Effectsofgamma irradiation onthe emergence oflarvae of Curculio sikkimensis (Heller) (Coleoptera: Curculionidae) andCydia kurokoi (Amsel) (Lepidoptera: Tortricidae)

[報 文] Effects of gamma irradiation on the emergence of larvae of Curculio sikkimensis (Heller) (Coleoptera: Curculionidae) and Cydia kurokoi (Amsel) (Lepidoptera: Tortricidae)

Taro IMAMURA, Setsuko TODORIKI, Akihiro MIYANOSHITA and Toru HAYASHI

National Food Research Institute, 2-1-12 Kannondai, Tsukuba, Ibaraki 305-8642, Japan

ガ ンマ線照射 に よるク リシギ ゾウム シ (Curculio sikkimensis(Heller)

(Coleoptera: Curculionidae))と ク リ ミ ガ((Cydia kurokoi(Amsel)

(Lepidoptera: Tortricidae))の 幼 虫 の 防 除

今村 太 郎,等 々力 節子,宮 ノ下 明 大,林 徹

独立 行 政 法人 食 品総 合 研 究所(〒305-8642茨 城 県 つ くば市観 音 台2-1-12)

Summary

The effects of gamma irradiation on the emergence of larvae of the chestnut weevil, Curculio sikkimensis (Heller), were investigated. One hundred chestnuts were irradiated in a 60Coirradiator (Gammacell 220, Nordion, Canada) at a dose rate of 0.40 kGy/h. The doses at which irradiation was carried out were 50, 100, 200, 300, 400, 500 and 1000 Gy.

After treatment, the chestnuts were kept atat25℃,70% RH and emerged larvae were counted daily. Larvae of the nut fruit moth, Cydia kurokoi (Amsel), also emerged from the chestnuts. The data on the chestnut weevil were subjected to probit analysis and the LD 99.9 of weevil larvae was estimated to be about 500 Gy.

developed countries for most purposes due to its Introduction ozone layer depleting effects. Hence, development The chestnut weevil, Curculio sikkimensis (Heller) of an alternative method is urgently needed. (Coleoptera: Curculionidae), is distributed over Japan, Irradiation by gamma rays is thought to be a safe Korea and Russia. This weevil is a major pest of and residue-free alternative. Numerous researcher chestnuts in Japan. Female weevils oviposit into have studied the efficacy of gamma irradiation on chestnut seeds before the chestnut seeds are other weevils, such as the maize weevil (Sitophilus havested. The larvae grow within the seeds from zeamais Motschulsky), the rice weevil (S. oryzae which they emerge as last-instar larvae. The larvae (L.)) and the granary weevil (S. granarius (L.))1)-3). cause damage to the quality of the chestnuts (Fig. 1). We predicted that gamma irradiation would effectively The control of the chestnut weevil has up to disinfest chestnuts contaminated with chestnut weevil now been dependent on fumigation of harvested larvae. chestnuts with methyl bromide. However, the usage This paper reports on the effects of gamma of methyl bromide is to be phased out by 2005 in irradiation on the emergence of chestnut weevil

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kept at 25℃,70%RH, and emerged larvae were

counted daily. Treatments were replicated 3 times.

The data were subjected to probit analysis4)

using the maximum likelihood method5).

Results and Discussion

Table 1 shows the number of emerged larvae from 100 chestnuts. Larvae of the nut fruit moth, Cydia kurokoi (Amsel) (Lepidoptera: Tortricidae), also emerged from the chestnuts. The number of emerged (a) weevil larvae decreased with increasing dose, and no larvae emerged from chestnuts irradiated at doses of 400 Gy and higher. The number of emerged larvae of C. kurokoi also decreased with increasing dose, and no larvae emerged from chestnuts irradiated at doses of 300 Gy and higher, although few larvae emerged even from the untreated control. The LD99.9 of the chestnut weevil larvae was estimated by probit analysis to be 497 Gy, so gamma irradiation would effectively disinfest chestnuts (b) contaminated with chestnut weevil larvae at this Fig. 1 Damage to chestnuts by chestnut weevils: (a) dose. In this study, few larvae of C. kurokoi were Chestnut weevil larva within a chestnut; (b) observed, but this moth sometimes damages Chestnut with holes made by chestnut weevil chestnuts more seriously than the chestnut weevil. larvae. Further research will be needed to estimate the LD99.9 of this moth. larvae from chestnut seeds. Acknowledgements Materials and Methods This study was supported financially by the Chestnuts (variety 'Tsukuba') were harvested on Budget of Nuclear Research of the Ministry of 30 September 2002 in Ibaraki prefecture. Treatments Education, Culture, Sports, Science and Technology, were carried out on 2 and 3 October. One hundred based on the screening and counseling by the chestnuts were irradiated in a 60Co irradiator Atomic Energy Commission. (Gammacell 220, Nordion, Canada) at a dose rate of References 0.40 kGy/h. The doses were 50, 100, 200, 300, 400, 500 and 1000 Gy. After treatment, the chestnuts were 1) Aldryhim Y. N. and Adam E. E.: Efficacy of

Table 1 The number of emerged larvae of C. sikkimensis and C. kurokoi (mean±SE) from 100 chestnuts

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gamma irradiation against Sitophilus granarius 和 文 要 旨 (L.) (Coleoptera: Curculionidae), J. Stored Prod. Res., 35, 225-232(1999). ク リ シギ ゾ ウ ム シ(Curculio sikkimensis(Heller))の 2) Brown G. A. et al.: Gamma radiation effects on 幼 虫 の 出現 に対 す る ガ ンマ 照 射 の 影 響 を調 査 した 。 60Coガ ンマ 線 照 射 装 置(Gammacell220 Sitophilus zeamais and S. granarius, J. Econ. ,Nordion, Entomol., 65, 203-205 (1972). カ ナ ダ)を 用 い,100個 の ク リ を,0.40kGy/hの 線 3) Tilton E. W. et al.: Effects of gamma radiation on 量 率 で,50,100,200,300,400,500お よ び1000Gy Rhyzopertha dominica, Sitophilus oryzae, Tribolium で 照 射 した 。 照 射 処 理 後 の ク リ は25℃,70%RHで confusum and Lasioderma serricorne, J. Econ. 貯 蔵 し,果 実 か ら 出 現 す る幼 虫 を 毎 日計 数 し た 。 同 Entomol., 59, 1393-1368(1966). 時 に ク リ ミ ガ(Cydia kurokoi(Amsel))に 対 す る 効 4) Finney D. L.: Probit Analysis, 3rd Edition, 果 も観 察 した 。 ク リ シ ギ ゾ ウ ム シ幼 虫 の 生 残 デ ー タ Cambridge University Press, Cambridge (1971). を プ ロ ビ ッ ト解 析 した と こ ろ,LD99.9は 約500Gy 5) StatSoft Japan: STATISTICA TMUser's Manual, で あ る と推 測 され た 。 2nd Edition, StatSoft inc., Tokyo (in Japanese) (2004年7月6日 受 理) (1999).

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