Study On Effects Of Environmental Factors On The Decay Of Tussah Pupa In The Expansion Of Chouioia Cunea Yang

Parasitoid Chouioia cunea Yang is being widely used in China as an effective biological control agent against the fall webworm Hyphantria cunea?Drury?,a major quarantine pest in the world.In the process of large-scale artificial rearing of the parasitoid,Antheraea pernyi?Geurin-Meneville?tussah pupa is used as a substitute host.But the decay of the tussah pupa has been the main problem which greatly plagues the producers of the worms and directly affects quality and production costs of the parasitoid.In this research,parasitoid and tussah pupa,provided by the Forestry Pest Control Center,Zhangjiakou City,were used as experimental materials to study causes of tussah pupa decay and the corresponding preventive measures.The results will give important guiding significance for the parasitoid preservation and large scale artificial rearing.The main findings were as the followings:?1?According to the necrotic characteristics of the Antheraea pernyi?Geurin-Meneville?tussah pupa,the decay were divided into three types:non-parasitic decay,parasitic decay and zombie.The non-parasitic decay could be further divided into three sub-types according to the degree of decay as the followings.The first was called mild decay with white tussah pupa skull and similar appearance with the normal tussah pupa but they died already.After dissection,the decay degree of the content was not high with no obvious changes compared with the healthy ones.The second was moderate decay with black tussah pupa skull and slightly softened body.After dissection,dark brown juice could be seen.The third seemed severe rotten with pink tussah pupa skull and the diseased body was very fragile.After dissection,contents deteriorated into a yellow liquid with rotten egg smell.Parasitic decay could be further divided into two sub-types according to the development of parasitic wasps and the decay degree of inclusions.The first sub-type was characterized by small amount of parasitic wasps with underdevelopment.The tussah pupa skull was reddish brown and the abdomen was very soft.After anatomy,the inside tissue was completely disintegrated into yellow viscous liquid with acid odor.The second sub-type came up with much larger amount of parasitic wasps with seemingly normal development.The tussah pupa skull was reddish-brown and the abdomen was soft and inelastic.After anatomy,live parasitic wasps could be seen and tussah pupa inside tissue degraded into yellow juice.Zombie was contaminated by Beauveria bassiana.The tussah pupa was covered by the fungi and the carcass was stiff.After dissection,the contents were solid and hard.?2?In the process of wasps implantation,the humidity in the chamber affected the decay of the tussah pupa.The decay rate was the lowest,only about 3.923%with the chamber condition of RH30%.However,the average decay rate would reach 45.49%with the condition of RH90%.The rate showed a significant upward trend with the increase of indoor temperature and humidity and the latter played a more important role on decay degree.?3?In the process of wasps implantation,the temperature in the chamber affected the decay of the tussah pupa.The decay rate was the lowest,only about 3.923%with the chamber condition of 25?.However,the average decay rate would reach 8.24%with the condition of 28?.?4?In the rate of non-parasitic decay and parasitic decay reached between 24%and26.667%when a non-parasitic or parasitic rotten tussah pupa was placed in the middle of the healthy chamber.But the decay rate could decrease to 4%and 10.667%when the rotten tussah pupa was placed far from the healthy tussah pupa without contact with each other.The health tussah pupa would only be slightly polluted with low decay rate of about5.333%when a zombie tussah pupa was place in the middle of the healthy tussah pupa.?5?In the process of wasps implantation,the ratio of the parasitoid and tussah pupa greatly affected the parasitic rate and the decay rate.The parasitic rate was about 72%,and the decay rate was as high as 20%when the ratio was 40⁵0:1.Other ratio were also tried.The parasitism rate could reach above 91%with decay rate of 2.22%and 5.56%when the ratio was adopted as 90¹00:1 and 140¹50:1 respectively.The ratio of 100:1 seemed to be the optimum selection in the large scale wasps implantation.?6?The number of hosts and humidity conditions in the chamber also had certain influence on the decay rate.85 pieces of tussah pupa per box were cultured in RH30%and the decay rate was about 1.57%,which was much lower than that of 110 pieces and 60pieces of tussah pupa per box.The decay rate increased with the increase of the humidity for the same number of hosts.?7?The eligible disinfectant effect could be fulfilled for the implantation chamber by using different disinfectant.In this research,75%alcohol,84 liquid disinfectant and 0.1%benzalkonium bromide solution all got the satisfying similar disinfection effect,without significant difference with the new boxes?P>0.05?.But there was a significant difference?P<0.05?before and after the disinfection.Using 84 disinfectant and New Zemin disinfection,the average decay rate was reduced to 2.353%but the failed-parasitic rate was as high as 13.33%.While with 75%alcohol disinfection,the average decay rate was0.787%,and the failed-parasitic rate also decreased to 2.350%.So 75%alcohol was the best choice as it reduces the decay rate and increased the parasitism rate at the same time.?8?When the tussah pupa was chopped and stored at a low temperature,the different storage time affected the decay that occurs during the implantation process.Under the same humidity conditions,their decay rates had no significant difference between the fresh and those who were at cold storage for 30 days?P>0.05?.But there was a significant difference between them and those stored for 60 days and 90 days?P<0.001?.The decay rate of tussah pupa stored for 90 days was much higher than that of 60 days after storage.The decay rate of tussah pupa with the same storage days increased with the increase of indoor humidity.?9?Wasps adult emergence rate decreased and decay rate increased with longer low-temperature storage time at any wasps developmental stage.When cold stored at 4°C for 20 days at the pre-pupa stage,Wasps adult emergence rate could reach up to 89%with the decay rate of 3.97%.The Wasps adult emergence rate decreased to 61%with the the decay rate of as high as 14%when the the 3^rd larva and 4^th larva were cold stored at 4°C for 40 days.The decay rate was much lower when bee tubes,instead of carton and the cultivation basket,were used during the cold storage.?10?The decay prevention measures?1?Select good quality of pupa in the process of wasps implantation and choose moderately sized and plump healthy pupa with white and cyan skull top.?2?Long time storage of the tussah pupa is not suitable and should be kept no more than 30d at 4°C.?3?The temperature and humidity in the wasps implantation room should be controlled at 25°C and RH 30%.?4?The proportion of parasitoid and tussah pupa should be about 90¹00:1.?5?The number tussah pupa in each bee box should be moderate.?6?Reused bee box should be avoided as possible and if only reused ones are available,75%alcohol for disinfection should be adopted.?7?During the storage process of the adult bee,the storage temperature should be controlled at about 4°C.4^thh larvae is also preferable when cold stored and the storage time should be no more than 40d.