The use of meconia to nondestructively detect sublethal infections in heliothines (Lepidoptera: Noctuidae).

The utility of using meconia to nondestructively detect entomopathogens of lepidopterous heliothines was examined. Early-instar tobacco budworm [Heliothis virescens (F.)] or cotton bollworm [Helicoverpa zea (Boddie)] larvae were inoculated with cytoplasmic polyhedrosis virus (CPV), Serratia marcescens Bizio, or Nosema heliothidis Lutz and Splendor, and the presence of each of the entomopathogens in adults and the meconia discharged during adult eclosion was determined. As the dose of CPV occlusion bodies and N. heliothidis spores but not S. marcescens cells ingested by larvae increased, a greater number of both adults and meconia were infested with the entomopathogens. For all three entomopathogens, no difference was observed between males and females for any of the parameters tested. The accuracy of the meconium method for predicting the presence of the entomopathogens in the adults (i.e., number of individuals in which meconia and adults were both positive, or meconia and adults were both negative) was > or = 92% for CPV, and > or = 79% for S. marcescens and N. heliothidis. Very few false negative predictions (i.e., the meconium was negative but the adult was positive) were observed for CPV (< or = 1%). The prevalence of false negative predictions ranged from 2 to 9%, and 5 to 21% for S. marcescens and N. heliothidis, respectively. The prevalence of false positive predictions (i.e., the meconium was positive but the adult was negative) was < or = 7% for CPV, < or = 13% for S. marcescens, and 0% for N. heliothidis. The results of this study demonstrate that although not absolute, the meconium method will be an efficacious method to detect nondestructively entomopathogens causing sublethal infections in heliothines, and possibly other insects, and thereby facilitate the rearing of specific pathogen free insects.

Activity and Persistence of Steinernema carpocapsae and Spodoptera exigua Nuclear Polyhedrosis Virus against S. exigua Larvae on Soybean.

Experiments were conducted to assess the effects of the entomopathogenic nematode Steinernema carpocapsae and Spodoptera exigua multinucleocapsid nuclear polyhedrosis virus (SeMNPV), alone and in combinations, on mortality of the beet armyworm, S. exigua, larvae on soybean. In 1991 tests, field-grown soybean plants were treated with S. carpocapsae at 0.3 and 0.6 nematodes/cm(2) of leaflet, SeMNPV at 20 and 40 polyhedral inclusion bodies (PIB)/cm(2), and all possible combinations. Treated leaflets were collected from plants and bioassayed with 5-day-old larvae. The combination of S. carpocapsae at 0.6 nematodes/cm(2) + SeMNPV at 40 PIB/cm(2) produced significantly higher larval mortality (61.7%) compared with either S. carpocapsae (24.8-35.1%) or SeMNPV (26.5-33.7%) alone. In 1992, similar tests were repeated using S. carpocapsae at 0.2 and 0.5 nematodes/cm(2), and SeMNPV at 14 and 35 PIB/cm(2). The combination of 0.5 nematodes/cm(2) + 35 PIB/cm(2) resulted in significantly higher larval mortality (64.0%) than either pathogen alone (41.5-49.0%). Steinernema carpocapsae and SeMNPV produced additive effects on beet arlnyworm mortality. Persistence of S. carpocapsae was 12-24 hours and SeMNPV was 96-120 hours on soybean.

Susceptibility of Periplaneta brunnea (Dictyoptera: Blattidae) to the nematode Steinernema carpocapsae (Rhabditida: Steinernematidae).

Brown cockroaches, Periplaneta brunnea Burmeister, were exposed to increasing population densities of the entomogenous nematode, Steinernema carpocapsae (Weiser), All Strains. A total of 160 adult cockroaches were used, 40 for each of four treatments: 0, 3,000, 30,000, and 300,000 infective juveniles added to 50 cm3 of sand. Population densities of 30,000 and 300,000 infective juveniles per 50 cm3 sand were the most effective treatments, killing 55% of the P. brunnea. The highest population density of nematodes, 300,000 infective juveniles per 50 cm3 sand, killed 93% of the P. brunnea, and produced a more rapid mortality when compared with other population densities.

Residual quantities of streptomycin sulfate in haemolymph and tissue of Heliothis virescens reared on treated diet.

The study showed that streptomycin sulfate was present in both tissue and blood of insects fed with the antibiotic-treated diet. Changes from larval to pupal to adult stages were accompanied by decreases in antibiotic concentration. During transformation from pupa to adult most of the antibiotic was discarded with the meconium. Eggs from adults reared from larvae fed on the antibiotic-treated diet were free of streptomycin. The antibiotic did not adversely affect insect development.

Effect of tetracycline hydrochloride on the physical and chemical properties of Heliothis virescens larvae.

The effects of various levels of tetracycline hydrochloride on the feeding habits, larval growth, and the metabolism of lipids, carbohydrates and proteins of Heliothis virescens were studied. Regression analysis showed that larval weight, fatty acids and glycogen decreased exponentially with increasing concentration of antibiotic, whereas protein showed a linear decrease. Larval feeding was initially decreased when antibiotics were added to the diet but there was no difference after 24 hr.