Mass Rearing and Field Release of an Eulophid Wasp,

Ching-Chin Chien, Shui-Chen Chiu and Shiu-Chih Ku
Department of Applied Zoology
Taiwan Agaricultural Research Institute
Wufeng, Taichung 41301, Taiwan, ROC , 2001-05-01

Introduction

The eulophid wasp, Tamarixia radiata, is a native parasitoid of the citrus psyllid, Diaphorina citri, in India. It has been reported that T. radiata gave control of the citrus psyllid on Reunion Island, in the Indian Ocean. The mass rearing of this parasitoid becomes important when it is adopted as a biocontrol agent against the citrus psyllid. T. radiata was introduced to Taiwan from Reunion Island between 1983 and 1986. The wasps were reared and released in the field after quarantine, and successfully became established. The techniques of mass rearing and field release of T. radiata are described as follows.

Life Cycle of T. Radiata

The completion of the life cycle, from egg to emergence, of this parasitoid (Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6, Fig. 7, Fig. 8) takes about 12 days at 25^OC, 14L:10D. The egg, larval, prepupal and pupal stages lasted 2, 4, 1 and 5 days, respectively. When the wasps were supplied with 20 psyllids daily, the female lived 12-24 days and laid 166-330 eggs. A longevity of 34 days was observed when the female was fed on honey but not supplied with a host.

The adult female deposits eggs on the ventral part of the host, between the thorax and the abdomen. The newly hatched larva sucks fluid from the site where it is closely attached to the host's integument. At the 2nd instar, it crawls onto the ventral part of the host's thorax and feeds there. By the time the larva has matured, it has sucked up all the fluid and the host has become mummified. When the psyllid becomes mummified, the mature larva spins around to attach itself to the leaves or branches of the citrus tree. There it turns to a prepupa, and then molts into a pupa.

Cultivation of the Host Plant

One thousand young trees of Cantonese lemon, Citrus limonia, cultivated in pots in the greenhouse, served as the host plants for the citrus psyllid, D. citri. The trees were divided into five groups, and were pruned weekly. At pruning, all leaves were removed to stimulate the growth of new flushes which were used to rear psyllid nymphs for about two weeks. Shade, water and nitrogen fertilizer should be provided to encourage the development of new flushes.

If leaf miners or aphids were found on the young trees, these were controlled by an application of 50% malathion E.C. (800 x) or 44% dimethoate E.C. (1,000 x).

Common jasmine orange (Muraya paniculata) is the favorite host plant for citrus psyllid in the field. Adult psyllids (Fig. 10) are attracted to lay eggs on the newly sprouted leaves (Fig. 11).

Psyllid Rearing in the Laboratory

Twigs or branches of common jasmine orange on which citrus psyllids had laid their eggs were collected from the field and brought to the laboratory. All lateral branches without psyllid eggs were removed, while twigs with eggs were kept moist in a plastic beaker until the nymphs appeared. Plastic beakers containing water 1 cm deep were placed in the incubator at a temperature of 25°C, and a photoperiod of 14:10 (L:D). The water was renewed daily. After three or four days, the top 3 cm of these twigs with their psyllid nymphs (Fig. 13) were transferred onto new leaves of the potted Cantonese lemon (Fig. 14). These potted plants infested with psyllids were kept in the laboratory at 25 ± 1°C and 70-90% RH.

Mass Rearing of T. Radiata in the Laboratory

T. radiata was reared at 25 ± 1°C and 70-90% relative humidity. Fifteen parasitoids were introduced into a plastic cylinder (16 cm in diameter and 30 cm high), which was covered at the top with a piece of screening cloth (1,764 meshes/inch). This cylinder was placed over the potted host plant, which had been previously infested with 300 5th-instar nymphs of citrus psyllid (Fig. 15). One day after exposure, the parasitoids were in turn transferred to another pot. Five days after exposure, the hosts became mummified and turned a dark brown color. Five days later still, the pot was covered with a plastic cage in which to collect the adult parasitoids. Honey must be supplied soon after the adults emerge (Fig. 16).

Release of T. Radiata in the Field

Two methods were developed for the field release of this parasitoid. In one, a nylon screen net was used to cover branches heavily infested with the 5th instar psyllid nymphs (Fig. 17). The net was tightened round the bottom after the parasitoids had been introduced, and was then removed two days later. In the other method, parasitoids were released directly onto branches or twigs where psyllid nymphs were found (Fig. 18). In both cases, a glass vial (1.5 cm in diameter and 7 cm high) was used to transfer the wasps.