HIGHER DIPTERA PESTS OF LIVESTOCK AND POULTRY: SCREWWORM FLIES
Location: Screwworm Research
Title: Effect of adult screwworm male size on mating competence
Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 22, 2011
Publication Date: March 20, 2011
Citation: Pitti, A., Skoda, S.R., Kneeland, K.M., Berkebile, D.R., Molina-Ochoa, J., Chaudhury, M.F., Youm, O., Foster, J.E. 2011. Effect of adult screwworm male size on mating competence. Southwestern Entomologist. 36(1):47-60.
Interpretive Summary: Prior to eradication from the U.S., Mexico, and Central America, using the sterile insect technique, screwworms were severe, economically important pests of animals. If screwworms were reintroduced to the U.S., estimates of losses to the livestock industry approach $1 billion per year; losses to wildlife, pets and humans are inestimable. To protect from reintroduction, screwworm flies are mass produced, sterilized and released at a barrier established at the border of Panama and Colombia. Sterile flies must be competent in the field. At times, for unknown reasons, the mass produced flies are small in size. We developed a method to produce small flies in the laboratory and compared them to ‘normal’ sized flies. Although the small flies mated successfully with normal-sized females, small flies mated with fewer females than did normal-sized males. When normal-sized males and small males were placed together with adult female screwworms, small males were only 41% as competitive. With this knowledge, if the mass production facility is producing small flies the program responsible for maintaining the barrier can adjust the release rate to better protect from this pest reinvading the areas currently free of screwworms.
Screwworms, Cochliomyia hominivorax (Coquerel) (Diptera: Calliphoridae), were devastating pests in parts of North America and Central America before their eradication by means of the sterile insect technique (SIT). Now, a barrier is maintained to prevent re-entry of screwworms from endemic regions to those free of screwworms. For SIT, barrier maintenance requires the mass rearing of millions of competitive insects, their sterilization by irradiation and release into infested areas. Weight of the mature larvae (or pupae) is used for assessing fly quality for mass reared screwworms. A method for producing flies of different sizes in the laboratory was developed. Small and large male flies were then compared for sexual performance. A standardized measure of the wing length was established to characterize adult size. This measure correlated positively with larval and pupal weights. Although small males mated successfully, they mated with fewer females than large males when each was placed alone with a group of females. When placed in cages together with females and large males, small screwworm males were out-competed (41.18% as competitive) by the large males. Although behavior of male screwworm flies in laboratory conditions has not been demonstrated to be similar under field conditions, knowledge of mating competitiveness of sterile males of different sizes is valuable to the screwworm eradication program.