Evaluation of Damage to Common Beans by Larvae and Adults of Diabrotica balteata and Cerotoma facialis

Abstract

Damage to beans by feeding of larvae and adults of Diabrotica balteata LeConte and Cerotoma facialis Erickson was evaluated under greenhouse and field conditions. 2nd and 3rd instars were more damaging than 1st instars and caused stand losses of up to 100%. In general, although C. facialis larvae were more damaging than those of D. balteata, both caused significant reductions of leaf area in plants that survived infestation at 1,4, and 7 days after seeding. No significant reduction in leaf area was found when 14-day-old or older plants were infested with 10 larvae per plant.

The effect of adult feeding on yield was measured at different growth stages of the plant. Mixed and pure populations of these species at the rate of two and four adults per plant caused losses of up to 60% during the initial period of growth (8 to 15 days) and to a lesser extent during flowering. No significant damage was detected at other stages of the growth cycle. Since average adult field populations (0.6 to 1.0 adults per plant) are below these critical levels, it is concluded that, in areas in which the adults are not acting as virus vectors, the common practice of spraying against these insects is seldom justified.