Effects Of Plant Nutrition On Behavior, Development And Population Parameters Of Bemisia Tabaci (Gennadius)

Due to the invasion of B biotype, Bemisia tabaci occurred greatly and caused seriouseconomical damage on cotton, ornamental plants and vegetable crops in the recent years inChina. With the aims to seek for environment-friendly population regulation technologies andto elucidate the inter-relationships between host plant nutrition and the sweetpotato whitefly,we investigated the effects of soil potassium fertilization and soil-applied N, P and K fertilizerson development, survival, host selection and life table parameters of Bemisia tabaci.Additionally, we tested the relationship between adult preference for host leaf age andoffspring performance. The results are as follows.In this paper, duration, survivorship, larval size, adult host selection and life table parametersof Bemisia tabaci laboratory population and potassium content in cucumber leaves wereinvestigated to determine the influence of potassium fertilizer, by setting 0 mg/L, 30 mg/L, 60mg/L, 120 mg/L and 240 mg/L five potassium concentration treatments for cucumber plants.The results showed that duration, survivorship and size of the whiteflies on the cucumberplants provided with different potassium concentrations were different. The total duration fromegg to adult on plants with the 240 mg/L potassium concentrations was 21.4 days, and 18.3days with the 60 mg/L potassium concentrations. The total survival rates of the whiteflies fromegg to adult were 71.4%, 84.7%, 83.8%, 76.2% and 64.8% on plants with 0 mg/L, 30 mg/L,60 mg/L, 120 mg/L and 240 mg/L potassium concentrations, respectively. In the choiceexperiment, the number of adults and deposited eggs per plant were significantly higher onplants with 60 mg/L potassium concentration than on those with others. Potassium content incucumber leaves didn't increase with concentration increase of the applied potassium fertilizersolutions, the highest presenting in cucumber leaves treated with 30 mg/L K₂O solution. Theintrinsic rate of population increase (r_m) of whitefly populations on cucumber plants treatedwith 0 mg/L to 240 mg/L potassium fertilizer were 0.14, 0.17, 0.17, 0.15 and 0.13, respectively;and net reproductive rate (R₀), 47.79, 111.55, 115.18, 61.96 and 49.58, respectively. Therefore,cucumber plants with high potassium content in leaves are suitable for whitefly populationgrowth.To further elucidate the effects of soil-applied N, P and K fertilizers on the relationshipbetween host and the sweetpotato whitefly, Bemisia tabaci, we investigated the duration,survivorship, larval size, host selection, fecundity and longevity of the whiteflies on cucumberplants treated by different fertilizer levels. The results showed that soil-applied fertilizer havesignificant effects on larval duration. Soil-applied fertilizers had no effects on survival rates ofeggs and young nymphs, but significantly affected survival rates of old nymphs and sizes of allnymphs. Adults preferred cucumber plants treated with medium nitrogen and withoutpotassium and phosphorus and disliked those treated with high nitrogen, potassium and phosphorus. Longevity and fecundity of the whiteflies were the shortest and lowest oncucumber plants treated with phosphorus only. Population of the whiteflies increased by 108.21folds on cucumber plants treated with nitrogen, potassium and phosphorus, while on plantstreated with phosphorus only, by 26.23 folds.Additionally, preference of Bemisia tabaci adults for cucumber leaf ages and its relationshipwith offspring performance in terms of duration and survivorship were investigated, andpreference of whitefly adults was correlated to trichome density on leaves of different leaf agesin this paper. The results showed that: Leaf age had a significant effect on adult host selection;the adults preferred leaves in the middle stratum of cucumber plants for feeding andoviposition. Leaf age had no significant effect on duration and survivorship of Bemisia tabaciimmatures, except durations of egg and 4th instar nymph. Significantly negative correlationexisted between trichome density and leaf age preference of B. tabaci adults at the initial stageof exposure, but at later stages of exposure, no significant correlation existed.Results of this paper showed that, cucumber plants with high potassium treated or treatedwith phosphorus only were unsuitable for whitefly population growth, but treated with highnitrogen were suitable for whitefly population growth, and whiteflies disliked feeding andoviposition on the plant with high or low trichome density. Therefore, in our productionpractices, we can reduce the economical damage caused by whiteflies through adjustedfertilizer using or selected anti-insects species. Also, the results of this paper provide abrand:new thought to make a environment-friendly population regulation technologies ofwhiteflies.