Sex Differences In The Resistance Of Silkworm Bombyx Mori To Organophosphorus

Domesticated silkworm(Bombyx mori), insect of Lepidoptera Bombycidae, origin from wild silkworm. After long-term of artificial selection, the silk production of domesticated silkworm has been increased by a big margin. However, with a week resistance against pesticides, domesticated silkworm present great death rate because of pesticides poison in silkworm industry, which become a restriction for the development of the industry. To better tackle this issue, many institutions devote great efforts in the resistance-related research of domesticated silkworm.The gender and resistance to drugs of insects has remained a hot spot for research these years. As a big country of sericiculture, China proceeded gender-oriented sericiculture experiments in the early of 1950-1960s. After many comparative experiments of male and female Bombyx mori, we know that in the same breed, male Bombyx mori need less folium mori while have higher leaves-to-silk transformation rate, more layers of cocoon and higher silk production rate than female ones. In the latest 50 years, scholars around the world conduct extensive research on the gender control of silkworm. The culture of male Bombyx mori and popularization of male Bombyx mori-specific culture techniques are the key to further promote silkworm cocoon production efficiency, economic return and additional value of silk production, whereas there is no systematic research focused on the difference between male and female Bombyx mori because of the lack of comparative experiment of female. This experiment adopts a cocoon color-specific species of domesticated silkworms, whose gender can be easily distinguished in the nit stage according to their nit color, so with 100% of discrimination rate, it is convenient for us to proceed drug resistance-related experiments.In order to identify the relationship between the gender of domesticated silkworms and their resistance to phoxim pesticide, we adopt the cocoon color-specific species of domesticated silkworm as the material to research the semi-lethal dose(LC50)of phoxim pesticide to different instars of both male and female Bombyx mori with leaf-dipping method. The results show that in each instar, the LC50 of phoxim pesticide of male silkworms are 407.811 ng.mL-1, 1291.245 ng.mL-1, 2046.462 ng.mL-1, 3376.183 ng.mL-1, 5428.747 ng.mL-1 from 1 to 5 age respectively, 1.03,1.14,1.05,1.05,1.07 folds higher than female ones, among which 2 and 5 age are most obvious.Using the species mentioned above, we conduct experiments to learn the differences of the glutathione S- transferase (GST), acetylcholinesterase (AChE) and Carboxylesterase(CarE) activity between male and female Bombyx mori. Our research is based on newly exuviated larvae at different instars and seven tissues, including head, midgut, fat body etc of 5-age and 3d ones. Activity of three enzymes are measured according to Ellman enzyme activity measurement. The result exhibits different enzyme activities respectively. GST activity measurement shows that after the induction of pesticide, the enzyme activity of male Bombyx mori are increased largely, with highest activity in the head and fat body. The GST activities of fat body after pesticide induction are inhibited broadly, while increased in females'head tissue, which may attribute to the relation between head function and gender. The AChE activity of fat body is inhibited after pesticide induction while that of head is increased. AChE activity of male Bombyx mori is decreased while increased in female ones in midgut. The difference of AChE activity between male and female may be related to their different sensitivity toward phoxim. The CarE activity research shows that female have higher CarE activity in their head, sericterium, blood and malpighian tubes, which are not affected by pesticide, than male.Real-time PCR was applied to investigate the expression discrepancies of detoxic genes between male and female Bombyx mori, comparing the expression differencies of major detoxic genes among male and female individuals and tissues. Results showed that there were obvious differences in the expression of detoxic genes beween two genders. In addition, the acivities of GST and AChE were in accordance with the expression profiles of corresponding genes. However, carboxylesterase activity kept in a low stage while its expression was high. Therefore, carboxylesterase mutant may exist in Bombyx mori. Tissue data showed obvious differences in the expression levels of the selected six genes beween male and female, which was particularly significant in head and germen. 80% of the issue data pointed at a significant higher level of expressions of the selected genes in males than in females, which provided substantial sopport for the theory of male Bombyx mori bearing higher drug resistence compared with female ones, further contributing to the study of relations between the gender and the ability of drug resistence in Bombyx mori.