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United States Department of Agriculture

Agricultural Research Service

Title: A Comparison of Size, Sex Ratio, and Dispersal in Three Coccinellids

Authors
item ELLIOTT, NORMAN
item Kieckhefer, Robert
item FRENCH, BRYAN
item Lee, J - USDA-OICD

Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 10, 1998
Publication Date: N/A

Interpretive Summary: Coccinellids (lady beetles) play an important role in the biological control of aphids in some agricultural crops in the United States. However, their effectiveness as biological control agents is highly variable. Relationships between body size, sex ratio, dispersal, and abundance patterns of three closely related coccinellid species were investigated. A ranking of species with respect to relative variation in body size among years was Hippodamia parenthesis > H. tredecimpunctata tibialis > H. convergens. Sex ratio varied among species similarly, with H. parenthesis having the most female biased sex ratio and H. convergens having the least. The propensity for dispersal displayed the opposite arrangement, being smallest for H. parenthesis and largest for H. convergens. If a population in a year was composed of large adults, larvae were abundant the next year for H. convergens and H. tredecimpunctata tibialis. If adults of these two species were abundant in a particular year, there was a shift in sex ratio toward more males the following year. A high percentage of females in a particular year tended to result in an abundance of immatures the following year. Comparison of the size and sex ratio of coccinellids caught in agricultural fields and on flight interception traps stationed adjacent to fields, indicated that males and females of each species from field collections were generally larger than those from traps. The results are important from the standpoint of understanding the life history strategies of coccinellids that permit them to exploit pest aphid populations in ephemeral agricultural ecosystems. Greater understanding of coccinellid ecology may eventually lead to ways to improve their effectiveness in biological control of aphids.

Technical Abstract: Relationships between body size, sex ratio, dispersal, and abundance patterns of three coccinellid species [Hippodamia convergens, H. tredecimpunctata tibialis, and H. parenthesis] were investigated. Body size differed significantly among years for all three species. Sex ratio differed from 1:1 for two of three species, and among years for all species. A ranking of species with respect to relative variation in body size among years was H. parenthesis > H. tredecimpunctata tibialis > H. convergens. The range of variation in sex ratio varied in an identical fashion. A dispersal index, representing a species propensity for flight, displayed the opposite arrangement, being smallest for H. parenthesis and largest for H. convergens. If a population in a year was composed of large adults, larvae were abundant the next year for H. convergens and H. tredecimpunctata tibialis. If adults of these two species were abundant in a particular year, there was a shift in sex ratio towards more males the following year. A high percentage of females in a particular year tended to result in an abundance of immatures the following year. Comparison of the size and sex ratio of coccinellids caught in agricultural fields and on flight interception traps stationed adjacent to fields indicated that females and males of each species from field collections were larger than those from traps.

Last Modified: 7/28/2014