Autodissemination of Insect Growth Regulator, Methoprene, with Two Formulations Against Aedes albopictus

Control methods for invasive mosquitoes of Aedes aegypti and Aedes albopictus (Diptera: Culicidae) in Indonesia

The two invasive mosquito species in Indonesia are Aedes aegypti and Ae. albopictus. These mosquitoes are a serious nuisance to humans and are also the primary vectors of several foreign pathogens, such as dengue, Zika, and chikungunya viruses. Efforts must be made to reduce the possibility of mosquito bites and the potential for disease transmission. Given the invasion of these two Aedes species, this approach should be considered as part of an integrated strategy to manage them. This review discusses existing and developing control techniques for invasive Ae. aegypti and Ae. albopictus, with an emphasis on those that have been and are being used in Indonesia. Environmental, mechanical, biological (e.g., Bacillus thuringiensis and Wolbachia), and chemical (e.g., insect growth regulators and pyrethroids) approaches are discussed in this review, considering their effectiveness, sustainability, and control methods.

Evaluation of a Methoprene Aerial Application for the Control of Culiseta melanura (Diptera: Culicidae) in Wetland Larval Habitats

Eastern equine encephalitis virus (EEEV) is an arbovirus endemic to the eastern United States. Human cases are rare but can be serious. The primary enzootic vector is Culiseta melanura (Coquillett) (Diptera: Culicidae), an ornithophagic mosquito. We conducted an aerial application of a granular methoprene formulation in Hockomock Swamp (Massachusetts), which represents a focus of EEEV transmission. Water collected from inside and outside Cs. melanura crypts was evaluated in bioassays of early fourth instar Cs. melanura larvae using treated and untreated water. Adult eclosion rates were 36% significantly lower in treated compared with untreated water (P < 0.05). Eclosion rates for water collected from inside crypts were significantly higher (62%) than rates from outside crypts (30%) (P < 0.05), indicating higher efficacy outside crypts. We tested whether reduced methoprene efficacy inside the crypts was due to reduced chemical penetration into this habitat. Chemical water analyses confirmed that methoprene concentrations were lower inside the crypts (0.1 ± 0.05 ppb) compared to water from outside crypts (1.79 ± 0.41 ppb). The susceptibility of Cs. melanura to methoprene was also determined to allow for comparison against concentrations observed in water collected from the field (LC-95: 1.95 ± 0.5 ppb). Overall, methoprene-treated water prevented mosquito development for up to 4 wk, but with a reduction in efficacy between 4- and 6-wk post-application. Our results suggest that aerial methoprene applications can effectively treat open water in wetlands but may not provide efficacious control of Cs. melanura due to an inability to penetrate larval habitats.

Indirect transfer of pyriproxyfen to European honeybees via an autodissemination approach

The frequency of arboviral disease epidemics is increasing and vector control remains the primary mechanism to limit arboviral transmission. Container inhabiting mosquitoes such as Aedes albopictus and Aedes aegypti are the primary vectors of dengue, chikungunya, and Zika viruses. Current vector control methods for these species are often ineffective, suggesting the need for novel control approaches. A proposed novel approach is autodissemination of insect growth regulators (IGRs). The advantage of autodissemination approaches is small amounts of active ingredients compared to traditional insecticide applications are used to impact mosquito populations. While the direct targeting of cryptic locations via autodissemination seems like a significant advantage over large scale applications of insecticides, this approach could actually affect nontarget organisms by delivering these highly potent long lasting growth inhibitors such as pyriproxyfen (PPF) to the exact locations that other beneficial insects visit, such as a nectar source. Here we tested the hypothesis that PPF treated male Ae. albopictus will contaminate nectar sources, which results in the indirect transfer of PPF to European honey bees (Apis mellifera). We performed bioassays, fluorescent imaging, and mass spectrometry on insect and artificial nectar source materials to examine for intra- and interspecific transfer of PPF. Data suggests there is direct transfer of PPF from Ae. albopictus PPF treated males and indirect transfer of PPF to A. mellifera from artificial nectar sources. In addition, we show a reduction in fecundity in Ae. albopictus and Drosophila melanogaster when exposed to sublethal doses of PPF. The observed transfer of PPF to A. mellifera suggests the need for further investigation of autodissemination approaches in a more field like setting to examine for risks to insect pollinators.

Autodissemination approaches have attracted a significant amount of attention for mosquito control because of the advantages of self-delivery of small amounts of highly potent insect growth regulators (IGRs) such as pyriproxyfen (PPF) to oviposition locations. However, while PPF may be delivered to oviposition locations by the mosquito vehicles, these treated mosquitoes may also be delivering PPF to nectar sources that other insects may visit, in particular important insect pollinators. Here we have examined for the direct transfer of PPF to nectar sources and the indirect transfer to the European honey bee. We show PPF is being deposited on artificial nectar sources and is being indirectly transferred to European honey bees. The results are discussed in reference to the potential risks to important insect pollinators of using autodissemination approaches for mosquito control.

TRUCK-MOUNTED NATULAR 2EC (SPINOSAD) ULV RESIDUAL TREATMENT IN A SIMULATED URBAN ENVIRONMENT TO CONTROL AEDES AEGYPTI AND AEDES ALBOPICTUS IN NORTH FLORIDA

Preemptive treatment of dry habitats with an ultra-low volume (ULV) residual larvicide may be effective in an integrated vector management program to control populations of container-inhabiting Aedes mosquitoes, key vectors of Zika, dengue, and chikungunya viruses. We exposed dry, artificial containers placed in exposed and protected locations to Natular 2EC (spinosad) larvicide applied with a truck-mounted ULV sprayer in a simulated urban setting in North Florida, and later introduced water and Ae. aegypti or Ae. albopictus larvae to conduct bioassays. Up to 50% mortality was observed in bioassays, indicating further analysis of spinosad as a residual treatment application.