Comparative studies on muscle microstructure and ultrastructure of Mythimna separata Walker treated with wilforgine and chlorantraniliprole

We attempted to elucidate the comparative effects between wilforgine and chlorantraniliprole on the microstructure/ultrastructure of muscle tissue in Mythimna separate larvae. The typical toxicity symptoms of M. separata larvae upon wilforgine treatment was feeding cessation and flaccid paralysis, whereas feeding cessation and contraction paralysis were the main poisoning symptoms wrought by chlorantraniliprole. Light-microscopy observations showed that the microstructure of muscle tissue could be damaged by wilforgine and chlorantraniliprole, and the death of insects was associated with muscle lesions. Muscle tissue was loose after wilforgine treatment but constricted muscle tissue was observed upon chlorantraniliprole treatment. Transmission electron microscopy showed that wilforgine and chlorantraniliprole could disrupt endomembranes and plasma membranes. These results suggest that wilforgine can induce microstructural and ultrastructural changes in the muscles of M. separata larvae; the sites of action are proposed to be calcium receptors or channels in the muscular system.

Microstructural and ultrastructural changes in the muscle cells of the oriental armyworm Mythimna separata Walker (Lepidoptera: Noctuidae) on treatment with wilforine

This study investigated the mode of action of wilforine, an alkaloid with insecticidal properties, extracted from Tripterygium wilfordii Hook f., on the microstructure and ultrastructure of the muscle cells of larvae and adults of the oriental armyworm Mythimna separata Walker. The bioassay results showed that wilforine had oral toxicity against both M. separata larvae (LC₅₀=63μg/mL) and adults (LC₅₀=36μg/mL). The typical toxicity sign was paralysis leading to death. Both light and electron microscope observations revealed that damage to the muscle cells increased with poisoning time in larvae and adults treated with the LC₈₀ dose of wilforine. Histopathological examinations in the muscle cells of M. separata adults showed that there were large cytoplasmic spaces, disrupted Z-lines and swollen mitochondria in the muscle cells. Further, the sarcoplasmic reticulum was excessively dilated and fragmented; the nuclear membrane was ruptured; nuclear material was overflowing; and the myolemma was damaged. The similar pathological changes in the muscle cells of oriental armyworm larvae were observed, as above. In addition, a medullary sheath structure appeared and crystalline inclusion was also observed in the muscle cells of M. separata larvae. In conclusion, wilforine could induce pathological changes in the muscle cells of oriental armyworm larvae and adults, leading to their death; thus, the active site of action of wilforine maybe located in the muscle tissue of insects.

Haematological, biochemical and histopathological alterations induced by abamectin and Bacillus thuringiensis in male albino rats

The renal- and hepato-toxicity induced by abamectin pesticide (Vertimec) and a commercial form of a bio-insecticide Bacillus thuringiensis (Agerin) in male albino rats were evaluated. Blood picture and blood glucose level were investigated. Male albino rats were administered dietary doses each equivalent to 1/10 or 1/100 of the LD50 values of each toxicant for 30 consecutive days. Abamectin was found to pose risks of renal- and hepato-toxicity in rats, since the biochemical parameters of liver function (i.e. aspartate aminotransferase activity, alanine aminotransferase activity, acid phosphatase activity, albumin, and total protein levels) and kidney function (uric acid and creatinine concentration) were severely affected. These effects were verified by histopathological examination of liver and kidney tissues. Likewise, some haematological indices (i.e. erythrocyte count, leukocyte count and haemoglobin concentration) were also influenced; in addition abamectin might cause hypoglycaemia. On the other hand, the above-mentioned lesions were less pronounced in the case of Bacillus thuringiensis -treated rats.

Efficacy of systemic insecticides on the gall wasp Quadrastichus erythrinae in wiliwili trees (Erythrina spp.)

BACKGROUND

Erythrina gall wasp (EGW), Quadrastichus erythrinae Kim, was first found on Oahu Island, Hawaii, in April 2005. Its rapid spread and infestation in wiliwili trees (Erythrina spp.) have brought an urgent need to suppress its population. Little is known about the control of EGW in wiliwili trees.

RESULTS

Among the systemic insecticides abamectin, dinotefuran and imidacloprid, applied via trunk injections or soil drenches, injections of imidacloprid showed better control of EGW in wiliwili trees. All the imidacloprid injection treatments had varying levels of effectiveness against EGW, but not the soil drench. The levels of imidacloprid were higher in lower canopies than those in the other parts within a tree. Imidacloprid remained detectable 1 year after treatment. The trees injected with the products IMA-jet and Merit 200 SL via Arborjet had lower infestation severity ratings for the entire growth season and carried more imidacloprid than those with Imicide via Mauget or Pointer via Wedgle injections.

CONCLUSION

The results indicate that, among the three insecticides tested, imidacloprid is most effective against EGW in the trees. Concentrations of imidacloprid in the leaves need to be 4 mg kg(-1) or higher for good EGW control.