Pesticide fatigue
pesticide levels thought safe for pollinators may prove harmful for the wild bee, says a Canadian study. It shows adult bumblebees exposed to significant levels of the pesticide spinosad during larval development have impaired foraging (food collecting) ability.
In developed countries, about one third of human food depends on pollinating activity (essential for flowers to turn into fruit/ vegetable/ foodgrain). Wild bees are believed to contribute significantly to pollination. Although several pesticides are known to be toxic to bees, toxicity testing has largely been restricted to direct lethal effects on adult honeybees. The researchers say sub-lethal effects on bumblebees could be going unnoticed, and other bee species could also be affected.
Lora Morandin and colleagues at Canada's Simon Fraser University tested the effects of different levels of spinosad on bumblebee colony health and foraging ability. Spinosad is a natural pesticide derived from bacteria belonging to the genus Actinomycetes. It is used in more than 30 countries including the us, Canada and the uk, to combat common crop pests such as caterpillars and thrips. Bee colonies were fed the pesticide in a way that mimicked contact in an agricultural setting. Adult bees and developing larva were exposed to spinosad in pollen. The bees' foraging ability on an array of complex artificial flowers was then evaluated.
High levels of spinosad residues (about 10 times what bees experience in the environment) caused rapid colony death. Colonies exposed to more realistic levels of spinosad in pollen did not show any lethal effects and only minimal immediate effects on colonies' health. However, bees that were fed realistic levels of spinosad during larval development were slower foragers. They took longer to access complex flowers, resulting in longer handling times and lower foraging rates. The bees also displayed trembling, which impaired their ability to land on the flowers and probe the flower tubes. This impaired foraging ability in bumblebees could result in weaker colonies and lower pollination of crop plants, according to Morandin.
Adult bees that have been exposed to a pesticide during larval development may display symptoms of poisoning not detected with current tests required by regulatory agencies, she adds.
Testing of new pesticides should include examination of lethal and sub-lethal effects on wild bees, the scientists conclude. Such testing will help develop pesticides and use recommendations that minimise impact on wild bees, leading to healthier populations of bees and potentially better crop yields.