L.C. Lewis

Late-Instar European Corn Borer (Lepidoptera: Crambidae) Tunneling and Survival in Transgenic Corn Hybrids

Abstract Field studies were conducted in 1996 and 1997 to determine injury by and survival of late-instar European corn borer, Ostrinia nubilalis (Hübner), on genetically altered Bacillus thuringiensis Berliner corn, Zea mays L. Cry1Ab events 176, Bt11, MON810, and MON802; Cry1Ac event DBT418; and Cry9C event CBH351 were evaluated. Plants of each corn hybrid were manually infested with two third-, fourth-, or fifth-instar O. nubilalis. Larvae were held in proximity to the internode of the plant above the ear with a mesh sleeve. Larvae were put on the plants during corn developmental stages V8, V16, R1, R3, R4, R5, and R6. This study shows that not all B. thuringiensis hybrids provide the same protection against O. nubilalis injury. Hybrids with B. thuringiensis events Bt11, MON810, MON802, and CHB351 effectively protected the corn against tunneling by late-instar O. nubilalis. Event 176 was effective in controlling late-instar O. nubilalis during V12 and V16 corn developmental stages; however, significant tunneling occurred by fourth instars during R3 and R5. Event DBT418 was not effective in controlling late-instar O. nubilalis during corn vegetative or reproductive stages of development. Whether the B. thuringiensis hybrids satisfied high- and ultrahigh-dose requirements is discussed.

Interaction of larval age and antibiotic on the susceptibility of three insect species to Bacillus thuringiensis

Abstract The addition of chlortetracycline hydrochloride to bioassay diets increased the LC50S of the HD-1 isolate of Bacillus thuringiensis 2.4–67.1 times when bioassayed against 4-day-old larvae of Trichoplusia ni, Heliothis virescens, and Ostrinia nubilalis. There were no significant differences in LC50 s when bioassays were conducted with neonate larvae in the presence or absence of antibiotic, nor were there any highly significant differences between the LC50 s for HD-1 when neonate larvae were used in the presence or absence of antibiotic or when 4-day-old larvae were used in the absence of antibiotic. Viable counts of B. thuringiensis did not increase over time in any of three bioassay diets. There were no differences in activity of pure chlortetracycline hydrochloride and veterinary grade Aureomycin. There was a direct correlation between amount of antibiotic and elevation of HD-1 LC50 s when 4-day-old larvae were used. LC50 elevation in presence of antibiotic first appeared in 2-day-old larvae.

Impact of Nosema pyrausta, Nosema sp., and a nuclear polyhedrosis virus on Lydella thompsoni within infected Ostrinia nubilalis hosts

Abstract The individual impact of two microsporidia and a nuclear polyhedrosis virus infection within larvae of the European corn borer, Ostrinia nubilalis , on a tachinid parasitoid, Lydella thompsoni , was studied. Nosema sp. primarily infected the Malpighian tubules and muscle tissue of the O. nubilalis hosts. Pupation of L. thompsoni from hosts infected with Nosema pyrausta or Nosema sp. and eclosion of adult L. thompsoni after development in N. pyrausta -infected hosts was not significantly (α = 0.05) reduced. However, no L. thompsoni were able to eclose as adults after development within Nosema sp.-infected O. nubilalis larvae. Infection of O. nubilalis larvae by a mint looper, Rachiplusia ou , nuclear polyhedrosis virus (Ro M NPV) did not significantly (α = 0.05) affect pupation or eclosion of L. thompsoni . Viral polyhedral inclusion bodies were found within the alimentary canal of L. thompsoni maggots within Ro M NPV-infected O. nubilalis hosts.

Effects of the microsporidium Nosema pyrausta (Microsporida: Nosematidae) on the egg parasitoid, Trichogramma nubilale (Hymenoptera: Trichogrammatidae)

Trichogramma nubilale developing in Nosema pyrausta-infected eggs of the European corn borer, Ostrinia nubilalis, were directly affected by the microsporidium. Microsporidian spores, which were confined to the gut lumen in the larval stage, were found in the adjacent tissues of the gut epithelium, muscle, and nervous system of the pupal and adult stages. This infection resulted in a significantly reduced adult emergence rate and fecundity of the parasitoid.

Toxic effects of spore/crystal ratios of Bacillus thuringiensis on European corn borer larvae

Abstract Bioassays to determine LC 50 values of spores and crystals of four varieties of Bacillus thuringiensis grown on nutrient agar plates were carried out against neonate and 6-day-old European corn borer, Ostrinia nubilalis , larvae. The four bacterial varieties were equally toxic against the neonates, but only B. thuringiensis var. kenyae , var. galleriae , and var. kurstaki were toxic to 6-day-old larvae. B. thuringiensis var. tolworthi was inactive against 6-day-old larvae. Different ratios of pure spores and crystals of the bacteria also were tested against neonate and 6-day-old larvae. Pure spores are not pathogenic to neonates or 6-day-old larvae. Pure crystals were toxic to both ages of the larvae, but a combination of spores and crystals was necessary for maximum larval mortality.

Histopathology of transovarial transmission of Nosema pyrausta in the European corn borer, Ostrinia nubilalis☆☆☆

Abstract Ostrinia nubilalis larvae, neonate to 5th instar, were exposed to 100, 200, 400, and 800 Nosema pyrausta spores/mm2 diet surface for 48 hr. Infections were evident in the reproductive tissues in all insects 7 days after exposure, regardless of the stadium in which and the dosages of spores to which the larvae were exposed. The microsporidian spores were found infecting the epithelial layers and stroma cells of the larval ovarian tissues. In larvae that had a more intense infection, the germ cells were also infected. The process of histolysis and histogenesis occurring during the pupal stage did not interfere with infection of the ovarian tissues. The microsporidian spores remained in the infected tissues, and infections progressed into adult reproductive tissues, where trophocytes and oocytes enveloped in follicles were infected. Consequently, these infections resulted in the transovarial transmission of the microsporidium.

Feeding deterrent response of corn insects to β-exotoxin of Bacillus thuringiensis☆☆☆

Abstract Exotoxins produced by three varieties of Bacillus thuringiensis were added at different concentrations to the diets of the black cutworm, the fall armyworm, the European corn borer, and the house fly. By day 7 of treatment, mortality of the three lepidopterans was higher at the lower concentrations of exotoxin than at the higher concentrations tested; by day 14 of treatment, mortality was 90% of greater at all the exotoxin concentrations tested. In the house fly tests, mortality increased with increasing exotoxin concentration. Additional lepidopteran tests were run to study both the anomalous effect of toxin concentration on mortality and the effect of feeding inhibition evident by day 7 but not day 14 in treatments with high concentrations of the toxins. The tests, run with the European corn borer and with β-exotoxin calcium salt, showed that both effects could be attributed to a “feeding deterrent” associated with the toxin, and that the deterrent was not odoriforous and did not degrade over time. Apparently, the insects ate very little of the diets high in exotoxin, stopping quickly upon receiving a high dosage of the deterrent, but, nevertheless, having consumed enough toxin to be killed over time (between 7 and 14 days).

Fungi associated with eggs and first-instar larvae of the European corn borer☆☆☆

Abstract Fungi isolated from field-collected egg masses of the European corn borer, Ostrinia nubilalis , were identified as Alternaria spp., A. porri, Fusarium spp., Fusarium oxysporum, Beauveria bassiana, Mucor spp., and an unidentified yeast. Most fungi were associated with predator injury to the egg mass. Bioassay of fungi on egg masses, however, showed that Alternaria spp. and A. porri reduced the hatch of both injured and uninjured egg masses, and Mucor sp. reduced the hatch only when the egg mass was injured.

Treatment of Ostrinia nubilalis larvae with Fumidil B to control infections caused by Perezia pyraustae

Abstract Fumidil B has the potential of substantially reducing the level of Perezia pyraustae infection in laboratory colonies of the European corn borer, Ostrinia nubilalis. Drug levels of 200 to 12,000 ppm of prepared diet significantly reduced the level of P. pyraustae infection. Higher levels (e.g., 12,000 ppm) tend to increase the time to pupation and reduce the pupal weights, whereas levels up to 1500 ppm do not severely affect time to pupation, pupal weights, percentage survival, or egg production. Levels up to 12,000 ppm improved all aspects of adult fecundity. Fumidil B can be added to the diet at a diet temperature of 71°C (160°F) at levels as low as 200 ppm and still significantly reduce the level of P. pyraustae infection.

Impact of Vairimorpha necatrix and Vairimorpha sp. (Microspora: Microsporida) on Bonnetia comta (Diptera: Tachinidae) within Agrotis ipsilon (Lepidoptera: Noctuidae) hosts☆☆☆

Abstract The effect of Vairimorpha necatrix and Vairimorpha sp. on Bonnetia comta developing within pathogen-treated black cutworm, Agrotis ipsilon , hosts was studied. Parasitism by B. comta did not interfere with the near 100% mortality of A. ipsilon caused by either Vairimorpha species. Both microsporidia decreased the number of B. comta able to pupate from a. ipsilon hosts, the days required for adult parasitoid eclosion, and the weights of the puparia. Only in the V. necatrix treatments, however, were these effects significant ( P Duncans (1955) multiple range test. The impact of each microsporidium on the parasitoid increased with an increase in the concentration of spores to which A. ipsilon was exposed. Both Vairimorpha species had a more detrimental effect on female B. comta than they did on male B. comta . Histological examination of B. comta maggots within V. necatrix - and Vairimorpha sp.-infected A. ipsilon showed the spores primarily restricted to the gut lumen. In older B. comta , dissected from dead Vairimorpha -infected hosts, the guts containing spores were much distended, some to the point that most other parasitoid tissues were absent. This suggests that the detrimental impact the host microsporidian infections had on the parasitoid were related to a nutritional deficiency caused by the accumulation of nondigestable spores in the parasitoids gut lumen.