Preference Of Rice Leaf Folder For Different Rice Growth Stages And Host Plant Species

The rice leaf folder（RLF）Cnaphalocrocis medinalis Guenée,is one of the most important migratory pests in rice.Since the 1990s,rice cropping patterns have changed greatly in the main rice-producing areas in southern China,showing a trend of diversification and complexity,such as single-or double-season rice,single-and double-season rice mixed cultivation,rice and maize intercropping or rotation,wheat and rice rotation.The emerging cropping patterns provides an uninterrupted food source and suitable habitat for rice pests,and consequently,will exert an impact on their populations.Given that,this thesis investigated the occurrence of RLF and some other arthropods in field plots with mixed cropping of single-and double-season rice.Further,the effects of rice growth stages and host plants on RLF performance and preference and food utilization efficiency were measured under laboratory conditions.These studies would contribute to RLF monitoring and controlling under the diversified and complicated rice cropping patterns.The main results are as follows:1.Occurrence of RLF and some arthropods under rice mixed-cropping pattern.A field plot experiment was established in Xing’an County,Guangxi situated in the Xianggui Corridor to investigate the influence of inter-cropping of one-and two-season rice on field population dynamics of migratory insect pests and their natural enemies during 2017 to 2018.The results show that adults of the RLF in early-rice fields were immigrant;in middle-rice field,they were immigrant and/or locally produced;while in late-rice field,they were basically emigrant.Egg deposition of RLF peaked during end of May to the last quarter of June,corresponding to stem elongation and booting stage of early-rice,which resulted in heavy leaf rolling during the last quarter of June to early July in the early-rice field.Eleven species of parasitoids were identified from eggs and larvae of RLF,parasitism of larvae was high in early-and middle-rice field.Planthopper population size was high in early-and middle-rice,the white-backed planthopper dominated on early-and middle-rice while the brown planthopper occurred more on late-rice.Population size of predators was high in late stages of rice,ratio of spider to planthopper reached as high as 1.4-6.3 in late-rice field.These results indicate that,under inter-cropping of one-and two-season rice,due to high immigration in the early season and the increasing role of natural enemies in the late season,insect pest occurrence is high in early-and middle-rice while low in late-rice in the Xianggui Corridor area.2.Performance on and preference for rice plants of different stages in the RLF.The result indicated that the larval feeding on TS had the highest emergende rate and fecundity,and feeding on BS showed the highest survival and pupation rate,the adult life expectancy were also the longest.In addition,although the 1^st instar larvae had no significant difference in rice at different growth stages,the 3^rd instar larvae preferred feeding on TS and BS than on SS.Besides,the 3^rd instars feeding on BS had the highest food consumption（FC）,relative consumption rate（RCR）,and relative growth rate（RGR）.In the cage tests,females deposited more eggs on TS and BS than on SS.The Y-type olfactory tests similarly showed that females preferred rice odors significantly to blank control,and obviously preferred TS and BS odors over SS odor.Our results showed that on rice in different growth stages,the larval performance and the adult preference of rice RLF were in accordance with the prediction of PPH.Among them,BS is more suitable for the growth and development of RLF.3.Performance on and preference for different host plants of the RLF.Three host plants,rice,corn,and wheat,were used to study the larval performance and the adult preference of the RLF,and measure nutrient utilization efficiency of the 3^rd instar larvae.The results revealed that the 1^st and 3^rd instar larvae significantly preferred to feedding on corn leaves.In no-choice test,the female moths obviously tended to lay more eggs on rice and corn,in choice test,the female moths laid the highest amount of eggs on rice,and reached 3.67eggs per hill.In addition,the 3^rd instar larvae feeding on corn leaves had the highest food consumption（FC）,approximate digestibility（AD）,relative consumption rate（RCR）,and relative growth rate（RGR）,while the efficiency of conversion of ingested food（ECI）and the efficiency of conversion of digested food（ECD）were the lowest;although the 3^rd instar larvae fed on wheat leaves with the lowest FC and RCR,the ECI and the ECD were the highest.These results demonatrated that on different host plants,the larval performance and the adult preference of RLF were not in accordance with the prediction of PPH.Among them,corn is more suitable for larvae feeding,and rice is suitable for adults depositing.