YIELD RESPONSE OF SOYBEANS TO CONSECUTIVE GROWTH STAGE DEFOLIATION BY THE MEXICAN BEAN BEETLE, EPILACHNA VARIVESTIS MULSANT, AND METHODS OF PREDICTING DEFOLIATION FROM FIELD SAMPLE ESTIMATES OF MEXICAN BEAN BEETLE NUMBERS AND PLANT LEAF AREA

STEVEN PAUL NOLTING, Purdue University

Abstract

Field studies were conducted to determine the developmental and consumptive rates of the Mexican bean beetle, Epilachna varivestis Mulsant, measure the yield response of soybeans to different consecutive growth stage defoliations by the Mexican bean beetle and, develop a method of estimating soybean leaf area based on plant characteristics. Nylon mesh cages were used to confine individual larvae, pupae and adults on Williams 82 leaflets. The duration of the pupal, adult and each of the four larval stages, consumption during the larval and adult stages, and sex of adults were recorded. Caged Wiliams 82 soybean plots were defoliated by Mexican bean beetles over consecutive growth stages. Defoliations were initiated at different reproductive stages of growth, and terminated at the end of the beginning seed growth stage. Defoliations were also performed on later stages of growth. The consecutive growth stage defoliations produced linear defoliation-percentage yield loss relationships. The duration and level of accumulated defoliation by the beginning seed or full seed growth stage determined the slope of the regression. The yield component affected by the reduction in yield was weight/seed. Methods of estimating leaf area were based on location, number, and area of leaflets data obtained from soybean varieties Century, Essex, Pixie, and Williams 82. Models describing area for main and axillary leaves as well as for the whole plant were developed. The most accurate of the models used submodels for axillary, expanded and expanding main leaf areas.

Degree

Ph.D.

Subject Area

Entomology

COinS