Hong Sun Kim

Some Biochemical Evidence on the Selective Insecticide Toxicity between the Two Aphids, Aphis citricola and Myzus malisuctus (Homoptera: Phididae), and Their Predator, Harmonia axyridis (Coleoptera: Coccinellidae)

Abstract This experiment was carried out to compare the differences in biochemical enzyme activity on the selective insecticide toxicity between the two species of aphid, Aphis citricola van der Goot and Myzus malisuctus Matsumura, and their predator, Harmonia axyridis Pallas. Esterase activities between the two species of aphids and between the two stages of H. axyridis were significant different. Glutathione S-traasferase (GST) activity toward 1-chloro-2, 4-dinitrobenzene (CDNB) was much higher than 1, 2-dichloro-4-nirobenzene (DCNB) in all species tested. No DCNB conjugation was detected in A. citricola and M. malisuctus. The predator, H. axyridis, had much higher GST activity than the preys, A. citricola and M. malisuctus. GST activity toward CDNB in H. axyridis adult was highest, even 6.2-fold higher activity than H. axyridis larva. M. malisuctus had much higher GST activity than A. citricola. The degree of acetylcholinesterase (AChE) inhibition by phosphamidon among all three species tested was significantly varied. The concentration of phosphamidon required for 50% AChE inhibition was lowest in H. axyridis larva, while highest in M. malisuctus. There fore, elevated GST activity and target-site insensitivity may be largely associated with the differential susceptibility between larva and adult of H. axyridis. However, differential susceptibility between A. citricola and M. malisuctus may be due to other various biochemical mechanisms responsible for the multiple selective toxicity, including elevated GST activity and target-site insensitivity.

Insecticide Resistance in the Tobacco Cutworm, Spodoptera litura (Fabricius) (Lepidoptera: Noctuiae)

Abstract Field populations of the tobacco cutworm, Spodoptera litura (Fabricius), showed resistance to commonly used insecticides. Development of resistance in the field populations to pyrethroids (cypermethrin, deltamethrin, ethofenprox, ethofenprox+PAP and fenvalerate) ranged from 100- to 2,700-fold, showing the highest resistance level to deltamethrin. Resistance to organophosphorus insecticides (chlorpyrifos, chlorpyrifos-methyl, EPN and pyraclofos) ranged from 2- to 32-fold with the highest level to chlorpyrifos. Resistance to carbamates (carbaryl and methomyl) ranged from 4- to 80-fold with the higher level to carbaryl. Detoxifying enzyme assays revealed that esterase and glutathione S-transferase activities were varied from 2- to 6-fold among the field populations. In addition, the bimolecular rate constants for inhibition of acetylcholinesterase by dichlorvos, eserine and monocrotophos showed 1.5-, 4.5- and 4.3-fold differences, respectively, between two different field populations. These results indicated that the broad spectrum of insecticide resistance observed in the filed populations was due to multiple resistance mechanisms, including increased detoxification of these insecticides and insensitive acetyl-cholinesterase.

Electrophoretic Pattern of Larval Esterases in Field and Laboratory-selected Strains of the Tobacco Cutworm, Spodoptera litura (Fabricius)

Abstract This research was performed to find out and characterize the specific esterase isozymes related to OP and pyrethroid resistance in the tobacco cutworm Spodoptera litura (Fabricius). Two laboratory strains (DSR5 and CSR4) of S. litura, selected with deltamethrin and chlorpyrifos-methyl, had higher larval esterase activities than Hamancollected (HC) strain. Ten esterase isozymes were separated in the wild HC strain on 6.5% nondenaturing polyacrylamide gel electrophoresis (pH 8.3), but only 5 of them were detected in the two strains selected with insecticides. The isozymes were designated from E1 to E10 according to their mobility to cathode. E4 was stained more strongly in both laboratory-selected strains than in HC strain. The frequency of E2 in DSR5 strain was higher than in HC strain. E2 and E4 were proved to be arylesterase and carboxyesterase, respectively, according to enzyme inhibition tests. Thus decreased number and increased intensity of esterase bands in DSR5 and CSR4 strain may be associated with insecticide resistance, resulting from selections successively with insecticides for several generations.

Cellular immune responses and FAD‐glucose dehydrogenase activity of Mamestra brassicae (Lepidoptera: Noctuidae) challenged with three species of entomopathogenic fungi

Abstract.  Cellular immune responses and glucose dehydrogenase activity are examined in the larvae of Mamestra brassicae (Lepidoptera: Noctuidae) injected with three entomopathogenic fungi, Beauveria bassiana, Nomuraea rileyi and Paecilomyces tenuipes. Total haemocyte count and the number of spherulocytes increase significantly over 2 h in larvae infected with N. rileyi, the most virulent fungal pathogen of M. brassicae. However, glucose dehydrogenase is not activated in the haemolymph of larvae inoculated with N. rileyi. By contrast, P. tenuipes, the least virulent fungal species, but with the highest proteolytic activity, activates glucose dehydrogenase and the number of nodules formed is significantly larger in larvae inoculated with P. tenuipes. It is suggested that the different virulence of each fungal species is caused by specific immune responses in the larvae. Haemopoiesis is affected by the fungal conidia and this is investigated by culture of the haemopoietic organs of M. brassicae in vitro. The proportion of spherulocytes discharged from the organs is typically high after all of the fungal treatments. In addition, the anterior and posterior haemopoietic organs, according to the histological locations in larva, show different patterns of haemopoiesis in response to fungi.

Induction and Termination of the Reproductive Diapause in the Minute Pirate Bug Onus strigicollis Poppius (Hemiptera: Anthocoridae)

Abstract This study was carried out to investigate the effect of the photoperiod and temperature on the reproductive diapause in Orius strigicollis. The photo-period and temperature affected nymphal development, adult longevity, diapause induction, and diapause termination in O. strigicollis. At 18 °C, nymphs developed significantly faster at a photoperiod of 8:16 (L:D) h than at a 12:12 (L:D) h. When kept at 15°C and 9:15 (L:D) h continuously from the 2nd instars, the longevity of adult O. strigicollis was much shorter than that from the 4th instars, but their longevity was not different between the genders. At 18°C, when continuously kept under short photoperiod from the first three nymph stages, 100% of adults entered the reproductive diapause within 40 days after adult eclosion. From the 1st to 3rd instars, O. strigicollis displayed a long-day response with a critical photoperiod between 12 h and 14 h at 18°C within 20 days after adult eclosion. When continuously kept at 15°C and 18°C with a 9:15 (L:D) h photoregime from the 2nd instars, all females entered the reproductive diapasue, while the diapause incidence at 20 °C and 25 °C was quite low even within 20 days after adult eclosion. No diapause incidence was found when only the egg or the first three nymph stages were kept at 18°C and 8:16 (L:D) h, while the later two nymph stages showed a slight increase in diapause incidence. Combined exposure from the nymph to adult stages to 18°C and 8:16 (L:D) h is necessary to attain 100% of diapause incidence. Diapause in O. strigicollis was terminated rapidly as long photoperiod and/or lower temperature was treated.

Cold Hardiness of Diapausing Rice Stem Borer, Chilo suppressalis Walker (Lepidoptera: Pyralidae)

Abstract This study was carried out to investigate the supercooling point (SCP), cold hardiness, and content of glycerol in the rice stem borer, Chilo suppressalis , larvae field-collected at different dates to understand the relationship between diapause and cold hardiness. Field-collected C. suppressalis larvae became cold-hardy from late autumn and higher level of survival was maintained from October to April. Lab-reared C. suppressalis larvae pre-treated at 0°C for 1 h or 2 h enhanced their survival to low temperature (-10°C). The SCP of C. suppressalis larvae changed seasonally, with dramatic decrease toward February and then drastic increase again from March onwards. The osmolality and protein content of field-collected C. suppressalis larvae showed their peak in January, and then dramatically declined afterwards. Overwintering C. suppressalis larvae have the ability to accumulate glycerol. Higher osmolality may be closely linked to lower SCP. This lower SCP probably develops a high level of cold hardiness during diapause development. The thermal hysteresis activity of C. suppressalis larva field-collected increased gradually to 12.7± 1.6°C in January, and then gradually declined afterwards. It can be recognized that field-collected C. suppressalis larvae have the thermal hysteresis proteins. Diapause- induced C. suppressalis larvae (kept at 15°C under a photo-period of 10L: 14D h) enhanced a significantly higher survival and osmolality. In diapause-destined C. suppressalis , therefore, increased cold tolerance can be linked to the diapausing state itself.

Effect of the Juvenile Hormone Analog, Fenoxycarb on Termination of Reproductive Diapause in Scotinophara lurida (Burmeister) (Heteroptera: Pentatomidae)

Abstract This study was carried out to investigate a role of the juvenile hormone analog, fenoxycarb (FC) in terminating the reproductive diapause in the black rice bug, Scotinophara lurida (Burmeister) (Heteroptera: Pentatomidae). FC-treated adults collected at different dates developed their ovaries sooner than untreated ones. Topical application of FC accelerated diapause termination of field-collected S. lurida in which FC-treated adults exhibited early oviposition. In FC-treated males, development of their accessory glands and testes accelerated appeared to be prompted. These results suggest that various physiological overwintering traits related to diapause in this species may in part be under gonadotrophic endocrine control.

Toxicity of Insecticides and Metabolism of Deltamethrin in Helicoverpa assulta Guenéee and Spodoptera litura Fabricius

This experiment was carried out to evaluate the effects of synergists on toxicity of deltamethrin and to investigate the pharmacokinetics of deltamethrin in Helicoverpa assulta Gueneee and Spodoptera litura Fabricius. Susceptibilities of H. assulta and Haman-collected S. litura to 7 insecticides revealed different responses between the 2 species. The different susceptibility of the 2 species to deltamethrin was correlated with the differences in the penetration and metabolism. Larvae of H. assulta pretreated with synergists (piperonyl butoxide (PB), S-benzyl-O, O-diisopropyl phosphorothioate (IBP), and diethyl maleate (DM) were more sensitive to deltamethrin, with the highest synergism ratio (SR = 6.8) being observed with PB. Significant differences in synergism among synergists were not observed. For S. litura, the highest SR(=8.8) was observed with PB. At all time periods, the penetration of 14C-deltamethrin was relatively faster to S. litura than to H. assulta. Time (hrs) required for 20% (t20) of the applied doses to be excreted from treated S. litura was 1.5-fold faster than that of H. assulta. Higher synergism and longer retention in larval body of S. litura by the addition of PB suggest that the mixed function oxidase be a major factor in detoxification of deltamethrin. The combined use of PB with deltamethrin, and possibly other pyrethroids, might indicate a potential for controlling field populations resistant to deltamethrin and other pyrethroids.

Effect of a JH Analog, Fenoxycarb, on Egg Development of Scotinophara lurida (Burmeistetr)

Abstract This study was carried out to investigate an effect of a juvenile hormone (JH) analog, fenoxycarb (FC), on egg development of the black rice bug, Scotinophara lurida (Burmeister). FC-treated S. lurida females could oviposit significantly earlier and more eggs than the untreated control. This gonadotropic effect of the JH analog followed a dose-dependent manner with a maximum over 200 μg doses per adult. Though developmental period of live eggs laid from the FC-treated females was not significantly different from the control, the FC treatment gave significantly adverse effects on the following embryonic development of S. lurida.