AN OVERVIEW OF CROP INSECTS RESEARCH UNIT BOLL WEEVIL RESEARCH ACTIVITIES

Authors: Spurgeon, Dale; Raulston, Jimmy; Summy, Kenneth

Submitted to: Minutes of International Cotton Pest Work Committee
Publication Type: Proceedings
Publication Acceptance Date: 1/15/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: The redirection of research of the Crop Insects Research Unit of the Subtropical Agricultural Research Laboratory and preliminary results of research are discussed. Use of a blood enzyme (juvenile hormone esterase) to assess boll weevil reproductive diapause (a condition of dormancy enhancing overwintering survival in which boll weevil reproductive organs fail to develop) was investigated. Juvenile hormone esterase levels in th blood were related to length of boll weevil life, but they could not be used to accurately predict dormancy. Survival patterns of boll weevils suggested that differences in boll weevil life span were caused by natural variation within the population rather than existence of separate reproductive and dormant populations. Cool temperatures during the winter increased survival of weevils, and survival decreased again with return of warm weather in the spring. Additional studies indicated that temperature, ,quality of the food supply, and crowding affect development of boll weevil reproductive organs. Also, males showing the signs of dormancy were able to successfully mate females. A trapping system in northeastern Mexico was used to monitor boll weevil movement in that area. Trap captures indicated that the boll weevil is most common in areas of cotton production, but weevils were also captured in areas many miles from cotton. Capture of weevils at sites far from cotton suggest that movement of boll weevils between the northern and southern cotton production areas of northeastern Mexico is likely.

Technical Abstract: The redirection of research of the Crop Insects Research Unit of the Subtropical Agricultural Research Laboratory and preliminary results of research are discussed. Use of a juvenile hormone esterase (JHE) assay to assess boll weevil reproductive diapause was investigated. Relationships between JHE titers and longevity were significant but variable among cohorts. No discriminating titer of JHE could be identified that distinguished diapausing from non-diapausing weevils. Survival curves were characteristic of senescing rather than diapausing populations. Cool winter temperatures enhanced survival but mortality rates increased with the higher temperatures of spring. Additional studies indicated that temperature, host quality and physical characteristics, and crowding were important determinants of boll weevil reproductive commitment. Also, males exhibiting diapause characteristics successfully inseminated females. A trapping system in northeastern Mexico was used to assess seasonal pattern of boll weevil dispersal within that region. Trap captures were greatest near cotton production areas, but weevils were captured at all trapping sites. Capture of weevils at sites remote to cotton suggest that persistent if low level interchanges between weevil populations of all cotton production regions of northeastern Mexico is likely.