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Evaluation Of Host Plant Quality And Host Selection Behavior Of Spodoptera Litura (Fabricius)

Posted on:2008-03-23Degree:MasterType:Thesis
Country:ChinaCandidate:M W PuFull Text:PDF
GTID:2143360215474704Subject:Agricultural Entomology and Pest Control
Abstract/Summary:PDF Full Text Request
The selection and utilization of host plants for Spodoptera litura (Fabricius) were studied in this paper. Effects of twelve host plants on the development, fecundity, survival and nutrition utilization of S. litura in Yangzhou were reported.Fitness and nutrition utilization indices of S. litura were combined for the integrated evaluation of the host plants quality, and the relationship between the major nutrition compounds, secondary metabolites of host plants and the fitness and nutrition utilization of S. litura was discussed. In addition, the host plant selectional preference of different instar larvae and adults for six different host plants was examined and the mechanism of host plant selection was preliminary discussed. The results were as following:1) The duration of different developing stages were evidently influenced when the larvae were fed on different host plants, and the influence varied with different developing stages. The larvae reared on Pigweed had the shortest larvae duration (average 12.48 days), while the longest larvae duration on soybean (average 16.02 days). The sequence of host plants fed on which the larvae had larvae duration from long to short was soybean, Cotton, Cowpea, Common Amaranth, Pepper, Alligator weed, Cabbage, Greengrocery, Water Spinach, Tomato, Taro and Pigweed. There were no significant differences among the duration of prepupa when the larvae were fed on the different host plants. The duration of pupae had significant differences, the longest on Water Spinach (average 10.85 days), and the shortest on Taro (average 7.14 days). The sequence of host plants fed on which the larvae had pupae duration from long to short was Water Spinach, Greengrocery, Cabbage, Cotton, Common Amaranth, Cowpea, soybean, Pepper, Alligator weed, Pigweed, Tomato and Taro. Adult life-span was significantly affected by the host plants, with the longest on Water Spinach (average 9.62 days) and shortest on Alligator weed (average 5.96 days). The sequence of host plants fed on which the larvae had adult life-span from long to short was Water Spinach, Taro, Cabbage, Tomato, Pigweed, Pepper, Common Amaranth, Greengrocery, Cotton, Cowpea, soybean and Alligator weed. The accumulative survival rates were 80%-90%, and were mostly affected by the larvae survival and eclosion rate. There were significant differences in pupae weight, sexual differentiation and fecundity of adults when fed on different host plants, and the pupae weight was found to be significantly related to the fecundity of adults. Host plants also had impact on the nutrition utilization, and the indices of Relative consumption rate (RCR), Relative growth rate (RGR), Approximate digestibility (AD), Efficiency of Conversion of digested food (ECD) and Efficiency of conversion of ingested food (ECI) were significantly different between the larvae reared on different host plants.Eight indices, including larvae duration, adults life-span, accumulative survival rate, No. of eggs laid by adults, RGR, AD, ECD and ECI, were combined for the integrated evaluation on the quality of twelve host plants, and the result indicated that the order of suitability of host plants for S. litura was Cabbage, Taro, Water Spinach, Pigweed, Tomato, Cowpea, Common Amaranth, Greengrocery, Pepper, Cotton, Alligator weed and soybean.The contents of water, total Nitrogen, soluble sugar, amylum, total sugar, total phenolics in plant and the C/N ratio had significant differences among the twelve host plants. The relationship between the major nutrition compounds, secondary metabolites of host plants and the indices of fitness and nutrition utilization was studied by grey relational analysis (GRA) in our study. The results showed the water content was the major factor affecting the development, fecundity, survival and nutritional utilization, while total Nitrogen content and C/N had no effect on the fitness and nutrition utilization indices. Soluble sugar and total sugar would effect the growth of larvae, pupae duration, life-span of adult and the nutrition utilization, and amylum together with total phenolics were affection factors for the growth of larvae and RCR. Meanwhile, amylum content of host plant played a role on the sex ratio of adults.2) Six host plants, including Water Spinach, Cotton, Common Amaranth, Cabbage, Tomato and Pepper, were selected to conduct the experiment for host plant selection of the larvae and adults of S. litura. The results showed that the newly hatched larvae of S. litura had weak selection preference which increased according to the growing of larvae, while the 4th instar larvae had obvious preference to host plants. Water Spinach and Pepper were proved to be the most favorite plants for the larvae of S. litura. The ovipositional preference to host plants of the adults was significantly different. The adults oviposited more frequently on Cabbage and Water Spinach, while the eggs laid on Tomato and Pepper were few.By studying the host selectional preference of larvae and adults of S. litura with different host plant experience, we found that the host preference of the second generation neonate of S. litura with different feeding host experience was not obvious compared with the control. The"learning"behavior was strongly exhibited in the 2nd instar and 4th instar larvae of S. litura. The feeding experience of larvae had impact on its host selection, and the preference to a host plant for the larvae would be enhanced after feeding on it. Further more, the host plant experience of larvae had no affection on the ovipositional preference of adults.Our study also showed the host preference of larvae and adults of S. litura wasn't correlated with their development, fecundity and survival when fed on the host plants. The major nutritional compounds or nutrition index such as soluble sugar, total nitrogen and C/N didn't have relation to the larvae host selection, while total phenolics restrained larvae feeding preference. The adults preferred to oviposit on plants which had higher water content, and there were no significant relationship between host preference of S. litura adults and soluble sugar, total Nitrogen, C/N and total phenolics.
Keywords/Search Tags:Spodoptera litura (Fabricius), Host plant quality, Fitness, Nutritional utilization, Grey relational analysis, Host selection, Feeding preference, Ovipositional preference, Learning
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