ 25 ], as well as with LHW with Bti [ 20 ]. However, to drastically reduce the potential effect of biocides on non-target organisms, it is crucial to develop lures that specifically target Ae .…”

“…plant, microbial, conspecifics and heterospecifics) [ 13 – 15 ], with the presence of immature conspecifics being a strong determinant of the breeding site choice. Yet, laboratory experiments evidenced that eggs- and larval-holding waters strongly stimulate females for egg-laying, suggesting the presence of a pheromonal signal [ 16 – 20 ]. This preference is also observed under field conditions, where females preferred to lay eggs in containers that have previously held larvae or pupae [ 20 – 22 ].…”

“…Yet, laboratory experiments evidenced that eggs- and larval-holding waters strongly stimulate females for egg-laying, suggesting the presence of a pheromonal signal [ 16 – 20 ]. This preference is also observed under field conditions, where females preferred to lay eggs in containers that have previously held larvae or pupae [ 20 – 22 ]. The presence of immature stages, whose chemical signature is thought to originate from both larvae and their associated bacteria [ 13 , 17 , 23 – 25 ], is likely interpreted by females as a suitable site for larvae development [ 15 ].…”

Coagulation-Flocculation: A potential Application for Mosquito Larval Source Management (LSM) with No Insecticide Resistance

“…Numerous studies indicated that the process of selecting breeding sites for female mosquitoes is mediated by multiple factors such as vision [36], smell [37], and pheromone [38]. We speculated in this study mosquitoes' oviposition behavior is mainly in uenced by vision.…”