Investigation of High Humidity Requirement for Infection of Bemisia tabaci (Hemiptera

The suitable humidity condition for infecting whitefly, Bemisia tabaci (Gennadius), with two commercial mycoinsectisides, BotaniGard ES (Beauveria bassiana formulation) and Mycotal (Lecanisillium muscarium formulation) was investigated. The second instar nymph of B. tabaci on a leaf disc was inoculated with 1/500 or 1/1,000 dilutions of BotaniGard ES or Mycotal, respectively, by a dipping method. Based on infection rates of the inoculated whiteflies, which were exposed to >99% RH for various periods and then transferred to 50% RH, the requisite high humidity period for 90% infection was estimated to be 47 and 82 h in BotaniGard ES and Mycotal, respectively. In a tomato greenhouse in autumn 2009 and 2010 in Ibaraki, humidity under tomato leaves was higher than the ambient humidity, whereas the period at >99% RH was about 14 h per day. When the inoculated whiteflies were reared under a fluctuating humidity cycle of 14-hour exposure to >99% RH and 10-hour exposure to 50% RH, the infection rate of these whiteflies increased significantly in comparison with that of the whiteflies reared at 50% RH following 14-hour exposure to >99% RH. This result reveals that the intermittent high humidity cycle enhances the fungal infection of B. tabaci.