Sampling Transgenic Corn Producing Bt Toxins for Corn Earworm Injury

Area of Science:

• Agricultural Entomology
• Pest Management
• Quantitative Ecology

Background:

• Transgenic corn hybrids expressing Bacillus thuringiensis (Bt) proteins are widely used for insect control.
• Helicoverpa zea (corn earworm) remains a significant pest, necessitating effective sampling methods.
• Understanding spatial distribution patterns of pest injury is crucial for developing efficient sampling plans.

Purpose of the Study:

• To analyze kernel injury patterns caused by Helicoverpa zea in Bt and non-Bt corn hybrids.
• To determine the impact of injury levels on sample size requirements for population estimation.
• To provide the first sampling recommendations for estimating H. zea populations in corn ears.

Main Methods:

• Sampled 7,260 corn ears from Bt and non-Bt hybrids in North and South Carolina (2012-2017).
• Quantified kernel injury area caused by H. zea feeding.
• Applied statistical analyses including chi-square tests, variance-to-mean ratios, Taylor's power law, and Iwao's regression to assess spatial distribution and sample size needs.

Main Results:

• Observed nonrandom distributions of kernel injury for all hybrids (P < 0.0001).
• Injury levels and spatial distribution patterns were similar between Bt and non-Bt hybrids within families.
• Required sample sizes for precise population estimates were high, especially at low injury levels, and varied between Bt and non-Bt hybrids.

Conclusions:

• The study established the first sampling recommendations for estimating H. zea populations based on corn ear injury.
• Sampling efficiency depends on injury levels and hybrid type, influencing the number of samples needed for accurate estimates.
• These findings support optimized pest monitoring strategies in diverse corn cropping systems.