Unraveling the Host Plant Alternation of Cacopsylla pruni – Adults but Not Nymphs Can Survive on Conifers Due to Phloem/Xylem Composition

Abstract

Plant sap feeding insects like psyllids are known to be vectors of phloem dwelling bacteria (‘Candidatus Phytoplasma’ and ‘Ca. Liberibacter’), plant pathogens which cause severe diseases and economically important crop damage. Some univoltine psyllid species have a particular life cycle, within one generation they alternate two times between different host plant species. The plum psyllid Cacopsylla pruni, the vector of European Stone Fruit Yellows (ESFY), one of the most serious pests in European fruit production, migrates to stone fruit orchards (Prunus spp.) for mating and oviposition in early spring. The young adults of the new generation leave the Prunus trees in summer and emigrate to their overwintering hosts like spruce and other conifers. Very little is known about the factors responsible for the regulation of migration, reasons for host alternation, and the behavior of psyllids during their phase of life on conifers. Because insect feeding behavior and host acceptance is driven by different biotic factors, such as olfactory and gustatory cues as well as mechanical barriers, we carried out electrical penetration graph (EPG) recordings and survival bioassays with C. pruni on different conifer species as potential overwintering hosts and analyzed the chemical composition of the respective plant saps. We are the first to show that migrating psyllids do feed on overwintering hosts and that nymphs are able to ingest phloem and xylem sap of coniferous trees, but cannot develop on conifer diet. Analyses of plant saps reveal qualitative differences in the chemical composition between coniferous trees and Prunus as well as within conifer species. These differences are discussed with regard to nutritional needs of psyllid nymphs for proper development, overwintering needs of adults and restriction of ‘Ca. P. prunorum’ to Prunus phloem.

Survival and development of potato psyllid (Hemiptera: Triozidae) on Convolvulaceae: Effects of a plant-fungus symbiosis (Periglandula)

“…Previous accounts of association between potato psyllid and Convolvulaceae include rearing trials and field observations. Some care must be taken in interpretation of the field records, as field observations can lead to inflated ideas of true host range of psyllids due to the willingness of these insects to colonize and feed upon plant species that nonetheless fail to support nymphal development [ 7 , 11 , 68 ]. In this study, we followed the strict published guidelines of Burckhardt et al [ 7 ] in defining psyllid “host plant” as a species that allows egg-to-adult development.…”

Phloem Metabolites of Prunus Sp. Rather than Infection with Candidatus Phytoplasma Prunorum Influence Feeding Behavior of Cacopsylla pruni Nymphs

“…Of the compounds detected in the phloem centrifugates (Table 4), caffeic acid is of particular interest. Its possible positive influence on the feeding behavior of C. pruni deserves further investigation, because this metabolite was also detected in phloem sap of Prunus domestica but not in conifers, which are no suitable hosts for feeding and development of C. pruni's offspring (Gallinger and Gross 2018). Hydroxycinnamic acids are commonly known as constitutive plant defenses against herbivores (Rehman et al 2012).…”

“…P. prunorum'-infected plants. The importance of volatile organic compounds released by plants on C. pruni host preference and the importance of phloem chemistry on C. pruni development has been addressed previously (Gallinger et al 2019, Gallinger andGross 2018). Thus, the objective of the present research was to investigate the importance of gustatory cues on the host plant choice of C. pruni using two Prunus species that exhibit different degrees of sensitivity to ESFY phytoplasma infection.…”

Metabolomic Characterization of Olive Xylem Sap Reveals Differences According to Plant Age and Genotype

“…Additionally, the age of the host plant and seasonal changes are factors affecting xylem sap composition [23][24][25]. Several studies have characterized the xylem sap composition of woody plant species [e.g., 22,[26][27][28][29]. However, to our knowledge, only one study has characterized the xylem sap composition of olive trees [30] despite of being one of the most remarkable tree crops in the Mediterranean Basin.…”