Abstract:

Juvenile hormone and testosterone are important insect hormones. In order to understand the effects of juvenile hormone and testosterone on the egg-laying ability of Coccinella septempunctata, in this study, we used artificial diets supplemented with different concentrations of juvenile hormone analog (ZR-515) and testosterone to feed adult ladybird beetles, and analyzed the feeding frequency, mating frequency, egg production and hatching rate of eggs of C. septempunctata in different feeding treatments. The results showed that: (1) there was no significant difference between the feeding frequency and egg production of each group with the addition of ZR-515 at 50, 5, 0.5 and 0 μL/L in J-a, J-b, J-c and J-ck, respectively, and the mating frequency of group J-c was significantly higher than that of groups J-a and J-b. (2) 0.1, 0.01, 0.001, and 0 mg/L testosterone (corresponding to treatment groups T-a, T-b, T-c, and T-ck) were added to the treatments. There were no significant differences in feeding frequency, egg production, and egg hatching rate among the groups, but the mating frequency in the T-a group was significantly higher than that in the T-ck group. (3) Treatments with additions of 10, 1, 0.1, 0.01, 0.001 mg/L of testosterone and 0.5 μL/L ZR-515 (corresponding to treatment groups JT-a, JT-b, JT-c, JT-d, JT-e) were set up with 0.5 μL/L ZR-515 alone as the control (JT-ck). There was no significant difference in feeding frequency among each treatment, while the JT-c group was extremely significantly higher than the JT-e group and significantly higher than the JT-d group. Egg production from high to low was JT-d [(59.53±9.81) eggs]> JT-c [(53.53±9.22) eggs]> JT-e [(34.86±7.84) eggs]> JT-b [(34.13±6.48) eggs]> JT-ck [(31.13±5.17) eggs]> JT-a [(7.80±2.58) eggs], JT-d group was significantly higher than JT-a, JT-b, JT-e, and JT-ck groups, while JT-c group was significantly higher than JT-a, JT-e, and JT-ck groups. The results of this study indicated that supplementing artificial diets with only 0.5  μL/L of the juvenile hormone analog ZR-515 and 0.1 mg/L testosterone increased the mating frequency of C. septempunctata, but did not significantly improve egg production. However, when 0.1 mg/L testosterone and 0.5  μL/L ZR-515 were added together, the mating frequency, egg production, and egg hatching rate were significantly higher than those fed with the diet containing only 0.5 μL/L ZR-515.

Key words: aphid, Coccinella septempunctata, juvenile hormone, testosterone, biological control