In southern California, underground storm drain systems (USDS) can produce significant numbers of arbovirus vectors such as Culex quinquefasciatus and are thought to be foci of West Nile virus activity in urban landscapes. USDS are typically comprised of hundreds to thousands of miles of horizontal drain channels, and thousands of catch basins and manhole chambers. In comparatively recent suburban developments, the linkage among stormwater collection points is less extensive than in the systems in cities and older suburbs. These newer underground basins are often connected to infiltration or detention basins. Standing water in USDS provides developmental sites for immature mosquitoes and the moist, cool environment of USDS is favorable for resting and overwintering adult mosquitoes.
Due to restricted accessibility of breeding sources in these systems, controlling mosquito populations in USDS continues to be a challenging task for vector control districts. In addition to a lack of access to many mosquito developmental sites within the confined space of USDS, current mosquito abatement methods are problematic in other ways. Vector control is costly, often requiring multiple treatments per mosquito season and necessitating several personnel to gain entry to underground sites and manipulate vector control equipment. Application of a residual adulticide to the vertical walls of manholes reduces emerging mosquito populations, but does not achieve satisfactory levels of control because of dispersal of adult mosquitoes within, and into, USDS. Moreover, prohibiting pesticide residues from contaminating drain lines requires time consuming procedures that do not allow the control of mosquitoes in the horizontal main trunk lines. Bacterial larvicides provide an environmentally friendly alternative to chemical insecticides for mosquito control, but delivery of product to aquatic developmental sites in trunk lines is problematic. As municipalities are required to meet more stringent water quality total maximum daily loads (TMDLs) for stormwater, mosquito control agents that include particulates in the formulations might likely be problematic.
Entomo-pathogenic fungi (e.g., Beauveria bassiana, Metarhizium anisopliae) are contact bioinsecticides with no chemical residue and little potential for behavioral avoidance and resistance evolution in the target insects. The fungi are safe (e.g., approved for use on edible crops), not toxic to vertebrates and environmentally friendly. These naturally occurring soil-dwelling species are capable of controlling multiple insect pest species. Fungal spores germinate on the insect surface and hyphae invade and kill susceptible insects in 3-14 days. The efficacy of fungi against particular insect species differs among fungal strains, spore concentrations and environmental conditions (e.g., temperature, humidity).
The goals of this project are to investigate the effectiveness of two fungal strains as biocontrol agents of mosquitoes inhabiting underground storm drain systems (USDS). We (i) investigated the infectivity and persistence of the two fungal species in replicate USDS in the Coachella Valley using two types of bioassays, (ii) surveyed for the presence and fungal infection of mosquito populations in USDS in the Coachella Valley, and (iii) examined the efficacy of commercially available formulations of the two fungi against Culex quinquefasciatus mosquitoes in laboratory bioassays. These studies have been supported by the Coachella Valley Mosquito and Vector Control District and the Mosquito Research Foundation.