COMPARATIVE LIFE-HISTORY STUDIES OF FRANKLINIELLA-OCCIDENTALIS AND THRIPS TABACI (THYSANOPTERA, THRIPIDAE) ON CUCUMBER

Shortly after its invasion into Europe, the western flower thrips, Fra nkliniella occidentalis (Pergande), became a more severe pest of green house crops than the onion thrips, Thrips tabaci Lindeman. To test whe ther this differential pest status was due to a larger capacity of pop ulation increase, a comparative life history study was carried out on cucumber (Cucumis sativus cv. Corona). Experiments at 25 degrees C sho wed that the egg-to-egg period of F. occidentalis was shorter, but its peak ovipositional rate was lower and its offspring sex ratio more ma le biased. These differences resulted in a slightly lower intrinsic ra te of population increase (r(m)) for F. occidentalis than for T. tabac i (0.166 vs. 0.176/day). It was shown experimentally that between 15 a nd 28 degrees C, developmental rate of F. occidentalis is linearly rel ated to temperature, with a theoretical threshold temperature similar to the value reported for T. tabaci (10.9 vs. 11.5 degrees C). It is a rgued that the r(m)-value of F. occidentalis will not be higher than t hat of T. tabaci for any temperature within this range. Alternative ex planations for the difference in pest status between the two thrips sp ecies are discussed.