Effects of Thrips palmi and western flower thrips (Thysanoptera: Thripidae) on the yield, growth, and carbon allocation pattern in cucumbers

Mixed infestations of thrips composed of approximately 94% Thrips palmi Karny and 6% Frankliniella occidentalis (Pergande), resulted in significant reductions in total cucumber yield, mean fruit size, and total fruit. No significant reductions were observed at 9.4 thrips-days/cm2 (0.48 thrips/cm2 at peak densities). As the number of thrips-days increased to a maximum of 45.0 per cm2, reductions of 54.2% in total fruit weight at final harvest were observed. Highly significant linear regressions between the total number of thrips-days per leaf and the various agronomic variables were obtained. Total yields for the season were reduced 10% by the highest level of thrips damage, possibly because 70% of all yield was harvested before significant build up of thrips populations. Moderate, yet significant, changes in growth patterns were associated with feeding damage by thrips. Less total leaf dry weight was associated with heavy feeding damage