Electropenetrography application and molecular-based virus detection in mealybug (Hemiptera: Pseudococcidae) vectors of Cacao swollen shoot virus on Theobroma cacao L.

Abstract

Cacao swollen shoot virus (CSSV) is a peril exclusive to the West African cacao-growing countries; causing the Cacao swollen shoot virus disease. This study was set out (1) to analyse the feeding behaviour of two West African and one non-West African mealybug species, Planococcus citri (Risso) and Pseudococcus longispinus (Targioni Tozzetti) and Ps. viburni (Signoret) respectively on CSSV-free cacao. and (2) to provide molecular-based information on the ability of these mealybugs to acquire and transmit the ‘New Juaben’ CSSV strain from CSSV-infected cacao. Electrical penetration graph (EPG) analysis established that these three mealybug species performed both extracellular (C, E1e, F, G and Np waveforms) and intracellular (E1 and E2 waveforms) feeding activities on cacao which were typical of stylet-possessing, phloem-feeding, virus transmitting hemipterans. Waveform F reported in this study is the first for Pl. citri, Ps. longispinus and Ps. viburni feeding on cacao. The competitive feeding efficiency of Ps. viburni on cacao highlights its potential as a ‘new’ vector of CSSV. PCR-based results show that Pl. citri, Ps. longispinus and Ps. viburni can acquire CSSV after a 72-h access acquisition period (AAP). DNA sequences of CSSV were detected in leaf tissues of the test plants after a 30-day post 72-h inoculation access period (IAP) by the viruliferous mealybug individuals. It is the first report, with molecular evidence, of T. cacao serving as an acceptable host to Ps. viburni.