Inter- and intraspecific variation in performance of thrips on Chrysanthemum accessions

Populations of pest insects can differ in their responses to resistant plants, which can significantly impact the durability of plant resistance. Differential fitness of populations of thrips Frankliniella occidentalis Pergande (Thysanoptera: Thripidae) has been reported previously and other thrips species, such as Thrips tabaci Lindeman (Thysanoptera: Thripidae) and Thrips parvispinus Karny (Thysanoptera: Thripidae), may not be affected by plant resistance. In this study, we assessed the performance of F. occidentalis populations collected in the Netherlands on various Chrysanthemum accessions (Asteraceae) and characterized the genetic diversity of these populations. Analysis of the mitochondrial CO1 gene revealed five distinct haplotypes among F. occidentalis individuals from different populations, belonging to both the glasshouse and lupin strains. Significant differences in the development of thrips larvae (from the L1 to L2 stage) across five F. occidentalis populations on the five evaluated Chrysanthemum accessions were found. Two accessions, Chrysanthemum seticuspe (Maxim.) Hand.-Mazz. PB-MB133 and Chrysanthemum x morifolium Ramat. cv. Penny Lane, were consistently resistant, exhibiting low larval development for all F. occidentalis populations. We also examined the resistance of the Chrysanthemum accessions against T. tabaci and T. parvispinus. When comparing thrips larval performance on various Chrysanthemum accessions for the three thrips species, we found significant effects of plant accession, thrips species and their interactions on larval development. Penny Lane exhibited suppression of larval development for only F. occidentalis, whereas C. seticuspe PB-MB133 suppressed larval development of all three thrips species tested. Interestingly, C. seticuspe PB-MB132, previously identified as susceptible to F. occidentalis, suppressed T. parvispinus development, indicating that in C. seticuspe multiple mechanisms of resistance might be present. In conclusion, our findings demonstrate that thrips populations infesting Chrysanthemum differ in virulence, highlighting the importance of screening for resistance with multiple populations. Moreover, our study identified Chrysanthemum accessions exhibiting resistance against multiple thrips species.