Abstract:

The results of bioassay and field efficacy tests of the nuclear polyhedrosis virus of Chihuo zao Yang were reported in this paper.Early third-instar larvae were fed on jujube tree leaves immersed with polyhedral inclusion bodies(PIB)suspension of virus.Mortality of larvae increased with the increasing of concentration of polyhedral inclusion bodies suspension.The LC₅₀ and 95% confidence limits were 3.65 × 10⁵ and 4.04 ×10⁴ ~ 3.13 ×10⁶PIBs/mL, respectively.The LT₅₀ values for the virus concentration of 2.5 ×10⁷, 1.25 ×10⁷, 2.5 ×10⁶, 1.25 ×10⁶ and 2.5 ×10⁵ PIBs/mL were 7.49, 7.94, 9.08, 9.57 and 10.01 days, respectively.A study on larval susceptibility to a concentration of 2.5 ×10⁶ PIBs/mL virus suspension indicated that the LT₅₀ values increased with the increasing of instar(from 5.97 days for early second instar larvae to 12.57 days for early fourth instar larvae).Mortality decreased with the increasing of instar (96.7 % for early second instar larvae, 73.3 %for early third instar larvae and 30.0% for early fourth instar larvae).Mortality of larvae decreased and the LT₅₀ values increased at a low temperature(16 ℃±1 ℃) and at a high temperature(35 ℃±1℃)in contrast to a middle temperature(21 ℃±1 ℃or 26 ℃±1 ℃). The field-release testing were conducted on 8th of May, 1998, when 85% of the larval population consisted of the second and third instar larvae and on 17th of May, 1998, when 85% of the larval population consisted of the third and fourth instar larvae, with virus suspension 2.5 ×10⁶, 5 ×10⁶, 2.5 ×10⁷ and 5 ×10⁷. The adjusted mortility were 90.33%, 90.35 %, 91.80 %, 92.29 % for the first spraying and 66.03 %, 67.31 %, 65.69 %, 69.38 % for the second spraying, respectively, which were analyzed statistically of ANOVA and Duncan' s new multiple-range test.The results from field-release testing indicated that the best time for control Chihuo zao Yang was the first ten-days of May in Taigu, Shanxi and the concentration suitable for control was 2.5 ×10⁷ PIBs/mL, with which the adjusted mortility was higher and the cost was lower.

Key words: Chihuo zao Yang, Nuclear polyhedrosis virus, Bioassay, Field efficacy tests