Development of Frankliniella occidentalis on flowers of different horticultural hosts and relationship with flower compounds

The western flower thrips, Frankliniella occidentalis (Pergande), is one of the pests with most adverse effects on global crop production. F. occidentalis is also a key invasive pest of vegetables, fruits and the wider horticultural and/or ornamental plants in China. It causes direct damage through feeding and ovipositioning, but also significant indirect losses by transmitting plant viruses. Significant plant damage by F. occidentalis has been observed in recent years with the degree of damage differing with plant species. This has made it extremely difficult to fully understand the differences in damage as a lot of factors relating with plants and insect pests. So far, there has been little research on F. occidentalis damages to horticultural host plants. In order to verify the effect of different horticultural host plants on the development of F. occidentalis, the development and survival of F. occidentalis on flowers of five horticultural plants (Rosa chinensis, Dianthus caryophyllus, Lilium brownie, Pelargonium hortorum/ and Pharbitis nil) were studied. The research also studied the relationships of F. occidentalis development with the contents of nutriments (soluble protein and soluble sugar) and secondary compounds (tannin, flavone and phenolic) of flowers of five horticultural plants. The results showed that the shortest time for F. occidentalis to complete one generation was on R. chinensis (11.02 days) and the longest was on P. nil (13.21 days). The survival rates of F. occidentalis at different stages were different on different flowers. In short, the highest generation survival rate was on L. brownie (84%) and the lowest was on P. hortorum (76%). There were also significant differences in the contents of nutriments and secondary compounds among the five host flowers. The highest content of soluble protein was in R. chinensis (12.39 mg·g^-1), significantly higher than that in the other host flowers, while the lowest was in P. nil (4.57 mg·g^-1). Soluble sugar content decreased in the order of L. brownie (6.83 mg·g^-1), D. caryophyllus (6.15 mg·g^-1), P. hortorum (4.26 mg·g^-1), R. chinensis (3.38 mg·g 1) and P. nil (2.25 mg·g 1). Tannin content increased in the order of R. chinensis, D. caryophyllus, L. brownie, P. hortorum and P. nil. Both flavone and phenolic contents were highest in P. hortorum (respectively 6.01 mg·g 1 and 2.45 mg·g^-1) and lowest in R. chinensis (respectively 2.88 mg·g^-1 and 0.64 mg·g^-1). Correlation analysis showed that while the developmental velocity of F. occidentalis was significantly positively correlated with the content of soluble protein (R = 0.896, P = 0.040), it was negatively correlated with the contents of tannin (R = 0.917, P = 0.01), flavone (R = 0.921, P = 0.014) and phenolic (R = 0.905, P = 0.013) of host flowers. There was no correlation between the rate of development of F. occidentalis and the content of soluble sugar of host flowers (R = 0.40, P = 0.505). Also the rate of survival of F. occidentalis had no significant correlation with any of the chemical compounds tested. It was therefore concluded that some of the chemical compounds of the host flowers had significant effect on the development of F. occidentalis. The higher the content of soluble protein, the more favorable the development of F. occidentalis. However, the higher the contents of tannin, flavone and phenolic, the less favorable the development of F. occidentalis.