Behavioral, Ultrastructural and Chemical Studies on the Honeydew and Waxy Secretions by Nymphs and Adults of the Asian Citrus Psyllid Diaphorina citri (Hemiptera: Psyllidae)

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.

Quality Matters: Influences of Citrus Flush Physicochemical Characteristics on Population Dynamics of the Asian Citrus Psyllid (Hemiptera: Liviidae)

“…citri nymphs secrete copious amounts of a sugary tube-like substance covered by white waxy materials [21]. ACP adult females feeding on young shoots also produce white excretory substances, but males produce clear sticky droplets [22]. Interestingly, these secretions are seldom seen or are less abundant when adults are feeding on mature and fully developed leaves and stems which would suggest marked differences in phloem composition of young versus matured shoots.…”

Effect of host‐plant and infection with ‘Candidatus Liberibacter asiaticus’ on honeydew chemical composition of the Asian citrus psyllid, Diaphorina citri

“…ACP is an important economic pest of citrus because it transmits 'Candidatus Liberibacter asiaticus' (CLas) which causes the citrus greening disease, huanglongbing (Halbert & Manjunath, 2004). In addition to the transmission of CLas, direct feeding on the phloem sap and production of large amounts of honeydew may also contribute to further economic losses (Ammar et al, 2013). Honeydew excretions of phloem-feeding insects are mainly composed of sugars and often contains small amounts of amino acids (Dhami et al, 2011).…”

“…The nymphs produce a continous white thread of waxy honeydew excretion (Ammar et al, 2013). The nymphs produce a continous white thread of waxy honeydew excretion (Ammar et al, 2013).…”

“…The length of these threads may reach many times the body length and its width ranges from 30 to 100 lm (Ammar et al, 2013). In general, female's honeydew is whiter, more solid, and less sticky than honeydew from males (Ammar et al, 2013). In addition, the color and texture of honeydew produced by females is also different from that produced by males.…”

“…Males excrete their honeydew directly behind their bodies after bending the end of their abdomen downward, whereas female adults push the honeydew droplets upward and sideward after twitching their wings and bending their abdomen (Ammar et al, 2013). By pushing the excreted honeydew droplets away from their body, ACP females prevent eggs and young nymphs from being contaminated or covered by their sticky honeydew (Ammar et al, 2013).…”