ENTOMOPHAGA 25 (2), I980, 187-192

DR YINI D PARASITOIDS OF RICE LEAFHOPPERS AND

IN THE PHILIPPINES

II. R E A R I N G TECH N IQ U ES

PLANTHOPPERS

GIRISH CHANDRA (1)

Department of Entomology, The International Rice Research Institute, P.O. Box 933, Manila, Philippines

Three new techniques of rearing dryinids parasitising rice hoppers were deve- loped, namely, laboratory rearing technique for detailed observations, device for transporting and rearing field-collected hoppers to estimate percentage parasitism and a breeding technique.

Satisfactory techniques for studying dryinids' behavior and development or for rearing field-collected hoppers were not available to date. In most cases, studies were made in Petri dishes and glass tubes containing host plant, which proved unsatisfactory because of reduced aeration and accumulation of excessive moisture, particularly in tro- pical climate. Some workers used a smaller tube for holding the plant and a larger one to serve as cover (PAGDEN, 1934; WALOFF, 1975) but the disadvantages described above persisted and, in addition, rearing large number of hosts was still cumbersome. Therefore, 3 new techniques were developed and found satisfactory for conducting various studies on dryinids parasitizing rice leafhoppers and planthoppers.

REARING CAGE FOR DETAILED OBSERVATIONS

Studies of the biology, behavior and development of dryinids often required close examination through a binocular microscope. A cage was developed in which parasi- tized hoppers could be reared individually and close observations of larval development as well as feeding and parasitization behavior of the adult could be made.

The cage (fig. 1) was a transparent plastic tube measuring 160 mm x 24 mm and open at both ends. A nylon mesh was fixed on the upper end of the tube for aeration. One or 2 small holes were made on the sides of the cage for inserting aspirator. These holes were plugged with cotton. A rubber stopper which fits in the lower end of the cage was especially cut and bored to hold the roots of the rice plant while the aerial parts remained

(1) Present address : Dept. of Zoology, University of Delhi, Delhi 110007, India.

188 G. CHANDRA

inside the cage (fig. 1, B-F). The stopper was first cut through at the upper 1/3. A small hole was then bored through the middle of the upper piece while a larger hole was made in the lower piece. Both pieces were then rejoined with an adhesive. The small hole in the narrow upper portion permited the stem of the rice seedling to pass through. The larger cavity in the lower portion of the stopper held the roots. A longitudinal incision along one side of the stopper allowed the roots to be placed in the cavity and the stem in the smaller hole (fig. 1 E). The plant was inserted in the cage through its lower open end and the stopper was put firmly in place. Thecage was placed erect in a Petri dish filled with water. The insects were introduced through the small holes in the cage wall. Since the roots remained in water outside the cage, there was no accumulation of moisture in the cage. When changing food plants the cage was closed with an ordinary stopper. The cage can be placed under the binocular microscope for close observations. During such observations it is advisable to plug the base of the rubber stopper with cotton to prevent dripping of water.

TRANSPORTING AND REARING FIELD-COLLECTED HOPPERS TO ESTIMATE PERCENT PARASITISM

Because the incubation period of the dryinid egg is 4 days and it is almost impossible to detect it by dissection, the % parasitism determined by dissecting field-collected hoppers is not accurate, t3XAr, E (1976) and 0TAKE et al. (1976) made similar observations when

they too underestimated the ~o parasitism determined from dissection of field-collected hoppers without prior rearing. It is necessary, therefore, to rear the hoppers. In this study the method used involved rearing of field-collected hoppers for 7-8 days in the cage described below and then examining the dead and alive (chloroformed) hoppers under a binocular microscope to determine % parasitism. Since the dryinid sac is left on host's body after the emergence of the parasite larva, an examination of all the reared hoppers, living and dead, will give a true picture of the field parasitism.

The rearing cage, developed for the observation purposes was also useful for trans- porting live hoppers from the field to laboratory for parasite rearing. The main disad- vantages of the traditional system of rearing hoppers in glass tubes or plastic cages, such as excessive moisture, difficulty in changing food plants, contamination by soil-inhabiting nematodes and difficulty in rearing large number of hoppers, were eliminated with this cage.

The rearing cage consisted of a 17 x 12 cm cylindrical transparent plastic container with a removable top (fig. 2). For aeration, a piece of nylon mesh-cloth was fixed to the top and another to the side opening. A large hole was made in the screw-cap of the glass vial. This top was firmly cemented in a hole at the bottom of the plastic container, thereby permitting unscrewing of the glass vial while its lid remained attached to the cage. Rice seedling roots were inserted in the water-filled vial and a plastic ring with a small hole which fitted in the vial-lid, was fixed around the seedling stems. The space left around the stems was then plugged with cot ton. .Rice seedlings can be easily inserted into the cage through the large hole in the vial-lid. One or 2 wet filter papers on the bottom of the cage held sufficient moisture for the hoppers. Field-collected hoppers were released in the cage with an aspirator through the small holes in the cage wall. The holes were then plugged with cotton. About 100 hoppers can be reared in the cage, changing the plants twice a week. The cage proved very handy in transporting parasitized hoppers since there was no leakage of water from the vial and enough food, space and aeration

REARING TECHNIQUES OF DRYINIDS 189

Nylon mesh ~

Transparent plastic tube

Rice plant

Hole for inserting aspirator

Rubber stopper

B

\

0 1

E

, M F

FIG. 1. Dryinid rearing cage for detailed observations.

190 o. CHANDRA

was available to the hoppers. The emerged parasite larvae usually pupated on the leaves or on cage walls and were collected while changing the plants. For rearing in the labo- ratory, a rubber stopper of the kind used in the breeding cage, could be used for holding the plants instead of the glass vial and plastic ring, and the cage could be placed on a clay pot filled with water. This facilitates feeding changes and prolongs survival of the plants.

DRYINID BREEDING CAGE

Breeding of dryinids was attempted using field-collected or lab-reared hosts main- tained on a susceptible rice variety. A cage was developed in which large number of hoppers could be maintained and yet frequent changes of the host plants were readily made.

The cage (fig. 3) was made of 2 transparent plastic containers of 15 cm height and 13 cm diameter. The bottom of each container was cut off and edges were rejoined together producing a single cylindrical cage which had removable lids at either ends. Two nylon mesh windows and several small holes for inserting aspirator were made in the cage walls. On each lid 3 holes were made in which glass vial-caps with large holes were fixed.

.~sh

l o f vial

) e r

FIG. 2. Cage for transporting and rearing field-collected parasitized hoppers.

REARING TECHNIQUES OF DRYINIDS

Viol hd

)le

191

opper

Ible hd

nesh

v

"ent :)ntainer

it

3er

,topper

le lid

Nater

FIG. 3. Dryinid breeding cage.

The function of the vial caps was to keep the rubber stoppers tight and outside the cage. A small hole was bored through a rubber stopper which would fit in the vial-cap and was slit longitudinally down 1/2 of the stopper. By stretching apart sides of the stopper, rice stem was inserted into the hole of the stopper, which upon release fitted tightly around the stems just above the roots. The rice plant was inserted through the bottom of the

192 G. CHANDRA

cage, through the hole in the vial lid. The rubber stopper fits in the vial-lid, separating the aerial parts of the plants inside the cage from the roots outside. Similarly 2 other rice plants were inserted through the remaining 2 holes. The entire cage was then placed on a clay pot filled with water. The 3 holes on the upper lid of the cage were closed with cork stoppers. The hoppers and dryinid females were released into the cage through the small holes on the sides of the cage which were then plugged with cotton. Wilting of rice ~plants depended upon the density of hoppers maintained in the cage. Fresh rice plants were introduced through the holes in the top of the cage in the similar fashion as described above and the whole cage was inverted. A slight tapping on the cage transferred the insects to fresh plants. The old plants were then removed and the holes closed with stoppers. One or 2 filter papers at the bo t tom of the cage maintained enough humidity and absorbed honey dew excreted by the hoppers.

A icage of this size can maintain 300-500 hoppers depending on their stage, with a change o f rice plants twice a week. A larger cage can be used for breeding large numbers. It is advisable to introduce some 2nd-4th instar host nymphs frequently since they are preferred as food by Pseudogonatopus. With Haplogonatopus and Echthrodelphax, on the other hand, a mixture of 1st and 2nd instar nymphs would yield good results sinc~ 2nd ins- tars are preferred by these parasites. The degree of parasitism achieved in the cages varied in different seasons.

ACKNOWLEDGEMENTS

The author is grateful to Dr. V. A. DYCK, Entomologist and Dr. J. A. LITSINGER, Associate Entomo- logist, LR.R.I., for their continued interest in this work and for facilities and guidance.

RI~SUMI~

Les dryiinides parasitoides des cicadelles du riz aux Philippines. II. Techniques d'61evage.

Trois nouveUes techniques d'61evage de dryiinides parasite s des cicadelles du riz ont 6t6 mises au point. L'une pour l'61evage en laboratoire en vue d'observations pr~cises, un syst6me pour le transport et l'~levage de cicadelles r6colt6es dans la nature afro d'6valuer le pourcentage de parasitisme et une technique d'61evage permanent.

REFERENCES

OTAKE, A. - - 1976. Natural enemies of the brown planthopper. In : The Rice Brown Planthopper . - Proc. Seminar Food& Fertilizer Technology Center for the Asian & Pacific Region 1976, 42-57.

OTAKE, A., SOMASUNDARAM, P. H. & ABEYKOON, M. B. - - 1976. Studies on population of Sogatella furcifera HORV~,XH and Nilaparvata lugens S T~ [Hemiptera : Delphacidae] and their parasites in Sri Lanka. - - Appl. Entomol. Zool., 11,284-294.

PAGDEN, H . T . - - 1934. Notes on hymenopterous parasites of padi pests in Malaya. - - Sci. Ser. Dep. Agr. S..S & F.M.S., 13, 1-13.

WALOrF, N. - - 1975. The parasitoids of the nymphs and adult stages of leafhoppers [Auchenorryncha : Homoptera] of acidic grassland. - - Trans. R. Entomol. Soe. Lond., 126, 637-686.