G. Michael Chippendale

Juvenile hormone titer determinations in the southwestern corn borer, Diatraea grandiosella, by electron capture-gas chromatography.

Abstract A procedure is described for analysis of the three known juvenile hormones (JHs) at physiological levels in 5–10 gram samples of insect hemolymph or whole bodies. The method employs conversion of the oxirane ring of the JHs to their respective 11-methoxy-10-pentafluorophenoxyacetate esters, allowing use of gas-liquid chromatography/electron capture detection for qualitative and quantitative analysis at picogram levels. The method is used to determine the JH titers of the southwestern corn borer, Diatraea grandiosella , as a function of developmental stage. The results show that diapausing larvae contain significant titers of all three known juvenile hormones, thereby supporting the theory that larval diapause in this species is under the control of the corpus allatum.

Effect of the ecdysone agonists, RH-2485 and tebufenozide, on the southwestern corn borer, Diatraea grandiosella

The effect of the ecdysone agonists RH-2485 (proposed name methoxyfenozide) and tebufenozide (RH-5992), was examined on eggs and larvae of the southwestern corn borer, Diatraea grandiosella Dyar. Both compounds exhibited a concentration-dependent ovicidal activity. More than 95% of eggs died when egg masses were dipped in solutions of 100 or 200 mg liter -1 of either compound in acetone + distilled water (1 + 1 by volume). Although some eggs treated with 1 or 10 mg liter -1 of the compounds hatched, the survival rate was low. Newly hatched larvae were fed for seven days on an artificial diet containing RH-2485 or tebufenozide. The LC 50 values were 0.049 mg kg -1 for RH-2485 and 0.185 mg kg -1 for tebufenozide, showing that RH-2485 was about four times more active than was tebufenozide. Although increasing the time of exposure to either compound decreased the LC 50 value significantly, the relative potency of RH-2485 versus tebufenozide was not changed. Newly ecdysed 4th-instar larvae fed with diets containing 0.125, 0.25 or 0.5 mg kg -1 RH-2485 or tebufenozide ceased feeding approximately 8 h after exposure, indicating that larvae had prematurely entered a molting cycle. Larvae treated with RH-2485 ecdysed earlier and died more quickly than those treated with tebufenozide. Ingestion of sublethal concentrations of RH-2485 (0.005 and 0.01 mg kg -1 ) or tebufenozide (0.03 and 0.06 mg kg -1 ) retarded larval growth, and decreased pupal weight and adult emergence. Increasing exposure time to tebufenozide tended to increase the larval mortality, significantly retarded larval growth, and decreased the mean weights of male and female pupae and adult emergence. RH-2485 (0.125 and 0.25 mg kg -1 ) and tebufenozide (0.25 and 0.5 mg kg -1 ) were lethal to newly hatched larvae, even after diets containing these compounds were held for 20 days at 30°C under long days (16 h light: 8 h dark). Our results suggest that field trials to assess the potential of RH-2485 and tebufenozide to control D. grandiosella are warranted.

INSECT DIAPAUSE, THE SEASONAL SYNCHRONIZATION OF LIFE CYCLES, AND MANAGEMENT STRATEGIES

Diapause permits insect survival under adverse climatic conditions and synchronizes the life cycles of individual insects within a population as welt as with their food supply. The question is addressed about how the state of diapause might be more fully exploited for insect control than it is at present. Methods currently used and new approaches that might be developed to disrupt the seasonal synchronization and diapause of plant‐feeding insects are discussed. For example, the agronomic practices of carefully timed planting dates, use of early maturing varieties, and the destruction of crop residues are well‐established methods for suppressing populations of pest insects on many crops. In contrast, the possibility of disrupting insect diapause through, for example, the use of non‐diapausing strains, seasonally inappropriate environmental cues, or hormones or antihormones requires much additional research. Although the ecological, physiological, and endocrinological aspects of insect diapause have received much study, practical methods have yet to be developed to interfere with the programming of diapause. Using the larval diapause of the southwestern corn borer, Diatraea grandiosella, and the adult diapause of the Colorado potato beetle, Leptinotarsa decemlineata, as examples, some aspects of research into diapause are reviewed. Included is a discussion of the role of temperature cycles, the titre and function of juvenile hormone, and the role of some animo acids present in high titre in the haemolymph. Several areas requiring further research are suggested.

Establishment and characterization of an Ostrinia nubilalis cell line, and its response to ecdysone agonists.

SummaryA cell line derived from embryonic tissues of the European corn borer, Ostrinia nubilalis (UMC-OnE), was established in EX-CELL 401 medium containing 10% fetal bovine serum. The cells grew in suspension, and were mainly spherical in shape. The cell doubling times at the 17th and 79th passages were 56 and 36 h, respectively. DNA amplification fingerprinting showed that the DNA profile of the OnE cell line was different from that of the southwestern corn borer, Diatraea grandiosella (UMC-DgE), and that of the cotton bollworm, Helicoverpa zea (BCIRL-HZ-AM1). The OnE cell line was responsive to treatments of 20-hydroxyecdysone and the ecdysone agonists, methoxyfenozide (RH-2485) and tebufenozide (RH-5992). These compounds caused similar effects on the cells, which included cell clumping and decreased cell proliferation. The clumps were observed on the third day of incubation, and became larger after 7 d of incubation. After 168 h of incubation, methoxyfenozide and tebufenozide were 35 and 11 times more effective, respectively, in inhibiting proliferation of the OnE cells than was 20-hydroxyecdysone.

Characteristics of apolipophorin-III of the southwestern corn borer, Diatraea grandiosella

Abstract Apolipophorin-III was isolated from the lipophorin-free fraction of larval plasma of the southwestern corn borer, Diatraea grandiosella , because significant amounts of apolipophorin-III were found to be present in the hemolymph not associated with lipophorin. Apolipophorin-III, purified using ammonium sulfate precipitation, cation exchange chromatography, and gel filtration, was shown to be a nonglycosylated polypeptide with 17 kDa mol. wt, as determined by SDS-PAGE and silver staining. The amino acid composition of apolipophorin-III showed similarities to published compositions of apolipophorin-III isolated from other insects. The N-terminal sequence of apolipophorin-III (DAPSTTPPQDXEKKAAEFQKTFTEQXNQLANK), is highly homologous to that of apolipophorin-III of Manduca sexta . Antiserum raised against purified apolipophorin-III was used to demonstrate an immunochemical identity between the isolated apolipophorin-III and that associated with lipophorin. This antiserum cross-reacted with apolipophorin-III of M. sexta , and antiserum raised against M. sexta apolipophorin-III cross-reacted with apolipophorin-III isolated from D. grandiosella , demonstrating an immunochemical relationship between the proteins, and providing confirmatory evidence for the identity of the isolated protein. These antisera did not react with the putative apolipophorin-III of the cricket, Acheta domesticus . Using immunoprecipitation by the apolipophorin-III antiserum of D. grandiosella , the synthesis and secretion of [ 3 H]apolipophorin-III by the fat body in vitro was shown to be maximal in 13–15 day-old larvae, with a transit time of ca 23 min.

Effect of the ecdysone agonists, methoxyfenozide and tebufenozide, on the lady beetle, Coleomegilla maculata

Andi Trisyono1,2, Benjamin Puttler 1 & G. Michael Chippendale 1,∗ 1Department of Entomology, 1-87 Agriculture Building, University of Missouri Columbia, MO 65211, USA; 2Current address: Department of Entomology and Plant Pathology, Faculty of Agriculture, University of Gadjah Mada, Yogyakarta 55281, Indonesia ∗Author for correspondence (Phone: 573-882-7488; Fax: 573-882-1469; E-mail:chippendaleg@missouri.edu)

Relationship between dietary lipids, midgut lipids, and lipid absorption in eight species of Lepidoptera reared on artificial and natural diets

Abstract Lipids present in the diet, midgut lumen, and midgut tissue were analyzed by thin-layer chromatography in larvae of eight species of Lepidoptera representing three families. Pieris brassicae reared on Brassica oleracea, Heliothis zea , reared on Zea mays , and Anticarsia gemmatilis , reared on Glycine max , were found to digest leaf galactosyl diglycerides, phosphatidylcholines, and phosphatidylglycerols. Triacylglycerols were present as minor lipids in these diets. During digestion of leaf lipids, several polar lipids accumulated in the midgut lumen of P. brassicae , but only trace amounts were observed in the midgut lumen of the other species examined. Midgut tissue lipids of all species were relatively similar, but species differences were observed in the synthesis of some lipids in midgut tissue. Although little esterification of sterols occurred in the midgut tissue of P. brassicae , sterol esters were prominent in the midgut of H. zea, H. subflexa and Diatraea grandiosella . Among the midgut tissue lipids of P. brassicae , triacylglycerols were found to have the most rapid turnover rate, suggesting that triacylglycerols have a critical role in the transfer of lipid across the gut wall.

In vitro synthesis and secretion of lipophorin by the fat body of nondiapause and prediapause larvae of the southwestern corn borer, Diatraea grandiosella.

Abstract The capacity of the fat body of nondiapause, prediapause and diapause larvae of the southwestern corn borer, Diatraea gradiosella , to synthesize and release lipophorin was examined in vitro using [ 3 H]leucine as the radiotracer. Synthesis and release of [ 3 H]lipophorin by the fat body peaked in 11–13 day-old fifth instar nondiapause larvae, which coincided with their feeding period. The rate of lipophorin synthesis in the fat body of newly ecdysed pupae was extremely low. Synthesis and release of [ 3 H]lipophorin by the fat body of prediapause larvae occurred at the highest rates in 20–35 day-old fifth and sixth instars, and declined to virtually undetectable levels after larvae entered diapause around 40 days-of-age. Immunoprecipitation of [ 3 H]lipophorin from fat body of 13 day-old nondiapause larvae that had been pulse-labeled with [ 3 H]leucine showed that the half life of lipophorin synthesis and processing was about 40 minutes. Release of total protein and lipophorin from the fat body of 13 day-old nondiapause larvae into Graces medium was inhibited by 56 and 60%, respectively, when 10 μg/ml tunicamycin was incorporated into medium.

In vitro release of lipophorin from the fat body of nondiapause and diapause larvae of the Southwestern corn borer, Diatraea grandiosella

The release of lipophorin and total protein was examined from the fat body of nondiapause and diapause larvae of the southwestern corn borer, Diatraea grandiosella, incubated in vitro in Graces medium. The characteristics of the released lipophorin were compared to those of the high-density lipophorin present in the hemolymph of nondiapause and diapause larvae. Over a 4 h incubation period, the fat body of nondiapause larvae released about 1.5 times more total protein and 2 times more lipophorin per mg dry weight than did that of diapause larvae. Lipophorin isolated from the medium in which fat bodies of nondiapause and diapause larvae had been incubated and from the plasma of nondiapause and diapause larvae had similar mean densities of 1.115, 1.112, 1.117 and 1.119 g/ml, respectively. Although the lipid classes detected in lipophorin isolated from the fat body incubation medium and hemolymph were identical, more polar lipids and less diacylglycerol were associated with lipophorin isolated from fat body incubation medium then were associated with lipophorin isolated from the hemolymph. Sterols accounted for about 11% of the total lipids of lipophorin isolated from the fat body incubation medium, whereas they accounted for about 20% of the total lipids of lipophorin from hemolymph. We conclude that the fat body of feeding nondiapause larvae and nonfeeding diapause larvae releases high-density lipophorin.

Effect of a hypolipidemic agent on the growth and development of the southwestern corn borer, Diatraea grandiosella

Abstract The hypolipidemic agent, 5-tetradecyloxy-2-furanocarboxylic acid (TOFA), blocks acetyl-CoA carboxylase, the rate-limiting step in the synthesis of fatty acids. We examined the effect of dietary TOFA on larval growth and development of the southwestern corn borer, Diatraea grandiosella . Dietary levels of 200 and 300 ppm TOFA (wet wt) suppressed both growth and development. A reciprocal transfer experiment using the control and a 300-ppm TOFA diet showed that TOFA must be ingested throughout the larvae period to have a deleterious effect. TOFA holds promise as a tool when a block in fatty acid synthesis will add insight into insect lipid transport, use or metabolism.