Role of antioxidant defense during different stages of preadult life cycle in European corn borer (Ostrinia nubilalis, Hubn.): Diapause and metamorphosis

Antioxidant enzymes, total glutathione (GSH), and ascorbic acid (ASA) were determined in whole body homogenates of nondiapausing larvae, diapausing larvae during the diapausing period (October, December, and February), and in pupae emerged from both diapausing and nondiapausing larvae of the European corn borer (Ostrinia nubilalis, Hubn., Lepidoptera: Pyralidae). The activities of catalase, selenium nondependent glutathione peroxidase (GPx), and glutathione-S-transferase (GST), as well as the content of GSH and ASA, were found to vary throughout the larval diapause. Compared to diapausing larvae, nondiapausing larvae were higher in levels of catalase, GPx, GST, and dehydroascorbate reductase (DHAR) activity. GSH content was also increased. However, nondiapausing larvae contained less ASA than diapausing ones. Pupae had higher GPx and GST activity and an increased ASA content compared to larvae. The pupae emerged from nondiapausing larvae had higher GST, glutathione reductase (GR), and DHAR activities, but lower GPx activity and ASA content than those emerged from diapausing larvae. Correlation analysis revealed differences in the way the antioxidant level is equilibrated for a particular stage and developmental pattern. The results suggest that cellular antioxidants are involved in both the protection of cells and the regulation of redox levels during the pre-adult stages of Ostrinia nubilalis. Arch. Insect Biochem. Physiol. 55:79-89, 2004.     

Host age and host selection byTrichogramma nubilale

Selection byTrichogramma nubilale (Ertle & Davis) for different aged egg masses ofOstrinia nubilalis (Hübner) was examined by separating components of parasitism. FemaleT. nubilale were exposed to egg masses of 2 different ages (freshly laid egg masses versus 1, 2, 3 or 4 day old egg masses), and the age of the initial egg mass inspected, number and percent of eggs and egg masses parasitized, and the emergence rate of pharate parasitoids was recorded. When there was a large difference in age between young and old egg masses, ♀♀ inspected initially more young egg masses (>2 days difference), parasitized a greater percent of young egg masses (>2 days difference), and parasitized more eggs/parasitized egg mass in young egg masses (>3 days difference) than old egg masses. Females did not discriminate between host age when hosts were similar in age. Successful emergence of parasitoids was greater from younger eggs than older eggs, although emergence was better from one-day-old eggs than from fresh eggs. These results imply that when the hosts were sufficiently different in age, ♀♀ were attracted to younger egg masses more than older egg masses, and they tended to remain ovipositing for longer periods of time on younger egg masses than older egg masses. Moreover, ♀♀ appeared to prefer to oviposit in hosts in which their young are more likely to complete development.      

<Emphasis Type="Italic">Trichogramma Brassicae</Emphasis> and SLAM<Superscript>®</Superscript>, an Integrated Approach to Managing European Corn Borer and Corn Rootworms

European corn borer, Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae); western corn rootworm (WCRW), Diabrotica virgifera virgifera LeConte; and northern corn rootworm (NCRW), Diabrotica barberi (Smith & Lawrence) (Coleoptera: Chrysomelidae) are important pests of corn, Zea mays L., that occur simultaneously in the US Corn Belt. Areawide management strategies for northern and western corn rootworm in Iowa, Kansas, South Dakota, Illinois, and Indiana, and for the Mexican strain in Texas, use SLAM^®, which contains cucurbitacin, a feeding stimulant, and a small amount of the insecticide carbaryl. This management strategy is environmentally sound because it introduces a substantially lesser amount of chemical insecticide into the environment than prophylactic soil insecticide applications for WCRW management. To develop a management program for both corn pests, the compatibility of SLAM^® to control CRW, along with a biological agent to manage European corn borer, was investigated. Laboratory studies were conducted using the egg parasitoid Trichogramma brassicae (Bezdenko) (Hymenoptera: Trichogrammatidae). In experiments in which SLAM^® and T. brassicae were evaluated as components of a management system, SLAM^® did not affect parasitism or parasitoid emergence rates. Trichogramma brassicae displayed vigorous biotic fitness, emergence rates, sex ratios, and fecundity over the duration of the study. Data collected under these laboratory conditions indicated that SLAM^® had no adverse effect on the quality of T. brassicae, indicated by its ability to reproduce in the filial generation.     

Genetic structure and gene flow among European corn borer populations from the Great Plains to the Appalachians of North America

• 1 Earlier population genetic spatial analysis of European corn borer Ostrinia nubilalis (Hübner) indicated no genetic differentiation even between locations separated by 720 km. This result suggests either high dispersal resulting in high gene flow or that populations are not in migration–drift equilibrium subsequent to their invasion of the central U.S.A. in the 1940s.
• 2 To discriminate among these two possibilities, samples were collected at 12 locations in eight states from New York to Colorado, a geographic scale that is three‐fold greater than previously tested. Eight microsatellite markers were employed to estimate genetic differentiation and gene flow among these populations, and to test for isolation‐by‐distance.
• 3 Although pairwise F_ST estimates were very low, there was a significant isolation‐by‐distance relationship.
• 4 Wright's neighbourhood area (i.e. the surface area covered by a panmictic group of individuals within a larger continuous distribution) was calculated as 433 km², and the radius indicates that approximately 13% of O. nubilalis adults disperse a net distance >12 km per generation from their natal source.
• 5 Analyses indicated significant differentiation between the north‐eastern region (New York and Pennsylvania) and the region combining sample locations from Ohio to Colorado, suggesting the potential for isolation of populations by topographic barriers in the Northeast.
• 6 Taken together, the results suggest that O. nubilalis exhibits substantial gene flow over long distances and that the lack of genetic differentiation between populations across hundreds of kilometres is not simply a result of migration–drift disequilibrium arising from the recent range expansion.

     

Field observations of Ostrinia nubilalis eclosion and post‐eclosion activity of females around their natal plants

Abstract The early part of the post‐eclosion, pre‐mating period were examined under field conditions for Ostrinia nubilalis. Post‐eclosion behavior of 25 and 21 females during the first and second flight periods were observed until they left their natal site. Summer generation larvae were reared under field conditions and the timing of adult eclosion was observed. Eclosion occurred at two times during the day, peaking before dawn and before dusk; 46% of females and 56% of males eclosed during the morning period and the rest eclosed during the evening period. After eclosion, females spent 30–60 min expanding their wings. Their typical behavior was to remain calmly on their natal site. None of the females exhibited calling behavior before leaving. All females left their natal sites sometime before dawn. The probability of leaving increased with time. Leaving rates were not significantly different between females of the first and second flight. These field observations indicate that females have several possibilities for pre‐mating movement, which might allow females to move out from their natal field before mating. In addition, we also discuss the influence of pre‐mating movements in relation to the rate of Bacillus thuringiensis (Bt) resistance evolution.