| The western flower thrips, Frankliniella occidentalis (Pergande) is a worldwide important invasive pest. It also causes indirect damage by transmitting Tomato spotted wilt virus (TSWV), which results in greater damage than that of direct feeding. Currently the insecticide resistance in F. occidentalis has become a prominent problem. Whether or not the resistance can affect the virus transmission in F. occidentalis is not clear. In the present study, spinosad-susceptible and-resistant F. occidentalis were used. A molecular method for detecting TSWV was established, by which the TSWV occurrence in Beijing area was investigated. In addition, the virus carrying rate in single thrips was detected. The virus titer was compared between spinosad-susceptible and-resistant F. occidentalis when after different virus acquisition time. The virus transmission efficiency between the two strains was also compared after a 48 h virus acquisition time. The feeding haviours between the two strains being treated with TSWV were compared by using electrical penetration graph (EPG) technique. The specific findings are as follows:1. Specific primers were designed according to the nucleocapsid protein (N) gene of TSWV S RNA conserved sequence, and the sensitivities of four methods for detecting TSWV were compared. The results showed that a 397-bp fragment can be amplified by the specific primers, and the sequence showed a homology of up to 99% with published TSWV nucleotide sequence. The sensitivity of qRT-PCR for detecting TSWV was 15,625-fold, 3,125-fold and 125-fold higher than those of the rapid detection test strip (RDTT), double sandwich enzyme-linked immunosorbent assay (DAS-ELISA) and conventional PCR, respectively. Moreover, qRT-PCR method can be accurately quantified. Conventional PCR showed a higher sensitivity, but it cannot be accurately quantified. DAS-ELISA is suitable for batch qualitative detection but it needs a longer detection time. RDTT is the fastest method, but the sensitivity is the lowest. Suitable detection methods can be selected according to the symptom degree and the experimental condition. Using conventional PCR techniques and sequencing we confirmed that TSWV have occurred in chili in the areaes around Beijing and in Shandong Jining.2. The virus titer in susceptible F. occidentalis treated by TSWV was significantly higher than that in the resistant F. occidentalis after feeding for 0.5-24h, and no significant difference was found at 48 h. In addition, the virus titer in resistant individuals was significant higher than that of susceptible thrips at 12 h. The possible reasons is that metamorphosis occurs from the first instar nymphs to the second at 12 h, and the second instar nymph to prepupa at 48 h, respectively, which would result in great physiological changes in thrips and then cause the great changes in virus titer in the two strains.3. In susceptible F. occidentalis individuals, the total virus transmission efficiency 51.0%, among which the males was 68.1% and females and 33.8% respectively. In resistant F. ocidentalis individuals, the total virus transmission efficiency was 44.4%, and 60.0% and 28.8% in males and females, respectively. There was no significant difference in virus transmission between the two strains. However, the virus transmission of males was significant higher than that of females in each strains.4. The virus titer in transmitted F. occidentalis were significantly higher than those non-transmitted F. occidentalis in both the strains. The virus titer in transmitted male thrips was significantly lower than that of females. However, no significant difference was found between susceptible and resistant strains whether transmitted or non-transmitted males and females.5. The feeding behaviors in females differed significantly between the two stains after acquisition of TSWV but not in males. The short ingestion and long ingestion between the two strains had no significant difference. Generally, spinosad resistance had no impact on the virus transmission. Because males are the main vector to transmit TSWV, no significant difference in feeding behaviors in males may be one of the reasons for no significant difference in virus transmission between the two strains. |
PDF Full Text Request