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

摘要

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