Responses of Detoxifying, Antioxidant and Digestive Enzyme Activities to Host Shift of Bemisia tabaci (Hemiptera: Aleyrodidae)

The polyphagous B-biotype of Bemisia tabaci （Gennadius） has demonstrated a high capacity to adapt to numerous hosts from diverse plant families. To illustrate induced responses by the host plant, biochemical research on eight plant-insect interaction correlative enzymes, representing detoxifying, antioxidant and digestive pathways, were investigated. Transferring whitefly adults to Zhongmian 23 from the pre-adapted host Zhongmian 41 induced activities of carboxylesterase （by 1.80-fold）, glutathione S-transferase （by 3.79-fold）, proteinase （by 1.62-fold） and amylase （by 2.41-fold） activities, hut decreased polyphenol oxidase （by 1.89-fold） and peroxidase （by 1.88-fold）. However, transferring whitefly adults to the favorite host abutilon from Zhongmian 41 was associated with increased activities of cytochrome P450 monooxygenase （by 1.61-fold） and amylase （by 1.42-fold）, and decreased activities of polyphenol oxidase （by 2.96-fold） and peroxidase （by 2.07-fold）. Our results, together with previous studies, proved that multiple pathways are involved in coping with host shifts by polyphagous herbivores, and the taxonomic status and preference of the host transferred would affect which pathway would be induced. These results would represent a key challenge in developing long-term sustainable insect control strategies.

Effect of Benzo[a]pyrene on Detoxification and the Activity of Antioxidant Enzymes of Marine Microalgae

The objective of this study was to examine the effect ofbenzo[a]pyrene （BaP） on the detoxification and antioxidant systems of two microalgae, Isochrysis zhanjiangensis and Platymonas subcordiformis. In our study, these two algae were exposed to BaP for 4 days at three different concentrations including 0.5 μg L-1 （low）, 3 μg L-1 （mid） and 18 μg L-1 （high）. The activity of detoxi- fication enzymes, ethoxyresorufin O-deethylase （EROD） and glutathione S-transferase （GST） increased in P subcordiformis in all BaP-treated groups. In 1. zhanjiangensis, the activity of these two enzymes increased at the beginning of exposure, and then de- creased in the groups treated with mid- and high BaP. The activity of antioxidant enzyme superoxide dismutase （SOD） increased in/. zhanjiangensis in all BaP-treated groups, and then decreased in high BaP-treated group, while no significant change was observed in P subcordiformis. The activity of antioxidant enzyme catalase （CAT） increased in I. zhanjiangensis and P subcordiformis in all BaP- treated groups. The content of malondialdehyde （MDA） in Isochrysis zhanjiangensis increased first, and then decreased in high BaP-treated group, while no change occurred in P. subcordiformis. These results demonstrated that BaP significantly influenced the activity of detoxifying and antioxidant enzymes in microalgae. The metabolic related enzymes （EROD, GST and CAT） may serve as sensitive biomarkers of measuring the contamination level of BaP in marine water.

Relationship Between the Development of Methamidophos Resistance and the Activities of Three Detoxifying Enzymes in Brown Planthopper, Nilaparvata lugens

Methamidophos resistance of brown planthopper(BPH), Nilaparvata lugens was selected in laboratory for 19 generations (F1 to F19). The resistance development in BPH was approximatively shaped as the letter 'S' : resistance change was small before the fifth generation and after the fifteenth generation, and the changing pattern was sharp between the fifth and the fifteenth generation. Esterase might play an important role in the resistance development, because the esterase activity and the number of individuals with high activities increased along with the resistance development. The esterase activities of insecticide-sensitive population S, field population F0, its selective generations F5, F10 and F15 were highly correlated with the resistance ratios of these generations, and the coefficient was 0.9899. Mixed-function oxidases and glutathione S-transferase also might play some roles in the resistance development, but the big change in the activities of the two detoxifying enzymes both took place before the tenth generation.

THE ROLES OF DETOXIFYING ENZYMES AND AChE INSENSITIVITY IN METHAMIDOPHOS RESISTANCE DEVELOPMENT AND DECLINE IN NILAPARVATA LUGENS

Methamidophos resistance of brown planthopper ( Nilaparvata lugens Stl, BPH) was selected in laboratory. After successive selection for 9 generations, the selection was ceased by rearing BPH without contact with any insecticide for 9 generations. In the full course, the successive changes of esterase activity, MFO activity, GSTs activity and AChE insensitivity were analyzed. The results showed that the change of esterase activity was high correlated with that of methamidophos in the full course, which indicated that esterase played very important role both in the resistance development and in the resistance decline. However, the change of AChE insensitivity only significantly correlated with that of resistance in the development stage, and the change of MFO activity or GSTs activity only significantly correlated with that of the resistance in the decline stage, which indicated the changes of AChE insensitivity, MFO activity or GSTs activity only played some roles in different stages of the resistance change.

Influence of rice black streaked dwarf virus on the ecological fitness of non-vector planthopper Nilaparvata lugens （Hemiptera： Delphacidae）

Rice black streak dwarf virus （RBSDV） is transmitted by the small brown planthopper （SBPH）, Laodelphax striatellus （Fallen）. Non-vector rice brown planthopper （BPH）, Nilaparvata lugens （Stal）, shares the same host rice plants with SBPH in paddy fields. The changes in nutritional composition of rice plants infected by RBSDV and the ecological fitness of BPH feeding on the infected plants were studied under both artificial climate chamber and field conditions. Contents of 16 detected amino acids and soluble sugar in RBSDV infected rice plants were higher than those in the healthy ones. On the diseased plants BPH had significantly higher nymphal survival rates, nymphal duration of the males, weight of the female adults, as well as egg hatchability compared to BPH being fed on healthy plants. However, there was no obvious difference in female nymph duration, longevity and fecundity. Defense enzymes （superoxidase dismutase, SOD and catalase, CAT） and detoxifying enzymes （carboxylesterase, CAE and glutathione S-transferase, GST） in BPH adults fed on diseased plants had markedly higher activities. The results indicate rice plants infected by RBSDV improved the ecological fitness of the brown planthopper, a serious pest but not a transmitter of the RBSDV virus.

Resistance and fitness costs in diamondback moths after selection using broflanilide, a novel meta-diamide insecticide

The diamondback moth (DBM) Plutella xylostella (L.) (Lepidoptera: Plutellidae) is an insect pest found around the world that feeds on cruciferous crops. The DBM has become resistant to most insecticides in current use in the field. Broflanilide is a novel meta-diamide insecticide that binds to a new site on the γ-aminobutyric acid receptor and very efficiently protects against most pests in the order Lepidoptera, including DBM. In this study, the resistance of a laboratory-bred susceptible strain of DBM to broflanilide and the fitness costs posed by broflanilide to the DBM were evaluated. The DBM had no obvious resistance to broflanilide after 10 generations of selection. The realized heritability h2 was 0.033, suggesting a low risk of resistance developing in this strain. The F10 generation had no cross-resistance to the insecticides abamectin and endosulfan (which target the γ-aminobutyric acid receptor) and chlorantraniliprole (which targets a non-γ-aminobutyric acid receptor). The specific activities of important detoxification enzymes (cytochrome P450 monooxygenase, esterase, and glutathione S-transferase) were not obviously altered. However, the larval stage was prolonged and the adult stage was shortened significantly in F11 generation than the F0 generation. The total preoviposition period TPOP significantly prolonged 1.90 d in F11 generation. The fitness value Rf (0.93) was lower for the F11 generation than the F0 generation. The results indicated that long-term exposure to broflanilide exerts clear fitness costs in the DBM. This information will be useful in identifying reasonable broflanilide application guidelines for managing broflanilide resistance in the DBM.