CULTURAL CONTROL AND MICROCLIMATE EFFECTS ON IMMATURE BOLL WEEVIL MORTALITY IN CHIHUAHUAN DESERT COTTON FIELDS

摘要

Low relative humidity and high temperatures in cotton fields in the New Mexico Chihuahuan desert dramatically reduced immature boll weevil survival. The degree of survival was also affected by cultural practices that affected crop microclimate. Bollweevils in infested squares placed in cotton furrows for 10 days in early season had 100 percent mortality. After canopy closure when temperatures were lower and relative humidity higher, some adults emerged from squares, but emergence varied with management practices. Rows oriented north/south had 38 percent emergence compared to 9 percent emergence in rows oriented east/west. Narrow row cotton with 7-inch row widths had higher survival of boll weevils, lower temperatures and higher relative humiditythan standard 40-inch row widths. Mean daily high temperature in-furrow was 39 deg F lower in 7-inch rows compared to 40-inch rows with mean highs of 90 deg F and 129 deg F respectively. Relative humidity in-furrow was also significantly lower in 40-inchrows with lows of 17 percent RH compared to 24-25 percent RH in 14-inch and 7-inch rows. Squares under the plant canopy had 34 percent emergence of adults compared to 6 percent emergence of squares in the center of the furrow. In a controlled chamber test at 79 deg F, low RH reduced adult emergence, and resulted in an extended emergence time and a shorter adult lifespan. Adult emergence was 91 percent at 50 percent RH vs. 41 percent at 17 percent RH. Adult lifespan was much shorter at 17 percent RH with mean lifespan of 20 days compared to 42 days for those reared and maintained at 50 percent RH. Adult emergence was also delayed 2 days at 17 percent RH compared to those at 50 percent RH. These results indicate that natural mortality due to high temperatures and low RH is very high in the desert valleys of the Chihuahuan desert. Also, higher relative humidity, lower temperatures and higher survival of boll weevil in narrow row cotton suggest that the increasing use of narrow row cotton in arid/semi-arid areas will result in higher boll weevil populations and damage.