The potential use of insect-specific fungi to control grain storage pests in empty grain stores
About this project
Stored grain and grain products are at risk of infestation by insects and mites. However, some OP pesticides currently used to control these pests are being withdrawn from use and methyl bromide will be phased out for most uses by the end of 2004. Alternative approaches for the control of storage pests are needed urgently. This project aimed to collect UK isolates of naturally-occurring insect specific fungi and evaluate their use for grain store structure treatments.
Samples were collected from UK storage premises and approximately 70,000 insect cadavers were processed. Fungal isolates were established in laboratory culture. Molecular and biological characterisation of 8 isolates, identified as Beauveria bassiana, was completed. These and some additional isolates from the CABI Bioscience Genetic Resource Collection (GRC) were tested in a primary laboratory screen against four representative stored-food pests.
The most successful isolates were mass-produced and taken forward to a secondary laboratory screen to obtain dose-response data for the four species tested previously. The most effective isolates gave mortalities close to 100% for beetles and moths, and around 75% for mites and psocids. Some healthy grain beetles also succumbed to B. bassiana by picking up a lethal dose of spores from dead insects showing signs of external sporulation of the fungus. The potential of PC Floor Traps for disseminating spores was also demonstrated.
The effects of temperature and relative humidity (RH) on isolate efficacy were assessed. It was found that to obtain good control, particularly of the beetles, high humidity close to 100% RH was needed for the first 24 hours of exposure. Methodologies were evaluated for assessing efficacy and persistence of formulated fungal isolates applied to various grain store building materials under UK storage conditions.
Tests with the most promising formulation from the secondary screen, a 1:4 Codacide and water mix, revealed that this carrier was not suitable for use in dusty environments because it remained very sticky on non-porous surfaces. The survival and persistence of individual spores on construction materials were also assessed at a range of temperature/RH combinations; spores showed higher persistency in dry powder form than when formulated in oil.
The results of the laboratory efficacy tests showed that UK isolates of B. bassiana have the potential to control a range of arthropod pests in UK grain stores. However, before this potential can be realised in practice, it will be essential to conduct further research to improve spore formulation and delivery systems.
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