An interlaboratory comparison of data on brain cholinesterase activity in forest songbirds exposed to aerial application of Zectran®

Zectran^® (4-dimethylamino-3,5-xylyl N-methyl-carbamate), a carbamate insecticide (active ingredient [AI] mexacarbate), was aerially applied to two 300 ha plots of coniferous forest at dosage rates of 70 and 140 g AI/ha, respectively. The brains of 288 birds collected from the treated areas and 84 birds from untreated areas were sagittally sectioned into approximately equal halves. Each of the laboratories participating in the study, the Forest Pest Management Institute (FPMI) and the Canadian Wildlife Service, Atlantic Region (CWS), assayed one half of each brain for cholinesterase (ChE) activity and the results were compared. The ChE estimates of the two laboratories on half brains from the same birds were poorly correlated (R=0.136, P<0.05) and differed significantly (P<0.00005). The reasons for this are uncertain. Despite the discrepancy in ChE estimates, however, separate statistical analysis of each data set produced the same general conclusion: the ChE response to Zectran^® exposure was statistically significant but biologically unimportant. In both data sets, statistically significant ChE responses by niche and time since spraying were found. The dosage rate emitted from the airplane was a better predictor of ChE activity in the canopy niches than was volume deposited at ground level, but volume deposited was a more useful predictor for ground birds in most situations. These results are discussed in the context of a proposal to develop a reference file of normal brain ChE activities of common wildlife species.     

The effect of aerial application of Zectran® on brain cholinesterase activity in forest songbirds

The carbamate insecticide Zectran^® (active ingredient [AI] mexacarbate) was applied aerially to two 300 ha blocks of coniferous forest, one at a dosage rate of 70 g AI/ha and the other at 140 g AI/ha. Brain cholinesterase (ChE) activity was determined in 372 exposed and control forest song-birds representing seven species. Brain ChE activity was similar among controls of all species studied. Among exposed birds, ChE activity was lowest in individuals from the high-dose block, although differences were not statistically significant. Warbler ChE activity showed a statistically significant relationship to dosage rates. Spray deposit was four times as great on the high-dosage block as on the low one. Zectran^® provides a margin of safety to songbirds exceeding that of the organophosphorus insecticide fenitrothion which is currently used on a widespread operational basis against spruce budworm (Choristoneura fumiferana) in New Brunswick, Canada.     

Alterations in acetylcholinesterase and electrical activity in the nervous system of cockroach exposed to the neem derivative, azadirachtin

Botanical insecticides are relatively safe and biodegradable, and are readily available sources of bioinsecticides. In recent years, the neem derivative, azadirachtin, has been examined as an alternative to synthetic insecticides because of its broad-spectrum insecticidal action. Because many of the natural products and synthetic compounds used in the control of insect pests are known to exhibit electrophysiological effects, in this paper we focused our studies on the alterations in the activity of the enzyme acetylcholinesterase (AChE) and electrical activity in the nervous system of the cockroach, Periplaneta americana, exposed to azadirachtin. Exposure to azadirachtin produced an excitatory effect on spontaneous electrical activity as well as cercal sensory-mediated giant-fiber responses in the cockroach. Topical exposure to sublethal doses of azadirachtin did not result in any significant alterations in the AChE activity in different regions of the nervous system. We suggest that azadirachtin exerts excitatory action on the electrical activity in the nervous system of cockroach by interfering with the ion channels in the nerve membrane, the probable target of several insecticides.     

Cholinesterase response in native birds exposed to fenitrothion during locust control operations in eastern Australia

Huge aggregations of flightless locust nymphs pose a serious threat to agriculture when they reach plague proportions but provide a very visible and nutritious resource for native birds. Locust outbreaks occur in spring and summer months in semiarid regions of Australia. Fenitrothion, an organophosphate pesticide, is sprayed aerially to control locust plagues. To evaluate fenitrothion exposure in birds attending locust outbreaks, we measured total plasma cholinesterase (ChE), butrylcholinesterase (BChE), and acetylcholinesterase (AChE) activities in four avian species captured pre- and postfenitrothion application and ChE reactivation in birds caught postspray only. Eleven of 21 plasma samples from four species had ChE activity below the diagnostic threshold (two standard deviations below the mean ChE activity of prespray samples). Granivorous zebra finches (Taeniopygia guttata) and insectivorous white-winged trillers (Lalage sueurii) had significantly lower mean plasma total ChE, BChE, and AChE activity postspray, while other insectivores, white-browed (Artamus superciliosus) and masked woodswallows (Artamus personatus), did not. Cholinesterase was reactivated in 19 of the 73 plasma samples and in one of three brain samples. We conclude that native bird species are exposed to fenitrothion during locust control operations. This exposure could have detrimental impacts, as both locust outbreaks and avian reproductive events are stimulated by heavy summer rainfall, leading to co-occurrence of locust control and avian breeding activities.