Laboratory evaluation of the horizontal movement of pyriproxyfen to larval microcosms by gravid Aedes albopictus (Skuse) and Aedes triseriatus (Say)

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Title: Laboratory evaluation of the horizontal movement of pyriproxyfen to larval microcosms by gravid Aedes albopictus (Skuse) and Aedes triseriatus (Say)
Author: Chism, Billy Dell
Advisors: Charles S. Apperson, Chair
Michael Linker, member
Edward Vargo, member
Abstract: Horizontal movement of the insect growth regulator (IGR) pyriproxyfen to larval microcosms by gravid container-inhabiting mosquitoes, Aedes albopictus (Skuse) and Aedes triseriatus Say, was evaluated under laboratory conditions. In larval susceptibility bioassays determining emergence inhibition (EI), both species were found to be highly susceptible to the IGR. Aedes albopictus exhibited an EI50 of 0.200 ppb, while Aedes triseriatus was 7 and 3.5x more susceptible with an EI50 of 0.0288 ppb. A randomized complete block experimental design was used for each species to evaluate the horizontal transfer of the IGR by gravid females force contacted with pyriproxyfen-treated oviposition strips. For Ae. albopictus, experiments were blocked by treatment rate of pyriproxyfen (0.2, 0.3 and 0.4 mg/cm2). Effects of numbers of treated females (1, 3 and 5 females per bioassay cage) on horizontal movement of the IGR was evaluated within each treatment rate. One treatment rate of pyriproxyfen (0.2 mg/cm2) was evaluated for Ae. triseriatus. A significant (P<0.05) curvilinear response in emergence inhibition was observed in Ae. albopictus and Ae. triseriatus over the three population densities of treated females evaluated. Notably, the shape of the response curves for the two species were opposite. Lower but equivalent levels of mortality were achieved at densities of 1 and 3 treated Ae. triseriatus females per cage with significantly higher levels of inhibition of emergence observed at 5 females per cage. At 1,3, and 5 females per cage, mortality of Ae. triseriatus averaged 20.8%, 26.9%, and 70.4%, respectively. For Ae. albopictus, mortality at the higher two population densities was similar and significantly larger than was observed at the lowest population density. Mean mortality of Ae. albopictus ranged over the 3 treatment rates from 3.5 to 30.2%, 47.8 to 67.3%, and 58.6 to 73.1% at densities of 1,3 and 5 females per cage, respectively. Amounts of pyriproxyfen transferred by gravid females were estimated from the log dose-probit mortality data obtained in larval bioassays.In binary choice bioassays, horizontal transfer of biologically active amounts of pyriproxyfen from treated (0.3 or 0.4 mg/cm2) to untreated microcosms was achieved by Aedes albopictus. Three microcosm configurations were utilized in an attempt to manipulate mosquito oviposition behavior to increase the amount of IGR transferred. Emergence inhibition (37.8%) for microcosms completely wrapped in black paper was significantly higher (P>0.05) than two other configurations utilized. Forcibly exposing gravid females to pyriproxyfen-treated surfaces did not affect their fecundity. However, mean percent egg hatch between egg clutches laid in the 1st and 2nd gonotrophic cycles declined significantly (P<0.05) by 30%. To assess the residual activity of pyriproxyfen, 1st instar Ae. albopictus were added to microcosms used in forced-contact experiments. Mosquito mortality declined markedly indicating that pyriproxyfen was not highly residual in larval microcosms. Use of IGR-treated oviposition containers to achieve horizontal movement of pyriproxyfen to mosquito oviposition sites in the field is a promising management technique. However, laboratory results were often variable, suggesting that interactions between females within the oviposition site caused a differential transfer of pyriproxyfen to larval microcosms. Comparative studies of the oviposition behavior of each mosquito species are warranted and would potentially provide information needed to improve the technique.
Date: 2001-05-30
Degree: MS
Discipline: Entomology
URI: http://www.lib.ncsu.edu/resolver/1840.16/2360


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