Abstract
The Asian citrus psyllid (ACP), Diaphorina citri (Hemiptera: Psyllidae) is the primary vector of the bacterium causing citrus huanglongbing (citrus greening), the most serious disease of citrus worldwide. Psyllids and other hemipterans produce large amounts of honeydew, which has been used previously as an indicator of phloem sap composition and insect feeding or metabolism. Behavioral, ultrastructural and chemical studies on ACP, its honeydew and waxy secretions showed important differences between nymphs, males and females, and suggested some mechanisms by which the psyllids, especially nymphs and adult females, can minimize their contamination with honeydew excretions. The anal opening in ACP, near the posterior end of the abdomen, is on the ventral side in nymphs and on the dorsal side in adult males and females. Video recordings showed that adult males produce clear sticky droplets of honeydew gently deposited behind their body on the leaf surface, whereas adult females produce whitish honeydew pellets powerfully propelled away from the female body, probably to get their excretions away from eggs and newly hatched nymphs. ACP nymphs produce long ribbons or tubes of honeydew that frequently stay attached to the exuviae after molting, or drop when feeding on the lower side of citrus leaves. Furthermore, honeydew excretions of both nymphs and adult females are covered with a thin layer of whitish waxy material ultrastructurally composed of a convoluted network of long fine filaments or ribbons. This material is extruded from intricate arrays of wax pores in the circumanal ring (around the anus) that is found in nymphs and females but not in males of ACP or other psyllid species. Infrared microscopy and mass spectroscopy revealed that, in addition to various sugars, honeydew excretions of ACP nymphs and females are covered with a thin layer of wax similar in profile to ester waxes.
Highlights
The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Psyllidae) is an invasive species that was found originally in southwestern Asia, but has spread to many countries in South, Central and North America starting in the 1990 s [1,2]
Honeydew excretions by hemipterans are the result of feeding on the phloem sap, which has very high sugar content and osmotic pressure
The high sugar content and osmotic pressure of phloem sap is countered by sucrose-transglucosidase activity in their guts, which transforms excess sugar into long-chain oligosaccharides voided as honeydew excretion [8]
Summary
The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Psyllidae) is an invasive species that was found originally in southwestern Asia, but has spread to many countries in South, Central and North America starting in the 1990 s [1,2]. In addition to causing sooty mold growth on the host plant, which may inhibit photosynthesis [7], honeydew of psyllids and other hemipterans is known to attract many ant species [9,10]. These ants may protect hemipteran species from their natural enemies thereby compromising biological control [11] or lead to changes to ecosystem composition and dynamics [12,13]
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