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

Abstract

The pink bollworm, Pectinophora gossypiella (Saunders), remains a significant pest of cotton (Gossypium spp.) in the southwestern United States, but is not known to be established in the primary cotton production areas of the southeastern United States. Absence of P. gossypiella may be the result of federal regulatory action (e.g., 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 southeastern United States might affect mortality of diapausing, preconditioned, and nondiapausing larvae of P. gossypiella. In constant temperature incubators set between 22 and 5°C (0% moisture, 0:24 [L:D] h), nondiapausing prepupal (fourth or fifth instar) larvae died more quickly at lower temperatures. At 5°C, 90% of the cohort was dead after 12 d. Similarly, prepupal larvae that had been reared under diapause inducing conditions (20°C, 10:14 [L:D] h) since neonate stage also died more quickly at lower temperatures. A separate developmental assay indicated that the larvae were not in diapause. In this case, 26 d at 5°C were required to achieve 90% mortality. For diapausing, prepupal larvae collected from the field, mortality was greatel at 5°C than at any other temperature tested, but larvae could withstand 5°C for 60 d before 90% of the cohort died. In response to moisture, as soils at 10°C became saturated (>195% gravimetric soil moisture), most diapausing larvae (≃60%) died within the first 10 d of the experiment. These studies suggest that diapausing, late instar larvae of P. gossypiella are more resilient to the effects of low temperature than nondiapausing individuals and are able to tolerate high soil moisture for moderate lengths of time. Temperatures and soil moistures in the southeastern United States are not sufficiently cold or wet to completely preclude establishment of P. gossypiella.