Seasonal variation in percentage of striped cucumber beetles (Coleoptera: Chrysomelidae) that vector Erwinia tracheiphila

Striped cucumber beetles, Acalymma vittatum (F.), were tested for their ability to vector Erwinia tracheiphila, the causal agent of bacterial wilt, to muskmelon plants. Beetles were tested from 3 locations in a large muskmelon production area in southwestern Indiana over a 4-yr period. Individual beetles were allowed to feed on muskmelon plants for 0, 12, 24, 48, and 72 h every 4 wk during the growing season. The percentage of infected beetles that transmitted the pathogen to plants was recorded. There were no significant differences among years or collection locations for the percentage of infective striped cucumber beetles. In the early part of the season, approximate to 1% of overwintering beetles were found to be infective. The 2nd generation of beetles collected in July, August, and September had much higher percentages of infective beetles (8-12%). There was little variation in percentage infectivity of beetles in May or June over the 4-yr period, and high variation in beetle infectivity later in the season. When beetles fed on plants for 12 h, only 0.05% could transmit the pathogen. At 24 and 48 h of feeding, approximate to 2% of beetles were infective, whereas at 72 h of feeding, 5% of beetles were infective. There was a significant interaction between collection date of beetles and their feeding duration. At the longest feeding period of 72 h, < 2% of the beetles that were collected in May or June were infective, whereas approximate to 10% of the beetles were infective in July, August, and September. This study indicates that only 1% of the overwintering striped cucumber beetles in southwestern Indiana can infect muskmelon plants with E. tracheiphila. This should enable researchers to develop thresholds for this pest, reducing the need for unnecessary insecticide applications.