On the other hand, BPH acquires and transmits rice ragged stunt virus (RRSV; Reoviridae , Fijivirus ) 30–33) and rice grassy stunt virus (RGSV; Tenuivirus ) 33,34) by feeding on infected plants, accelerating the severe damage on growing rice plants. Although the role of detoxification enzymes in insecticide resistance has been clarified, the effects of virus infection on the activities of key detoxification enzymes such as CE, GST, and P450 in vector insects remain undescribed.
This study demonstrated that three different detoxification enzymes involved in insecticide resistance are affected by viral infection. Insecticide-susceptible BPH males showed a significant decrease in CE and GST enzyme activity when infected by RRSV. Buffer-injected uninfected male BPH individuals showed no difference in comparison to intact controls, indicating that RRSV infection induced the decrease in both enzyme activities. Decreases in GST and P450 activities have been reported in cases of bacterial infection, but not in cases of virus. 36,37) The Asian citrus psyllid, Diaphorina citri , infected with the Gram-negative bacteria Candidatus Liberibacter asiaticus (Las) shows significantly lower activity as compared to uninfected ones, suggesting that the defense response against the xenobiotic may be suppressed by the invading virus. Although there have been no reports that direct virus infection induced high activity of detoxification enzymes, it is reported that the p450 and GST of the detoxification enzyme increased in parasitized hosts with infection by a symbiotic virus, which is injected into the host hemocoel with the eggs of an endoparasitoid, Vestalis (= Cotesia ) plutellae–Plutella xylostella , host system. 38) Endoparasitoid wasps have a symbiotic DNA virus, a polydnavirus (PDV), which regulates the host immune system by the gene expression of the polydnavirus in the host cells when it is injected into a suitable lepidopteran host along with an egg. 39,40)
8. Synthesis of cDNA.
3. Development of insecticide-selected strains.
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Excel Tokei (Bell Curve) was used in addition to the analysis of variance performed on all data followed by the Tukey–Kramer multiple comparison test at the level of p <0.05.