A method of rearing the rice stem borer, chilo supplessalis walker, on germinated rice grains together with the results of feeding tests-香川大学学術情報リポジトリ

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Tech. Bull. Fac. Agr. Kagawa Univ.

A

METHOD O F REARING T H E RICE STEM BORER, CHILO

SUPPLESSALIS WALKER, ON GERMINATED RICE GRAINS

TOGETHER WITH T H E RESULTS O F FEEDING TESTS.

*

Hiroshi MATSUZAWA and Yoshitaka SASAKI

The method of rearing the rice stem borer, Chzlo supplessalzs WALKER, from generation to generation in the laboratory has not yet been established. Rearing in an artificial med. ium i s very desirable for obvious reasons, and completion of the larval development i s a r e - latively simple matter. However, i t has been very difficult to discover a way t o obtain the eggs of the next generation under artificial conditions.

In this laboratory, the method of rearing the ric? stem borer on germinated rice grains has been studied and seems to be adaptable to the artificial learing of successive gene- rations. In this paper, a description of the general technique of the rearing and the results of feeding tests will be presented.

Technique

For the obtaining of eggs of the rice stem borer. several methods are already in use; for example, introducing adult females captured in the field into a cage in which young rice plants a r e growing or another convenient method is t o place the adult females into a n enve- lope made of paraffin covered paper. For the present study, a pair of adults obtained in the labor ator y were introduced into

Fig 1 Equipment for copulation and egg laying of the adult moth (The cylinder of paraffin paper i s put into the conical beaker and a pair of moths is put into the paper cylinder On the bottom of the beaker, a moist filter paper is placed and the vinyl cover with a small hole is placed on the upper rim of the bea- ker The cylinder must be long enough to prevent the adult from creeping out)

a cylinder of paraffin paper which was placed i n a beaker a s shown in Fig. 1. Under these conditions, mating took place successfully and egg masses were deposited on the walls of the paraffin cylinder in the beaker.

When larvae hatched from these egg masses, young rice plant leaves were supplied temporarily a s food. Later the larvae were transferred to receptacles containing germinated rice grains. Development of the larvae steadily progressed a s they ate the roots of the germinated rice grains. At times i t was observed that even the embryo of the rice

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grain was eaten. I n order to keep t h e receptacles clean and insure a good supply of food, food exchanges were made about every 7 t h day in t h e first half of the rearing period, and every

5

t h day during the l a - tter half. The method of rearing i s shown in Fig. 2.

When the period of pupation drew near, and the full-grown larvae be- gan to creep around on the wall inside the paper receptacle, some folded pieces of paraffin paper we- er put into the beaker. The larvae

Fig 2 Method of rearing t h e rice stem borer on germi- nated r ice-grains.

A : 40W Fluorescent lamp, B : Rearing receptacles, C : Conical beaker (200cc). a : Wire netting, b : Germinated rice-grains

then crawled into the folds of p a -

per for pupation. T h e pupae obtained in this way were placed in other receptacles such as glass tubes or Petri's dishes, Under these conditions, the adult moth emerged within seve., ral days. The adult moth needs to be handled prudently. A constant temperature of 25OC and illumination (with a 40 Watt fluorescent lamp) for 16 hrs at least per day are two of t h e conditions maintained throughout all the rearing process.

The number of larvae per receptacle and the quantity of food must be regulated according to the size of the receptacle to obtain the best results.. The conditions for rearing i n this experiment are described as follows :

Temperature of rice seed germination : At 30°C after steeping for 5 days, the bud- length was about 2 - 3 mm.

Receptacles : Conical beakers of 200 cc capacity were used. Quantity of rice seeds : 200 g per receptacle were used.

Number of larvae per receptacle : 50

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100 during the 1st and 2 nd instar, and 20 - 30 during the 3 rd

-

6

t h instars.

For purposes of convenience, only the Nagao population of the rice stem borer in Kagawa prefecture was used.

Development of the rice stem borer

For the method mentioned above, the average developmental periods of the ice stem borer are as follows: egg 5 days, larva 37 days and pupa 8 days. This data is shown in Table 1

.

The total time required for the development of the rice stem borer is then 50 days on the average.

I n this experiment, 98 % hatching, 83 % pupation, 75 % emergence, and 0 5

%

appear

-

ance of the diapausing larvae were observed. However, it may be noted that the percen- tage was 80 - 85, 70 - 90 and 0.5 - 1.0 % respectively when all the results of the past s e - veral experiments a r e taken into consideration

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52 Tech. Bull. Fac. Agr.. Kagawa Univ.

*

Egg masses

Table 1. Developmental period in days of the rice stem borer(25OC).

Number of Confidence limit of

Var iance

population mean (95%) variation (%)

Survival of t h e a d u l t moth and t h e fecundity of t h e adult female

The adult moth of the rice stem borer has a life span of about 6

-

7

days. The number of eggs (fecundity) produced by the adult female average 220. These results are shown i n Table 2. Data obtained from another series of rearing tests closely resemble those shown in Table 2.

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19.918 11.568

Table 2. Survival in days of the adult moth (25OC).

-

53.274 0.779 - Egg Lava Pupa -

Number of Sample Confidence limit of Coeff. of

Sex

/

individuals Min

.

-Max. Variance

tested

/

1

mean

I

population mean (95%) variation (%) Head capsule width of t h e f i r s t larval instar and t h e length of t h e

forewing of t h e adult moth

-

-34 845 - 38.457 7.378 - 7.888 Male 17 4 - 11 7.118 Female

1

29 1 - 1 1 5.828

The average width of the head capsule of the 1st instar larva was 0.27 mm. The average length of the forewing of the adult moth was 10 - 11 mm. These data are shown in Table 3.

Generally speaking, these data closely resemble data accumulated from other experiments.

5 000 36.646 7.633 44, 65 49

Table 3. Head capsule width of the 1st instar larva ( A ) and the fore wing length of the adult moth (B).

5 25 - 69

5 - 10

6.039 - 8.197

4.910

-

6,746

Number of Sample Confidence limit of Coeff. of

Item

1

individuals Min.-Max. Variance

tested

1

mean

1

population mean (95%) variation

4..410 5.815

29.503 41.369

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General considerations

Because of its simplicity and soundness, the above described method i s found to be very useful to demonstrate the various developmental stages of the rice stem borer. If one does not mind paying special attention to details, this method could probably be adaptable to the rearing of successive generations of this insect in the laboratory. At present, this method is offered as one of the most successful methods of rearing the rice stem borer under artifi- cial conditions. Should there be a desire to rear on a larger scale, i t is suggested that certain modifications and changes may become necessary especially in regard t o the instru- ments and receptacles whlch would be used. Continued experimentation along this line would undoubtedly prove fruitful. The authors' experience to date demonstrates that 5

-

6 successive generations per year can be successfully reared i n the labor ator y

.

Acknowledgements

The authors express their hearty thanks to the Former Prof. Dr. C. Harukawa of Ky6to University and Okayama University for his valuable suggestion and encouragement duriug this work,. Thanks are also due to Mr. T . Inaba and Mr. Y. Wakasugi of the authors' la- boratory for their kind helps during the work.

Summary

A method of rearing the rice stem borer, Chzlo supplessalzs WALKER on germinated rice grains together with the results of feeding tests especially on the development of the borer, the width of head-capsule of the larva, the length of forewing of the adult, the fecundity of the adult female etc. were described in the present paper. Some essential points of the rearing and some data on feeding tests were shown in Fig. 1-2 and Table 1-3. At present, this method seems to be one of the most successful methods of rearing the rice stem boxer under artifificial conditions and i t seems that

5

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6

successive generations per year can be soundly reared in the labor ator y

.

(Received May 30, 1964) References

Sata, Y. : J . Jap, Soc. Appl, Ent. 2001. ,8(1), 6--YO, (1964).

(This paper was not directly cited, because it was presented after the completion of the authors' paper .)

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