Attraction of the Mosquitoes Aedes aegypti and Aedes albopictus (Diptera: Culicidae) to a 3-Part Phytochemical Blend in a Mesocosm

Aedes aegypti (L.) and Aedes albopictus (Skuse) mosquitoes of both sexes were attracted to a 3-part volatile synthetic phytochemical blend but differed according to their component ratios, 7:3:2 or 1:1:1, and their initial concentrations. These arbovirus vectors were presented with the blends as baits in paired baited and blank CFG traps in a large greenhouse mesocosm. Ae. aegypti attraction was highest at a 7:3:2 blend ratio, but at a concentration half that found most effective for an anopheline mosquito species in outdoor screenhouses. Both lower and higher concentrations yielded substantially lower attraction scores for Ae. aegypti. By contrast, the few tests conducted on Ae. albopictus showed that it was not as sensitive to concentration, but again it was more responsive to the 7:3:2 ratio of components than to the 1:1:1 ratio. The two sexes of both species were represented equally in the trap catches, indicating the potential value of this and similar attractive blends for population surveillance and control of Aedes mosquitoes.

Efficacy of extended release formulations of Natular™ (spinosad) against larvae and adults of Anopheles mosquitoes in western Kenya

BACKGROUND

Larval source management is recommended as a supplementary vector control measure for the prevention of malaria. Among the concerns related to larviciding is the feasibility of implementation in tropical areas with large numbers of habitats and the need for frequent application. Formulated products of spinosad that are designed to be effective for several weeks may mitigate some of these concerns.

METHODS

In a semi-field study, three formulations of spinosad (emulsifiable concentrate, extended release granules and tablet formulations) were tested in naturalistic habitats in comparison to an untreated control. Cohorts of third instar Anopheles gambiae (Diptera: Culicidae) were introduced into the habitats in screened cages every week up to four weeks after application and monitored for survivorship over three days. A small-scale field trial was then conducted in two villages. Two of the spinosad formulations were applied in one village over the course of 18 months. Immature mosquito populations were monitored with standard dippers in sentinel sites and adult populations were monitored by pyrethrum spray catches.

RESULTS

In the semi-field study, the efficacy of the emulsifiable concentrate of spinosad waned 1 week after treatment. Mortality in habitats treated with the extended release granular formulation of spinosad was initially high but declined gradually over 4 weeks while mortality in habitats treated with the dispersable tablet formulation was low immediately after treatment but rose to 100% through four weeks. In the field study, immature and adult Anopheles mosquito populations were significantly lower in the intervention village compared to the control village during the larviciding period. Numbers of collected mosquitoes were lower in the intervention village compared to the control village during the post-intervention period but the difference was not statistically significant.

CONCLUSIONS

The extended release granular formulation and the dispersible tablet formulations of spinosad are effective against larval Anopheles mosquitoes for up to four weeks and may be an effective tool as part of larval source management programmes for reducing adult mosquito density and malaria transmission.

Prallethrin-induced excitation increases contact between sprayed ultralow volume droplets and flying mosquitoes (Diptera: Culicidae) in a wind tunnel

Female Culex quinquefasciatus Say (Diptera: Culicidae) mosquitoes were exposed to sublethal amounts of prallethrin, sumithrin, and piperonyl butoxide applied as ultralow volume (ULV) droplets in a wind tunnel. Mosquitoes were video recorded before, during, and after treatment, and the number and size of droplets on their bodies were later determined using a compound microscope. A positive correlation was found between mosquitoes that spent more time flying during the time of spraying and number of droplets on their bodies. Excitation, in the form of increased speed and duration of flight, was immediate in mosquitoes exposed to prallethrin, whereas exposure to sumithrin did not increase their exposure to the ULV droplets. The location of droplets on mosquitoes, the effects of droplet volume, and subsequent mortality are discussed.

A review of spinosad as a natural product for larval mosquito control

The effectiveness of spinosad for larval mosquito control is summarized based on available published literature and some heretofore unpublished studies. Spinosad is highly active against larvae of all mosquito species tested thus far. It is effective at similar dosages for all larval mosquito instars, with peak cumulative mortality occurring at 72 h posttreatment. More studies are needed to fully define spinosad's ovicidal properties and its impact on the pupal stage. High levels of organic matter and full sunlight are both factors that can negatively impact spinosad efficacy and longevity and should be considered when making use rate and retreatment decisions. Studies clearly show that spinosad technical active ingredient and current crop formulations are suboptimal for larval mosquito control and underrepresent spinosad's true activity. A series of spinosad formulations specialized for larval mosquito control will be sold commercially. Prior to its launch and widespread use, there is a need for additional baseline studies to clarify the natural geographic variation in susceptibility of field mosquito populations. Spinosad represents a new and effective natural product for the integrated management of larval mosquitoes. It possesses a unique mode of action not shared by any other insecticide and is shown to be minimally disruptive to most nontarget species tested thus far at its proposed field use rates.