Locusts

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APLC Environmental research and monitoring

Introduction
Invertebrates
Vertebrates
Novel pesticide monitoring techniques
Further reading

Introduction

The underlying objective of the APLC’s Environmental research and monitoring program is to quantify and minimise any environmental impact resulting from APLC locust monitoring and control operations. This is being achieved through two core research areas.

Collaborative research with some of Australia's leading universities on the effects of pesticides on non-target vertebrate and invertebrate fauna with an emphasis on the ecology of arid and semi-arid agro-ecosystems.
Development of a novel approach to pesticide monitoring and coupling this with the use of first tier level bioassays to assign biological significance to detected residues. This work is being undertaken with significant assistance of the National Research Centre for Environmental Toxicology (EnTox).

Outcomes from these two research areas are integrated with the APLC’s overall environmental management strategy through the APLC's environmental management system and will subsequently assist the APLC to minimise the environmental effects of its operations.

Invertebrates

Invertebrates are critical in regulating major ecosystem processes such as the recycling of organic matter, plant pollination and seed dispersal, and maintenance of soil structure to enable water penetration and nutrient availability. An understanding of the non-target invertebrate impacts of locust control operations is an important focus of on-going APLC research.

Previous research has investigated the non-target invertebrate impacts of fenitrothion ULV applied aerially at 267 and 381 g ai/ha. Experiments during 1990-1993 in the Riverina found that, at the higher 381 g ai/ha dose, numbers if most fauna groups had recovered after 28 days. The Collembola (springtails), Coleoptera (beetles), Hemiptera (true bugs) and Hymenoptera (ants) were the most sensitive invertebrate groups in both studies. Longer-term effects on Collembola abundance were seen on a small number of occasions at the 381 g ai/ha dose, but no difference in community structure was detected. It was concluded that the application of fenitrothion at either 267 or 381 g ai/ha has only short-term effects on the epigeal invertebrate fauna of the arid grasslands of eastern Australia.

Further research was undertaken from 2000 to 2002 using the current APLC fenitrothion application rate of 267g ai/ha and fipronil at 1.25 g ai/ha. Invertebrate populations were monitored after spraying using pitfall, yellow-pan and malaise traps. Analysis of these data is ongoing.

Research to quantify the non-target invertebrate impacts of fipronil is on-going. Preliminary results from field experiments conducted from 2006 to 2008 have shown significant effects on termite activity extending at least 26 months post-treatment. However, these experiments represent a worst cast scenario based on an aerial application rate of 1.25 g ai/ha applied as a blanket treatment. Since 2003, the APLC has typically used fipronil at a lower rate of 0.6 – 1.0 g ai/ha applied as a barrier treatment with 300 m between spray runs. Nonetheless, given the critical role that termites play in arid ecosystems, the potential impacts of pesticide application needs to be more thoroughly investigated. The APLC is now embarking on further research to determine non-target invertebrate impacts for a larger suite of taxonomic groups using the current spraying protocols. This work will use an integrated approach in association with vertebrate environmental research to document pesticide effects among different functional groups and across trophic levels.

Vertebrates

Locust numbers can increase rapidly after favourable rainfall and these mass hatchings are an ideal window of opportunity for locust control. However, late instar juvenile and adult female locusts are rich in protein (62% dry mass), fat (17% dry mass) and calcium. Increases in locust populations therefore also present insectivorous birds, mammals and reptiles with a readily available protein and fat source. Locust population increases are therefore likely to enhance the breeding success of many local and invading vertebrate predator species and may represent an important component of their annual diet and population cycle. The timing of locust control is such that it is likely to coincide with vertebrate breeding events (or annual moults in the case of birds), which make the locusts an important food source at this time.

Fenitrothion is an organophosphorus (OP) insecticide commonly used by the APLC for locust control. This pesticide acts by inhibiting cholinesterase (ChE) enzymes in both vertebrates and invertebrates. Therefore ChEs can be used as a biomarker in vertebrates where exposure to fenitrothion is suspected. Acetylcholinesterase (AChE) enables normal nerve function in both the peripheral and central nervous systems of animals. Our studies monitoring AChE activities in native vertebrates during locust control have shown that native bird and mammal species are exposed to fenitrothion during locust spraying. The native marsupials, Sminthopsis macroura (stripe-faced dunnart) and S. crassicaudata (fat-tailed dunnart) have been shown to have plasma AchE levels suppressed by up to 60% after locust spray campaigns, while plasma AChE activity in white-winged trillers and zebra finches collected after fenitrothion application were also significantly lower than those collected before. In 19 of 73 birds sampled post-spray there was evidence of OP exposure. Avian species exhibiting ChE depression included both insectivorous and granivorous species as well as birds of prey. Many of these birds were in the process of breeding or moulting, two of the most energetically expensive stages of the avian life cycle.

To complement this field research, we have also undertaken (in collaboration with the University of Wollongong) captive studies to investigate the effect of such exposure on selected physiological traits. The most pronounced effect of fenitrothion was on mammalian and avian locomotory performance, which could limit an animal’s ability to sustain activities at normal levels. We have also found that Australian native marsupials are 10-14 times more sensitive to fenitrothion than other non-native eutherian mammals more commonly represented in pesticide risk assessments.

There is very little research regarding the toxicological effects of fipronil in birds. Currently available information demonstrates there is high species-specific variability in fipronil sensitivity and this variability makes it extremely difficult to predict the toxicity of fipronil on unstudied species at high risk of exposure in the wild. Recent research undertaken at the University of Wollongong is aimed at determining fipronil sensitivity in native birds at risk of exposure to fipronil as a result of locust control operations. To date we have examined four previously unstudied species: house finch and zebra finch, budgerigar and king quail. Results so far demonstrate that fipronil is moderately toxic to budgies and the two finch species tested, and highly toxic to king quail.

Studies have also been undertaken on the ability of fipronil to impact upon successful hatching and development of chicks from eggs laid by females which have been exposed to fipronil. Studies undertaken to date indicate that fipronil can have significant effects on these outcomes, with a significant reduction in egg hatching rates and the successful development of chicks.
Although the effects of pesticide exposure identified so far are significant at the physioloigcal level, further research is underway to quantify the level at which these effects transfer to wild populations.

Research into novel pesticide monitoring techniques

Monitoring air and water quality is a key task for managers of environmental and public health. However, methods that are used for air and water quality monitoring are generally based on a sampling regime that uses individual samples representative only of the relatively short time when the sample is collected.

The APLC is currently working with the National Research Centre for Environmental Toxicology (EnTox) to develop passive samplers to monitor fenitrothion and fipronil application during locust control. Samplers showing promise for this purpose include polyethylene (PE) samplers for water and polyurethane foam (PUF) discs for air sampling.

Monitoring the effects of pesticides in the environment using an array of rapid in vitro bioassays enables a wide variety of potential target organisms and, within higher organisms, a large selection of potential toxic effects to be assessed. In order to protect environments and sensitive organisms, including humans, it is important to evaluate whether the pollutants at a given site cause measurable biological actions that could have an adverse effect on the organism involved.
A range of rapid toxicity tests have been developed and are available in the EnTox laboratory. These tests evaluate relevant toxic effects in a given sample as an indicator of the presence of particular chemicals in the environment which may exert this effect. For example the presence of organophosphate insecticides, such as fenitrothion, may be detected through the measurement of acetylcholinesterase inhibition. This innovative approach to residue monitoring and pesticide assessment enables the APLC to establish and evaluate a monitoring system where risk assessment is achieved through integration of exposure and effect based monitoring.

The aim of this collaborative work by the APLC is to develop a standardised set of monitoring tools which can be applied in the field during every locust control campaign undertaken by APLC. The results of this monitoring program will also tie in with APLC’s pesticide application research work, adding to the continuous improvement program aimed at minimising the off-target impacts of locust control.