Environmental zyxwvutsrqponmlkjihgf Toxicology and Chemislry, zyxwvutsrqponmlkji Vol. zyxwvutsrqpon 7, pp. 343-349, 1988 Printed in the zyxwvutsrqponm USA. Pergamon Press PIC 0730-7268/88 zyxwv $3.00 zyxwv + zyxw .OO Copyright zyxwvu 0 1988 SETAC EFFECTS OF AGRICULTURAL SPRAYING OF METHYL PARATHION ON CHOLINESTERASE ACTIVITY AND REPRODUCTIVE SUCCESS IN WILD STARLINGS zyxw (STURNUS VULGARIS) ) SUZANNE C. ROBINSON,* RONALD J. KENDALL, REXROBINSON, CRYSTAL J. DRIVER and THOMAS E. LACHER, JR. Institute of Wildlife Toxicology, Huxley College of Environmental Studies, Western Washington University, Bellingham, Washington 98225 (Received 16 May 1986; Accepted 20 April 1987) Abstract- In June 1984, methyl parathion (phosphorothioic acid O,O-dimethyl O-[4-nitrophenyl] ester) was applied at 1.4 kg a.i./ha to a cultivated field in Skagit Valley, Washington. Brain cho- linesterase (ChE) activity was determined in adult and nestling starlings (Sturnus vulgaris) in artificial nesting boxes on the peripheries of a treated and a control field for up to 1 week following appli- cation of the pesticide. Brain ChE activities in nestling starlings from the control field increased linearly from age 6 to 19 d. Brain ChE levels in chicks taken from the treated fields were more vari- able. From the treatment field, 92% of adults collected up to 7 d posttreatment exhibited marked depressions of brain ChE, while during the same period, 29% of the nestlings showed similar responses. A significant correlation was demonstrated between the levels of brain ChE depression in adult and in the nestling starlings collected from the same nests. Measures of reproductive success (i.e., hatching of eggs and fledging of young) were also deter- mined in a portion of the nestboxes to assess any potential adverse effects. The spraying of methyl parathion did not significantly reduce hatchability of the starling eggs. The mean (+sE) number of young fledged per nest on the sprayed field, 2.22 zyxwvut i 0.29, was not significantly different from that on the control site, 3.33 k 0.17. However, collectively, the number of nestlings fledging from the treatment field postspray was significantly lower than from the control field. Keywords- Organophosphate pesticides Cholinesterase activity Altricial birds Reproductive success Sturnus vulgaris INTRODUCTION Cholinesterase (ChE) inhibiting compounds such as the organophosphorus (OP) and carba- mate insecticides have increasingly been used in agriculture to replace the organochlorine pesticides that have been banned and restricted. Although OP chemicals, including methyl parathion, are less environmentally persistent than the chlorinated hydrocarbon pesticides they replace, many OPs are highly toxic to wildlife and have been shown to cause widespread mortality in exposed animals [ 11. Measuring the inhibition of brain ChE activity *To whom correspondence may be addressed: En- virosphere Company, 10900 N.E. 8th Street, Bellevue, Presented at the Symposium on Wildlife Toxicology, Sixth Annual Meeting of the Society of Environmental Toxicology and Chemistry, St. Louis, Missouri, Novem- ber 10-13, 1985. WA 98004-4405. is a tool that has been widely employed to assess the exposure of birds to OP and carbamate pesti- cides. Brain ChE inhibition exceeding 20% is generally considered indicative of exposure to a ChE-inhibiting compound, while greater than 50% inhibition is considered sufficient for attributing avian mortalities to OP or carbamate poisoning [2]. While many studies [l] have documented ChE inhibition in adult birds resulting from OP or car- bamate exposure, fewer researchers have addressed the anti-ChE activity of these compounds in altri- cia1 young [3-61. Even less research has focused on the potential impacts of pesticide exposure on the nesting success of altricial species under field con- ditions [6]. Quite often the application of pes- ticides coincides with the breeding activities of resident bird species. Birds living on or around croplands can be exposed to sublethal concentra- tions of OP compounds several times throughout a growing season and thus be subjected to the risk 343