Masters Theses

Date of Award

12-1991

Degree Type

Thesis

Degree Name

Master of Science

Major

Entomology and Plant Pathology

Major Professor

Jerome F. Grant

Committee Members

Vernon H. Reich, Charles R. Patrick

Abstract

The cereal leaf beetle (CLB), Oulema melanopus L. (Coleoptera: Chrysomelidae), was introduced into North America from southern Asia (Wellso 1986). Adult beetles were first collected and identified as O. melanopus from small grain fields in Berrien County, Michigan, in 1962 (Haynes and Gage 1981). Since its identification in the United States in 1962, the CLB has expanded eastward with the prevailing winds and now occupies an area from southern Canada to North Carolina and west to Missouri (Battenfield et al. 1982).

In Tennessee, the CLB was present in low numbers as early as 1972 (Haynes and Gage 1981). However, populations of this insect pest have increased during the last 20 years throughout Tennessee, primarily in the eastern and middle areas of the state (Grant and Patrick 1988). The CLB has been reported from 81 of 95 counties in Tennessee (Grant and Patrick 1991). Fortunately, the CLB is not a serious pest in most areas of Tennessee. However, the potential for problems exists if populations of CLB continue to increase and spread across the entire wheat-growing regions of the state (Grant and Patrick 1988, 1991).

A three-year study to provide information on the distribution and seasonal incidence of CLB on wheat in Tennessee has been conducted (Grant and Patrick 1991). However, little research, except for limited chemical efficacy studies, has been conducted on selected management strategies to control this pest. Research on other management tactics, such as the use of resistant wheat varieties, cultural control, and biological control, is necessary for the development and incorporation of appropriate management programs directed against CLB in Tennessee. Therefore, a two-year study was initiated to evaluate the influence of planting dates and varieties on populations of CLB on wheat. This study was conducted at the University of Tennessee Highland Rim Experiment Station (HRES) in middle Tennessee during 1990 and at the University of Tennessee Plant and Soil Science Field Laboratory/ Government Farm (GF) in eastern Tennessee during 1990 and 1991.

Planting date did affect CLB densities on wheat, and its influence on populations of CLB were consistent throughout this two-year study. Densities of CLB adults per five sweeps were greater in the early-planted wheat at HRES during 1990 and at GF during 1990 and 1991. Data suggest that adults were attracted to the early-planted wheat, where they mated. Adults then moved to the younger plants in the middle- and late-planted wheat. Higher densities of adults per 20 stems were found on late-planted wheat at the GF in 1990 and 1991. The density estimations of CLB on stems reflect the late-season populations of CLB or their F1 generation on wheat. These higher densities of adults in the later-planted wheat may result from the higher densities of eggs and larvae that were present in the later-planted wheat. The low numbers of eggs per 20 stems on early-planted wheat were consistent at the GF in 1990 and 1991, while the low numbers of larvae per 20 stems on early-planted wheat were consistent at all locations during both years.

The influence of wheat varieties on populations of CLB varied among locations and years. Densities of CLB adults per five sweeps were similar at HRES in 1990 and the GF in 1991 with high numbers of adults concentrated on Pioneer 2555. Pioneer 2555 lacks leaf pubescence, which suggests that it would be more preferable to CLB adults. However, egg and larval densities were low on Pioneer 2555. Large numbers of eggs and larvae were both found on Caldwell, a variety that is also absent of leaf pubescence, at both locations during both years. A high density of F1 adults per 20 stems were found on Caldwell at the GF during both years. This high density of F1 adults may result from the higher number of eggs and larvae per 20 stems on Caldwell at both locations and during both years. The low number of eggs per 20 stems on Pioneer 2555 were consistent at the GF during both years. These findings are similar to the low number of larvae also found on Pioneer 2555 at the GF during both years. Low densities of larvae were found on Saluda at HRES in 1990 and at the GF in 1991. Although information on the leaf pubescence of Saluda is not available, its effect on CLB is similar to Pioneer 2555. Because CLB populations responded differently to those varieties which lacked leaf pubescence, the lack of pubescence may not be a valid characteristic to use solely in the explanation of the impact of these varieties on CLB.

The combined use of planting date and variety may be beneficial in an integrated management program against CLB. The incorporation of these tactics into integrated pest management of CLB could improve wheat production and profitability in Tennessee by eliminating or reducing costs associated with insecticide application.

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