With each passing year in Texas' boll weevil eradication program, limiting boll weevil reproduction becomes ever more critical in attaining the goal of no weevil. This is particularly true regarding volunteer cotton that so often goes undetected and untreated. There are two main sources of this type of cotton; one is volunteer cotton that germinates in a subsequent crop planted in a field following cotton. This cotton can produce fruit and may be a source of continuing boll weevil populations. However, since this cotton is growing in another crop such as corn, with which it is competing, fruit production often is much more limited than that of cotton grown as a crop. A second source of volunteer cotton is from non-crop areas such as fence lines, drainageways, railroad rights-of-way, ranches or feedlots where cotton seed is fed to livestock, or where cotton seed is used in deer feeders which are often in remote areas of ranches. In these more open areas where cotton plants have little to no competition, they can grow quite large, producing lots of fruit that can be used by boll weevils for food and, more importantly, for reproduction. When the amount of fruit on cotton growing in a fence line was observed, it became apparent that the implications of volunteer cotton to the success of the boll weevil eradication program may be greater than we have suspected. As a follow-up, plants were “harvested,” fruits were counted, associated boll weevil damage was recorded, and weevils were reared from the fruit with egg-laying punctures.

Objectives:

  1. Determine the amount of fruit that volunteer cotton growing in more open areas might produce and which would serve as a source for reproduction and as a food source for overwintering boll weevils.

  2. Determine the level of boll weevil feeding and egg-laying on the fruit.

  3. Determine the potential level of reproduction by rearing boll weevils from collected fruit.

Materials and Methods: Cotton plants were harvested from fence lines at designated sites, the number of plants at each site was recorded and plants were taken to the office to be processed. Initial Site: The fruits were stripped from the 66 plants and all of the fruits, which were small bolls or larger, were combined. All fruits were examined for boll weevil feeding, egg-laying or emergence and resulting data were recorded. No fruit was held for weevil emergence since there was no evidence of recent egg-laying in any of the fruit. Alpha site: Plants were harvested and shed fruit on the ground were recovered. The fruits were stripped from each of two plants and the number of squares (small, large and open bolls) from each plant were recorded. Each fruit was subsequently examined for feeding, egg-laying or weevil emergence and the status of each fruit was recorded. Fruits with egg-laying punctures were placed in a rearing chamber (5-gal bucket with screen covering the portion of the lid that was cut out) and held until adult boll weevil emergence ceased. Adult boll weevil numbers were recorded. Sites 1 through 5: Methods were the same as those used at the Alpha site except that the fruits from each plant were not counted separately, by plant, but were combined. Also, all fruits from the five sites that had egg-laying punctures were combined and held in a rearing chamber for adult emergence. (Note: toward the end of the period that the fruits were held in the rearing chamber, a light misting with water and subsequent thorough mixing seemed to encourage adult emergence. Stirring the mass of cotton fruit once a day also seemed to stimulate adult emergence.)

Results: Nineteen weevils had emerged from the fruit examined from the 66 plants at the initial site. Alpha Site - One hundred and fifty-three (153) boll weevils emerged from the fruit that was collected on 4 and 16 October from the 2 plants at the Alpha site. With the 153 weevils that emerged in the lab, plus the 96 that had already emerged in the field, a minimum of 249 weevils were produced on 2 plants at the Alpha site. Sites 1 through 5 - One hundred and seventy-six (176) boll weevils emerged from the fruit collected on 16 October from the 12 plants at the 5 sites. With these 176 weevils, plus the 117 that had emerged in the field, there was a minimum of 293 weevils produced from these 12 plants. At least 561 weevils emerged from the volunteer cotton that I examined from this farm.

Discussion: There was another dozen or so large plants I did not examine that a TBWEF employee removed after the growers left the plants for two weeks subsequent to their being informed the plants needed to be destroyed. (Note: the growers were aware of these plants before I found them, personal communications). Assuming a 50:50 sex ratio, 100% survival of well-fed weevils in a mild winter climate and an average of 150 eggs per female, the weevils that emerged from this one farm represent the potential for over 42,000 eggs in 2008. When multiplied many times over by all of the volunteer cotton in the South Texas-Winter Garden Zone, it becomes apparent that volunteer cotton must not be ignored. The potential consequences for boll weevil eradication are too great.