A New Method for Short-Term Rearing of Citrus Psyllids (Hemiptera: Pysllidae) and for Collecting their Honeydew Excretions

Abstract

The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Psyllidae), is an eco nomically important pest of citrus in the United States, Asia and other parts of the world, as a vec tor of huanglongbing (HLB) or citrus greening, which is considered one of the world's most seri ous diseases of citrus (Gottwald 2010). Addition ally, large populations of ACP can damage plants directly through feeding and excretion activities; ACP feeds on citrus phloem tissues and produces copious amounts of honeydew excretions (Brian sky & Rogers 2007). ACP adults can feed on ma ture citrus leaves, but nymphs must have young tender flush to survive. For biological and patho gen-vector relation studies on ACP (e.g., Wen ninger & Hall 2007; Pelz-Stelinski et al. 2010) rearing of single or small groups of psyllid nymphs or adults on whole citrus plants takes considerable space, time and other resources. Here, we describe a new, simpler method for short-term rearing of ACP using detached mature citrus leaves for adults and detached young ter minal shoots for nymphs (Fig. 1). ACP adults and nymphs were reared singly or in small groups (5-10 per tube) in clear plastic (polypropylene) 50-ml conical centrifuge tubes (3 cm wide and 11.5 cm long; Fisher Scientific, Pitts burg, PA). Young psyllid adults (approximately 1 wk-old) were reared on detached, mature, me dium-size leaves of sweet orange (Citrus sinensis (L.) Osbeck var Ridge Pineapple). Leaf sizes used for adults ranged between 3-4 cm in width and 6-8 cm in length with petioles about 2-3 cm long. The petioles of these leaves were cut diagonally with a sharp razor blade, and each inserted in a small (0.3 or 0.5 mL) microfuge tube filled with water or a piece of moistened cotton wool (Figs. 1A and IE). A piece of Parafilm membrane was wrapped around the top of this tube and the petiole to keep insects from drowning or contact with water. The detached leaf and microfuge tube were then inserted into the rearing tube, and the psyllid adults were added to the latter. The rearing tube was covered with a screw cap that had been finely perforated by a hot needle for ventilation. For better ventilation, how ever, wider holes can be cut in the plastic cap and a piece of fine mesh screen placed under the screw cap to prevent escape of the psyllids. The tubes were kept in an environmental chamber at 25°C and 14 h light per day. The clear plastic wall of the rearing tubes al lowed close observation and photography of the enclosed psyllids during their various activities either by the naked eye or through a stereomicro scope with minimal disturbance (Figs. IB-IE). For example, adults were observed feeding for long periods in their normal feeding posture (Fig. IB) mainly on the midrib or other veins on either side of the detached leaves. They were also observed excreting honeydew droplets regularly (Fig. IE), and occasionally laying eggs (Fig. IB in set), although they normally prefer younger leaves for laying eggs (Brlansky & Rogers 2007). Survival of young adults under the above condi tions on detached mature leaves, that were changed to fresh ones weekly, was 89, 80 and 75% after 2, 3, and 4 weeks, respectively (n = 130 adults). It was later observed, however, that ma ture leaves can stay fresh in the rearing tubes at least for 2 weeks.