Sensitivity of the stripe-faced dunnart, Sminthopsis macroura (Gould 1845), to the insecticide, fipronil; implications for pesticide risk assessments in Australia.

A lack of toxicity data quantifying responses of Australian native mammals to agricultural pesticides prompted an investigation into the sensitivity of the stripe-faced dunnart, Sminthopsis macroura (Gould 1845) to the insecticide, fipronil (5-amino-3-cyano-1-(2,6-dichloro-4-trifluoromethylphenyl)-4-trifluoromethylsulfinyl pyrazole, CAS No. 120068-37-3). Using the Up-And-Down method for determining acute oral toxicity in mammals (OECD) median lethal dose estimates of 990 mg kg-1 (95% confidence interval (CI) = 580.7-4770.0 mg kg-1) and 270.4 mg kg-1 (95% CI = 0.0->20,000.0 mg kg-1) were resolved for male and female S. macroura, respectively. The difference between median lethal dose estimates for males and females may have been influenced by the older ages of two female dunnarts. Consequently, further modelling of female responses to fipronil doses used the following assumptions: (a) death at 2000 mg kg-1, (b) survival at 500 mg kg-1 and (c) a differential response (both survival and death) at 990 mg kg-1. This modelling revealed median lethal dose estimates for female S. macroura of 669.1 mg kg-1 (95% CI = 550-990 mg kg-1; assuming death at 990 mg kg-1) and 990 mg kg-1 (95% CI = 544.7-1470 mg kg-1; assuming survival at 990 mg kg-1). These median lethal dose estimates are 3-10-fold higher than available LD50 values of 94 mg kg-1 for a similarly sized eutherian mammal, Mus musculus (L. 1758) and 97 mg kg-1 for Rattus norvegicus (Birkenhout 1769). Implications for pesticide risk assessments in Australia are discussed.

Fenitrothion, an organophosphorous insecticide, impairs locomotory function and alters body temperatures in Sminthopsis macroura (Gould 1845) without reducing metabolic rates during running endurance and thermogenic performance tests.

Endemic Australian mammal species are exposed to pesticides used for locust control as they occupy the same habitat as the target insect. The authors examined the impact of an ultra-low volume formulation of the organophosphorous insecticide fenitrothion (O,O-dimethyl-O-[3-methyl-4-nitrophenol]-phosphorothioate) on a suite of physiological measures that affect the ability of animals to survive in free-living conditions: locomotory and thermogenic functions, metabolic performance, body mass, and hematocrit and hemoglobin levels. Plasma and brain cholinesterase activity in relation to time since exposure to pesticide were also determined. An orally applied dose of 90 mg kg(-1) fenitrothion reduced running endurance in the stripe-faced dunnart, Sminthopsis macroura, by 80% the day after exposure concomitantly with a reduction of approximately 50% in plasma and 45% in brain acetylcholinesterase activity. These adverse effects disappeared by 10 d postexposure. Maximal metabolic rates reached during running were unaffected by pesticide, as were body mass and hemoglobin and hematocrit levels. Maximal cold-induced metabolic rate (measured as peak 2 min metabolic rate attained during cold exposure), time taken to reach peak metabolic rate on cold exposure, cumulative total oxygen consumed during shivering thermogenesis, and body temperature before and after cold exposure were unaffected by fenitrothion. Dunnart rectal temperatures showed a reduction of up to 5 °C after exposure to fenitrothion but returned to pre-exposure levels by 10 d postdose. Such physiological compromises in otherwise asymptomatic animals demonstrate the importance of considering performance-based measures in pesticide risk assessments.

Insecticide residues in Australian plague locusts (Chortoicetes terminifera Walker) after ultra-low volume aerial application of the organophosphorus insecticide fenitrothion.

The need for locust control throughout eastern Australia during spring 2010 provided an opportunity to quantify residues of the organophosphorus insecticide fenitrothion on nymphs of the Australian plague locust, Chortoicetes terminifera Walker. Residues were collected across the different physiological states--live, dead, and debilitated (characterized by ease of capture, erratic hopping, and the inability to remain upright)--of locust nymphs observed following exposure to fenitrothion. The time course of residue depletion for 72 h after spraying was quantified, and residue-per-unit dose values in the present study were compared with previous research. Fenitrothion residue-per-unit dose values ranged from 0.2 µg/g to 31.2 µg/g (mean ± standard error [SE] = 6.3 ± 1.3 µg/g) in live C. terminifera nymps, from 0.5 µg/g to 25.5 µg/g (7.8 ± 1.3 µg/g) in debilitated nymphs, and from 2.3 µg/g to 39.8 µg/g (16.5 ± 2.8 µg/g) in dead nymphs. Residues of the oxidative derivative of fenitrothion, fenitrooxon, were generally below the limit of quantitation for the analysis (0.02 µg/g), with 2 exceptions--1 live and 1 debilitated sample returned residues at the limit of quantitation. The results of the present study suggest that sampling of acridids for risk assessment should include mimicking predatory behavior and be over a longer time course (preferably 3-24 h postspray) than sampling of vegetation (typically 1-2 h postspray) and that current regulatory frameworks may underestimate the risk of pesticides applied for locust or grasshopper control.

Fenitrothion, an organophosphate, affects running endurance but not aerobic capacity in fat-tailed dunnarts (Sminthopsis crassicaudata).

We measured aerobic metabolism during cold exposure and exercise performance (run duration and oxygen consumption while running at 1 m s(-1)) in the fat-tailed dunnart Sminthopsis crassicaudata, a dasyurid marsupial, before and after ingestion of 30 mg kg(-1) of fenitrothion, an organophosphate (OP) pesticide. Running endurance of OP-exposed animals was less than half that of control animals over the first 3 days after dosing and 55% of control animal endurance on day 5 post-dose. Despite these declines, peak metabolic rate at this running speed (9.3 times basal metabolic rate; BMR) was unaffected by OP exposure. Peak metabolic rate (PMR) and cumulative oxygen consumption during a 1-h exposure to conditions equivalent to -20 degrees C did not differ between OP-treated and control dunnarts, with PMR averaging 11 times BMR. We conclude that fenitrothion-induced exercise fatigue is not due to limitations in oxygen or substrate delivery to muscle or in their uptake per se, but more likely relates to decreased ability to sustain high-frequency neuromuscular function. The persistence of locomotor impairment following OP exposure in otherwise asymptomatic animals emphasizes the importance of using performance-based measures when characterising sublethal effects of pesticide exposure in an ecological context.

A case study of the Australian Plague Locust Commission and environmental due diligence: why mere legislative compliance is no longer sufficient for environmentally responsible locust control in Australia.

The Australian Plague Locust Commission (APLC) manages locust populations across 2 million square kilometers of eastern Australia using the aerial application of chemical and biological control agents to protect agricultural production. This occurs via a preventative control strategy involving ultralow-volume spray equipment to distribute small droplets of control agent over a target area. The economic costs of, and potential gains stemming from, locust control are well documented. The application of insecticides, however, to fragile arid and semiarid ecosystems is a task that brings with it both real and perceived environmental issues. The APLC is proactive in addressing these issues through a combination of targeted environmental operational research, an ISO-14001-aligned Environmental Management System (EMS), and links with environmental regulatory and research institutions. Increasing due diligence components within Australian environmental legislation dictate that mere legislative compliance is no longer sufficient for industries to ensure that they meet their environmental obligations. The development of external research links and the formulation of an EMS for locust control have enabled the APLC to identify environmental issues and trends, quantify objective environmental targets and strategies, and facilitate continuous improvement in its environmental performance, while maintaining stakeholder support. This article outlines the environmental issues faced by the APLC, the research programs in place to address these issues, and the procedures in place to incorporate research findings into the organization's operational structure.