Date of Award

1989

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Entomology

First Advisor

Seth J. Johnson

Abstract

The microhabitat distribution of velvetbean caterpillar (VBC), Anticarsia gemmatalis Hubner (Lepidoptera: Noctuidae) was studied in soybean field cages and fields during 1985, 1986 and 1987. Larval density did not affect pupal horizontal distribution patterns related to direction and distance from the plant row. Pupae were found equally on both sides of soybean plant rows in a cage study. Pupae were found on and below the soil surface, but not on the plant. In 51 cm row spacing, both equal number and similar dispersion pattern of pupae were found on either side of the plant row. In 91 cm row spacing, pupal densities were slightly biased to the north side (4:6) of the plant rows in 1986 and this trend was extreme (2:8) in 1987 when plant canopy was barely closed. The degree of plant canopy closure appeared to influence pupal horizontal distribution. In 91 cm row spacing, pupal densities varied inversely with distance from the row. Taylor's power law analyses indicated that VBC pupal spatial dispersion patterns were random in both 51 and 91 cm row spacings for a sample unit (90 by 90 cm) and a subsample unit (90 by 15 cm parallel to the plant row and 15 by 90 cm across the plant row in 51 and 91 cm row spacings, respectively). Significant linear relationships between larval and pupal densities were found for all three larval size classes (small, 1st and 2nd instars (0-12.5 mm long); medium, 3rd and 4th instars (12.5-25 mm long); large, ($\geq$25 mm long)) in 51 and 91 cm row spacing fields in 1986 but only for medium larvae in 1987. Simple linear regression equations were developed to predict pupal density from larval density. The survivorship and predation of VBC pupae were studied in 1986 and 1987. Seven species of insects including ground beetles, tiger beetles, earwigs and the red imported fire ant, Solenopsis invicta Buren, were identified in laboratory feeding trials as VBC pupal predators. Predation was the principal mortality factor, accounting for 37.5 to 95.2% mortality in plots with fire ants. (Abstract shortened with permission of author.).

Pages

162

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