| Carotenoids are widely distributed in nature and play many vital roles in organisms,but most animals can not synthesize carotenoids de novo,and must acquire them from diet.Carotenoids-based coloration is an important aposematic signal,and assumed to be uniformity and conspicuousness with the selection pressure.The multicolored Asian lady beetle,Harmonia axyridis,is a highly polyphagous predator,and feeds on various aphid species and other insects.Bright red,carotenoid-derived elytra coloration of H.axyridis acts as an important aposematic signal to potential predators.That how the lady beetles utilize dietary carotenoids as aposematic pigments remains unanswered and is of great biological significance to understand the interaction of predator and preys.In this study,H.axyridis was used as a model to solve the following puzzles: what strategies will H.axyridis adopt to allocate and deposit carotenoids on elytra,and whether there were any differences of the elytra coloration after feeding on aphids that contain different carotenoids? What is the trade-off of carotenoids that have been deposited in the elytra of H.axyridis when dietary resource is limited? Dose juvenile hormone(JH),an important regulator of color polymorphism in insects,control this process? In addition,will one gene that control body coloration affect the translocation of carotenoids for aposematic coloration? Finally,in addition to serve as pigments,what are the effects of carotenoids on the development,survival and reproduction of H.axyridis.The larvae of H.axyridis were raised with aphids,Myzus persicae,and the red and green morphs,Acyrthosiphon pisum,and established three H.axyridis colonies named M-Har,RA-Har and GA-Har,respectively.In this study,the following experiments were conducted:1)First,the color morph preference of RA-Har and GA-Har,and the fitness of H.axyridis on green and red morph pea aphid were studied.The fourth instar larvae,newly emerged female and male adults of RA-Har and GA-Har did not show any prey preference(GA-Har males consumed more green morph).Well-fed as well as starved fourth instar larvae of M-Har also exhibited similar prey selection of red and green morph pea aphid.For the fitness of RA-Har and GA-Har,they had similar body weights,predation capability and fecundity,and the times required for each larval stage's development was also not significantly different.While,RA-Har had significantly higher egg hatch rate and tended to produce their eggs on other sites versus on plants.2)For M-Har and RA-Har,carotenoids deposited on the elytra of H.axyridis were in accordance with those in their diets(aphids).However,three more carotenoids were found in the elytra of GA-Har than those in green morph pea aphid.The total concentration of carotenoids as well as orange hue of the elytra varied significantly among the three colonies both at newly emerged stage(NEA)and 20 days after emergence(DAE).At NEA,the concentration of carotenoids was significantly higher in GA-Har than in M-Har and RA-Har,but the elytra orange hue was significantly lower in RA-Har.After emergence,adults in the three colonies selectively accumulated carotenoids to make the elytra redder(conspicuous)than newly emerged individuals,while the concentration of carotenoids was significantly higher in M-Har and GA-Har than in RA-Har,and the elytra orange hue was significantly lower in M-Har.3)The newly emerged adults were fed with artificial diets that were supplemented with different doses of a JH analogue(0.5,5,50,500 ?g/g(methoprene/pork liver powder)and named as AD-A,AD-B,AD-C and AD-D,respectively).AD-0 was indicated as control that free of methoprene.At 20 DAE,the concentration of carotenoids and the main components in elytra as well as orange hue were compared among the treatments.The trade-offs of carotenoids in elytra were regulated by JH,and depending on the concentrations.On AD-0,carotenoids in elytra were significantly decreased compared to the newly emerged adults.However,on AD-D,the concentration of carotenoids in elytra were greatly higher than those on AD-0,and the elytra orange hue was significantly lower than that of newly emerged adults,but the changes of carotenoids were different in different colonies.For M-Har,the contents of lycopene and ?-carotene were increased but others decreased,and the total concentration greatly increased;for GA-Har,the content of most carotenoids slightly increased,but the total concentration had no significant difference with those in newly emerged adults;for RA-Har,the content of one unknown type of carotenoids(detected at 11.24 min)increased,while others decreased,and the total concentration of carotenoids greatly decreased.4)The genetic basis of a novel light-colored mutant(gr)of H.axyridis was conducted in laboratory.The biological characteristics and carotenoids in elytra as well as its HSB value were compared between the mutant(HAM)and wild type(HAW).Genetic results confirmed that gr was a recessive homozygote and controlled by a single allele on autosome,and this mutant was a deficiency in melanin synthesis.HAM was also an adaptive deficiency.For newly emerged adults,the elytra hue was significantly higher in HAM than in HAW,but it is opposite for saturation.The concentration of carotenoids in the elytra of HAM was significantly higher than that in HAW;three carotenoids(two unknown types(detected at 6.35 min and 16.50 min)and lycopene)in the elytra of HAM was several folds of that in HAW,but,compared to HAW,less ?-carotene and ?-carotene were detected in the elytra of HAM.5)In addition,the effect of supplementation of ?-carotene on feeding efficiency of artificial diets and their application for mass rearing of H.axyridis larvae were studied.Three ?-carotene-amended artificial artificial diets were developed(0.3,3 and 30 ?g/g(?-carotene /pork liver powder)),and named as AD-L,AD-M and AD-H.AD-0 was the control that free of any ?-carotene.Feeding on artificial diet AD-H,the survival of first to fourth instar of H.axyridis was significantly higher than that on AD-0,and the survival of each stage pre-pupation was similar to that fed on aphids.Compared to aphid fed larvae,H.axyridis which was raised with artificial diets had significant longer pre-imaginal development time and less body weight of newly emerged adults.On M.persicae,compared to aphid fed H.axyridis,the fourth instar larvae raised with AD-H had similar number of aphid consumption,and preferred preying non-parasitized aphids to newly parasitized by Aphidius gifuensis,an aphid parasitoid;the adults raised with AD-H produced fewer eggs(still be almost 28),but had similar pre-ovipostion period and egg hatch rate.Taken together,aphid species greatly affected the carotenoids deposited in the elytra of H.axyridis.But the lady beetles selectively allocate ingested carotenoids to make the elytra conspicuous,and showed to have evolutionary stratigies in accordance with the components of carotenoids in aphids.Under the condition of carotenoids limited in diets,JH was proved to play important roles in regulation of the trade-offs of carotenoids in the elytra and produce redder elytra coloration at 20 DAE.The translocation and deposition of ingested carotenoids into elytra was also regulated by some genes that exhibited pleiotropy effects.Supplementation of carotenoids is a novel approach to improve artificial diet quality,and showed to have great potential in mass rearing of H.axyridis. |
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