Analysis of the Effects of a Dielectric Barrier Discharge on Arthropod Pests

Abstract

Atmospheric pressure plasma discharge (APPD) has been intensely studied in the past fifteen years as a method of sterilization. The effects of APPD on insects were previously unknown. The purpose of this study was to examine whether plasma could be useful for insect and mite control, determine the mode of action on arthropods, and optimize the discharge in order to achieve the shortest APPD treatment times. A positive correlation was found between exposure time to APPD and insect mortality with the level of mortality also increasing with time after treatment for western flower thrips, Frankliniella occidentalis (Pergande), tobacco thrips, Frankliniella fusca (Hinds), Asian tiger mosquito, Aedes albopictus (Skuse), two-spotted spider mite, Tetranychus urticae Koch, and German cockroach, Blattella germanica (L.). Generally, mortality was negatively correlated with the weight of the insect. Cockroaches exposed to APPD for 60, 90, 120 and 180s lost on average 7.5 &#177; 0.8, 8.1 &#177; 0.6, 8.7 &#177; 0.4, and 10.1 &#177; 1.1 (&#177;1 SEM) mg of water weight, respectively, which was an increase over that of the controls. The metabolic rate of cockroaches exposed to plasma for 180 s increased from 0.80 &#177; 0.03 to 1.07 &#177; 0.04 ml of oxygen consumed mg-cockroach -1 h-1 at STP. The level of cuticular hydrocarbons identified by EI GC-MS were not significantly affected by plasma exposure in the green peach aphid, Myzus persicae (Sulzer), German cockroach, and citrus mealybug Planococcus citri (Risso) except for a reduction in n-tritriacontane only in the latter. However, changes in the behavior of cockroaches after plasma exposure including the loss of photo-, vibro-, and thigmotropic responses, inability to right themselves, and hyperexcitatory symptoms, suggests that the site-of-action of APPD in insects is the nervous and/or neuromuscular system. The LT50 of German cockroaches, western flower thrips, and citrus mealybugs 24 h after exposure to a 37&deg;C helium discharge was 333.77, 28.72, and 999.95 s, respectively. The LT50's 24 h after exposure to a 37&deg;C, 0.5% oxygen/99.5% helium discharge was 232.67, 19.99, <13.83 s, respectively. The LT50 of German cockroaches, western flower thrips, and citrus mealybugs 24 h after exposure to the 50 &#177; 2&deg;C, helium discharge was 117.80, 13.83, and 26.62 s, respectively. No mortality resulted in German cockroaches or citrus mealybugs after exposure to a helium atmosphere followed by 50&deg;C air, however the LT50 of western flower thrips was 29.04 s, based on the mortality recorded 24 h after treatment. The addition of oxygen or heat to the discharge resulted in higher mortality in cockroaches and mealybugs but not thrips.