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Risk to small mammals from utilising caches of pesticide-treated seeds - PS2326

Description
Under EU regulations plant protection products (pesticides) should not pose unacceptable risks to terrestrial vertebrates. Pesticides applied to seeds to control fungi and insects may also be toxic to mammals and birds, which risk injury if they consume pesticide-treated seeds. The length of time such animals may be exposed to treated seeds, and thus are likely to be at risk, begins at the time of planting and ends nominally at the time of germination (when the seed may no longer be attractive) or earlier if the particular pesticide has already degraded into non-toxic components. A potential extension to this exposure period has recently been recognised through the hoarding behaviour of some rodents that innately cache food for later use, perhaps during periods of food shortage. If the conditions under which seeds are cached inhibit germination or the degradation of pesticides, animals that utilise the stored seeds risk being poisoned days, weeks or months after the ‘normal’ exposure period has passed. At present the likelihood that small mammals will hoard solid pesticide formulations such as seeds or pellets is not considered during risk assessment. The objective of this project is to measure the likely increase in the exposure period caused when animals consume treated seeds stored in caches. One small mammal species most likely to be exposed to seed treatments and known to hoard food is the Wood mouse (Apodemus sylvaticus). Preliminary studies carried out under Project PS2308 revealed that mice utilise caches immediately but the rate of utilisation seems to be much slower if the seeds are initially rendered unpalatable by the treatment. Pesticide formulations invariably reduce palatability when alternative food sources are available, but they do not appear to inhibit the rate at which seeds are cached. Mice normally carry seeds between their teeth but, in common with all rodents, they can prevent items entering the mouth with folds of skin that pass across the jaws behind the incisors. As constituents in the formulation begin to decay, the seed becomes more acceptable, although not necessarily less toxic. In this project, the activities of Wood mice exposed to treated seeds will be observed under conditions which allow the animals to express their natural foraging behaviour. The rate at which hoarded untreated seeds are utilised will be compared with the rate for seeds treated with one or more pesticides by recording changes in the number, size and location of caches over time until most or all seeds are consumed. The data generated will add to that collected under the previous project to provide more robust estimates of the potential increase in the exposure period. The results will assist the Pesticide Safety Directorate by enabling them to demonstrate that hoarding of treated seed is important in extending exposure time and thus improve risk assessment procedures and reduce the risk to wildlife from pesticide use.
Objective
Under EU regulations plant protection products should not pose unacceptable risks to terrestrial vertebrates. Pesticides applied to seeds to control fungi and insects may also be toxic to mammals and birds, which risk injury if they consume pesticide-treated seeds. The length of time such animals are likely to be at risk begins at the time of planting and ends nominally at the time of germination (when the seed may no longer be attractive) or earlier if the particular pesticide has already degraded into non-toxic components. A potential extension to this exposure period occurs when rodents collect treated seeds and cache them for later use, perhaps during periods of food shortage. If the conditions under which seeds are cached inhibit germination or the degradation of pesticides, animals that utilise the stored seeds risk being poisoned days, weeks or months after the ‘normal’ exposure period has passed. At present the likelihood that small mammals will hoard solid pesticide formulations such as seeds or pellets is not considered during risk assessment.
Project PS2308 investigated the hoarding behaviour of wood mice (Apodemus sylvaticus) and the factors that determine how quickly seed caches are exploited. Singly-caged mice were offered different seed types treated with one of 4 approved pesticide formulations containing the active ingredients, fluquinconazole, imidacloprid, guazatine or tefluthrin. These pesticides were chosen, with the agreement of PSD, as they are normally applied to seeds, such as cereal grains, are relatively persistent and sufficiently toxic to present a long-term risk with minimal chance of avoidance or mortality on first encounter. They did not inhibit mice from hoarding, suggesting that such behaviour is probably innate. To explore hoarding under more natural conditions, preliminary trials were conducted in which pairs of mice were released into large arenas and offered fluquinconazole-treated or untreated seeds. The rates of hoarding and subsequent utilisation of the seed caches were recorded. Mice utilised caches immediately, removing seed from several caches each night. It appeared that a constituent of the pesticide formulation rendered freshly treated seeds unpalatable, slowing the utilisation rate initially, even though mice instinctively dehusk seeds, such as peas, thereby removing at least some of the formulation. Upon exposure to the arena conditions, treated seeds became more acceptable and the rate increased. Reduced seed palatability was also apparent during the cage test: tefluthrin-treated seeds were the least palatable. These results suggest that one of the main factors determining the utilisation rate and any increase in the exposure period is the palatability of treated seeds and not food shortage. Comparing utilisation rates for untreated seeds with those for seeds treated with fluquinconazole and tefluthrin allows this factor to be explored with greater precision.

Objective
1) To complete a minimum of 5 replicates of each combination of seed type (wheat and peas) and treatment (untreated control, fluquinconazole, tefluthrin) to provide more statistically robust estimates on the potential increase in the risk exposure period (31/03/06).

Project Documents
• Final Report : Risk to small mammals from utilising caches of pesticide-treated seeds   (9298k)
Time-Scale and Cost
From: 2005

To: 2006

Cost: £16,936
Contractor / Funded Organisations
Central Science Laboratory
Keywords
Environmental Effects              
Mammals              
Pest and Weed Control              
Pesticide use              
Pesticides              
Plants and Animals              
Wildlife              
Fields of Study
Pesticide Safety