| Trichogramma parasitoids are the most important biological control agents of lepidopterous pests.At present,there are more than 1,200 lepidopteran pests that can be effectively controlled through mass production of Trichogramma species.The fecundity of Trichogramma can directly affect its ability to control target pests.Therefore,understanding the phenomenon of self-regulation of Trichogramma egg maturation in different environments,and then clarifying the influence of that phenomenon on their fecundity,can help Trichogramma to be used in the prevention and control of pests with high efficiency and low cost.Here in this study,we compared four Trichogramma species(i.e.,T.dendrolimi,T.chilonis,T.ostriniae and T.leucaniae)under different ecological conditions through methods such as reproductive system development and anatomy of egg development in the body.Use anatomy and other methods to grasp the morphology of Trichogramma eggs in the body;based on the reproductive structure,by measuring the changes of Trichogramma parasitism and egg holding capacity under different factors(i.e.,mating,nutritional status,host adaptation,etc.).The research on the key factors affecting the egg development of Trichogrammahas been discussed in details.The main results of the study are as follows:1.In this experiment,the ovaries of the female Trichogramma wasps were dissected,and the eggs were classified into three grades by referring to the published method of grading.Grade Ⅰ egg: The egg was nearly spherical;Grade Ⅱ egg: The egg was elliptical,one end was relatively pointed,and the other end near the base of the fallopian tube was obtuse.The egg shape was not full,and the yolk filling degree was≥ 1/2 the volume of the egg chamber;Grade Ⅲ egg:similar to the shape of the Grade Ⅱ egg,but the egg shape was more full,and the entire egg chamber was filled with yolk.Through measurement and observation,it was found that the morphology and size of the eggs of the four Trichogramma species were similar.2.Fed with different nutrient certainly affected the development of Trichogramma eggs inside the body.This experiment was set into four treatments: i.e.,did not feed wasps,wasps fed with clean water,fed with honey water and fructose water,and the time gradient setting was 4,8,12,16,20,24,48 and 72 h.The results showed that all the four Trichogramma species had a certain number of mature and immature eggs when they first emerged.The number of eggs in the body increased significantly within 4 hours of emergence.After 4 hours,the amount of eggs held by the four Trichogramma species showed different trends.For T.dendrolimi,the number of eggs in the body was more consistent with time in the treatment where T.dendrolimi wasps were kept hungry and where fed with only water.In both treatments,the number of eggs in T.dedrolimi female showed a trend where it first increased and then decreased,and the egg holding volume reached at the highest peak after 12 hours of emergence.In the treatment where wasps were fed with honey water and fructose water,compared with the previous two treatments,the amount of eggs held by Trichogramma was significantly increased.Although the changed trend of the amount of eggs in the body also increased first and then decreased,the time of peak egg laying was extended to 20 h.For T.chilonis,there was no significant difference in the amount of eggs held in the body of wasp,Trichogramma with time without fed or fed with clean water.In the treatment of honey and fructose,compared with no feeding and feeding with water,the amount of egg holding increased significantly.In addition,the nutrients prolonged the peak egg laying time of the wasp.Within 24 hours,the amount of eggs conceived in wasp was gradually increased,and it decreased significantly after 48 and 72 hours.The amount of eggs held by T.ostriniae was gradually increased in the treatment of no feeding and water feeding,but there was no significant change in the amount of eggs held by feeding honey and fructose.Among the above four treatments,there was no significant difference in the amount of eggs held by the T.ostriniae after 12 hours of development.Nutrients only accelerate the maturation of the eggs of T.ostriniae.There was no significant change in the amount of eggs held by T.leucaniae in the above four treatments,and there was no significant difference between the treatments.Nutrients have no significant effect on the amount of eggs held by the wasp.3.For the mated and unmated four Trichogramma species,after comparing the egg holding capacity in different time periods(4h,8h,12 h,16h,20 h,24h),it was found that mating behavior has a significant effect on the egg holding capacity in the body of Trichogramma.In mated T.dendrolimi 0-24 h,the amount of eggs in the body showed a gradual decline,and the amount of eggs in 24 h was the least significant.There was a slight upward trend in the amount of eggs held by the unmated T.chilonis,but there was no significant difference among the treatments.The amount of eggs held by the mated T.chilonis increased first and then decreased,and the amount of eggs held at 20 and 24 hours decreased significantly.The amount of eggs held in the unmated T.chilonis was almost unchanged,and there was no significant difference between the treatments.In mated and unmated T.ostriniae,the amount of egg holding gradually increased with time,and the amount of holding eggs under 4h and 8h treatments was significantly lower than other treatments.The number of eggs in the mated and unmated T.leucaniae hardly changed,and there was no significant difference between the treatments.For the four Trichogramma species mentioned above,the amount of eggs in the unmated wasp species was higher than the amount of eggs in the mated Trichogramma species.Except for T.dendrolimi 4h and T.chilonis 20 and 24 h,there were significant differences among other treatments.4.Provide different numbers of host rice moth eggs(20,40,80,150 and 300),parasitic amount and egg holdingandtotal eggs(parasitic amount+egg holding)of the four Trichogramma species in six time periods(4,8,12,16,20 and 24h).The investigation of the amount of eggs and the total amount of eggs(parasite amount + egg holding)found that in all time periods,with the increase of the number of provided hosts eggs,the amount of parasitism increased,and the amount of eggs held,and the total amount of eggs decreased.The number of parasitized eggs of the four Trichogramma species on 20,40,80,150 and 300 rice moth eggs for 24 hours,for T.dendrolimi were 13.4,32.0,46.6,60.8 and 79.9 eggs;for T.chilonis were13.5,18.4,25.4,29.3 and 36.0 eggs;for T.ostriniae were 10.0,16.3,36.0,36.6 and 44.9 eggs,and for T.leucaniae 10.3,27.6,29.5,32.4 and 34.3 eggs.The maximum number of eggs laid by the Trichogrammawas when were provided with 300 host eggs.Although the number of host eggs(such as 80,150)provided by most treatments is greater than the maximum number of eggs laid.The amount of parasites under these treatments did not reach the maximum egg production.From the above results,it can be seen that Trichogramma has the ability to evaluate the number of eggs laid by the number of hosts.5.The study compared the four Trichogramma species amount of parasitism,the amount of egg holding and the total amount of eggs(parasitic amount + egg holding)of four Trichogramma species when they parasitized different suitable hosts(rice moth eggs,manually-extracted unfertilized eggs of Chinese oak silkworm and naturally laid eggs by A.pernyi eggs).All four Trichogramma species can parasitize rice moth eggs well,and their parasitic amount,egg holding amount,and total egg amount show similar changes with the prolongation of parasitic time.The specific findings were that the amount of parasitism gradually increased,the amount of eggs holding gradually decreased,and the total amount of eggs rises to a stable level.On rice moth eggs,the parasitic amount of Trichogramma was significantly higher than that of manually-extracted unfertilized eggs of Chinese oak silkworm and naturally laid eggs by A.pernyi.On the above-mentioned two kinds of host eggs,due to the different adaptability,the parasitism of the four Trichogramma species and the development of the eggs in the body showed great differences.The T.dendrolimi and T.chilonis can better parasitize manually-extracted unfertilized eggs of Chinese oak silkworm.The parasitic amount and total egg amount of the two kinds of wasps gradually increase with the extension of the parasitic time,and the amount of eggs holding gradually decreased.The T.ostriniae cannot parasitize the eggs of the manually-extracted unfertilized eggs of Chinese oak silkworm,and the total amount of eggs is the amount of egg holding,showing a gradual upward trend.There is no significant difference between the time periods after 8 hours of parasitism.The prolonged time of parasitism of T.leucaniae can gradually adapt to themanually-extracted unfertilized eggs of Chinese oak silkworm A.pernyi.It shows a small amount of parasitism from 16 h,and the parasitic amount gradually increased at 20 and 24 h.The amount of egg holding in its body decreased slightly from 16 h,while the total amount of eggs,there was a slight increase at 16 h.However,for the parasitic naturally laid eggs by A.pernyi,T.dendrolimi and T.chilonis can only parasitize a small amount,while the other two species cannot.The egg holding capacity and total egg volume of the four parasitic wasps showed that there was no significant change in the parasitic volume of T.dendrolimi in each time period,and the egg holding volume and total egg volume in the body showed a gradually decreasing trend.There was a slight decrease in the amount of eggs conceived by T.chilonis and the total amount of eggs at 20 and 24 hours,but there was no significant difference in each time period.The total amount of eggs of T.ostriniae was the amount of eggs concealed in the body,showing a gradual upward trend,and there was no significant difference between the various time periods after 8 hours of parasitism.The amount of eggs concealed and the total amount of eggs in the T.leucaniae did not change significantly with the prolongation of the parasitic time.The results shows that the suitability of different hosts to different Trichogramma was significantly different,and the host with different suitability significantly affects the parasitism of Trichogramma,which in turn affects the development of eggs in the wasp species. |
