Studies On The Biological Characteristics Of Sycanus Croceouittatus And Its Control Effect On Spodoptera Frugiperda

Spodoptera frugiperda,as a new invasive migratory agriculture pest,poses a great threat to the food security production in China.Therefore,emergency chemical pesticides are generally used for prevention and control in current production.With the colonization of S.frugiperda in China,finding and using local natural enemies for biological control of S.frugiperda has become an important task for the sustainable management of this insect.In China,S.frugiperda first discovered in the corn fields in Pu’er City,Yunnan Province in January 2019.Based on the investigation of Pu’er corn fields,it was found that Sycanus croceouittatus,with a large population,could well prey on the larvae of S.frugiperda,speculating it could be an important predator of S.frugiperda in China.In order to better protect and utilize this natural enemy,the biological characteristics of S.frugiperda such as the morphological characteristics,development and reproductive capacity at different temperatures,hunger tolerance,as well as its predation and field control effects on S.frugiperda were systematically studied in order to provide a basis for the biological control of S.frugiperda.The main results were as follows:1.The suitable temperature range for the development of S.croceouittatus was 20℃～30℃,and the growth and development cannot be completed when the temperature was lower than 15℃ and higher than 35℃.The duration of S.croceouittatus gradually shortened with rising of temperature.Using the linear regression method,the development starting temperature of the egg,nymph and adult of S.croceouittatus were 13.11℃,15.79℃ and 6.20℃,respectively.The survival rate of S.croceouittatus reached the highest at 25℃.S.croceouittatus’s adult lifespan shortened with rising of temperature.The number of eggs laid by a single female increased with with rising of temperature,and there was no significant difference in the number of eggs laid by a single female at 25℃ and 30℃.The population trend index I of S.croceouittatus at 25℃ reached the maximum value of 97.69,indicated that 25℃ was most suitable for the growth,development and reproduction of S.croceouittatus population.2.The hunger tolerance of S.croceouittatus was significantly weakened with the increase of temperature in the range of 15℃～35℃.At the same temperature,S.croceouittatus had a longer duration of hungry tolerance than the nymphs,and the duration of starvation tolerance of the 5th instar nymphs was longer than that of the 2nd instar nymphs.At 15℃,the 2nd and 5th instar nymphs,females and males of S.croceouittatus had the longest hunger tolerance duration,which were 25.10,86.70,104.50 and 99.4d,respectively.At 35℃,the 2nd and 5th instar nymphs,females and males of S.croceouittatus had the shortest hunger tolerance duration,which were 6.40,24.20,30.10 and 26.80d,respectively.3.when the the 5th instar nymphs,the 2nd instar nymphs,females and males of S.croceouittatus preyed on the S.frugiperda,S.croceouittatus drages and suckes the prey fluid with stylet.The 5th instar nymphs and adults of S.croceouittatus can suck all the prey fluid until only their epidermis were left,and then looked for the next prey.4.The predation ability of S.croceouittatus is closely related to temperature.At 15℃and 20℃,the predation of S.croceouittatus was lowt.At 25℃～35℃,the predation of low-instar(2nd instar)nymphs,high-instar(5th instar)nymphs and adults of the S.croceouittatus on the 2nd instar larvae of S.frugiperda conformed to the Holling Ⅱfunctional response model,and the parameters of functional response at different temperatures were different.At 30℃,the maximum predation of the 2nd nymphs,5th instar nymphs,the female and male adults of S.croceouittatus reached the maximum,which were 12.048,66.667,100.000,and 53.632,respectively.The treatment time was the shortest at 30℃,with 0.083,0.015,0.010 and 0.019d,respectively.The above results showed that S.croceouittatus had the strongest predation ability on S.frugiperda at 30℃.5.Under the condition of fixed prey density,the density of S.croceouittatus had an interference response to its predation,which conformed to the Hassell interference response model.The equation was E=0.259P-0.364(R=0.992,F=177.864,P=0.000),and the interference coefficient(m)was 0.364,which showed that as the density of S.croceouittatus increase,the total predation increased and the average predation decreased.6.Field nets were used to study the control effect of S.croceouittatus on S.frugiperda.The results showed that S.croceouittatus can prey on the larvae of S.frugiperda in large quantities at the corn heart leaves in the field,indicating S.croceouittatus had a good potential for control of S.frugiperda.The relative control effects of S.croceouittatus were 57.81～94.28%,53.36～92.86%,51.86～85.71%after releasing according to the ratio of 1:10,1:15 and 1:20 on the first 1,3,7,and 14 days.After 35%chlorantraniliprole(75g/hm2)was applied on the 1,3,7,and 14 days,the control effects were 69.34～91.14%.Our results showed that S.croceouittatus has a good control effect on S.frugiperda.In summary,S.croceouittatus can reproduce in large numbers under suitable temperature conditions,and has strongly hunger tolerance.It has a good control effect on S.frugiperda and has great potential to become the dominant natural enemy of S.frugiperda.