Implications of larval mortality at low temperatures and high soil moistures for establishment of pink bollworm (Lepidoptera : Gelechiidae) in southeastern United States cotton

The pink bollworm, Pectinophora gossypiella (Saunders), remains a significa nt pest of cotton (Gossypium spp.) in the southwestern United States, but i s not known to he established in the primary cotton production areas of the southeastern United States. Absence of P. gossypiella may. be the result o f federal regulatory action (eg, monitoring, quarantine, and eradication), climate, or other ecological factors. The objectives of this study were to determine how low temperatures; and high soil moisture common to the southe astern United States might affect mortality of diapausing, preconditioned, and nondiapausing larvae of P. gossypiella. In constant temperature incubat ors set between 22 and 5 degreesC (0% moisture, 0:24 [L:D] h), nondiapausin g prepupal (fourth or fifth instar) larvae died more quickly at lower tempe ratures. At 5 degreesC, 90% of the cohort was dead after 12 d. Similarly, p repupal larvae that had been reared under diapause inducing conditions (20 degreesC, 10:14 [L:D] h) since neonate stage also died more quickly at lowe r temperatures. A separate developmental assay indicated that the larvae we re not in diapause. In this case, 26 d at 5 degreesC were required to achie ve 90% mortality. For diapausing, prepupal larvae collected from the field, mortality was greater at 5 degreesC than at any other temperature tested, but larvae could withstand 5 degreesC for 60 d before 90% of the cohort die d. In response to moisture, as soils at 10 degreesC became saturated ( >195 % gravimetric soil moisture), most diapausing larvae (approximate to 60%) d ied within the first 10 d of the experiment. These studies suggest that dia pausing, late instar larvae of P. gossypiella are more resilient to the eff ects of low temperature than nondiapausing individuals and are able to tole rate high soil moisture for moderate lengths of time. Temperatures and soil moistures in the southeastern United States are not sufficiently cold or w et to completely preclude establishment of P. gossypiella.