Western Flower Thrips Feeding Damage On Susceptible and Resistant Impatiens Varieties

Western flower thrips (Frankliniella occidentalis (Pergande)) has become an increasingly significant pest problem in greenhouse ornamental production. Alternative strategies are needed to manage this pest because of limited number of available products and the ability of thrips to develop resistance. It is essential to evaluate thrips damage and to develop action thresholds for the implementation of either conventional or alternative management programs. This study was conducted to better understand the damages caused by thrips on thrips susceptible and resistant impatiens (Impatiens wallerana), ‘Dazzler Violet’ and ‘Super Elfin Red’, respectively. Plants at week 3, 6, or 9 in their production period were inoculated with 0, 25, 50, or 75 female adult thrips. Thrips were allowed to feed and develop on plants for a week and were removed by insecticide sprays. Plants were grown in the greenhouse for another three weeks and plant responses to thrips damages were evaluated by weekly observations. Visual damage ratings and number of leaves exhibiting damage symptoms increased when thrips inoculation density increase. ‘Dazzler Violet’ had more damaged leaves and fewer flowers than ‘Super Elfin Red’. However, these cultivars had similar visual damage ratings for the same treatment combinations of plant age x thrips inoculation density. Plant age at the time of inoculation affected plant response to thrips damage, that younger plants exhibited more severe damage. These results suggest that plant age and thrips population levels on a plant are important factors to consider when developing action thresholds.