| Visual observations, combined with scanning electron microscopy and electronic monitoring of the feeding of Frankliniella occidentalis, the western flower thrips, revealed that it fed in a piercing-sucking manner. The mouthparts consisted of a single, left mandibular stylet and paired, interlocking maxillary stylets. Ultrastructural evidence showed all three stylets to be innervated by mechanoreceptors. The paired maxillary stylets which form the feeding tube were able to be extended at least 40 {dollar}mu{dollar}m. During electronic monitoring of thrips feeding, two distinct patterns were produced. One pattern representing short-duration feeding, and another pattern representing long-duration feeding. Examination of the paraglossae of five thrips species, Frankliniella occidentalis, F. schultzei, F. fusca, Thrips tabaci and T. palmi, comparing sensilla on larvae, prepupae, pupae and adult stages, revealed the presence of 20 paraglossal sensilla. Comparisons of the paraglossal sensilla between all adults and larval stages found them to be nearly identical, consisting of the same type, same number, and occurring in the same sequence. Only the prepupal and pupal stages had sensilla that appeared vestigial, smaller and appressed against the paraglossae. Sectioning of the paraglossal sensilla revealed that there were one to three dendrites varying in functional type innervating each sensillum. Ultrastructural evidence suggests that some of the paraglossal sensilla have a dual mechanosensory and chemosensory function. Internal gustatory chemosensilla were found in the precibarium and cibarium. Based on these findings, a sequence of thrips host selection behavior has been proposed. |
