Effects of Citrus tree phenology on color morphology and candidatus liberibacter asiaticus acquisition potential of Diaphorina citri kuwayama (Hemiptera: Liviidae)

The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Liviidae) is an economically significant pest that vectors the bacterial pathogen Candidatus Liberibacter asiaticus (CLas), associated with Huanglongbing (HLB) disease. Diaphorina citri adults exhibit three abdominal color variants of blue, grey, and yellow, which are linked to traits such as flight ability, insecticide resistance, and CLas acquisition. Color morph composition of field-collected D. citri from commercial citrus groves and residential trees in South Texas were evaluated to determine the seasonality of the three variants and assess their CLas status. D. citri samples were evaluated for their sex ratio, morphometric parameters, CLas status, and presence of endosymbionts. In both settings, the yellow color morph was dominant when young flush shoots are present, while the blue morph was the dominant color between flush cycles. Laboratory studies indicated D. citri color morphs were interchangeable depending on flush stage. On mature shoots, blue D. citri remained blue, but a significant proportion of grey and yellow also turned blue within two weeks. In contrast, on young flush shoots, yellow remained yellow while some blue and grey D. citri morphed into yellow. There was no significant effect on color morph on the percentage of CLas-positive psyllid, but there was a trend of higher bacterial titer in yellow relative to blue morphs. Multivariate analysis indicated that maximum temperature and total rainfall four and six weeks prior to D. citri collection were negatively correlated with the percentage of CLas-positive psyllids. The primary and secondary endosymbionts, Candidatus Carsonella ruddii and Candidatus Profftella armature, were present in all three D. citri color morphs. This study showed that citrus tree phenology regulated the color morph composition of D. citri, which can affect CLas transmission and dynamics in groves as well as the effectiveness of vector management