PREFERRED TECHNIQUE FOR ADULT SEX DETERMINATION OF THE BOLL WEEVIL, ANTHONOMUS GRANDIS BOHEMAN (COLEOPTERA: CURCULIONIDAE)

Authors: Sappington, Thomas; Spurgeon, Dale

Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/2/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: Scientists who study boll weevils often must determine the sex of individuals before an experiment is performed. A common technique for determining the sex of an adult weevil requires only a visual examination of the weevil's snout. However, the snout characters observed are variable, and the scientist's ratings subjective, so that this method is only about 90% accurate. A completely accurate method for determining boll weevil sex was described 35 years ago. This technique (called the tergal-notch method) requires that the weevil be held on its back while the abdomen is pressed gently with a blunt probe to expose the edge of a hard plate (a tergite), which is smooth in the female but distinctly notched in the male. This technique has not gained wide acceptance, because it is perceived as too slow for processing large numbers of weevils and because the original drawings are not entirely adequate for someone attempting to learn it. In this paper we eliminate these objections by demonstrating that the tergal-notch method is fast enough for most applications and by clearly illustrating it with photographs and interpretive drawings. This method is quickly learned, with experienced users in our laboratories routinely processing 200-300 weevils per hour with 100% accuracy. Therefore, the tergal-notch technique is the preferred method for determining boll weevil sex under all but a few special circumstances.

Technical Abstract: Determining the sex of boll weevil adults is complicated by the lack of a discreet, gender-specific, externally visible character. However, the posterior edge of the male's 8th tergite is distinctively notched and can be revealed by gentle probing. Though completely accurate as originally described 35 years ago, this method has not gained wide acceptance because of the perception that it is too slow for processing large numbers of weevils and because the original illustrations are not entirely adequate. In this paper we illustrate the tergal-notch method of sexing with photographs and interpretive drawings. This method is quickly learned and fast enough for most applications. Experienced users in our laboratories routinely sex 200-300 weevils per h. The common alternative technique of sexing by relative snout characteristics is only 88-90% accurate. The latter method should only be used under special circumstances and with an awareness of the sacrifice in accuracy.