Effects Of Interaction Between Constitutive And Induced Resistance In Soybean Plants On Fitness Traits And Behaviour Of Spodoptera Litura And Its Parasitoid

During the co-evolutionary process of plants and herbivores,plants evolved a variety of defensive mechanisms.These defensive mechanisms include constitutive and induced resistance.The herbivore induced resistance of plants as important adaptation not only affects the current feeding herbivores,but also affect the subsequent herbivores and their natural enemies.In this study,I chosed soybean cultivars with varying constitutive resistance as model plants,used three herbivore-feeding modes to induce soybean resistance,examing effects of interaction between constitutive and induced resistance in soybean plants on fitness traits and behaviour of Spodoptera litura and its parasitoid Meterous pulchricornis.Four questions were addressed.(1)What are the effects of constitutive resistance levels of soybean on the life history traits of S.litura and M.pulchricorni?(2)What are the effects of interaction between constitutive and induced resistance in soybean plants on the trypsin inhibitor contents in the leaf,detoxifying enzymes and proteases in S.litura larvae?(3)What are the effects of interaction between constitutive and stem leaf herbivores induced resistance in soybean plants on life history traits of S.litura and M.pulchricorni?(4)What are the effects of interaction between constitutive and root nematode induced resistance in soybean plants on the life history traits of S.litura and M.pulchricorni?Main results and conclusions obtained from the study are summarized below.1 Effects of soybean cultivars on food consumption and utilization efficiency of Spodoptera litura larvaeTo examine effects of soybean cultivars with varying constitutive resistance levels on S.litura larvae in nutritional ecology traits,we randomly choosed 7 soybean cultivars from a line of genotypes varied in resistant levels to feed S.litura 4th larvae.We used two approaches to analyze data:using mixed effects model to evaluate the effects of soybean cultivars on variability in food consumption and utilization efficiency;empoying one-way ANOVA to detect differences in food utilization indices between soybean cultivars.The results from the first approach showed that food consumption and final body weight of 4th larvae varied greatly across soybean cultivars.The results from the second approach showed that the food utilization indices had significant differences across soybean cultivars,and soybean cultivars influenced food utilization indices of larvae,the indices being lowest when larvae fed on high resistant cultivar but highest when larvae fed on low resistant cultivar.Results of this study suggest that resistance of soybean cultivars affect food consumption and utilization efficiency of S.litura.2 Effects of soybean resistance on variability in life history traits of the higher trophic level parasitoid M.pulchricornisTo extrapolate the influence of plant cultivars varying in resistance levels to hosts on parasitoid life history traits,we estimated variation in parasitoid developmental and reproductive performances as a function of resistance in soybean cultivars,which were randomly chosen from a line of resistant genotypes.Our study showed that the parasitoid M.pulchricornis varied widely in offspring survival and lifetime fecundity,but varied slightly in development time and adult body size,in response to the soybean cultivars that varied in resistance to the host S.litura.Furthermore,the variability in survival and lifetime fecundity was different in the 2nd than in the 4th instar host larvae,varying more in survival but less in lifetime fecundity when attacking the 4th than 2nd instar larvae.Our study provides further evidence supporting that plant resistance to herbivorous hosts have variable effects on different life history traits of higher trophic level parasitoids.3 Influence of herbivore feeding on trypsin inhibitor in the leaf of soybean cultivarsTo explore effects of herbivore feeding damage on the trypsin inhibitor contents in the leaf of soybean cultivars,we randomly chose three soybean cultivars varying in the reisistant level,which were damaged by chewing-feeding Spodoptera exigua larvae or phloem-feeding Aphis glycines.The results showed that trypsin inhibitor contents in leaves increased initially and then decreased with leaf areas consumed by chewing S.exigua larvae,rising to the peak at 30%leaf areas consumed.Though trypsin inhibitor contents in the leaf flunctuated with feeding time by both S.exigua and A.glycines,the general trend appeared increasing initially and then decreasing,peaking at day 4-5 by S.exigua feeding and day 5 by A.glycines feeding.Results of this study suggest that feeding damage type have differential effects on trypsin inhibitor contents in leaves of soybean cultivars.4 Effects of herbivore-feeding induced soybean defenses on detoxifying enzymes and proteases of Spodoptera litura larvaeThis study explored effects of constitutive and inducible defenses of soybean plants,elicited by feeding damage from either the chewing feeding herbivore S.exigua or phloem feeding insect A.glycines,on S.litura larval detoxifying enzymes and proteases.We randomly chose three soybean cultivars with varying levels of constitutive resistance.In the first trial,we measured activity of detoxifying enzymes and proteases when S.litura fed on treated soybean leaves moulted to the 2nd instar.In the second trial,S.litura 4th instar larvae were analyzed in the activity of detoxifying enzymes and proteases at 3,6,9,12,24,36,48,or 72 h after feeding on respective treated plants.Our study indicated that feeding on soybean plants damaged by either S.exigua or A.glycines,S.litura 2nd instar larvae increased in activity of glutathione-S-transferase,carboxylesterase and alkaline-like enzyme,but decreased in activity of cytochromes P450,total protease,weak alkaline trypsin-like enzyme and chymotrypsin-like enzyme.For S.litura 4th instar larvae feeding on soybean plants damaged by S.exigua or A.glycines,(1)glutathione-S-transferase and carboxylesterase fluctuated in activity irregularly before 24 h post feeding,and then increased steadily;(2)cytochromes P450,decreased steadily with feeding time;(3)total protease increased 12 h post feeding and then decreased;(4)weak alkaline trypsin-like enzyme and chymotrypsin-like enzyme increased initially then decreased,and leveled off;(5)active alkaline-like enzyme fluctuated in complex ways depending on feeding damage type,decreasing when damaged by S.exigua but then increased when damaged by A.glycines.Results of this study suggest that constitutive resistance level and herbivore-feeding induced defenses in soybean plants in interaction influence activity dynamics of detoxifying enzymes and proteases of S.litura larvae.5 Influence of constitutive and herbivore-damage induced soybean defenses on developmental performances of Spodoptera litura and Meterous pulchricornisThis study investigated associative effects between constitutive and inducible defenses of soybean varieties,elicited by feeding damage from either the polyphagous herbivore S.exigua or phloem feeding insect A.glycines,on developmental and reproductive parameters of the host S.litura and its parasitoid M.pulchricornis.Our study indicated that both leaf-chewing and phloem-feeding damage to soybean plants had negative effects on the herbivore S.litura larvae across its life history,as measured by development time,survival to adult,and adult body weight at emergence.Such effects were stronger overall in magnitude for the highly constitutive resistance plant cultivar,and for the damage by the chewing herbivore to soybean cultivars at low and medium constitutive resistance levels.Both leaf-chewing and phloem-feeding damage treatments had negative effects on the parasitoid,prolonging development time,decreasing parasitoid survival to adult and lifetime fecundity,but such negative effects varied depending on constitutive resistance levels.While the chewing damage-induced defense had a stronger negative impact than did the phloem-feeding on parasitoid fecundity at the low and medium constitutive resistance levels,the two types of feeding damage had a similar impact at the high constitutive resistance level.We conclude that constitutive resistance level and herbivore-feeding induced defenses in soybean plants can interact to have negative effects on the developmental and reproductive performances of a caterpillar and its parasitoid.6 Effects of root nematode feeding and plant constitutive resistance on above-ground caterpillar host and M.pulchricornisThis study investigated the impact of below-ground root herbivory by the nematode Heterodera glycines on development and reproduction of the host S.litura and its parasitoid M.pulchricornis,mediated through three soybean cultivars varying in constitutive resistance to the lepidopteran host.Our study indicated that root infected nematodes had negative effects on the herbivore S.litura larvae across its life history,as measured by developmental time and adult body weight at emergence.Such effects varied in magnitude depending on the soybean cultivars varying in constitutive resistance,with the most defended cultivar having the strongest effects on caterpillar life-history traits.Soybeans with nematode larvae infected roots also had negative effects on the parasitoid by prolonging its development time,reducing adult body size,decreasing survival to adult,and lowering lifetime fecundity,with these negative effects varying by soybean constitutive resistance level.Our research shows that below-ground herbivores may interfere with biological control services provided by parasitoid wasps mediated by adverse changes in plant defense through their aboveground herbivore hosts.Our study emphasizes an important role plant constitutive resistance plays in below-ground feeding-induced plant defenses to herbivores and their effects on parasitoids on higher trophic levels.7 Effects of soybean resistance on the host patch foraging behavior of Meteorus pulchricornisTo explore effects of the interaction between soybean resistance and other behaviors on the patch-foraging behavior of M.pulchricornis,this study used factorial design with 3 factors at 2 levels:soybean cultivars(high and low resistance),patches visited or not by conspecific,and parasitoids with or without the experience of patch-foraging.Experiments were carried out in large clear cages.Our study indicated that the patch leaving tendency of parasitoids were higher on low than high resistant soybean cultivars,higher from the patch that had been visited than from fresh patch,and higher for parasitoids with patch-visiting experience than without.In addition,the patch residence times for parasitoids with patch-visiting experience were shorter than those without.Soybean cultivars and patches visited or not by conspecific,patches visited or not by conspecific and parasitoids with or without the experience of patch-foraging,both can interact to effect on the number of parasitoid ovipositor stings.On the high resistant soybean cultivar,the number of ovipositor stings of parasitoid without patch-foraging experience were lower than parasitoids with patch-foraging experience when on patches not visited by conspecific,but the opposite was true when patches visited by conspecific.On the low resistant soybean cultivar,the number of ovipositor stings varied slightly on two kinds patch,between parasitoids with and without patch-foraging experience,and was greater on fresh patches than the visited by conspecific parasitoids.We conclude that soybean resistance,host patch quality and parasitoid experience can influence foraging behaviors of M.pulchricornis.