| Frankliniella occidentalis,an invasive pest with a wide host range,has caused serious damage in many areas of China since its introduction.Thrips hawaiiensis is a native pest with a wide host range of flowering plants,and it particularly damages mangoes in coastal areas.The two thrips share similar ecological niches and are especially harmful to flowering hosts.Moreover,they showed distinct population advantages on different flowers owing to their different host adaptations.The floral industry is economically important in China,and thrips are prominent pests that negatively affect flower quality and production.To date,few studies have been conducted to compare the biological and ecological characteristics of F.occidentalis and T.hawaiiensis.In this study,we investigated the feeding behaviors of field thrips and the population growth of thrips on different indoor hosts.Additionally,the adaptability of the two species to different flowering hosts was examined.A differential analysis was conducted of the hosts' physical and chemical properties(including their color,volatiles,secondary substances and nutrients),along with an examination of the different responses of the thrips' energy substances(soluble sugar,soluble protein and fat),detoxification enzymes(cytochrome P450,carboxylesterase,phosphatase,glutathione transferase and acetylcholinesterase)and protective enzymes(superoxide dismutase,catalase and peroxidase)on different hosts.Finally,we analyzed the physical and chemical adaptation mechanisms of the two species to different hosts.1 Feeding habits of thrips on their hosts Field investigation showed that both F.occidentalis and T.hawaiiensis were found to injure 21 kinds of flowering plants,but with different host preference.Rosa rugosa,Rosa chinensis and Tagetes erecta were the most suitable host plants for F.occidentalis,while Gardenia jasminoides and Hydrangea macrophylla were the most suitable host plants for T.hawaiiensis.The two thrips species showed opposite host suitability levels on R.rugosa and G.jasminoides,but the same host suitability level existed for Gerbera jamesonii.2 Field population dynamics and indoor population development of thrips(1)Field population dynamics of thrips The population dynamics of two thrips species on three hosts were studied for 3 years from 2016 to 2018.The population size of F.occidentalis on R.rugosa was greater than on G.jamesonii,followed by G.jasminoides,while for T.hawaiiensis,the population size order was G.jasminoides > G.jamesonii > R.rugosa.Over the 3-year period,the population ratio of the two thrips species changed somewhat on the same flower.On R.rugosa,the population sizes of F.occidentalis were 3.56,2.79 and 3.01 times those of T.hawaiiensis,respectively.On G.jamesonii,the population ratios were nearly 1:1.On G.jasminoides,the T.hawaiiensis populations were 1.92,2.18 and 2.11 times greater than those F.occidentalis,respectively.(2)Indoor thrips population development Short-term growth studies of indoor populations revealed that,beginning with the same thrips populations feeding on three kinds of petals for the same time period(15,30 and 45 d),the populations of F.occidentalis on rose were greater than on Gerbera daisy,followed by on gardenia,while for T.hawaiiensis,the population size order was G.jasminoides > G.jamesonii > R.rugosa.When a 1:1 ratio of F.occidentalis and T.hawaiiensis were fed on the same host for the same time(15,30 and 45 d),the former had a larger population than if fed on R.rugosa,but a smaller one than if fed on G.jasminoides.When fed on G.jamesonii for 15 d,the former had a larger population than the latter,but when fed for 30 d and 45 d,the two thrips populations were almost the same size.Indoor observations of populations revealed that the developmental periods of thrips on R.rugosa,G.jamesonii and G.jasminoides were significantly different.The developmental periods of F.occidentalis were 9.38,9.85 and 10.62 d,respectively,while for T.hawaiiensis,they were 10.92,10.06 and 9.69 d,respectively.Similarly,the survival rates of the two species on different hosts were significantly different,with the generational survival rates of F.occidentalis on R.rugosa,G.jamesonii and G.jasminoides hosts being 84.33%,79.00% and 74.33%,respectively,and those of T.hawaiiensis being 80.67%,74.00% and 59.00%,respectively.When fed on the same hosts,the developmental duration for the former on R.rugosa and G.jamesonii was significantly shorter than that of the latter,but significantly longer than the latter when fed on G.jasminoides.On R.rugosa,the generation survival rate of F.occidentalis was significantly higher than that of T.hawaiiensis,but lower than that of T.hawaiiensis when fed on G.jasminoides.There was no significant difference in the survival rates of the two thrips when fed on G.jamesonii.The total amounts of eggs laid by the two thrips species on the three flowers were also significantly different.F.occidentalis laid totals of 128.58,101.80 and 87.74 eggs per female on R.rugosa,G.jamesonii and G.jasminoides,respectively,while T.hawaiiensis laid totals of 59.88,73.80 and 91.38 eggs per female,respectively.On R.rugosa and G.jamesonii,the total amount of eggs laid by the former was significantly higher than the latter,but on G.jasminoides they laid almost the same amounts of eggs in total.The life tables of the two thrips on different flower hosts demonstrated that their life table parameters were significantly different among the hosts.The net proliferation rates(R0)of F.occidentalis on different hosts,were in the following order: R.rugosa(65.15)> G.jamesonii(49.09)> G.jasminoides(38.66),while for T.hawaiiensis the R0 order was: G.jasminoides(47.91)> G.jamesonii(36.84)> R.rugosa(27.47).The intrinsic growth rate,or rm,of two species of thrips on different hosts followed a similar trend.When both thrips fed on R.rugosa,F.occidentalis had greater R0 and rm values than T.hawaiiensis,but the opposite was found when they were fed on G.jasminoides.When fed on G.jamesonii,the former had a significantly higher R0 than the latter,but they had almost the same rm.3 Determination of differences in physical and chemical characteristics of flowering hosts(1)Effects of host' color and volatiles on thrips' behavior Using the RGB color model and leaf method test,we determined that F.occidentalis showed a host preference based on color in the following order: R.rugosa > G.jamesonii > G.jasminoides,while for T.hawaiiensis,the order was as follows: G.jasminoides > G.jamesonii > R.rugosa,indicating that flower color has an important influence on the host selection of thrips.The Y-tube and four-arm olfactometer tests showed that the volatiles of the three flowers were attractive to both thrips.The strengths of the attractions of different flower volatiles to F.occidentalis came in the order of R.rugosa > G.jamesonii > G.jasminoides,while for T.hawaiiensis,the order was G.jasminoides > G.jamesonii > R.rugosa,which indicated that host volatiles have guiding effects for thrips when choosing a host.A further GC-MS analysis showed that there were significant differences in the constituents and contents of volatiles from the three flowers.There were 23,16 and 36 compounds detected in the volatiles of R.rugosa,G.jamesonii and G.jasminoides,respectively,with 3,5-dimethoxytoluene(24.94%),trans-3-pentene-2-ketone(52.31%)and L-linalool(52.06%),respectively,having the greatest contents.(2)Flower nutrient content determination Significant differences were found in the contents of soluble sugar,soluble protein,free amino acids and other nutrients among the three flowers.The soluble sugar content was highest in G.jasminoides(23.75 mg·g-1),followed by G.jamesonii(20.67 mg·g-1),and the lowest content was in R.rugosa(12.41 mg·g-1).The contents of soluble protein and free amino acids were highest in R.rugosa,at 110.04 and 94.74 mg· g-1,respectively,followed by G.jasminoides at 78.44 and 65.33 mg· g-1,respectively,and the lowest contents were found in G.jamesonii,at 28.77 and 25.44 mg·g-1,respectively.(3)Determination of secondary substances in flowers Significant differences were found in the tannic acid,flavone,alkaloids and total phenol contents.The highest tannic acid content(7.01 mg·g-1)was found in G.jamesonii,followed by G.jasminoides(5.74 mg·g-1)and rose(4.66 mg·g-1).The total phenol contents of different hosts followed the order: G.jamesonii > G.jasminoides > R.rugosa.The flavone content in G.jasminoides was the highest(9.03 mg·g-1),but was not significantly different from that of G.jamesonii(8.60 mg·g-1).The lowest content was found in R.rugosa(2.89 mg·g-1).There was no significant difference in the alkaloid contents among the three hosts.(4)p H values of petal cells The p H value of the petal cell solution from G.jamesonii was the highest(5.89),being significantly greater than those of R.rugosa and G.jasminoides,but there was no significant difference between the p H values of the latter two hosts.4 Effects of host-switching stress on the energy substances in thrips Significant differences were found for the soluble sugar,soluble protein and fat contents of thrips fed on R.rugosa,G.jamesonii and G.jasminoides.F.occidentalis and T.hawaiiensis fed on rose contained the lowest contents of soluble sugar(7.43 and 7.33 ?g per thrips,respectively),and those fed on G.jasminoides contained the highest content(8.62 and 7.58 ?g/individual,respectively).The soluble protein content of F.occidentalis was found in the order of R.rugosa > G.jamesonii > G.jasminoides,while for T.hawaiiensis the order was G.jasminoides > G.jamesonii > R.rugosa.No significant difference in body fat content was found in F.occidentalis fed on R.rugosa and G.jamesonii,but their body fat contents were significantly higher than when fed on G.jasminoides.Additionally,no significant difference in body fat content was found in T.hawaiiensis fed on G.jasminoides and G.jamesonii,but their body fat contents were significantly higher than when fed on R.rugosa.During mutual switching stress among the three flowers,with short switching times(1,3,6,9,12,24 and 48 h),the soluble sugar contents of the two thrips increased or decreased significantly compared with the control group.When treated in the same manner,there were no significant changes in the soluble protein and fat contents,indicating that soluble sugar could respond to host conversion stress in time.With mutual switching for multi-generation(F1–F4 generations)between high preference and low preference host,the soluble sugar contents of the two thrips increased or decreased similarly.Both of the soluble protein and fat contents in the two thrips species decreased when migrating from high preference to low preference host,opposite trends were observed on the soluble protein and fat contents when migrating from low preference to high preference host.Therefore,the responses of different energy substances of thrips were different between the short-time and multi-generational switchings.The same energy substance also had different responses in different thrips.In general,energy substances in the thrips became stabilized after 2 to 3 generations of adaptation on the hosts.5 Effects of host-switching stress on detoxification enzyme and protective enzyme of thrips Significant differences in the activity levels of different detoxification enzymes were found in thrips fed on different hosts.The activity levels of cytochrome P450 enzyme,carboxylesterase,acetylcholinesterase,glutathione transferase and other detoxification enzymes in F.occidentalis were present in the order G.jasminoides > G.jamesonii > R.rugosa,but for T.hawaiiensis the opposite trend was found.Additionally,no significant difference was found in the phosphatase(ACP/ALP)activity levels between the two thrips.Similarly,different protective enzymes in the two hosts had significantly different activity levels.The superoxide dismutase(SOD)activity level in F.occidentalis was highest on R.rugosa and lowest on G.jasminoides,while there were no significant differences in T.hawaiiensis' s SOD activity levels on different hosts.There were no significant differences in the catalase(CAT)activity levels of the former on different hosts,but for T.hawaiiensis,the CAT activity was highest on G.jasminoides a and lowest on R.rugosa.There were no significant differences in the peroxidase(POD)activities of the two thrips on different hosts.Under the hosts' short-term switching stress(1,3,6,9,12,24 and 48 h),there were no significant changes in phosphatase(ACP/ALP),a detoxification enzyme shared by the two thrips.However,different detoxification enzymes in the same thrips showed different activity levels,but with no specific regularity,given the same host switching.For host multi-generational switchings(F1–F4 generations),when migrating from low preference to high preference host,the activity levels of detoxification enzymes in the two thrips increased gradually,except no significant change was found in phosphatase(ACP/ALP).When the shift occurred in the opposite direction,the detoxification enzyme activity levels decreased gradually.After 1,2,and up to 3 generations of adaptation on the new hosts,the activity levels of thrips' detoxification enzymes became stabilized.Similarly,the protective enzymes of thrips were significantly affected by the short-term stress of changing to different hosts.The same protective enzyme in the two thrips,and the different protective enzymes in the same thrips,showed different activities,but no specific regularity.For the host multi-generational switching process,the SOD and CAT activities of the two thrips decreased gradually,when migrating from high preference to low preference host,except POD showed no significant differences after each switching.When the opposite shifts occurred,the SOD and CAT activities of the two thrips species increased gradually.In general,the protective enzyme activity levels of thrips became stabilized on the new hosts after more than one generation of adaptation.Based on these studies above,the differences in the host preference and host adaptability between the invasive pest F.occidentalis and the native species T.hawaiiensis were clarified.The differences in the host adaptation mechanisms of physiology and ecology between the two thrips species were also elucidated,based on the analysis in the differences in physical and chemical properties of hosts and physiological responses of thrips to host-switching.In short,these results provide the basis for the key control of thrips pests on flower plants,also provide basic data and theoretical basis for forecasting,disaster mechanism understanding and effective control of invasive pests. |
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