Characterization and Correlation of EPG Waveforms of Bactericera Cockerelli (Hemiptera: Triozidae): Variability in Waveform Appearance in Relation to Applied Signal

Abstract

AbstractThe tomato-potato psyllid, Bactericera cockerelli (Sulc) (Hemiptera: Triozidae), was recently shown to be a vector of “Candidatus Liberibacter solanacearum” (Lso), a phloem-limited bacterium that is the putative causal agent of “zebra chip” in potato and unnamed diseases in other solanaceous species. Despite its importance, very little is known about B. cockerelli stylet probing behaviors that control transmission of Lso to its host plants. Herein, we report the first study characterizing the electrical penetration graph waveforms representing stylet penetration behaviors of the B. cockerelli feeding on potato. Waveforms produced by adult B. cockerelli on potato were also correlated using light microscopy of salivary sheath termini in plant tissue after probes were artificially terminated during the identified waveforms. In addition, behavioral activities were inferred based on electrical origins of waveforms as well as similarities in waveform appearances with those of other psyllids, aphids, and whiteflies. Adult B. cockerelli produced six waveform families and four types, which represent the following proposed biological meanings: family A, initial penetration and sheath salivation; family B, penetration of epidermal cells; family C, secretion of most of the salivary sheath and stylet pathway in mesophyll and parenchyma, with two types, C1 and C2, of unknown meaning; family D, initial contact with phloem cells; family E, activities in phloem cells, with two types, El, putative phloem salivation, and E2, phloem sap ingestion; and family G, xylem ingestion. In addition, a previously unreported variant of waveform G was characterized and correlated with applied signal type. Variation in D and G waveform appearances was correlated with polarity, type, and magnitude of applied signal. Results suggest that active phloem sap ingestion during E2 may play a critical role in acquisition of Lso bacterial cells. E1 may be important in inoculation of the bacterium into phloem sieve elements because it may represent salivation into phloem sieve elements. Analysis of B. cockerelli waveforms could lead to faster development of resistant host plant varieties, strengthen integrated pest management strategies by incorporating alternative plant hosts, and maximize the efficiency of pesticides.