Date of Award

1980

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Entomology

Abstract

An adult population survey of 4 species of the noctuid subfamily Plusiinae was conducted in soybean ecosystems of south, south central and north central Louisiana. Sticky-traps baited with the synthetic sex pheromone (Z)-7-dodecen-1-ol acetate, or looplure, were used as the sampling tools for 2 soybean growing seasons. The soybean looper Pseudoplusia includens (Walker) reached the highest densities of the plusiine complex with 4 and 5 generations detected in the southern and central regions of the state. Moth density was greatest at Krotz Springs (south central site) during 1977 and 1978; the lowest levels were detected at Niblett (southern site). Males were collected at the southernmost site on or before the time of initial capture at either of the more northern locations. Initial captures occurred in mid-June (the first sampling period) at all 3 locations during 1977; however, the 1978 adults were initially captured in mid-June at Niblett and in early August at Krotz Springs and Bunkie. Highest levels of capture occurred in September at all sites during both years. Although Rachiplusia ou (Guenee) was found to contribute considerably to the plusiine population in June, adult densities were quite low during the later summer months. Trichoplusia ni (Hubner) and T. oxygramma (Geyer) seldom attained high levels at any location. Pheromone traps baited with 1000 ug of looplure were used in the assessment of population densities of adult P. includens. Estimates of adult density in the 3 soybean ecosystems were used to predict subsequent larval population densities at the 3 locations for the 2 growing seasons; simple linear regression equations were generated from these data. Regression coefficients increased with a northward progression during 1977, but low correlation coefficients existed between the adult and larval populations for all sites. Substantially higher correlation coefficients were determined for 1978, but the southern site unexpectedly exhibited the highest regression coefficient. The highest degree of correlation existed between P. includens adults and subsequent larval populations separated by a 2-week period at every site in 1977. However, during 1978 adult and larval populations separated by 4 weeks exhibited the highest correlation. Concentration differences of looplure were evaluated for field trapping efficiency and electrophysiological responses with P. includens, T. ni and R. ou. Traps baited with 1000 ug of the lure captured a significantly larger (P < .05) number of male P. includens and T. ni than any other concentration; R. ou males were caught at a greater rate in traps baited with 100 ug, significantly more (P < .05) than with 1000 ug. Electroantennogram (EAG) studies demonstrated that antennae of male P. includens have a lower response threshold to looplure than either T. ni or R. ou antennae, the latter demonstrating the highest significant threshold of response. No differences in the stimulus-response functions of the 3 species were detected.

Pages

107

Share

COinS