EFFECTS OF TEMPERATURE ON THE DEVELOPMENT OF Thrips nigropilosus Uzel (Thysanoptera: Thripidae) ON Mentha x piperita L. AND THE IMPACT OF PEST ON THE HOST PLANT

Thrips nigropilosus Uzel is a polyphagous species occurring mainly in temperate climates. Its life cycle depends on photoperiodic and temperature conditions. T. nigropilosus feeds on different plant species, but it is considered one of the most serious pests of pyrethrum plants causing serious economic problems. However, several additional agricultural host plants have been affected by T. nigropilosus, including spearmint, cucumber, and lettuce, indicating that this insect can significantly widen its habitats and occurs especially frequently in greenhouses. We report that T. nigropilosus massively attacked Mentha x piperita L. cultivated in greenhouses in central Poland and destroyed the entire mint crops within a short time. The study provided insight into the harmful effect of the thrips and showed that the length of the thrips developmental cycle was reduced with temperature increases from 18 to 26.6 degrees C. The lower threshold temperatures were 13.7, 10.2, 5.0, and 10.1 for eggs, larvae, pupae, and total development, respectively, and the thermal constant for the same developmental stages was 65.9, 90, 132.5, and 284.9-degree days. Both parameters were estimated by linear regression analysis. During our experiment, T. nigropilosus developed by thelytokous parthenogenesis. The morphological and anatomical changes in damaged plants were associated with the fact that the insect began feeding on the lower lamina surface close to the leaf midribs, but no damage to vascular bundles and glandular cells was observed.