Abstract
Mosquitoes have been a public nuisance and health problem since the Native Americans were the sole habitants of California. Wetlands, which provide habitat for a diversity of species, including a variety of insects, birds, and other wildlife, also provide habitat for numerous species of mosquitoes, which are vectors of disease. Organized mosquito control efforts began in the early 1900s with insecticides decreasing the number of mosquitoes and mosquito-borne diseases. Today, mosquito abatement includes surveillance and public awareness as well as the latest physical, biological and chemical means including the use of organophosphates and pyrethroids to reduce mosquito populations. Pyrethroids are a class of synthetic pesticides commonly used in ground based and aerial pesticide applications for control of adult mosquitoes. Today, more than 360 metric tons of pyrethroids are used annually for agricultural and non-agricultural use in California, whereas 125 metric tons of pyrethroids are used for mosquito abatement (CDPR 2008; Amweg, 2005). Widespread spraying of insecticides may have unforeseen effects on non-target insects, and it is unclear how populations of terrestrial insect communities will respond to the use of pyrethroids.
Previous research has examined the effects of pyrethroids on invertebrate communities and suggests that insecticides can have complex effects on community structure and functional interactions among species by changing behavior and predator prey relationships. Species responses are quite variable and pyrethroids are still poorly understood, especially in terrestrial habitats.
The objectives of this study were to examine the effects of pyrethroids on nontarget terrestrial insects to determine if species characteristics like functional groups ( e.g., predator, herbivore, pollinator, and parasite) and body sizes differentially respond to treatments. This study tests the following hypotheses: there will be no significant difference in mortality rates from exposure to pyrethroids through aerial spraying for
1) non-target insects, 2) insects of various functional groups, or 3) insects related to body size.
The study was conducted at Colusa NWR, in Colusa County, California. Field studies were conducted in the fall of2007 and included an insect collection to determine diversity of species in the area and a field experiment. The manipulative field experiment measured mortality rates of insects by placing insects in cages and/or bags and placing them at pre-selected locations within an insecticide treated site and an untreated site ( control). Bags contained a mean of eight insects of individual species from various functional groups and body sizes. The following species were used in the field experiment: dragonflies, damselflies, and lady beetles (predators); honey bees, solitary bees, cabbage white butterflies, and painted lady butterflies (pollinators); and crickets and katydids (herbivores). Mosquitoes (parasite) were also used in both locations to determine whether each location had been treated with pyrethroids.
The results showed that pyrethroid spraying significantly increased mortality rates of some insects. Mortality rates were related to sizes of species, with smaller-bodied insects having higher mortality rates than larger-bodied insects. Pyrethroids also caused higher mortality rates for pollinators and parasites at 1 hour and for all functional groups at 12 hours and 24 hours. The results of this study are consistent with other studies conducted on the effects of pyrethroids on insects. The results of this study highlight the unintentional effects of human activities on ecosystems and our need to further explore these in order to better manage ecosystems for human well being.