Sublethal pesticide effects on caterpillar and egg parasitoid performance

Overview

This research investigates how sublethal doses of spinosyn A and spinosyn D, the active insecticidal components of the pesticide Spinosad, affect both pest caterpillars and their natural biological control agents. The study focuses on Trichoplusia ni (cabbage looper) caterpillars and the egg parasitoid Trichogramma brassicae, which is widely used in integrated pest management programs. The goal is to understand whether pesticide residues at non-lethal concentrations can reduce pest fitness while still allowing crop damage, and whether smaller host eggs compromise parasitoid effectiveness.

The research addresses a critical question for sustainable agriculture: how do sublethal pesticide exposures ripple through pest-parasitoid food webs? Understanding these effects helps producers make informed decisions about combining biocontrol agents with pesticide applications, ultimately supporting more effective and environmentally responsible pest management strategies.

Technical specifications

Research approach:

• Determine the LD50 of a spinosyn A/D mixture for T. ni caterpillars
• Test sublethal concentrations (1/5th, 1/10th, and 1/100th of LD50) on caterpillar development and female pupal lipid content
• Measure egg size as a proxy for parasitoid host quality
• Use microCT scanning in collaboration with Dr. Pierre Dutilleul to monitor parasitoid development inside host eggs
• Apply molecular tools (qRT-PCR) to track T. brassicae development and diapause status
• Assess fecundity impacts through lipid content correlation with adult reproductive output

Key measurements include:

• Caterpillar developmental time and survival at sublethal doses
• Female pupal lipid reserves as indicators of fecundity
• Host egg size variation following pesticide exposure
• Parasitoid developmental progression and diapause outcomes

Technology readiness level

This is an early-stage research project in the planning and validation phase. The two-year study will support an MSc student at McGill University. The research combines established entomological methods with advanced imaging (microCT) and molecular biology techniques (qRT-PCR). Findings will contribute to evidence-based recommendations for integrated pest management programs that combine parasitoid biocontrol with compatible pesticide use.