Recent requirements for biomonitoring of urban stormwater runoff have raise
d the issue of toxic contributions from mosquito control products. A compar
ison of seven pesticides for their toxicity to target and nontarget organis
ms was conducted in field and laboratory trials to determine relative impac
ts in and around Craighead County, Arkansas. Twenty-four and forty-eight-ho
ur acute toxicity tests using Ceriodaphnia dubia, Daphnia magna, Daphnia pu
lex, and Pimephales promelas were employed with U.S. Environmental Protecti
on Agency (U.S. EPA) suggested procedures as standard test organisms. Addit
ional tests with resident mosquito fish, Gambusia affinis, and mosquito lar
vae, Anopheles quadrimaculatus, included ditch-receiving waters to compare
the somewhat sterile laboratory exposures to actual field conditions. Expos
ure to as much as 31.4 mu g/L of the pesticides Dursban(R), malathion, Perm
anone(R), Abate(R), Scourge(R), B.t.i, and Biomist(R) were required for eff
ective control of An. quadrimaculatus, whereas as little as 2.7 mu g/L resu
lted in substantial mortality of some nontarget organisms. These data sugge
st that prevailing application rates for effective mosquito control not onl
y affect nontarget organisms but may also confound stormwater and nonpoint
toxicity evaluations that utilize sensitive indicator species.