The potential of mosquito-indigestible phytoplankton for mosquito control.
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Mosquitoes systematics, life cycle as well as morphology and bionomics of developmental stages, mosquitoes borne diseases, ecology and reemergence, vectorial capacity of some domestic species were presented with regard to mosquitoes control by the integrated methods and ecological prophylaxis.
Methods to increase and preserve Dugesia tigrina for mosquito control purposes through cocoon production, mechanical sectioning and cold storage were examined. Cocoon production was an ineffective and unreliable means of increasing planarian numbers, with an average of only 0.19 cocoons containing 0.74 young produced per adult per week. In comparison, mechanical sectioning proved to be more appropriate for increasing the number of planaria. One hundred planaria averaging 8 mm in length could be sectioned into 600 segments in approximately 18 min; regeneration was achieved by approximately 94% of these segments, usually within 8 days after sectioning. Techniques were developed to store planaria at 10 degrees C until needed for field release.
Mosquito control began in New York City in 1901. Large-scale efforts to drain marshlands occurred through the 1930s, and aerial application of pesticide occurred as early as 1956. Components of early mosquito-borne disease control were reimplemented in 1999-2000 in response to an outbreak of West Nile virus, and included promoting public and health professional awareness regarding disease causation and prevention, providing free government laboratory testing, case reporting, mapping of mosquito breeding sites and their elimination or application of larvicide to them, and adult mosquito control. Because a potential for various mosquito-borne diseases in New York City persists, continued efforts are warranted to limit mosquito breeding, to monitor adult mosquito populations for the presence of human pathogens, and to establish protocols and capacity for adult mosquito control.
The use of various organophosphates to control mosquito populations is a common practice across the globe. We review the literature (LC50s) on dichlorvos, the primary breakdown product of Dibrom, and use laboratory and field experiments to determine the lethal and sublethal (bioassays) effects of dichlorvos on two widely distributed and ecologically important estuarine invertebrate species, the marsh grass shrimp, Palaemonetes pugio and the Eastern oyster, Crassostrea virginica. Laboratory results based on LC50s and sublethal acetylcholinesterase (AChE) inhibition activity bioassays indicate that adult grass shrimp are more sensitive (approximately 500 x ) to dichlorvos than juvenile oysters. Although potentially an important factor for intertidal or shallow-dwelling estuarine organisms, the toxicity of dichlorvos was not enhanced in the presence of simulated sunlight for adult P. pugio. The most notable decreases in AChE activity were for grass shrimp and oysters exposed to dichlorvos concentrations above those considered ecologically relevant. In field experiments, both species were deployed in cages in unsprayed (n = 2) and sprayed (n = 3) sites and water samples collected pre- and post-spraying. Quantifiable dichlorvos levels were measured at the two narrowest creek treatment sites following mosquito spraying, suggesting that overspray can occur and there was evidence of a sublethal AChE response at these same sites. However, experiments at the widest creek revealed no measurable dichlorvos or sublethal responses. Results from this research suggest that adult grass shrimp are more sensitive to dichlorvos than juvenile oysters. Spraying near small tidal creeks may have measurable impacts on resident species, while larger (wider) creeks appear to be capable of buffering organisms from transient fluxes of mosquito control agents that may enter the system.
Pyrethroid pesticides were applied via ground spraying to residential neighborhoods in New York City during July-September 2000 to control mosquito vectors of West Nile virus (WNV). Case reports link pyrethroid exposure to asthma exacerbations, but population-level effects on asthma from large-scale mosquito control programs have not been assessed. We conducted this analysis to determine whether widespread urban pyrethroid pesticide use was associated with increased rates of emergency department (ED) visits for asthma. We recorded the dates and locations of pyrethroid spraying during the 2000 WNV season in New York City and tabulated all ED visits for asthma to public hospitals from October 1999 through November 2000 by date and ZIP code of patients' residences. The association between pesticide application and asthma-related emergency visits was evaluated across date and ZIP code, adjusting for season, day of week, and daily temperature, precipitation, particulate, and ozone levels. There were 62,827 ED visits for asthma during the 14-month study period, across 162 ZIP codes. The number of asthma visits was similar in the 3-day periods before and after spraying (510 vs. 501, p = 0.78). In multivariate analyses, daily rates of asthma visits were not associated with pesticide spraying (rate ratio = 0.92; 95% confidence interval, 0.80-1.07). Secondary analyses among children and for chronic obstructive pulmonary disease yielded similar null results. This analysis shows that spraying pyrethroids for WNV control in New York City was not followed by population-level increases in public hospital ED visit rates for asthma.
The mosquito control potential of Gambusia affinis, a mosquito fish, was evaluated in rice fields in the Shahjahanpur district of Uttar Pradesh. This fish, at a stocking rate of 5 fishes/sq m, significantly reduced the larval and pupal densities in experimental fields as compared to control fields during the entire observation period of 42 days. Control of mosquito breeding in rice fields through this fish seems to be promising.
An integrated approach for the control of mosquitoes and the diseases they transmit will better enable sustainable control while helping to circumvent some of the problems associated with the use of conventional insecticides. Environmental methods and biological control are alternatives to chemical control and are key components of the integrated strategy. The use of vertebrate and invertebrate predators and entomopathogens as biological control agents and their role in integrated control programs is reviewed with emphasis on fish, Toxorhynchites mosquitoes, Notonecta species, predatory copepods, entomopathogenic bacteria, and the fungus Lagenidium giganteum. The successful implementation of these organisms will depend on an in-depth understanding of the ecology of both the targeted species and the biological control agents to be used. Thorough geographic reconnaissance will also be essential for the successful abatement of pest and vector mosquitoes. The success and sustainability of future programs, especially in developing countries, will rely not only on the use of the most appropriate technologies but also on the direct participation of the affected communities. Possible undesirable effects of biological control are also reviewed.
Piperonyl butoxide (PBO) is a synergist of pyrethroid pesticides found in many products for structural pest control, mosquito control, and home and garden uses. Because both PBO and pyrethroid residues potentially co-occur in urban creeks, this study determined if environmental levels of PBO were capable of synergizing pyrethroids in the environment. Three types of toxicity tests were conducted with the amphipod Hyalella azteca to determine the minimum PBO concentration required to increase toxicity of the pyrethroid permethrin: Sediment was spiked with permethrin only; permethrin and overlying water spiked with PBO; and permethrin, PBO, and overlying water spiked with PBO. In tests with PBO added to both water and sediment, PBO concentrations of 2.3 microg/L in water and 12.5 microg/kg in sediment reduced the permethrin median lethal concentration (LC50) nearly 50% to 7.3 mg/kg organic carbon (OC). Higher concentrations of PBO increased permethrin toxicity up to sevenfold. In exposures with PBO in water alone, 11.3 microg/L was required to increase permethrin toxicity. Urban creek sediments from California and Tennessee, USA, had PBO concentrations in the low microg/kg range; only one water sample was above the detection limit of 0.05 microg/L. Wetlands in northern California also were sampled after application of pyrethrins and PBO for mosquito abatement. Sediment and water PBO concentrations within 12 h of abatement spraying peaked at 3.27 microg/kg and 0.08 microg/L, respectively. These results suggest that environmental PBO concentrations rarely, if ever, reach concentrations needed to increase pyrethroid toxicity to sensitive organisms, though available data on environmental levels are very limited, and additional data are needed to assess definitively the risk.