Efficacy of Indigenous Isolates of Beauveria bassiana in Controlling Invasive Planthopper, Orosanga japonica

 Orosanga japonica (Hemiptera: Ricaniidae) is an invasive and polyphagous pest in the Palearctic region collected and reported from the northern part of Iran on citrus orchards in 2010. Nymphs and adults of the pest cause economic and critical damage to different plants by direct feeding and heavy deposits of honeydew on leaves. Despite various management practices, successful control of this pest has been difficult due to its rapid development and reproduction rate. Beauveria bassiana, an entomopathogenic fungus (EPF), has been extensively researched for its ability to manage a variety of insect pests and appears to be a potential alternative to conventional insecticides.

 In the present study, in the course of a forest survey in the distribution areas of O. japonica in Mazandaran province, larvae were infected with some native isolates of fungal mycelia were observed. After morphological and molecular identification, two fungal-infected specimens were confirmed as B. bassiana. Fungal collections were characterized by amplifying and sequencing the ITS region of rDNA using primers ITS1 and ITS4. The susceptibility of adults of O. japonica to two EPFs isolates was evaluated using the leaf dipping method and the direct spraying method under laboratory conditions. Data were analyzed using Analysis of Variance (SAS, 2002) with insect mortality as the response variable. Means were separated at alpha=0.01 using Duncan´s test. The LC50 and LC90 values of EPFs and the mean lethal times of LT50 were estimated by Probit analysis using SPSS Statistics 17.0

Two different fungal isolates presented white to cream colonies with irregular edges and powdery appearance, reproductive structures, and conidia with typical morphology, size, and color of B. bassiana species. The mean lethal concentration values (LC50) of isolate 1 and isolate 2 to were 4.00 × 106 and 3.3 × 106 conidia ml-1 (leaf dipping method) and 5.4 × 106 and 4.7× 106 conidia ml-1 (direct spraying method) on the adults of O. japonica respectively in the laboratory tests after 96 h post treatments, at 25°C and 60% relative humidity. The similarities of the ITS sequences of both two EPFs were 99-100% to those of B. bassiana in the GenBank database.

The natural pathogens of pests have long been known to play a significant role in the population dynamics of many important forest pests and provide assistance to manage pests and develop tools for management. Fungal diversity in the moist and temperate Hyrcanian forests can vary widely due to diverse ecological conditions. Generally, these findings could help establish an efficient management strategy for O. japonica as an invasive pest and the development of mycoinsecticide from an indigenous fungus. Future research could investigate the effect of other native EPF isolates and developing techniques in fungal formulation against O. japonica.