The Importance of Subterranean Mosquito Habitat to Arbovirus Vector Control Strategies in North Queensland, Australia

Abstract

In north Queensland, 14 localities were surveyed for mosquito larvae (third and fourth instar) during summer/autumn and winter from 1996 to 1999. Absolute population numbers in subterranean habitats, mainly service manholes and pits (97%) but also some wells, septic tanks, storm drains, and sumps, were expressed as a proportion of total numbers in these sites plus surface sites within a 100-m radius. When correction factors were applied to subterranean samples, the 472,477 larvae mainly of Aedes tremulus (Theobald) group, Aedes notoscriptus (Skuse), and Aedes aegypti (L.) comprised 78% of the total population. In relation to the proportion of the overall immature mosquito population from subterranean habitats (propsub), linear regression coefficients for minimum temperature, relative humidity, and Mesocyclops copepod prevalence were significant for winter data; but for summer, only relative humidity was significant. Linear regression coefficients for Mesocyclops prevalence approached significance (P = 0.061) in summer. When multiple linear regression was used to model propsub, 68% of the variation was accounted for by relative humidity and the prevalence of Mesocyclops. In the drier and cooler towns, increased use of subterranean sites during winter was caused by reduced availability of surface oviposition sites because of the dry season. In the wetter coastal towns, no such restrictions applied and ambient conditions remained more equitable all year round. Mesocyclops were surprisingly common, particularly in these coastal towns. Release of known numbers of Mesocyclops indicated that 3-sweep netting in service manholes was sensitive down to densities of one Mesocyclops per 10 liters, and overall recovery varied from 1 to 4%. In relation to control, service manholes represent a stable habitat for mosquito (7% positive overall) and Mesocyclops populations. If they remained wet, service manholes positive for mosquito immatures or Mesocyclops during summer/autumn had 96% and 85% chance, respectively, of being positive the following winter. Even allowing for the effect of drying, a mosquito-positive manhole had a 79% chance of remaining positive the following winter. In view of the importance of these sites as refuges from adverse ambient conditions, it is proposed that a winter control strategy using Mesocyclops presents a cost-effective control option to reduce the recolonization of surface sites when conditions become more suitable.

Mosquito-borne Diseases as a Consequence of Land Use Change

“…In fact, the potential risks from these breeding sites and refugia may be higher than previously expected. Researchers in Australia have found that subterranean habitats may account for as much as 78% of the vector mosquitoes during the dry season when surface water is scarce (Kay et al, 2000a). Additionally, these researchers have found that dengue virus exposure (transmitted by Aedes mosquitoes) is approximately 2.5 times greater for people living within 160 meters of a well or service manhole (Russell et al, 2002).…”

Control of aedes vectors of dengue in three provinces of Vietnam by use of Mesocyclops (Copepoda) and community-based methods validated by entomologic, clinical, and serological surveillance.

“…For aquaria or ornamental ponds, vases, discarded materials, ant traps, buckets, stone mortars, filter boxes, home distillery cooler tanks, jars, tanks for flushing toilets, and other smallto medium-capacity containers, the water was sieved through a 100-m mesh net, and immature mosquitoes were counted in a white tray. For outdoor concrete tanks (500-4,250 L), wells and metal drums (220 L), correction factors of 17, 5, and 3.5 were applied to the catch as calibrations for net sampling 6,7 and funnel trap 8 usage in analogous situations in north Queensland, Australia. The population size for each survey period was expressed as a percentage of the numbers of third or fourth instars in the original April 1998 pretreatment survey.…”

Effects of Metarhizium anisopliae conidia mixed with soil against the eggs of Aedes aegypti

“…This species lays eggs on substrates such as soils or vegetation close to the water's edge (Kay et al 2000;Reiter 2007; Luciana S Lobo and Christian Luz personal communication). Aedine eggs are not affected by the most common chemical or biological insecticides (Pérez et al 2007).…”