The effect of plant development on thrips resistance in Capsicum

Western flower thrips [Frankliniella occidentalis (Pergande)] is a worldwide pest insect that causes damage in pepper cultivation, so growers would benefit from host plant resistance. The objectives of this study were (1) to evaluate the effect of plant age on thrips resistance using nine Capsicum accessions with different levels of thrips resistance at three different plant ages, and (2) to study the effect of leaf age on thrips resistance in a resistant and a susceptible pepper accession. The fraction of first instar larvae that did not develop into second instar was used as a measure for thrips resistance. Our results show that plants start to develop thrips resistance when they are between 4 and 8 weeks old. This transition was most marked on the resistant accession CGN16975, on which about 50% of the L1 larvae developed into the next stage on 4-week-old plants, whereas none of them developed beyond the L1 stage on 8- or 12-week-old plants. Furthermore, it is shown that youngest fully opened leaves of the resistant accession CGN16975 are significantly more resistant to thrips than older leaves; 89% of the L1 larvae did not develop into the next stage on the youngest leaves, whereas 57% did not develop beyond the L1 stage on the oldest leaves. Young leaves of the susceptible accession CGN17219 are more susceptible than older leaves; 9 versus 52% of the L1 larvae did not develop into the next stage on young and old leaves, respectively. These findings can be used to improve integrated pest management strategies.