| The oak-silkworm, Antheraea pernyi Guerin-Meneville, is one of the best factitious hosts for Trichogramma mass production in China. However, presently only T. dendrolimi is massively produced with the large host eggs of oak-silkworm so that mass productions of most Trichogramma species and their implications for pest biological control have been limited. Previous results indicated that some Trichogramma species, such as T. leucaniae, had the capacity of parasitizing eggs of A. Pernyi and developing to adults, but only a few of parasitoids could break and craw out the host-egg shell. In this study, we selected T. dendrolimi and T. leucaniae as test parasitoid species. Through estimating and observing the biological parameters of two Trichogramma species simultaneously parasitize A. pernyi eggs under different conditions. We will determine the factors to influence synparasitism of both Trichogramma species on A. pernyi eggs and the possibility to cooperatively breeding them on the large eggs. The main results obtained as followed. 1. The influence of introducing parasitoid ways on synparasitism of both Trichogramma species on A. pernyi eggs.The parasitism rate of both Trichogramma species simultaneously parasitizing A. pernyi eggs was higher than that of separately parasitizing way. Total number of T. leucaniae and total emerging adults of T. leucaniae per host egg for both Trichogramma species simultaneously parasitizing were higher than those for separately parasitizing. Therefore both Trichogramma species simultaneously parasitizing A. pernyi eggs is the suitable way to develop the new product of breeding two Trichogramma species on the same large eggs. In addition, when two T. leucaniae females simultaneously parasitized an A. pernyi egg, 28.6% of parasitized eggs successfully emerged. However, no parasitoid adults emerged from host eggs when two T. leucaniae females separately parasitized 12 h on A. pernyi eggs.When one T. leucaniae female and five T. leucaniae females were simultaneously introduced to parasitize one A. pernyi egg, 8.8 T. leucaniae adults emerged, similar to that of one T. leucaniae female and one T. leucaniae female introducing way. However, when five T. leucaniae female and twenty-five T. leucaniae females were simultaneously introduced to parasitize five A. pernyi eggs, the parasitism rate reached to 98%, emergence rate reached to 81.6%, and total number of T. leucaniae and total number of T. leucaniae emergence per host egg increased to 42.1 and 26.7, respectively. 2. The influence of different condition on synparasitism of both Trichogramma species on A. pernyi eggs.When both Trichogramma species simultaneously parasitized A. pernyi eggs at 23-26℃, the parasitism percentage got to 90%. There was a tendency of parasitism percentage decreasing with the increase of temperature. There was the largest number of emerging T. leucaniae per egg at 26℃(3.5 adults), significantly higher than that of 23℃. The results indicated that 26℃ is the suitable temperature to develop the new product of breeding two Trichogramma species on the same large eggs. In addition, T. leucaniae preferred to parasitize A.pernyi eggs under low temperature condition. Particularly, there was 53.3% parasitism, 43.8% emergence of parasitized eggs when T. leucaniae individually parasitized A. pernyi eggs at 20℃.When both Trichogramma species simultaneously parasitized A. pernyi eggs at 50% and 80% RH, there were higher values of parasitism rate、emergence rate and total number of parasitoids and total number of emerging adults per host egg. Particularly, total number of T. leucaniae(9.6) and the number of emerging T. leucaniae(6.9) per egg at 80% RH were significantly higher than those at 50% and 60% RH. The results indicated that 80% RH is the suitable relative humidity to develop the new product of breeding two Trichogramma species on the same large eggs. In addition, T. leucaniae preferred to parasitize A.pernyi eggs under high humidity condition. The parasitism rate got to 83.3%, and the emergence rate got to 32% when T. leucaniae individually parasitized A. pernyi eggs at 90% RH.When both Trichogramma species simultaneously parasitized A. pernyi eggs under 19L:6D and 24L:0D, the parasitism rate got to 93.3%. Particularly, the emergence rate got to 96.4%, total number of T. leucaniae and total number of emerging T. leucaniae adults per host egg were 9.2 and 6.3, under 24L:0D, significantly higher than those of 0L:24D. The results indicated that 24L:0D is the suitable light condition to develop the new product of breeding two Trichogramma species on the same large eggs. In addition, T. leucaniae preferred to parasitize A. pernyi eggs under the light conditions of 10-14L;14-10 D, there was 83.3% parasitism, 33.3% emergence of parasitized eggs, 13.1 adults of T. leucaniae emerging. 3. Biological control potential of Trichogramma cooperatively bred by A. pernyi eggs on target pests.There was no significant difference in parasitism on armyworm eggs by T. dendrolimi or T. leucaniae bred using A. pernyi eggs and Corcyra cephalonica eggs. Generally, T. dendrolimi bred by A. pernyi eggs parasitized 42.3 armyworm eggs in 24 h, significantly higher than that parasitized by T. leucaniae regardless of factious host species. In addition, there was no effects of factious host species on the emergence, female progeny and development of two Trichogramma species on armyworm eggs. The results showed that there was similar biological control potential on target pests between parasitoids bred by the eggs of A. pernyi and C. cephalonica.Based on the biological parameters of synparasitism of two Trichogramma species on A. pernyi eggs under different conditions, the results preliminarily indicated that two Trichogramma species were suitable to cooperatively breed on A. pernyi eggs under the conditions of controlling the ratio of parasitoids to host egg at 1 T. dendrolimi : 5 T. leucaniae : 1 egg at 26℃, 80% RH and 24L:0D. |
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