Determination of the Median Latent Period of Two Tospoviruses inFrankliniella occidentalis,Using a Novel Leaf Disk Assay

A novel assay system, based on the use of the local lesion host Petunia×hybrida, was developed for studying the transmission of tospoviruses by the thrips Frankliniella occidentalis. Efficient transmission was obtained for two different tospoviruses, tomato spotted wilt virus (TSWV) and impatiens necrotic spot virus (INSV), reaching rates up to 55.1 and 92.5%, respectively. Because the majority of the thrips became viruliferous in the second larval stage, the median latent period (LP 50 ) was determined for this stage. The LP 50 values decreased with increasing temperatures. For INSV, the LP 50 values were 157, 103, and 82 h at 20, 24, and 27 C, respectively, and for TSWV, they were 171, 109, and 84 h at the respective temperatures