| Currently,the main approach to control crop insect pests in agricultural production is still dependent on using chemical pesticides.However,large application of chemical pesticides not only affects the quality of crops but also results in serious environmental pollution issues and severe toxic effects on non-target organisms.Therefore,it is urgent to promote sustainable development via biocontrol and integrated pest control.Recent studies have shown that employing the regulation and functions of soil fauna,such as the soil engineer earthworm,is a potential way to control crop insect pests.The stimulatory effects of earthworm(as well as earthworm-treated vermicompost)on plant growth have been well known,however,their impacts on plant resistance to pests were still in this infancy.First,a meta-analysis of the existing literature up to 2016 was performed to quantitatively analyse the effects of earthworms on plant growth and resistance in response to herbivory.Factors that might explain among-studies variation in the magnitude of the effects on plant resistance were further explored.Second,’Earthworm-Tomato-Western flower thrips’ system was used to explore how earthworm ecological type influences plant resistance against pest attack.Moreover,two more manipulative experiments were conducted to explore the effects of vermicompost on nematode-induced plant defence responses.The results would help mechanistically understand earthworms(and vermicompost)-mediated plant resistance,and design the environmental-friendly integrated pest management-The main results are as follows:Meta-analysis results indicated that earthworm presence increases plant growth and nutrients by 20%and 11%in response to herbivory,respectively.Overall,earthworms did not affect plant resistance against chewing herbivores,and even led to a 22%decrease in plant resistance against phloem-feeding herbivores(aphids).However,earthworm presence increased plant resistance against root-feeding nematodes and thrips by 11%and 81%,respectively.The magnitude of earthworm effects on plant resistance against herbivores(particularly phloem-feeding herbivores)was stronger when earthworm inoculations consisted of a mix of species and ecological types,and when densities of earthworms were high.In the ’Earthworm-Tomato-Western flower thrips’ experiment,permutational multivariate ANOVA showed that earthworm presence significantly changed soil properties(p＝0.001),and this translated in parallel changes of plant chemistry.Particularly,earthworm presence increased the concentration of leaf defence-related hormone jasmonic acid(p<0.05),as well as total phenolics in leaves(p<0.01)in response to thrips attack.Moreover,single earthworm inoculation particular with epigice-enodgeic earthworm Amynthas corticis increased plant resistance more than double earthworm inoculations(Amynthas cortices and Metaphire glillelmi)did,mainly by increasing the content of the defence-related phytohormone jasmonic acid and phenolic compounds instead of plant nutritious compounds,and vice versa.In the ’Vermicompost-Tomato cultivar-Root-knot nematode’ experiment,compared with inorganic fertilizer,vermicompost significantly decreased the numbers of nematode-induced galls on susceptible and resistant cultivar roots by 77%and 42%,respectively at 14dpi,and by 59%and 46%,respectively at 30dpi.Vermicompost also significantly increased root defence metabolite concentrations,defence related gene expression,and improved soil properties(p<0.05)except for mineral nitrogen.RDA analyses further indicated that soil properties particularly pH,root primary(C/N)and secondary defense metabolites(phenolics)were negatively associated with root gall.Moreover,soil microbial activity,pH and IAA concentration were positively associated with plant defense metabolites production and biomass for both susceptible and resistant cultivars.In the ’Vermicompost-Tomato genotype-Nematode’ experiment,compared with inorganic fertilizer,vermicompost significantly influenced soil pH,mineral nitrogen,available phosphorus,MBC,MBN,total carbon and total nitrogen(p<0.05)and increased plant shoot biomass.In the wild-type and JA over-expressing genotype of tomato plants,vermicompost increased nematodes-induced foliar JA concentration,thus up-regulating the expression of protease inhibitor genes and down-regulating the PAL gene expression,but decreased nematode-induced foliar SA concentration.Conversely,in the JA-deficient genotype,foliar JA concentration was quite low but SA concentration was notably increased by vermicompost,and the WRKY70 transcript levels up-regulation further triggered the suppression of JA-induced defense response.Finally,structural equation model showed that the fertilizer-mediated soil physicochemical properties significantly affected the nutritional status,chemical defense compounds and defense response gene expression in tomato leaves,ultimately inhibited the weight gain of Helicoverpa armigera(Hubner).Taken together,this study quantitatively analyzed the effects of earthworms on plant growth and resistance in response to herbivory.Manipulative experiments indicated that earthworms modified soil properties,plant growth and chemical defense allocation,in turn suppressing thrips abundance.In addition,vermicompost promoted the nematode-induced root and shoot defense via promoting soil properties.Furthermore,the vermicompost-mediated stimulatory effects were dependent on tomato cultivar or genotype.Moreover,vermicompost induced JA-mediated defences in JA over-expressing genotype of tomato plants but promoted SA-mediated defences in the JA-deficient ones These results provide a basis for developing earthworms and their subsidiary products in plan-insect interactions in light of the integrated management of pests. |
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