The risks posed by deltamethrin drift to hedgerow butterflies.

Area of Science:

• Entomology
• Pest Management
• Environmental Toxicology

Background:

• Pesticides are crucial for controlling agricultural pests.
• Understanding insecticide efficacy and non-target effects is vital for sustainable agriculture.
• Pieris rapae and Pieris brassicae are significant lepidopteran pests in cruciferous crops.

Purpose of the Study:

• To determine the susceptibility of Pieris rapae and Pieris brassicae to deltamethrin.
• To investigate the toxicokinetics and sublethal effects of deltamethrin exposure.
• To assess the risk of deltamethrin spray drift to these insect pests.

Main Methods:

• Topical application bioassays to determine LD50 values.
• Monitoring of mortality over extended periods post-treatment.
• Evaluation of sublethal effects including weight loss and developmental impacts.
• Residual exposure bioassays on treated cabbage leaves.
• Modeling of mortality risk from spray drift.

Main Results:

• LD50 values for both species showed prolonged declines, indicating slow deltamethrin metabolism or excretion.
• Sublethal deltamethrin exposure caused weight loss, feeding inhibition, and reduced adult size in P. brassicae.
• Toxic effects were observed in P. brassicae at extremely low residual deltamethrin concentrations.
• Spray drift modeling predicted high short-term risks to larvae at field-recorded deposition rates.

Conclusions:

• Deltamethrin exhibits persistent toxicity in Pieris species due to impaired metabolic or excretory processes.
• Sublethal effects and residual toxicity pose significant risks to pest populations.
• Spray drift management strategies, such as buffer zones, are necessary to mitigate ecological impacts.