Effects Of Juvenile Hormone Analogue On Reproduction And The Development And Predation Of F1 Generation In Harmonia Axyridis

In this paper, the effects of different levels of JHA on Harmonia axyridis ovarian development and fertility was investigated by adding JHA to the artificial diets, we also investigated the development of the offspring and tested the prevention and control potential of the offsprings on pea aphids. The best juvenile hormone analogue concentration has been screened to ensure the reproduction and offsprings’ normal development. The results will cotribute to the artificial rearing of Harmonia axyridis. The results are as follows:1.Effects of JHA on the ovarian development of Harmonia axyridis We fed virgin females the artificial diets which are mixed with different concentrations of JHA, then dissected their ovaries to determine the ovarian developments. Our results showed that application of JHA promoted the ovarian growth of Harmonia axyridis. Females treated of 100 mg/Kg、50 mg/Kg、25 mg/Kg、5 mg/Kg and 1 mg/Kg had the faster ovarian development, and their ovaries could be mature within 5-7 days. While, ovarian development of females treated with low application of JHA(0.1 mg/Kg) was delayed, it took more than 15 days to reached mature.2. Effect of JHA on the adult’s reproduction of Harmonia axyridis The adult’s reproduction were investigated after fed the paired adults with artificial diets which mixed with different concentrations of JHA, we hope to screen the most appropriate concentration of the JHA which can fit the H. axyridis’ reproductive needs. Our results showed that the application of JHA reduced the time required for mating, adults began to mate 5-9 days earlier than control adults which were fed with just artificial diet(CK1), but had no significant difference with adults reared with aphids(CK2) after treated with JHA. The mating frequency s of H. axyridis treated with JHA were significantly higher than those of the blank control(CK1) within 30 days. The mating frequency increased quickly when the JHA titers were low, and then decreased as the concentrations of JHA increasing. Among all the treatments, adults treated with 1 mg/Kg mated the most; In this test, JHA had no significant effect on mating duration. Application of JHA significantly increased the spawning rate. Compared with the blank control CK1, H. axyridis adults treated with JHA of 100 mg/Kg, 50 mg/Kg, 25 mg/Kg, 5 mg/Kg, 1 mg/Kg and 0.1 mg/Kg had increased 60.55%, 53.56%, 61.97%, 49.09%, 52.39% and 16.25% in the egg production rates separately. Most of the treated groups’ egg production rates were on the same level with the control group reared with aphids(CK2) except the of 0.1 mg/Kg treatment; The preoviposition showed consistent response to different concentrations of JHA, the preoviposition had no significant difference between the treated groups and the control group reared with aphids(CK2); The application of JHA effected the times of egg oviposition of H.axyridis. Females treated with JHA laid eggs more often, the times of egg oviposition increased first, and then decreased with JHA concentrations increasing. The times of egg oviposition reached to maximum when treated with JHA of 5 mg/Kg and 1 mg/Kg, and had no obvious difference with CK2; JHA could cause significant increase in the fecundity, as well as the times of egg oviposition, the number of eggs laid per female grew in the low concentrations and dropped with JHA concentrations increasing. Among all these treatments, females treated at dose of 1 mg/Kg had the largest egg laying amount(550.25±73.0). Females treated with JHA of 5 mg/Kg and 1 mg/Kg had no significant difference with CK2 in fecundity. The fecundity of all the treatments were 1 mg/Kg>5 mg/Kg>25 mg/Kg>50 mg/Kg>0.1 mg/Kg>100 mg/Kg; JHA had no effect on egg laid number per time in H. axyridis, most of the egg laid number per time was focused on 20-25. In consideration of mating and oviposition, 1 mg/Kg was the best concentration of JHA which can add to the artificial diet.3. Effect of JHA on the development of the filial generation In order to identify whether the JHA effects the correct development on the filial generation or not, we selected the eggs laid by the females treated with different doses of JHA randomly, investigated the hatchability, survival rate and the growth of the filial generation. The results showed that the hatchability of the eggs increased at first and then decreased with the JHA dose increase. The hatching rate order was as follows: 1 mg/Kg>5 mg/Kg>25 mg/Kg>50 mg/Kg>0.1 mg/Kg>100 mg/Kg. Offspring hatching rates of the treatment groups of 1 mg/Kg and 5 mg/Kg were similar to CK2 whose parental generation was reared with aphids. Under the test concentration of JHA, there were no significant differences in the larvae’ growth and developmental period of filial generation. Development durations of different stages of the filial generation were similar between treated groups and untreated group CK1. Compared with the offsprings produced by females fed on aphids, the offsprings of treated ones 4th-instar and pupae duration were shorter, but other instars durations were longer. Among all the treatments, the larvae survival rate was lowest at 45.8% when treated the parents with 100 mg/Kg of JHA. In addition to 100 mg/Kg treated, the survival rates of other treatment groups were not significantly different. The pupa and adult eclosion rates of all the treatment groups have achieved over 90%, and showed no significant difference with each other. No obvious effect on weight of newly emerged adult was found among treatments.4. Effect of JHA on the predatory functional response of the filial generation Predatory functional response of adult and 4th-instar of filial generation were studied to determine the controlling effect of F1 generation to Acyrthosiphum pisim. Our results showed that JHA had no negative impact on the predatory response of the offspring. The predatory function of filial generation could fit the Holling-Ⅱ. The filial generation had strong control effects to A. pisim.In conclusion, the optimum concentration of the JHA added to the artificial diet is 1 mg/Kg. At this concentration, the fecundity increased significantly, and there were no negative effects on. the offspring’s development and pest control potential.