No abstract

Plant extracts are currently studied more and more because of the possibility of their usage in plant protection. Many of the natural plant compounds which are used in the control of pests are known to affect the digestion and immune functions of insects. In this study, effects of Artemisia annua extract on the digestive enzymatic profiles and the cellular immune reactions of Eurygaster integriceps were investigated to reach a better understanding of its role in the control of this pest as the most destructive one in the production of wheat in the Near and Middle East, eastern and southern Europe and North Africa. Feeding and injection methods were used to study the plant extract effects on digestive enzymes and cellular immunity, respectively. When adult E. integriceps fed on food and water containing plant extracts, activity of the digestive enzymes, including alpha-amylase, alpha- and beta-glucosidases, protease and lipase, in addition to cellular immune reactions (total and differentiate hemocyte numbers, phagocytosis, nodule formation and phenoloxidase activity) against Beauveria bassiana were affected and significantly decreased in comparison with controls, in that the clear dose-response relationships were established with respect to enzyme activities and immune reactions. A. annua extract had a significant effect on kinetic parameters (Vmax and Km) of digestive enzymes and phenoloxidase activity so that the presence of the plant extract decreased the value of Vmax and increased Km, causing the reduction of enzyme affinity to the substrate, overall velocity of the reaction and finally interfering with the rate of breakdown of the enzyme-substrate complex. The understanding of fungal-induced immune responses and identification of factors regarding fungal virulence could be important in accelerating host death in a biological control scenario. Hence, the combination of botanical pesticides and microbes to control insect pest populations would be a safe and possibly rapid method to decrease their damage and environmental risk due to the use of chemical pesticides.

No abstract

Asiatic rice borer, Chilo suppressalis (Walker) (Lepidoptera: Crambidae), is a cosmopolitan and destructive pest in rice fields of the world. This pest was reported in 1973 in Iran, and it has since spread widely in rice, Oryza sativa L., fields throughout the country. In this study, we tried to evaluate comparative toxicity of diazinon in five colonies of C. suppressalis, collected from Babol (Ba), Amol (Am) of Mazandaran Province and Rasht (Ra), Sheikhmahale (Sh), and Gourabzarmikh (Go) of Guilan Province, northern Iran. The LD50 values were compared. We also evaluated the general esterases, alkaline phosphatase (ALP), glutathione transferase (GST), and acetylcholinesterase (AChE) activities from the five populations. The LD50 values of Ra, Ba, Am, and Sh (12.64, 11.4, 7.17, and 3.71 microg/mg larva(-1)) were 13.67-, 12.33-, 7.75-, and 4.02-fold higher than Go population (0.924 microg/mg larva(-1)). Using alpha-naphthyl acetate as substrate, the general esterase activities in Ra, Ba, Am, and Sh colonies were, respectively, 1.81-, 1.68-, 1.75-, and 1.35-fold more than those in Go population. When beta-naphthyl acetate was used as the substrate, activity ratio was measured 1.98-, 2.58-, 1.25-, and 1.24-fold compared with the Go population. Glutathione transferase activities in Ra, Ba, Am, and Sh populations were 1.27-, 1.68-, 0.98-, and 1.7-fold more than those in Go, when 1-chloro-2,4-dinitrobenzene was used as the substrate. When 1,2-dichloro-4-nitro-benzene was used as the substrate, activity ratio was measured 1.14-, 1.42-, 0.56-, and 0.95-fold compared with Go population. The ALP activity demonstrated a significant difference among these populations and in Ra, Ba, Am, and Sh larvae were 3.54-, 4.62-, 3.84-, and 2.18-fold more than Go. The AChE inhibition or I50 value was 0.19, 0.22, 0.31, 0.19, and 0.26 mM in Ra, Ba, Am, Sh and Go populations, respectively. However, the results showed no significant differences in studied colonies. These biochemical characterizations of general esterases ALP, GST, and AChE were consistent with diazinon bioassay in the five populations. It is inferred from increased esterase, alkaline phosphatase and glutathione transferase, activities that might play an important role in the increasing resistance in C. suppressalis to diazinon among these five populations.

In this study, five morphological types of circulating hemocytes were recognized in the hemolymph of the adult sunn pest, Eurygaster integriceps Puton (Hemiptera: Scutelleridae), namely prohemocytes, plasmatocytes, granulocytes, adipohemocytes, and oenocytoids. The effects of the secondary metabolites of the entomopathogenic fungus Beauveria bassiana on cellular immune defenses of Eurygaster integriceps were investigated. The results showed that the fungal secondary metabolites inhibited phagocytic activity of E. integriceps hemocytes and hampered nodule formation. A reduction of phenoloxidase activity was also observed. The data suggest that B. bassiana produce secondary metabolites that disable several immune mechanisms allowing the fungus to overcome and then kill its host. This characteristic makes B. bassiana a promising model for biological control of insect pests such as E. integriceps.