Edaphic studies on the population biology of the lesser cornstalk borer (Elasmopalpus lignosellus (Zeller)

Abstract

The objective of this study was to elucidate edaphic factors that contribute to population outbreaks of the lesser cornstalk borer (LCB). Outbreaks of the LCB are favored in years of high temperature and low rainfall, and are correlated with soils possessing high infiltration rates and low soil water retention capacities. Soil water properties of a Padina sand, Norwood loam, and a Miller clay were determined to ascertain the effects on LCB population biology. Adult longevity was 9.0 days at 25(DEGREES)C and 83% RH, and decreased with increasing temperature. Longevity was prolonged at the highest % RH for each temperature tested. Fecundity averaged 62.9 eggs/female at 25(DEGREES)C, and 6.5 eggs/female at 35(DEGREES)C. Percent relative humidity had no significant effect on fecundity at the temperatures tested. There was an inverse linear relationship between fecundity and temperature, and no significant relationships between % RH (vapor pressure deficits) and fecundity. Higher temperature reduced the duration of the ovipositional period, and 83% RH (lower VPD's) prolonged the ovipositional period regardless of temperature. Egg survival was 83-98% in air dry soils, and decreased with increasing soil saturation. Egg survival was highest in saturated sand (82%), and decreased to 6-11% in saturated clay and loam. Larval behavior was altered by soil saturation in 1st and 2nd instar LCB larvae. Increased soil saturation increased the escape response and aerial plant feeding of 1st and 2nd instar larvae; while 3rd and 6th instar larvae remained subterranean with increasing soil saturation. Predation of 1st, 3rd, and 5th instar larvae, by the lygaeid bug, Geocoris punctipes, increased as subterranean response increased; while predation by the spiders, Oxyopes salticus and Pardosa pauxilla remained constant with increasing subterranean response. Insect parasitism of 4th instar LCB larvae by Orgilus elasmopalpi, increased with increasing subterranean response, and remained unchanged with Habrobracon gelechiae. Mortality due to soil innoculated with Entomopoxvirus inoculated soil decreased with increasing subterranean response for 1st, 3rd, and 5th instar larvae. Pupal survivorship was primarily dependent upon the depth of the pupa in the soil. Pupae left undisturbed exhibited 80-100% adult emergence with no significant effect of soil type or % soil saturation on pupal mortality. Pupal mortality increased to 95% in saturated soils if the position of the pupa in the soil was disturbed. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI