Study On The Biological Characteristics And Controlling Efficacy Of Scutellista Caeruled Fonscolombe

Scutellista caerulea Fonscolombe is a dominant natural enemy of the rubber pest Parasaissetia nigra Nietner.Due to its unclear biological characteristics and lack of basic data,the propagation efficiency of this wasp and its further production and application were severely limited.In order to clarify the factors affecting the biology and population growth of this wasp,as well as its potential to control P.nigra,the author observed the emergence,mating,and parasitic behaviors of this wasp indoor.Also,the effects of host age,temperature,photoperiod and supplementary nutrition on the development and reproduction of the wasp were assessed.Additionally,parasitic function response of this wasp and the interference effect of its own density were studied.Present study aimed to clarify the biological characteristics of S.caerulea and its control effeciency on the important rubber pest,P.nigra,providing data support for its further expansion and utilization.The results of the study were as follows:1.Biological characteristics of S.caeruleaThe emergence of S.caerulea mainly undergoes two processes: molting and out of the hull.In a day,the male emergence peak period was 6:00-9:00,and the female emergence peak period was 9:00-12:00.The mating behavior of S.caerulea includes four stages:Searching and courtship,pre-mating,mating,and post-mating.The parasitic behaviors of the wasp could be divided into five steps,host searching,antennal detecting,ovipositor penetrating,ovipositing,and cleaning after oviposition.From the first to the third time of oviposition,the duration of the parasitic behaviors of a wasp decreased with the number of oviposition,whereas the duration of the parasitic behaviors increased with the number of oviposition since the fourth oviposition.At temperature of 27℃,S.caerulea generation lasted 22-27 d,of which the periods of egg,larva and pupa were 3 d,9-10 d and 10-11 d,respectively.2.The important factors affecting the development and reproduction of S.caeruleaS.caerulea is an ectoparasitic wasp parasitising P.nigra.When the hosts were in the early adult stage to the black adult stage,S.caerulea had the highest selection coefficient for the black adult of the P.nigra(0.57),whereas the selection coefficient for early adults was the lowest(0.07).The development duration shortened with the increase of the host age.The development duration was the longest when the hosts were the early adults,which was 31.8 d,whereas the shortest development duration was observed when the hosts were the black adult,which was 27.5 d.The number of S.caerulea emerged increased with the host age increase,but the host age had no effect on the sex ratio of emerged S.caerulea.Temperature has significant effects on the development and reproduction of S.caerulea.In the range of 18-33℃,the oviposition and parasitic rate of S.caerulea increase with the increase of temperature,however,the oviposition and parasitism rate began to decrease above 33℃.When the temperature was 18 ℃ or 36 ℃,S.caerulea was not able to complete its development.In the range of 21-33 ℃,the development of the wasp was accelerated and the number of emerged adults increased,when the temperature increased.In the range of 24-27℃,the proportion of female offspring was higher and the adult wasps had a longer longevity compared to other temperature.When the temperature was lower than 24°C or higher than 27°C,the female ratio and longevity of S.caerulea decrease and shorten.The photoperiod has significant effects on the oviposition,development and survival of S.caerulea.The number of eggs laid and the parasitism rate increased with the increase of the illumination time within one day.Adults did not lay any eggs when the whole day was dark.The tested photoperiod was in the range of 8L: 16D-16L: 8D.When the photoperiod was 14L: 10 D,the development period was the shortest and the number of emerged adults was the highest.The adult longevity was the longest in the photoperiod12L: 12 D,which were 34.4 d and 34.5 d for females and males,respectively.Additionally,the photoperiod had no effect on the sex ratio of the wasps.During the adult stage,supplementary nutrition such as the aqueous solutions of sucrose,fructose,honey,and glucose,was not only beneficial to the longevity and reproduction of S.caerulea,also significantly increased the number of eggs and parasitism rate.When supplementary nutrition was sucrose or honey,the S.caerulea longer longevity compared to other nutrition,but trehalose was extremely unfavorable for reproduction and survival of S.caerulea.Comprehensively considering parasitism rate,developmental duration,number of emerged wasps and adult longevity,the most suitable conditions for S.caerulea was parasitizing in black adult hosts in 27-33°C with 12-14 hours continuous illumination everyday,and the adult wasps were given sucrose or honey as supplementary nutrients.3.The control efficiency of S.caerulea on P.nigraThe parasitic function response of S.caerulea to P.nigra matched the Holling-Ⅱ andⅢ models.The ratio of the instantaneous attack rate to the processing time(a/Th)was used as the evaluation index.In the range of 21-36℃,the control efficiency of S efficiency.caerulea on P.nigra was maximum at 33℃.The control efficiency to the different ages of hosts were: black adult>brown adult>early adult.In addition,there was mutual interference among the individuals of S.caerulea,the interference was the strongest at 33°C.In a certain space,when the number of hosts was constant,the parasitism rate decreased with the increase of S.caerulea density,indicating that the intensity of apportioned competition and the interference effect increased with the increase of S.caerulea density.