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水田におけるコガタアカイエカ未成熟期の生存率と死亡要因


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Title: 水田におけるコガタアカイエカ未成熟期の生存率と死亡要因
Other Titles: Survival Rates of Immature Stages of Culex tritaeniorhynchus (Diptera, Culicidae) in Rice Fields under Summer Cultivation
Authors: 茂木, 幹義 / 森, 章夫 / 和田, 義人
Authors (alternative): Mogi, Motoyoshi / Mori, Akio / Wada, Yoshito
Issue Date: 30-Jun-1980
Publisher: 長崎大学熱帯医学研究所 / Institute of Tropical Medicine, Nagasaki University
Citation: 熱帯医学 Tropical medicine 22(2). p111-126, 1980
Abstract: コガタアカイエカ未成熟期の生存率と死亡要因を明らかにするために,長崎の水田で7月上旬から8月上旬にかけて野外実験を行なった.6月末の田植に続くこの時期は,コガタアカイエカの増殖の最盛期にあたる.水田に施用された農薬(殺虫剤,除草剤)が有効な間は羽化率は低かった.農薬の影響がない場合でも,捕食性天敵が自然状態で存在する枠内での羽化率は一般に低かった.5月の休閑田で行なった同様の実験(Mogi et al, 1980)に比べてはるかに高い羽化率が観察された場合もあったが,これは日生存率の増加によるのではなく,主として,高温による発育期間の短縮に帰せられた.農薬を散布された水田の捕食性天敵の種類や密度は無散布水田に比べて少なかった.天敵除去区では生存率は顕著に高くなった.フナ等の魚類は,卵,幼虫,いずれにとってもきわめて有効な天敵だと考えられた.また捕食性の水生昆虫の働きもきわめて大きいと思われた.これらの結果にもとづき,農薬がしばしば散布されるにもかかわらずコガタアカイエカの数が夏に急増する過程を分析し,農薬散布が一斉にされないために,広い地域をとれば常に農薬によって天敵の減少した好適な水田があること,すなわち水田の条件の異質性がコガタアカイエカの連続的な増加を可能にしている重要な要因であると結論した.同種の防除に天敵を積極的に利用する可能性について触れた. / Survival rates and mortality factors were examined on immature Culex tritaeniorhynchus released in experimental frames or cages set in rice fields in July, because this period following transplantation of young rice plants is the most active breeding season of the species in Nagasaki, Japan. Emergence rates were low during the period when agricultural chamicals (insecticides, herbicides) applied to rice fields remained lethal to tritaeniorhynchus larvae. Even when the effect of chemicals disappeared, emergence rates were generally very low in frames with a natural complex of predators. However, emergence rates in a few frames were much higher than those observed in fallow rice fields in May. This high emergence rate was due not to the increased daily survival rate but primarily to the shortened developmental period under high temperatures of midsummer. Predator density was lower in rice fields treated with agicultural chemicals than in untreated ones. Emergence rates increased remarkably in enemy-free cages. Fishes were considered to be very effective predators for eggs and larvae. Also, predacious insects appeared to make a large contribution to mortality during aquatic stages. Based on the results, there was analysed the process of population growth of tritaeniorhynchus in summer under the strong pressure of predation and agricultural chemicals. It was concluded that the heterogeneity in the condition of rice fields is a very important factor ensuring the continuous growth of tritaeniorhynchus populations in summer. Emphasis was put on the positive use of natural enemies to suppress tritaeniorhynchus populations in summer.
URI: http://hdl.handle.net/10069/4280
ISSN: 03855643
Type: Departmental Bulletin Paper
Appears in Collections:Volume 22, No. 2

Citable URI : http://hdl.handle.net/10069/4280

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