Effects Of Six Non-crop Host Plants And Host Switching On Spodoptera Litura

The common cutworm, Spodoptera litura is known to feed on more than 389 plant species from over 109 families worldwide (including crop host plants and non-crop host plants). At present, there are many study of the relation between S. litura and host that object is all crop plant, but in fact, many non-crop host plants exist around the crop fields (such as weed and lawn grass et al.). In this paper, we selected six non-crop host plants familiarly of the east area of China in comparison with cabbage and cotton on the development,fecundity of S. litura.,and analysised the relationship between the major nutritional compounds and the secondary metabolites of host plants of S. litura; studied the experience of switching from non-crop host plant to crop host plant that influenced on the development, fecundity, survival of S. litura and selection. The basic results were as following:1) The duration of different developing stages were evidently difference when the larvae were fed on the non-crop host plants in comparison with crop host plants, and different non-crop host plants were also diversity. The larvae reared on the Alligator weed had the longest larvae duration (average 20.06 days) which was evidently longer than crop host plant ( cabbage average 15.00 days, cotton average 18.70 days ), while other non-crop host plants were shorter than crop host plant. There were no significant differences among the duration of pupae when the larvae were fed on the different non-crop host plants in compare with cabbage (average 8.63 -9.04 days), but all longer than cotton (average 8.20 days).The adult life-span of S. litura feeding on the non-crop host plants was no significantly different comparison with cotton (average 5.77-8.26 days), however without exception shorter than cabbage (average 9.06 days). There were significant differences in pupae weight and fecundity of adults when fed on different kinds of host plant, the accumulative survival rates and sexual differentiation existed some diversities.2)The contents of water, soluble sugar,total sugar, total Nitrogen, total phenolics in plant and the C/N ratio had significant differences among the six non-crop host plants and two crop host plants, but the contents of amylum was no significant difference. The relationship between the major nutritional compounds, secondary metabolites of host plants and the indices of fitness was studied by grey relational analysis (GRA) in the study. The results showed the water content was the major factor affecting the development, fecundity, sexual differentiation and survival of S. litura,while soluble sugar had no effect on the fitness;total sugar had some influence on the adult life-span, sexual differentiation, survival, pupae weight and fecundity; total nitrogen had biggish impact on the development, survival and pupae weight; total phenolics and C/N played a great role on the fecundity.3) By comparison with mother and offspring of S. litura also feeding on the crop host plant, the mother fed on the species of non-crop host plants but the offspring diverted to feeding on the crop host plants that influenced on the development, the results indicated: the larvae duration of S. litura all prolong after switching host (with the exception of from pigweed to cabbage and cotton respectively);on account of the different host plants after switching, the duration of pupae existed difference, the duration of pupae S. litura switching from non-crop host plants to cabbage were shorter than cabbage to cabbage, while switching from non-crop host plants to cotton were longer than cotton to cotton (make an exception of switching from Alligator weed to cotton); after switching host the adult life-span of S. litura shorten and the accumulative survival rates and sexual differentiation had some difference comparison with feeding on the crop host plants; switching from non-crop host plants to cabbage, the pupae weight of S. litura at large increased (with the exception of switching from Purslane to cabbage), but switching from non-crop host plants to cotton, the pupae weight of S. litura all decreased; the fecundity of S. litura reduced after switching.4) After switching the host selectional preference trial of larvae of S. litura indicated that: the 2th instar larvae that the mother and offspring were all fed on the same non-crop host plants was apt to select the primary non-crop host plants, nevertheless after switching there existed some difference: switching from Pigweed and Clovet to cabbage and cotton respectively, the 2th instar larvae prefered Pigweed and Clovet to crop host plant, whereas switching from Alligator weed, Purslane, Redroot pigweed and Copperleaf to cabbage and cotton respectively the 2th instar larvae prefered crop host plants to primary non-crop host plants; however the 4^th instar larvae of S. litura that the mother and the offspring were all fed on the same non-crop host plants was apt to select cabbage which was one of the crop host plants, nevertheless after switching there also existed some difference: switching from Pigweed to cabbage and cotton respectively, the 4^th instar larvae preferred cabbage to Pigweed, however switching from Clovet to cabbage,the 4^th instar larvae preferred Clovet to crop host plant, switching from Clovet to cotton,the 4^th instar larvae preferred crop host plant to Clovet .