Physiological Studies on Thrips in Relation to Transmission of Tomato Spotted Wilt Virus

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Abstract
The hydrogen ion concentration of the midguts of larval and adult Thrips tabaci and T. imaginis is between pH 5.0 and 5.6. The oxidation-reduction potential at these values is between +0.184 and +0.262 V. There is thus no difference between thrips that are vectors and those that are not vectors of the virus causing tomato spotted wilt. Furthermore, the pH and Eh conditions in the midgut of larval T. tabaci are unsuitable for long survival of the virus. The larval midgut of T. tabaci is less thoroughly tracheated than that of the adult. The larval T. tabaci ingests a smaller amount of plant tissue than the adult. This quantity averages about 8.0 x 10-5 mg per insect per minute, when the insects were exposed to the leaf for a 30-min. feeding period. The entire epithelium of the midgut of larval and adult T. tabaci absorbs Fe and Cu ions. These data are discussed in relation to theories to account for the ability of larval and the inability of adult Thrips tabaci to transmit tomato spotted wilt virus.