Behavioral responses of Aedes aegypti male populations developed for Release of Insects Carrying a Dominant Lethal (RIDL) technology and a Malaysian wild-type population of two age groups (4-5 and 8-10 d old) were tested under laboratory conditions against chemical irritants and repellents using the high-throughput screening system device. Results indicate that all male Ae. aegypti test populations showed significant (P < 0.01) behavioral escape responses when exposed to alphacypermethrin, DDT, and deltamethrin at the test dose of 25 nmol/cm2. In addition, all populations showed significant (P < 0.05) spatial repellent responses to DDT, whereas alphacypermethrin and deltamethrin elicited no directional movement in the assay. These data suggest that genetic modification has not suppressed expected irritancy and repellency behavior. Age effects were minimal in both contact irritant and spatial repellent assays. The magnitude of irritant response, based on percentage responding, was stronger in the RIDL test cohorts as compared with the wild-type Malaysian population, but the impact, if any, that this increased behavioral sensitivity might have on the success of a RIDL strategy has yet to be defined. Information of the type reported in the current study is vital in defining the effects of genetic modification on vector behavior and understanding how these behaviors may influence the success of RIDL technology as they relate to other vector control interventions implemented in the same disease-endemic locale.
Dengue is the most important mosquito-borne viral disease. No specific treatment or vaccine is currently available; traditional vector control methods can rarely achieve adequate control. Recently, the RIDL (Release of Insect carrying Dominant Lethality) approach has been developed, based on the sterile insect technique, in which genetically engineered 'sterile' homozygous RIDL male insects are released to mate wild females; the offspring inherit a copy of the RIDL construct and die. A RIDL strain of the dengue mosquito, Aedes aegypti, OX513A, expresses a fluorescent marker gene for identification (DsRed2) and a protein (tTAV) that causes the offspring to die. We examined whether these proteins could adversely affect predators that may feed on the insect. Aedes aegypti is a peri-domestic mosquito that typically breeds in small, rain-water-filled containers and has no specific predators. Toxorhynchites larvae feed on small aquatic organisms and are easily reared in the laboratory where they can be fed exclusively on mosquito larvae. To evaluate the effect of a predator feeding on a diet of RIDL insects, OX513A Ae. aegypti larvae were fed to two different species of Toxorhynchites (Tx. splendens and Tx. amboinensis) and effects on life table parameters of all life stages were compared to being fed on wild type larvae. No significant negative effect was observed on any life table parameter studied; this outcome and the benign nature of the expressed proteins (tTAV and DsRed2) indicate that Ae. aegypti OX513A RIDL strain is unlikely to have any adverse effects on predators in the environment.
Dengue is the most important mosquito-borne viral disease. In the absence of specific drugs or vaccines, control focuses on suppressing the principal mosquito vector, Aedes aegypti, yet current methods have not proven adequate to control the disease. New methods are therefore urgently needed, for example genetics-based sterile-male-release methods. However, this requires that lab-reared, modified mosquitoes be able to survive and disperse adequately in the field.