Toxicity, and biological and biochemical effects of hexaflumuron on the elm leaf beetle, Xanthogaleruca luteola (Col.: Chrysomelidae)

The elm leaf beetle, Xanthogaleruca luteola Müll., is the most important pest of elm trees in Iranian cities. Insect growth regulators (IGRs) such as hexaflumuron are recommended to use in urban areas for their low toxicity to human and environment. In this study, the impact of the chitin synthesis inhibitor, hexaflumuron, was evaluated on some biochemical and biological characteristics of the elm leaf beetle under laboratory conditions. The toxicity of this insecticide investigated on the last instar larvae of X. luteola using leaf dip method (25 ± 2 ºC, 75 ± 10% relative humidity, 16 h (light): 8 h (dark)). LC30 and LC50 values were calculated at 53.45 and 122.02 ppm, 72 h post treatment, respectively. Biological and biochemical characteristics were evaluated for 3rd instar larvae, following 72 h feeding on the elm leaves treated with LC50 and LC30 concentrations of hexaflumuron. The LC30 and LC50 concentrations of hexaflumuron increased the duration of larval stage, 10.04 ± 0.24 and 9.27 ± 0.43 days, respectively, compared with the control, 7.07 ± 0.413 days. There were no significant differences in the duration of pupal stage for LC30 and LC50 concentrations and control group. Hexaflumuron significantly decreased adult longevity compared with the control. Several morphological abnormalities were also observed in treated larvae and pupae. The results showed significant reductions of carbohydrate, protein, glycogen and lipid contents at the LC30 and LC50 concentrations of hexaflumuron. The activities of the detoxifying enzyme glutathione S-transferase, general esterases (α-esterases and β-esterases) and the immunological enzyme phenoloxidase were significantly affected by hexaflumuron. Although the results are clearly indicative of the adverse effects of sublethal concentrations of hexaflumuron on the beetle pest, further investigations are required to improve the efficiency of the chemical for being viably used in integrated pest management programs against the elm leaf beetle

A study on Performance of Iranian Commercial Silkworm Lines under Heat and Cold Stress

One of the main objectives of the new breeding programs for silkworms is to consider the ability to withstand environmental fluctuations. In this study, the performance of the Iranian commercial silkworm lines was investigated under heat and cold stress. Seven Iranian commercial silkworm lines including 31, 32, 103, 104, 151, 153, and 154 were reared under standard conditions at Iran Silk Research Center. To induce heat and cold stress, 300 larvae on the third day of the fifth instar including three replicates of 100 larvae, were placed in an incubator at 35 °C and for 2 and 12 hours, respectively, and then returned to the standard rearing conditions at 25 °C until the end of the breeding period. The characteristics of cocoon weight (cw), cocoon shell weight (csw), and cocoon shell percentage (csp) were investigated under control and stress treatments. The generalized linear model (GLM) procedure of SAS software was used for statistical analysis. The results of the variance analysis showed that the effect of all sources of variance including genotype, stress, sex, two-way interaction effects of genotype × stress, genotype × sex, and stress × sex and three-way interaction effect of genotype × stress × sex were significant for all investigated traits. Therefore, the averages related to the three-way interaction effect of genotype × stress × sex were considered and discussed. The results of the comparison of the means showed that in general, the larvae of the control group, especially lines 154 and 153, had better performance in all the examined traits compared to the larvae under heat and cold stress groups and a significant difference was observed between them (P < 0.001). In the same way, the larvae of the heat stress group had a higher performance than the larvae of the cold stress group, which indicates the thermal tolerance of silkworm to higher temperatures than to low temperatures. In conclusion, the performance of Iranian commercial silkworm lines is affected by heat and cold stress conditions, and lines 154 and 153 had higher tolerance than other investigated lines and can be used and prioritized in the production of commercial hybrids in terms of resistance to temperature stress, production and economic statistics

Effect of Sweet Wormwood Artemisia annua Crude Leaf Extracts on Some Biological and Physiological Characteristics of the Lesser Mulberry Pyralid, Glyphodes pyloalis

The lesser mulberry pyralid, Glyphodes pyloalis Walker (Lepidoptera: Pyralidae) is a monophagous and dangerous pest of mulberry that has been recently observed in Guilan province, northern Iran. In this study, the crude methanol extract of sweet wormwood Artemisia annua L. (Asterales: Asteracaea) was investigated on toxicity, biological and physiological characteristics of this pest under controlled conditions (24 ± 1 °C, 75 ± 5% RH, and 16:8 L:D photoperiod). The effect of acute toxicity and sublethal doses on physiological characteristics was performed by topical application. The LC50 and LC20 values on fourth instar larvae were calculated as 0.33 and 0.22 gram leaf equivalent/ mL, respectively. The larval duration of fifth instar larvae in LC50 treatment was prolonged (5.8 ± 0.52 days) compared with the control group (4.26 ± 0.29 days). However larval duration was reduced in the LC20 treatment. The female adult longevity in the LC50 dose was the least (4.53 ± 0.3 days), while longevity among controls was the highest (9.2 ± 0.29 days). The mean fecundity of adults after larval treatment with LC50 was recorded as 105.6 ± 16.84 eggs/female, while the control was 392.74 ± 22.52 eggs/female. The percent hatchability was reduced in all treatments compared with the control. The effect of extract in 0.107, 0.053, 0.026 and 0.013 gle/mL on biochemical characteristics of this pest was also studied. The activity of α-amylase and protease 48 hours post—treatment was significantly reduced compared with the control. Similarly lipase, esterase, and glutathione S-transferase activity were significantly affected by A. annua extract

Inhibition of Digestive α-Amylases from Chilo Suppressalis Walker (Lepidoptera: Crambidae) by a Proteinaceous Extract of Citrullus Colocynthis L. (Cucurbitaceae)

The striped rice-stem borer, Chilo suppressalis (Walker) is one of the most important pest of rice worldwide. In this study, a proteinaceous extract from Citrullus colocynthis L. shows various degrees of inhibition to digestive α-amylases of C. suppressalis. Digestive α-amylases of larvae were inhibited by different concentrations (approximately 50%) of C. colocynthis amylase inhibitor (CCAI). One of the isozymes totally disappeared and the sharpness of another decreased on native-PAGE electrophoresis. The pH dependency of inhibition revealed that the enzyme was inhibited in a wide range of pH from 7-10, and the optimal pH of the enzyme occurred in lepidopteran larvae. The highest inhibition of α-amylase by CCAI was observed at 25°C; the temperature near the optimal temperature of amylolytic activity. A time-course experiment demonstrated that enzymatic activity was the highest, 30 min after the onset of the experiment, when the highest inhibition occurred. The enzyme kinetic studies using Lineweaver-Burk analysis, revealed a mixed inhibition of CCAI on α-amylase activity. The current study is the first basic one using α-amylase inhibitor against C. suppressalis. This study opens the way for transgenic rice varieties containing inhibitors

Evaluation of Origanum vulgare L. essential oil as a source of toxicant and an inhibitor of physiological parameters in diamondback moth, Plutella xylustella L. (Lepidoptera: Pyralidae)

The effect of essential oil of Origanum vulgare L. a medicinal plant was studied on toxicity, physiology and biochemical characteristics of diamondback moth Plutella xylustella L. in controlled condition. The LC10, LC30 and LC50 values were estimated 0.234, 0.710 and 1.528 percent (v/v) respectively for 3rd instar larvae. Repellency of essential oil under LC10 and LC30 concentrations was 22.8 ± 6.64 and 49.8 ± 6.95 percent respectively. Effect of plant essential oil on feeding efficiency was also evaluated under LC10 and LC30 concentrations. Approximately Digestibility (AD), Efficacy of Conversion of Ingested Food (ECI), Efficacy of Conversion of Digested Food (ECD), Relative Consumption Rate (RCR) and Relative Growth Rate (RGR) of the treated larvae showed a significant difference compared with the control. The effectiveness of plant essential oil on digestive enzymes under LC50 concentration for the survivors after 24 and 48 h after treatment was analyzed. Total protein and triglycerides were decreased significantly compared with the control. Activity of alkaline phosphatase and protease in treated larvae decreased compared with the controls. The lipase was increased 24 h after treatment compared with the control. Significant differences in detoxifying enzymes such as glutathione S-transferase and esterase were noted compared to controls. It is concluded that the essential oil used in the present experiment shows toxicity in higher doses. It is also concluded that the essential oil used did show considerable changes in repellency, feeding efficiency, reduced larval weight and changes in biochemical properties which may nominate it for further investigation in key insect pests

Feeding indices and enzymatic activities of carob moth Ectomyelois ceratoniae (Zeller) (Lepidoptera: pyrallidae) on two commercial pistachio cultivars and an artificial diet

Feeding indices and enzymatic activities of Ectomyelois ceratoniae (Zeller) were studied in a growth chamber under controlled conditions (29 ± 2 °C, relative humidity of 70 ± 5% and a photoperiod of 16:8 (L:D) hours) on two commercial Pistachio cultivars (Akbari and Kalequchi) and an artificial diet. Feeding indices of E. ceratoniae larvae differed significantly on three hosts (P < 0.05). The relative consumption rate was calculated to be 5.36 ± 0.009, 11.10 ± 1.49 and 10.631 ± 0.599 (mg/mg/day) on artificial diet, Akbari and Kalequchi cultivars, respectively. Carob moth larvae reared on Akbari cultivar showed the highest efficiency of conversion of digested food (ECD) (5.64 ± 0.43). The highest amount of efficiency of conversion of ingested food (ECI) was obtained on artificial diet but approximate digestibility (AD) was the lowest on this diet. The highest enzymatic activities of alpha-amylase, general proteases and lipase were observed in the midgut of larvae reared on artificial diet. Total protein and lipid value were highest in larvae that were reared on artificial diet