Document Type

Thesis - Open Access

Award Date

1987

Degree Name

Master of Science (MS)

Department

Entomology

First Advisor

David D. Walgenbach

Abstract

Cultivated sunflower (Helianthus annuus L.) is an economically important crop in the United States and South Dakota. Native to North America, oil seed varieties of cultivated sunflower are second only to soybeans as a source of vegetable oil. Sunflower seed harvested for both oil and confection in South Dakota was 59,711 hectares (ha) in 1975. This hectarage has increased, stabilized, and during the last six years, has averaged 218,600 ha per year. Sunflower production, however in Minnesota and North Dakota, has decreased during this same period. Sunflower breeding efforts and hybrid development have reached the point where cultivated sunflower has the genetic potential to yield 5,000 kg/ha. In the United States as well as South Dakota the grey seed weevil, Snicronyx sordidus and the red seed weevil, Snicronyx fulvus comprise the sunflower seed weevil complex. The red seed weevil (RSW) ranges from Illinois to California and the grey seed weevil (GSW) from New Jersey to California on cultivated sunflowers. The GSW has the widest range of all the Smicronyx weevils. The RSW has been an economically important pest in South Dakota since 1978 and also in North Dakota since 1980. The northeast quadrant of South Dakota has been the focal area of sunflower production in the state. As production has increased in that area, so have populations of the economically important insect pests. In North Dakota, increased production has meant increased pest populations. Seed weevils are considered the major problems among these pests. Seed weevil damage can be severe. The problems associated with a seed weevil infestation include seed weight reduction and reduced quality of the crop. This has led to a need for insecticidal treatments. An average of 75 percent of the hectarage planted to sunflower in South Dakota during the last six years has been treated with insecticides, with an average cost to growers of $12.20 per ha. A paucity of literature exists concerning the field biology of these weevils. Papers concerning the description and cursory biology of the RSIV have been published. The GSW was superficially included in these studies, but no specific economic information has been determined. This is due to a lack of the basic biological knowledge that is necessary to make such a determination. The objectives of this study were to determine the seasonal life cycle and infestation pattern of the GSW. Included were: a) fecundity studies by means of an artificial infestation in the field, b) determination of factors of seed weevil overwintering mortality and their depth of overwintering, and c) preliminary conditions for laboratory rearing.

Library of Congress Subject Headings

Beetles -- Habitat

Sunflowers -- Diseases and pests

South Dakota State University Theses

Format

application/pdf

Number of Pages

76

Publisher

South Dakota State University

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