Targeting a Hidden Enemy: Pyriproxyfen Autodissemination Strategy for the Control of the Container Mosquito Aedes albopictus in Cryptic Habitats

Abstract

Background: The Asian tiger mosquito, Aedes albopictus, is a vector of dengue, Chikungunya, and Zika viruses. This mosquito inhabits a wide range of artificial water-holding containers in urban and suburban areas making it difficult to control. We tested the hypothesis that female-driven autodissemination of an insect growth regulator could penetrate cryptic oviposition habitats difficult to treat with conventional insecticidal sprays.

Methodology: Oviposition preferences of Ae. albopictus females for open and cryptic cups were tested in semi-field experiments. Two conventional larvicidal sprayers were tested to determine droplet penetration and larvicidal efficacy in open and cryptic habitats using Bacillus thuringiensis var. israelensis (Bti) in the field. Finally, the efficacy of pyriproxyfen autodissemination stations was assessed in cryptic and open cups in residential areas during 2013 and 2014.

Principal findings: Gravid females strongly preferred cryptic (53.1±12.9 eggs/cup) over open (10.3±4.3 eggs/cup) cups for oviposition. Cryptic cups showed limited droplet penetration and produced 0.1-0.3% larval mortality with a conventional backpack and low-volume sprays of Bti. The autodissemination stations effectively contaminated these cryptic cups (59.3-84.6%) and produced 29.7-40.8% pupal mortality during 2013-2014. Significant pupal mortality was also observed in open cups.

Conclusions: The autodissemination station effectively exploits the oviposition behavior of wild gravid females to deliver pyriproxyfen to targeted oviposition habitats. Although the pupal mortality in cryptic cups was relatively lower than expected for the effective vector control. Autodissemination approach may be a suitable supporting tool to manage Ae. albopictus immatures in the cryptic habitats those are less accessible to conventional larvicidal sprays.

Fig 1

Large field cage (A) for assessing the oviposition preference of Ae. albopictus females in open (B) vs. cryptic (C) sentinel oviposition cups.

Fig 2

Autodissemination stations: (A) Model 2013 with top circular formulation cartridge. (B) A cartridge containing inner oil and outer powder formulation bands in 2013 model. (C) Model 2014 with side formulation cartridge. (D) A cartridge containing a dual layer of inner oil and outer powder formulation bands in 2014 model.

Fig 3

Droplet density (bar) and median size (line) in open and cryptic cups using backpack (A) and truck-mounted LV (B) sprayers. Letters above the bars and lines indicate significant differences (p<0.05). Data are shown as mean ± SE.

Fig 4

Weekly percent pupal mortality (A) and pyriproxyfen contamination (B) in open and cryptic cups during 2013 field experiment. Significant difference indicated by * (p<0.05). Data are shown as mean ± SE.

Fig 5

Weekly percent pupal mortality (A) and pyriproxyfen contamination (B) in open and cryptic cups during 2014 field experiment. Significant difference indicated by * (p<0.05). Data are shown as mean ± SE.