Bionomics and Sampling of the Imported Crucifer Weevil, Baris Lepidii Germar
Sherrod, Daniel Wallace
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Permalink
https://hdl.handle.net/2142/68015
Description
Title
Bionomics and Sampling of the Imported Crucifer Weevil, Baris Lepidii Germar
Author(s)
Sherrod, Daniel Wallace
Issue Date
1981
Department of Study
Entomology
Discipline
Entomology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Entomology
Language
eng
Abstract
The imported crucifer weevil, Baris lepidii Germar, is a minor pest of a wide range of cruciferous plants grown in central and southern Europe. In May of 1977 this insect was discovered infesting commercial horseradish fields in Illinois. A research program composed of several subsections was designed to obtain useful information on the bionomics of the imported crucifer weevil. The intent of the research was to obtain data which would be used in implementing a sound pest management program.
The weevil was reared in the laboratory on horseradish and the number of larval instars was determined using head capsule measurements. During the growing seasons of 1979 and 1980, horseradish from cultivated fields was examined on a weekly schedule to ascertain what stages (eggs, larvae, pupae, adults) were present. This information provided a profile of the age distribution of different stages of B. lepidii throughout the growing season. In addition field-collected adult females were dissected each week to examine ovarian development.
The temperature related development of B. lepidii was studied in the laboratory, greenhouse, and field. The developmental time for the eggs, larvae, and pupae at constant temperature was recorded for 15(DEGREES)C, 19(DEGREES)C, 21(DEGREES)C, 23(DEGREES)C, 25(DEGREES)C, and 27(DEGREES)C. Temperature control cabinets set at a 14 h light - 10 h dark photoperiod were utilized for this study. Using this information the developmental threshold temperature for the immature stages of B. lepidii was determined to be 7(DEGREES)C. The time required for development could then be expressed in terms of cumulative centigrade-degree days. An average of 805 centigrade-degree days are needed to complete development from oviposition to adult emergence. Greenhouse and field trails were designed to substantiate the laboratory results regarding developmental rate. Large clay flower pots (30 cm diameter) containing horseradish roots infested with known numbers of B. lepidii eggs were placed in greenhouse soil benches or in experimental field plots. Ambient and 8 cm soil temperatures were continuously recorded. Roots were then removed at weekly intervals and the growth state of all B. lepidii individuals present was recorded. Developmental rate in the field can be reliably predicted using the laboratory data.
A reliable method of determining population levels of the imported crucifer weevil was needed before any kind of sound pest management program could be implemented. The sampling methods examined included: (1) baiting fields with large horseradish roots prior to planting, (2) pitfall traps in cultivated fields, (3) visual examination of the plant crown and upper portion of the planted root, (4) a series of core samples over and around the plant, and (5) total removal of a square area ( 1/4 m('2)) surrounding a plant to a depth of 10 cm. These techniques were implemented using a stratified sampling design in June and again in August in at least 10 fields during both the 1979 and 1980 growing season. In addition a specified number of "sets" (propagative stock) were removed from each field just after planting and examined for the presence of B. lepidii eggs (B. lepidii can overwinter in either the adult or egg stage). The results of these separate sampling techniques were then related to the level of infestation of the harvested root for each test field. The reliability of each sampling method could then be evaluated in terms of its correlation with damage to the crop at harvest.
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