Growth inhibition and fruit distortion in okra (Abelmoschus esculentus) induced by the flea beetle Podagrica uniforma (Coleoptera: Chrysomelidae) herbivory

Abstract

Inhibition of okra growth in response to flea beetle injury was studied in both the screen house and field. In the screen house or field, 0,5, 10,20,30 and 40 pairs of Podagrica uniforma (Jacoby), representing six treatments, were introduced into different cages containing five 3-week-old okra plants, replicated three times. Data were collected on the number of flowers and branches, plant height, stem girth and functional leaf area in both experiments. With increasing densities of P. uniforma, days to 50% flowering and fruit initiation were prolonged by 1–13 days and 2–15 days, respectively. The beetle did not exhibit florivory but caused distortion of okra fruits, i.e. bending of fruit tips at the point of flea beetle-induced damage. From the 20-pair level (eight beetles per plant), there were significant reductions in plant height (up to 50%) and stem girth (up to 43%) in both the screen house and field. The number of distorted fruits showing bent tips was significantly higher relative to the control from the 5-pair level, and was more than 90% at the 40-pair level. Regression analysis indicated that plant height was a linear function of flea beetle population. Third-degree polynomial models best described the relationship between insect density and the number of bent fruits. χ2 analysis showed that these models derived from the screen house data were not significantly different from the field data models.