Effects of resistant and susceptible cassava germplasms on development and reproduction of Mononychellus mcgregori (Flechtmann & Baker) (Acari: Tetranychidae)
Fuping Lu1, Hui Lu1, Xiao Liang1,Qian Li1, Qing Chen1*,Jianqiu Ye2, Kaimian Li2
1) EPPI, CATAS; Haikou, Hainan, P.R.China；2) TCGRI, CATAS, Danzhou, Hainan, P.R.China
* , Registrant ID#4506
Mononychellus mcgregori is one of the most important pest mites of cassava. This mite originates from South America and in China it was recorded for the first time in Danzhou, Hainan, in 2008. Currently, it occurs in important cassava-growing regions in Guangxi, Guangdong and Yunnan, where it causes significant damage to crops causing 2–10% reduction in production in the case of slight damage, and up to 60% reduction in production in the case of serious damage. Experiments had confirmed that it can develop and reproduce normally on the leaves of rubber plants; this indicates that it also could cause significant harm to rubber tree. The detrimental effects of M. mcgregori have become one of the most important potentially limiting factors for the sustainable development of the cassava industry in China.
The application of resistant host genotypes is considered one of the most efficient and environmentally friendly means of pest control. To develop a preliminary understanding of the mite-resistance mechanisms of cassava germplasms, stably resistant cassava germplasms were obtained, the development and reproduction of M. mcgregori that fed on leaves of resistant (C1115, Myanmar, Colombia-4D and PII167) and susceptible (SwissF21, BRA900, ZM9066 and CM1210-10) cassava germplasms were compared in the laboratory. The results indicated the following: (1) feeding on susceptible versus resistant cassava germplasms significantly influenced the developmental rate of each M. mcgregori offspring stage evaluated. M. mcgregori developed faster on susceptible germplasms than on resistant germplasms. Susceptible germplasms demonstrated the shortest life cycle (＜4.00 d for eggs, ≤3.00 d for larvae, protonymphs and deutonymphs, 11.00~12.5 0 d for eggs to adults), whereas resistant germplasms showed the longest developmental duration (＞5.00 d for eggs, ＞4.00 d for larvae, protonymphs and deutonymphs, 18.50~21.00 d for eggs to adults); (2) Adults fed susceptible germplasms oviposited more eggs than those that fed on resistant germplasms. The total fecundity (eggs/female) ranged from 39.57 to 49.2 on susceptible germplasms, and significantly different results were observed for the mites that fed on resistant germplasms (from 6.53 to 15.40); (3) Egg hatchability was 77.00-98.00% on susceptible germplasms and 7.20-36.00% on resistant germplasms; (4) Overall, the higher the resistance level, the lower the percentage of female offspring. The lowest sex ratio was 78.43% (for mites that fed on the resistant germplasm, C1115), and the highest was 86.00% (for mites that fed on the most susceptible germplasm, BRA900). The offspring sex ratios were (almost) constant on susceptible cassava germplasms but were variable on resistant germplasms; (5) The lifespans of the adult mites was significantly influenced by the cassava germplasms, and they ranged from 18.00 to 21.00 days on susceptible germplasms and 7.00 to 13.00 days on resistant germplasms. This study provided experimental material and technical support for the breeding of mite-resistant cassava germplasms.