著者

松浦 誠 松浦 誠

出版者

三重大學農學部

雑誌

三重大学農学部学術報告 (ISSN:04624408)

巻号頁・発行日

no.69, pp.p1-131, 1984-12

被引用文献数

1

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The present study aims to clarify the specific difference in bionomic characters of the five Japanese <special>Vespa</special> species, <special>V. simillima xanthoptera CAMERON</special>, <special>V. analis insularis DALLA TORRE</special>, <special>V. crabro flavofasciata CAMERON</special>, <special>V. mandarinia japonica RADOSZKOWSKI</special> and <special>V. tropica pulchra BUYSSON</special>, which coexist in low mountain areas of southwestJapan. The life history, nesting habits, feeding habits, division of labour and population dynamics, are described primarily by comparing them with each other. The field work was mainly carried out in and near Kibi-Cho, Wakayama, suthern Japan during the period from 1964 to 1975. A total of 622 nests was observed in and near the study area, and consisted of 288 nests of <special>V. simillimm</special>, 164 of <special>V. analis</special>, 80 of <special>V. crabro</special>, 56 of <special>V. mandarinia</special> and 34 of <special>V. tropica</special>. Results obtained are as follows : 1)The annual life cycle of the five Vespa species consists of the following six periods, though a little variation in details of the cycle occurs among them : (1)pre-nesting, (2)solitary, (3)cooperative, (4)polyethic, (5)reproductive and (6)hibernating period. Hibernated queens come out from their hibernacula during the period from early April to early June in the following order : <special>simillima - mandarinia = crabro - analis - tropica</special>. All of the species found their colonies with a single queen which constructs an average of 35 - 40 cells and rears 10 - 15 larvae up to the pupal stage by herself. The first workers emerge from June to July in the following order with a difference of 5~6 weeks in peak dates between <special>V. simillima and V. tropica : siillima - crabro - analis - mandarinia - tropica</special>. The queens are still iuvolved with both extranidal and intranidal activities for a while after worker emergence. This cooperative period lasts for 2~8 weeks and its length is inversely related to the typical colony size. As the number of workers increases, the queens of all species, other than V. tropica become restricted to oviposition, leaving all the other tasks to the workers. This expansive stage lasted until the time when sexuals are produced and the duration of the reproductive period lasts about a month in each species. The disintegration of the colony ordinarily takes place from early September to late November in the following order : <special>trapica - crabro - analis - mandarinia = simillima</special>. The queens hibernates singly in hibernating spaces within the soil or rotten wood. 2) Nest site preference is classified into the open place and concealed place types. <special>V. analis and V. simillima</special> belong to the former and <special>V. tropica, and V. mandarinia</special> to the latter. The queens of <special>V. simillima and V crabro</special> tend to initiate their nests in narrow, covered places or underground cavities. When the nest become too large after the emergence of workers, the whole colony moves a new, more spacious site. 3)The shape of the completed queen nest was divided into the three types : bowl - shaped (<special>V. tropica and V. mandarinia</special>), ball - shaped (<special>V. crabro and V. simillima</special>) and flask-shaped (<special>V. analis</special>). The general shape of mature nests varies between the species of the open preference and those of the concealed place preference. In the former group (<special>V. simillima and V. analis</special>) the envelope is usually thick, covering the combs completely. In developed nests of these species the envelopes consist of multilayered shell - like sheets enclosing many air chambers among them. In the latter group (<special>V. crabro, V. tropica and V. mandarinia</special>), the envelope consists of only a few plate - like sheets with imperfect air chambers, and the lowest comb is always exposed. 4)The foods of <special>Vespa</special> consist of two well difined classes, carbohydrate and protein. The former are obtained from tree sap, honew -dew of aphids and psyllids, flower nectar, mushroom and syrup juice. The most important source for all the <special>Vespa</special> species was the tree sap exduing from apertures of living trees. Both intra - and interspecifically a distinct linear dominance order is recognized among the hornets visiting tree sap. Interspecific relationships among both queens and workers at food sources are as follows : <special>mandarinia - analis - crabro - simillima - tropica</special>. 5)Prey preftrence of <special>Vespa</special> differed characteristically with species. <special>V. simillima and V. analis</special> hunt a wide range of insects and spiders. <special>V. crabro</special> is regarded as a semi - specialist, preferring various kinds of cicadas, and is highly specialized behaviourally for capturing cicadas. <special>V. tropica</special> is a typical specialist, being almost exclusively dependent on the brood of polistine wasps for their protein food and the life cycle was synchronized with that of the prey wasps. <special>V. mandarinia</special> attacks in mass the colonies of other social wasps and honeybees, possessing an ability to hunt a wide variety of large insects and spiders. Group predation consists of three phases, hunting, slaughter and nest occupation. 6)The queen of <special>Vespa</special> hornets do not engage in cell initiation after worke remergence, though she still participate in intranidal activities for a while. 7)Any <special>Vespa</special> worker would perform any task within a few days after emergence without a labour schedule depending on age distinction as known in the honeybee. 8)In the case of <special>V. analis</special> worker oviposited a few days after the death of the queen. This 'substitution queen' was characterized by the following points ; (1)acting as the primary or sole egg-layer, (2)loss of hairs on the gena and mandibular base and polished head as in the queen, (3)cessation of all extranidal activities, (4)superior dominance, (5)receiving a great deal of food from the other workers, and (6)remarkable prolongation of life span. 9)Total duration of brood development from egg to adult varis on the average from 30.8 days in <special>V. simillima</special> to 40.1 days in <special>V. mandarinia</special>. There is a tendency for the larger the body size in adult hornets, the longer the duration became among the five species. 10)The survivorship curve during the polyethic period is of a convex type in each species ; remarkably low mortality during the immature stages and high mortality after the commencement of foraging activities in the adult stage. 11)After the emergence of sexuals, high mortality was observed throughout all developmental stages, particularly egg and 5th instar, which was probably caused by a decrease in attention given to the brood. 12)The general pattern of seasonal colony development in the five <special>Vespa</special> species is characterized by slow development in the early stage, followed by explosive development in the later stage and then the rapid and terminal decline after sexuals have been produced. The colonial life of <special>V. tropica</special> is about 3.5 to 4 months, while that of <special>V. simillima</special> 7 to 7.5 months. The other three species occupy intermediate positions between the two extremes, in the following order : <special>simillima - mandarinia - analis - crabro - tropica.</special> 13) Comparing the colony size at peak, the maximum number of cells was ca. 300 in <special>V. tropica</special>, ca 900 in <special>V. analis</special>, ca 4,500 in <special>V. mandarinia and V. crabro</special> and ca. 10,000 in <special>V. simillima</special>. 14)New queens emerged during the period ftom early September to late November in the following order : <special>tropica - arabro - analis - simillima - mandarinia</special>. Just prior to the production of new queens, the larva : worker ratio is reduced to its lowest level, below about 2.0, in each <special>Vespa</special> species. 15)The minimum number of workers in a mature colony which is considered as necessary to succeed in producing new queens varies with the species. In <special>V. tropica</special> they can be produced in a colony with more than ca. 20 workers, while in <special>V. simillima</special> colonies the number of workers present needs to reach at least ca. 300 workers. 16)The maximum number of sexuals present per colony varied from 56 new queens and 27 males in a <special>V. tropica</special> colony 1,692 new queens and 1,123 males in a <special>V. simillima</special> colony and is ranked as <special>simillima > mandarinia > crabro > analis > tropica</special>. In general it is recognized that the larger the colony, the more sexuals are produced not only in the same species but also among the five species. 17)Mortality factors working mainly at the nest level are divided into five main causes, (1)disappearance of queen, (2)natural enemies, (3)human interference, (4)climatic factors and (5)unknown causes. The end of <special>Vespa</special> colonies occurs very frequently during the solitary period and following cooperalive period when the queen continues to forage outside the nest, which is attributable to the disappearance of the queen. The heavy predation by <special>V. mandarina</special> results in the greatest proportion of all the unsuccessful nests at mature stage in each <special>Vespa</special> species except for <special>V. mandarinia</special>. In the case of <special>V. mandarinia</special>, destruction by beekeepers plays an important role in colony mortality of mature nests. 18) Annual fluctuations in the number of <special>V. simillima</special> colonies surveyed in four adjacent areas covering ca. 300 ha. gave a nest density of 0.01~0.03 nests per ha. during 12 years, and the total number of nests varied from 3~10 per year. 19) A mechanism to explain the coexistence of the five <special>Vespa</special> species in southwestern Japan is discussed from the view point of the occupation of different ecological niches including nest site, food preference and colony cycle.本論文では,日本の西南暖地の低山地から平地に同所的に生息する5種のスズメバチ属のハチ類,すなわち,キイロスズメバチ <special>Vespa simillima xanthoptera CAMERON</special>(以下キイロ),コガタスズメバチ <special>Vespa analis insularis DALLA TORRE</special>(以下コガタ),モンスズメバチ <special>Vespa crabro flavofasciata CAMERON</special>(以下モン),オオスズメバチ <special>Vespa mandarinia japonica RADOSZKOWSKl</special>(以下オオ),ヒメスズノバチ <special>Vespa tropica pulchra BUYSSON</special>(以下ヒメ)について,各種の生活史,営巣習性,採餌習性,分業,個体群の動態などを明らかにし,これらの種の共存の機構を考察したものである。 調査は1964年より1975年までの12年間にわたって和歌山県有田郡吉備町とその周辺の地域で行なわれ,総計622巣のスズメパチ属の巣を観察の対象としている。1. 生活史 生活史の質的変化を成虫の社会関係を中心に区分するとつぎの6段階,すなわち,(1)前営巣期(2)女王の単独営巣期(3〉女王と働きばちの共同営巣期,(4)分業期,(5〉繁殖カスト産出期,(6〉越冬期となる。越冬後の女王は4月上旬より6月上旬の間に,キイロ-オオ=モン-コガタ-ヒメの順に出現する。各種とも単雌創設で,受精したメス(=女王)のみが創巣し,単独営巣期に35~40房をつくり,そのうち10~15頭の幼虫を単独で育てあげる。最初の働きばちは6~7月に,キイロ-モン-コガタ-オオ-ヒメの順に羽化する。共同常巣期は2~8週間で,その長さは一般にそれぞれの種のコロニーサイズと関連があり,キイロのような大規模営巣型の種では短かく,コガタやヒメのような小規模営巣型の種では長い。働きばちの個体数の増加にともない,ヒメを除く他の4種では,女王は産卵活動に専念し,分業期の後半にほ,働きばちが女王をとりまくローヤルコートが出現する。オスと新女王はコロニーの働きばちの個体数が最多状態に達した時より約1ケ月以上にわたって産出され 交尾は巣外で行なわれる。営巣活動の終息は9月上旬より11月下旬までで,ヒメ-モン-コガタ-オオ-キイロの順となっている。 2. 営巣習性 営巣場所は開放空間型(コガタ),遮蔽空間型(モン,ヒメ,オオ),両空間型(キイロ)に区別される。キイロとモンは造巣当初は狭い遮蔽空間を選好する傾向があるが,働きばちの羽化後の7-8月に,より広い遮蔽空間(モン)および開放空間(キイロ)へコロニーが移住したのち新女王の産出を行なうことが多く,営巣末期の巣ではキイロ88.6%,モン53.5%が引越巣であった。巣の構造は,女王巣の場合,外被の形状により3型,すなわち,皿型(ヒメ,オオ),椀型(モン,キイロ),徳利型(コガタ)に区別される。成熟巣では,開放空間選好種のコガタとキイロでは,外被は貝殻状をした多数の空気室で構成され,ただ1個の側部の出入口を残して巣盤全体な完全に被護するが,遮蔽空間選好種のモン,ヒメ,オオでは,外被は不完全な空気室をもった数枚のシートで構成され,最下段の巣盤が常に露出して出入口を兼ねる。 3. 採餌習性 炭水化物源は5種ともに共通し,樹液,半翅目昆虫の甘露,花蜜,熱果,キノコ(シラタマタケ),空罐や空びん内に残されたジュースなどで,最も重要なものは樹液とキノコである。蛋白源となる獲物とその狩猟行動に顕著な種間差がみられる。キイロとコガタは「何でも屋」で,前者は8目44種以上の昆虫やクモな狩り,そのうちの60%は双翅目の成虫で占められたが,後者は8目53種以上でそのうち双翅目成虫37.9%についで膜翅目の有剣類成虫も32.2%を占め,アシナガバチ亜料やスズメバチ亜料の種も含まれる。モンは獲物の95%以上がセミ類によって占められるが,大型のトンボ,バッタなども捕らえる能力をもち「準専門家」とみなされる。ヒメは典型的な「専門家」で,アシナガバチ亜科の各種の巣を襲って,その幼虫と蛹の体液のみを摂取する。オオは単独ではドウガネブイブイなどの中型のコガネムシ類を中心に,多肉で動きの鈍い昆虫やクモを狩る「準専門家」であるが,同じ巣の働きばち集団が,同属他種のスズメバチ,クロスズメバチ属,ミツバチ属などの社会性ハチの巣を襲い,相手を全滅させたのち幼虫や蛸を掠奪する習性を発達させている。これが,明治以降にわが国へ導入されたセイヨウミツバチに対する集団攻撃の起源とみなされ,単独捕食期,集団殺戮期,占領掠奪期に区別して解析した。 4. 分業 女王は働きばちの羽化後は,外役,ついで内役の順に引退したのち産卵に尊念する。モンの女王の場合,巣づくり行動には,働きばちの出現後も約40日にわたって参加したが,この間に(1)育房の新設,(2)みずから野外で集めた巣材による外被や房壁の伸長,外被をかじりとって得た巣材による房璧の伸長,(4巣材を集めずに,働きばちが伸ばした直後の湿った房壁の再加工(薄く伸ばす)の順に停止とする。働きばちの日齢と仕事に関しては,5種ともに羽化後2日目巨より各種の内役を行ない,3~4日目にほ定位飛行ののち,すぐに巣材,食物,水などの採集活動に従事し,老齢化しても,巣の内外のあらゆる仕事をこなす能力をもつ。女王の亡失巣では,数日後に働きばちの一部の卵巣が発達し,女王の代位となる個体が出現する。コガタの場合,「代位女王」は次の特性をもつ。(1)唯一の,または最優位の産卵者としてオスを産出する,(2〉分業期の女王にみられるような体毛の脱落,および体表面が油じみた光沢なもつ,(3)あらゆる外役への不参加,(4)他の働きばちに対する優位行動,(5)他の働きばちからの頻繁な食物摂取,(6)寿命の著しい延長。 5. 個体群の動態 働きばちの卵から羽化までの発育所要日数は種によって異なり,分業期ではキイロの30.8日からオオの40.11日までの幅があり,大型種ほどその期間が長くなる傾向がある。働きばちの生存曲線は,5種ともに典型的な凸型を示し,卵から羽化後2-3日目までの非外役期では非常に死亡率が低いが,外役活動の開始とともに死亡が一定の割合で起こり,小型種ほど成虫の寿命が短い傾向を示した。また,新女王の羽化の始まったコロニーでは,働きばちの給餌対象が幼虫から新女王成虫へと転換し,そのため幼虫の餓死や非成虫個体に対する共食いが急増して,営巣活動の崩壊を促進した。営巣期間は種によって異なり,短期営巣型のヒメほ3.5~4ケ月に過ぎないが,長期営巣型のキイロほ7~7.5ケ月で,他の3種はキイロ-オオ-コガタ-モン-ヒメの順に両種の中間に位置する。営巣規模は顕著な種間差があり,小規模営巣型のヒメは最多育房数で300房であるが,大規模営巣型のキイロでは10,000房に達する。オオとモンは中規模営巣型とみなされ最多育房数で4,500房となるが,コガタは1,000房以下で小規模営巣型とみなされる。新女王の羽化期も種によって異なり.ヒメ-モン-コガタ-キイロ-オオの順に,9月上旬より11月下旬までの幅がある。新女王の産出にさきがけ,幼虫 : 働きばちの割合(L/W比)は各種とも全営巣期を通じて最低値に下降し,その値は2.0前後となっている。新女王の産出のために必要な働きばちの個体数は種によって著しく異なり,ヒメでは約20頭以上であるが,キイロでは少くとも300頭以上とみなされ,他種は両者の間に位置する。コロニーあた りの新女王とオスの産出数は,一般にコロニーサイズが大きくなるほどその数も多くなり,その最大値はキイロで新女王1,692頭,オス1,123頭,最少値はヒメで新女王56頭,オス27頭であり,5種ではキイロ>オオ>モン>コガタ>ヒメの順になっている。廃巣要因は,女王の亡失,天敵(オオスズメバチ,ハチクマ ,スズメバチネジレバネなど),人の干渉,気象,不明などで,5種ともに単独営巣期から共同営巣期の段階こおいて,女王の亡失による廃巣が最も多くなっている。巣の年次変動に関しては,キイロの場合,300haにおける12年間の成熟巣の数をみると3~10巣/年と低密度の安定型を示した。巣あたりの新女王の生産数の多さに比べ,巣の密度が非常に低いので,本種は強力な密度の自己調節能力をもつとみなされるが,他の4種もその可能性をもつ。以上の結果から,これら5種のスズメバチは,営巣習性,採餌習性,新女王の生産期などの生態的地位をそれぞれ異にすることによって相互の競争的関係を少なくして,同所的に生息を可能にしているものと推論した。