Author
|
Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 3/15/2007 Publication Date: 3/30/2007 Citation: Naranjo, S.E. 2007. Survival and Movement of Bemisia tabaci (Homoptera: Aleyrodidae)Crawlers on Cotton. Southwestern Entomologist Vol 32, No 1:17-23. Interpretive Summary: Bemisia tabaci (sweetpotato whitefly) is a key pest of many field and horticultural crops worldwide. Recent field studies have demonstrated that populations of this pest in cotton are subject to high levels of natural mortality during the immature stage. Most stages of immature whitefly are sessile and this facilitated the study of mortality because individual insects could be followed over time to determine the cause of mortality. However, after hatching from the egg, the early first instar nymph is mobile and aptly called a crawler. Prior field studies did not attempt to measure the mortality of this short, mobile stage and so overall estimates of mortality may be in error. Greenhouse and field studies were conducted to estimate survival rates of crawler stage. The survival of crawlers did not differ significantly between still-air and artificial wind treatments in the greenhouse and averaged 90% overall. Using a combination of cohort-based life table studies to measure egg mortality and recruitment studies to measure egg to settled 1st instar mortality in the field, crawler survival was estimated to average 89.2% over three study sites in central AZ. Overall results suggest that crawlers move very little on cotton and that survival is high under both greenhouse and field conditions. Generational mortality rates estimated from previous life table studies that excluded crawler mortality would increase by only 0.8% with the addition of this minor mortality component. Technical Abstract: Greenhouse and field studies were conducted to estimate survival rates of crawler stage Bemisia tabaci (Gennadius) Biotype B (=B. argentifolii Perring & Bellows) on cotton plants to enable more accurate life tables to be constructed for this important insect pest. The survival of crawlers did not differ significantly between still-air and artificial wind treatments in the greenhouse and averaged 90% overall. Over 99% of all surviving crawlers settled on the abaxial surface of leaves and 99.9% settled on the leaf where eggs were oviposited. Out of 4125 nymphs only five settled on leaves other than the leaf of origin and they all moved to leaves lower on the plant. Assuming that these individuals crawled rather than fell, the mean distance moved was at least 200 mm. Using a combination of cohort-based life table studies to measure egg mortality and recruitment studies to measure egg to settled 1st instar mortality in the field, crawler survival was estimated to average 89.2% over three study sites in Phoenix in Maricopa, AZ. Overall results suggest that crawlers move very little on cotton and that survival of the crawler stage is relatively high under both greenhouse and field conditions. Generational mortality rates estimated from previous life table studies in the field that excluded crawler mortality would increase by only 0.8% with the addition of this minor mortality component. |
