Feeding behavior of Asian citrus psyllid [Diaphorina citri (Hemiptera: Liviidae)] nymphs and adults on common weeds occurring in cultivated citrus described using electrical penetration graph recordings

Authors: GEORGE, JUSTIN - University Of Florida; KANISSERY, RAMDUS - University Of Florida; AMMAR, EL-DESOUKY - Oak Ridge Institute For Science And Education (ORISE); CABRAL, ITZE - University Of Florida; Markle, Larry; Patt, Joseph - Joe; STELINSKI, LUKATZ - University Of Florida

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/9/2020
Publication Date: 1/10/2020
Citation: George, J., Kanissery, R., Ammar, E., Cabral, I., Markle, L.T., Patt, J.M., Stelinski, L. 2020. Feeding behavior of Asian citrus psyllid [Diaphorina citri (Hemiptera: Liviidae)] nymphs and adults on common weeds occurring in cultivated citrus described using electrical penetration graph recordings. Insects. 11(1):48. https://doi.org/10.3390/insects11010048.
DOI: https://doi.org/10.3390/insects11010048

Interpretive Summary: The Asian citrus psyllid is a tiny insect (1/8 inch long) that transmits citrus greening disease. This is the most serious disease of citrus in the world. After they become infected with citrus greening, the trees stop producing edible fruit and typically die within a few years. Currently there is no cure for this disease. The psyllid has a mouth that works like drill to penetrate leaves and stems. The psyllid feeds on the phloem, the tissue that transports sugar sap, made from photosynthesis in the leaves, to the rest of the tree. The psyllid can also obtain moisture by feeding on the xylem, the tissue that transports water from the roots to the stems and leaves. The phloem and xylem are similar to long pipes and are located in the leaf veins in structures called vascular bundles. Although the psyllid feeds primarily on citrus trees, some scientists speculated that the psyllids might be able to use weeds as alternative food sources for survival when they are flying between citrus groves or when farmers spray the trees with insecticides. To determine if the psyllids could feed from weeds, we used a device called an electro-penetration graph (EPG for short). The EPG produces a graph that shows the feeding activity of the psyllid as it uses its mouth to probe through leaves and stems in search of vascular bundles. We conducted EPG recordings of psyllids trying to feed on three weed species that are commonly found in Florida citrus groves: Spanish daggers (Bidens alba) and dogfennel (Eupatorium capillifolium), which are both in the sunflower family, and Mexican primrose-willow, (Ludwigia octovalvis) which is related to evening primrose. As a basis for comparison, we also conducted EPG recordings of the psyllids feeding on citrus leaves and stems. The EPG recordings showed that the psyllids spent 19% - 22% of their time feeding on xylem on all three weed species as well as on citrus. However, the EPG recordings showed that, while the psyllids fed extensively on the phloem of the citrus leaves, they fed very little on the phloem of any weeds. After the EPG studies were finished, we examined the leaves and stems with a microscope and found that in the citrus leaves the psyllids had drilled into both the phloem and xylem, while in the weeds the psyllids had drilled only into the xylem. The psyllids could live for several days when they were kept on each of the weeds. This result suggests that the psyllids could survive on these plants for a short period of time when they must leave the citrus trees.

Technical Abstract: Asian citrus psyllid, D. citri (Diaphorina citri), transmits Candidatus Liberibacter asiaticus (CLas),the putative causal agent of Huanglongbing disease. Although they primarily feed on the phloem of citrus and related plants, when grove or host conditions are unfavorable, D. citri may be able to use weed species as alternate food sources for survival. To explore this possibility, electrical penetration graph (EPG) recordings (18 hours) were performed to investigate the feeding behavior of psyllid adults and nymphs on three common south Florida weeds (Bidens alba, Eupatorium capillifolium, and Ludwigia octovalvis). EPG recordings revealed that the proportion of time spent by D. citri feeding on xylem was similar on all tested weed species (19%–22%) and on the positive control (20%), the preferred host, Citrus macrophylla. Very little to no phloem feeding was observed on weed species by either nymphs or adults. Histological studies using epifluorescence microscopy showed that salivary sheaths were branched and extended into xylem of weed species, whereas they ended in phloem on citrus plants. No choice behavioral assays showed that adults can obtain some nutrition by feeding on weed species (xylem feeding) and they may be able to survive on them for short intervals, when host conditions are unfavorable.