Assessment of ecological features of Chrysocharis pubicornis (Hymenoptera:Eulophidae) as biological control agent of Liriomyza leafminers (Diptera:Agromyzidae) Liriomyza属ハモグリバエ類の生物的防除資材としてのプビコルニスヒメコバチの生態学的特性評価

博士論文

The eulophid Chrysocharis pubicornis (Zetterstedt) is a solitary pupal endoparasitoid of agromyzid leafminers. Although in Japan it is one of the dominant species in the parasitoid complex of the garden pea leafminer Chromatomyia horticola Goureau, C. pubicornis has been just occasionally recorded from the adventive leafminer species Liriomyza trifolii and L. sativae, unintentionally introduced into Japan in the 1990's. Because the adventive Liriomyza species larvae exit the mines and drop to the ground to pupate, as opposed to the native C. horticola whose larva pupates inside the mine in the host-plant leaves, it has been considered that, being C. pubicornis a pupal parasitoid, it cannot utilize the invasive Liriomyza leafminers efficiently. In the present study, I evaluated several ecological features of C. pubicornis to asses its potential as biological control agent of Liriomyza species, while considering the different life histories of the aforementioned leafminers. The following results were obtained: 1) Preimaginal development and summer diapause: The C. pubicornis development thresholds when reared on C. horticola were 7.4 and 7.2℃, and the thermal constants were 297.4 and 307.5 degree-days for males and females, respectively. In addition, the larval development showed a short-day-type photoperiodic response that was affected by temperature. Matured last instar larvae entered summer diapause in a proportion that increased with photoperiod and temperature, and the critical photoperiod was between 12 and 14 h at 25℃. Regardless of photoperiod, diapause terminated in most individuals when they were transferred from diapause-maintaining conditions to 15℃, but transferring to 25℃ resulted in low diapause termination. 2) Sensitive stage to diapause induction: During the 22-d C. pubicornis egg-larval period at diapause-preventing conditions (15℃° and 12L:12D), larvae of different ages were transferred to diapause-inducing conditions (25℃ and 16L:8D). Transferring 15-d-old or younger individuals resulted in a high percent of diapause induction (>60%), while the induction rate was low (<25%) when 18-d-old or older individuals were transferred. These results suggest that sensitivity to diapause is high in young larval instars but it decreases in the last instar. 3) The ability of C. pubicornis to locate and attack Liriomyza leafminers: In experiments with caged kidney bean plants infested with Liriomyza trifolii, female wasps were unable to attack hosts after the larvae exited the mines and dropped to the ground to pupate. However, a high percentage of larvae were parasitized when they were still in the mines, and while some were killed there, most of the parasitized larvae completed the larval stage and dropped to the ground to pupate. This shows that in addition to pupal parasitism occurring in leafminers that pupate inside the mines, C pubicornis can significantly attack those host species that pupate III the ground, such as Liriomyza spp., through larval and larval-pupal parasitism. 4) Preimaginal development on Liriomyza spp.: The development of C. pubicornis on L. trifolii and L. sativae at several temperatures was longer than that on C. horticola. Particularly at 22.5 and 25℃, the egg-larval period of a significant number of individuals developing on both Liriomyza species was protracted, although most of the individuals could complete development and emerge as adults. The hind tibia length, used as index of body size, varied significantly with temperature, host species and sex of wasps; it was longer when wasps developed on C. horticola than on any of the two Liriomyza spp., although the differences did not exceed 10%. No significant differences were found between tibia lengths of wasps reared on the Liriomyza spp.. Based on the above results, it is concluded that C. pubicornis is well adapted to develop on its main host, the native C. horticola. Moreover, it has ability to attack and complete development on the adventive Liriomyza spp.; however, the delayed development appears to reduce its potential for suppressing these adventive leafrniner species. The occurrence of summer diapause opens the possibility for long-term storage, which makes C. pubicornis an interesting candidate for suppressing leafminers in other genera, such as C. horticola.

プピコルニスヒメコバチ Chrysocharis pubicornis (Zetterstedt) は内部単寄生性の蛹寄生蜂であり､ナモグリバエ Chromatomyia horticola Goureau の天敵群集において優占的な種として知られている｡本種は､1990年代にわが国に侵入したマメハモグリバエ Liriomyza trifolii (Burgess) やトマトハモグリバエ Liriomyza sativae Blanchard から記録されているが､これら侵入害虫ハモグリバエは葉を加害した幼虫が潜孔から脱出し､土中で蛹化するという点で､葉の潜孔内で蛹化するナモグリバエと大きく異なっている｡このため､蛹寄生蜂である本種は Liriomyza 属ハモグリバエ類を利用できないと考えられてきた｡本研究では､このような寄主ハモグリバエ類の生態学的特性の違いを考慮しながら､生物的防除資材としてのプピコルニスヒメコバチの有効性を明らかにするため､生態学的特性に関する評価を行い､以下の結果を得た｡ 1)発育と夏休眠:寄主ナモグリバエにおける本種の発育零点は雄で7.4℃､雌で7.2℃､有効積算温量は雄で297.4日度､雌で307.5日度であった｡また､本種の休眠光周反応は短日型反応を示した｡休眠個体の割合は日長および気温の増加とともに高くなり､休眠誘起の臨界日長は25℃で12-14時間と推測された｡日長に関わらず､ほとんどの個体が15℃では休眠から覚醒したが､25℃では休眠からの覚醒は認められなかった｡ 2)休眠誘導感受期:卵幼虫期間の22日間でさまざまな日齢の個体を休眠覚醒条件(15℃､12L:12D)から休眠誘導条件(25℃､16L:8D)に移した｡その結果､15日齢以下の若い個体では60%以上の休眠率となった｡一方､18日齢以上の個体を移した場合には､休眠率は有意に低下した｡以上の結果から､休眠感受性は若齢幼虫で高く､終齢幼虫では低下することが明らかとなった｡ 3)Liriomyza 属ハモグリバエに対する寄主発見能力および寄生能力:葉から脱出し､土中で蛹化した寄主に対して雌蜂は寄生できなかったが､葉の潜孔内の幼虫に対しては高い割合で寄生した｡被寄生幼虫は潜孔から飛び出し､土中で蛹化した｡このことから､本種は従来考えられていた蛹寄生蜂としての寄主利用様式に加え､Liriomyza 属のように幼虫のみが葉にとどまる寄主に対しては､幼虫蛹寄生蜂としてふるまうことが明らかとなった｡ 4)Liriomyza 属ハモグリバエ類での発育特性:マメハモグリバエおよびトマトハモグリバエでの発育期間はナモグリバエでの発育期間に比べ長く､特に22.5℃および25℃では発育遅延が認められたが､ほとんどの寄生蜂幼虫は成虫まで発育した｡成虫体サイズの指標とした後脚脛節長は雌雄および発育温度によって有意に影響を受け､Liriomyza 属2種で育った寄生蜂の体サイズはナモグリバエで育った個体に比べ小さかったが､体サイズの減少は10%程度であった｡ 以上の結果から､プピコルニスヒメコバチは主要な寄主であるナモグリバエでの発育に良く適応していること､侵入害虫 Liriomyza 属ハモグリバエ類の幼虫を利用できることが明らかとなった｡しかし､Liriomyza 属ハモグリバエで認められた発育遅延は､プピコルニスヒメコバチの抑圧能力を低下させると考えられた｡一方､今回明らかとなった夏休眠は､生物的防除資材としてのプピコルニスヒメコバチの常温長日条件での長期保存を可能にするものであり､ナモグリバエを含めたハモグリバエ類の生物的防除での有効利用の道を開くものと期待される｡

鹿児島大学大学院連合農学研究科博士論文

The eulophid Chrysocharis pubicornis (Zetterstedt) is a solitary pupal endoparasitoid of agromyzid leafminers. Although in Japan it is one of the dominant species in the parasitoid complex of the garden pea leafminer Chromatomyia horticola Goureau, C. pubicornis has been just occasionally recorded from the adventive leafminer species Liriomyza trifolii and L. sativae, unintentionally introduced into Japan in the 1990's. Because the adventive Liriomyza species larvae exit the mines and drop to the ground to pupate, as opposed to the native C. horticola whose larva pupates inside the mine in the host-plant leaves, it has been considered that, being C. pubicornis a pupal parasitoid, it cannot utilize the invasive Liriomyza leafminers efficiently.### In the present study, I evaluated several ecological features of C. pubicornis to asses its potential as biological control agent of Liriomyza species, while considering the different life histories of the aforementioned leafminers. The following results were obtained:###1) Preimaginal development and summer diapause: The C. pubicornis development thresholds when reared on C. horticola were 7.4 and 7.2℃, and the thermal constants were 297.4 and 307.5 degree-days for males and females, respectively. In addition, the larval development showed a short-day-type photoperiodic response that was affected by temperature. Matured last instar larvae entered summer diapause in a proportion that increased with photoperiod and temperature, and the critical photoperiod was between 12 and 14 h at 25℃. Regardless of photoperiod, diapause terminated in most individuals when they were transferred from diapause-maintaining conditions to 15℃, but transferring to 25℃ resulted in low diapause termination.###2) Sensitive stage to diapause induction: During the 22-d C. pubicornis egg-larval period at diapause-preventing conditions (15℃° and 12L:12D), larvae of different ages were transferred to diapause-inducing conditions (25℃ and 16L:8D). Transferring 15-d-old or younger individuals resulted in a high percent of diapause induction (>60%), while the induction rate was low (<25%) when 18-d-old or older individuals were transferred. These results suggest that sensitivity to diapause is high in young larval instars but it decreases in the last instar.###3) The ability of C. pubicornis to locate and attack Liriomyza leafminers: In experiments with caged kidney bean plants infested with Liriomyza trifolii, female wasps were unable to attack hosts after the larvae exited the mines and dropped to the ground to pupate. However, a high percentage of larvae were parasitized when they were still in the mines, and while some were killed there, most of the parasitized larvae completed the larval stage and dropped to the ground to pupate. This shows that in addition to pupal parasitism occurring in leafminers that pupate inside the mines, C pubicornis can significantly attack those host species that pupate III the ground, such as Liriomyza spp., through larval and larval-pupal parasitism.###4) Preimaginal development on Liriomyza spp.: The development of C. pubicornis on L. trifolii and L. sativae at several temperatures was longer than that on C. horticola. Particularly at 22.5 and 25℃, the egg-larval period of a significant number of individuals developing on both Liriomyza species was protracted, although most of the individuals could complete development and emerge as adults. The hind tibia length, used as index of body size, varied significantly with temperature, host species and sex of wasps; it was longer when wasps developed on C. horticola than on any of the two Liriomyza spp., although the differences did not exceed 10%. No significant differences were found between tibia lengths of wasps reared on the Liriomyza spp..### Based on the above results, it is concluded that C. pubicornis is well adapted to develop on its main host, the native C. horticola. Moreover, it has ability to attack and complete development on the adventive Liriomyza spp.; however, the delayed development appears to reduce its potential for suppressing these adventive leafrniner species. The occurrence of summer diapause opens the possibility for long-term storage, which makes C. pubicornis an interesting candidate for suppressing leafminers in other genera, such as C. horticola.

プピコルニスヒメコバチ Chrysocharis pubicornis (Zetterstedt) は内部単寄生性の蛹寄生蜂であり、ナモグリバエ Chromatomyia horticola Goureau の天敵群集において優占的な種として知られている。本種は、1990年代にわが国に侵入したマメハモグリバエ Liriomyza trifolii (Burgess) やトマトハモグリバエ Liriomyza sativae Blanchard から記録されているが、これら侵入害虫ハモグリバエは葉を加害した幼虫が潜孔から脱出し、土中で蛹化するという点で、葉の潜孔内で蛹化するナモグリバエと大きく異なっている。このため、蛹寄生蜂である本種は Liriomyza 属ハモグリバエ類を利用できないと考えられてきた。本研究では、このような寄主ハモグリバエ類の生態学的特性の違いを考慮しながら、生物的防除資材としてのプピコルニスヒメコバチの有効性を明らかにするため、生態学的特性に関する評価を行い、以下の結果を得た。###1)発育と夏休眠:寄主ナモグリバエにおける本種の発育零点は雄で7.4℃、雌で7.2℃、有効積算温量は雄で297.4日度、雌で307.5日度であった。また、本種の休眠光周反応は短日型反応を示した。休眠個体の割合は日長および気温の増加とともに高くなり、休眠誘起の臨界日長は25℃で12-14時間と推測された。日長に関わらず、ほとんどの個体が15℃では休眠から覚醒したが、25℃では休眠からの覚醒は認められなかった。###2)休眠誘導感受期:卵幼虫期間の22日間でさまざまな日齢の個体を休眠覚醒条件(15℃、12L:12D)から休眠誘導条件(25℃、16L:8D)に移した。その結果、15日齢以下の若い個体では60%以上の休眠率となった。一方、18日齢以上の個体を移した場合には、休眠率は有意に低下した。以上の結果から、休眠感受性は若齢幼虫で高く、終齢幼虫では低下することが明らかとなった。###3)Liriomyza 属ハモグリバエに対する寄主発見能力および寄生能力:葉から脱出し、土中で蛹化した寄主に対して雌蜂は寄生できなかったが、葉の潜孔内の幼虫に対しては高い割合で寄生した。被寄生幼虫は潜孔から飛び出し、土中で蛹化した。このことから、本種は従来考えられていた蛹寄生蜂としての寄主利用様式に加え、Liriomyza 属のように幼虫のみが葉にとどまる寄主に対しては、幼虫蛹寄生蜂としてふるまうことが明らかとなった。###4)Liriomyza 属ハモグリバエ類での発育特性:マメハモグリバエおよびトマトハモグリバエでの発育期間はナモグリバエでの発育期間に比べ長く、特に22.5℃および25℃では発育遅延が認められたが、ほとんどの寄生蜂幼虫は成虫まで発育した。成虫体サイズの指標とした後脚脛節長は雌雄および発育温度によって有意に影響を受け、Liriomyza 属2種で育った寄生蜂の体サイズはナモグリバエで育った個体に比べ小さかったが、体サイズの減少は10%程度であった。### 以上の結果から、プピコルニスヒメコバチは主要な寄主であるナモグリバエでの発育に良く適応していること、侵入害虫 Liriomyza 属ハモグリバエ類の幼虫を利用できることが明らかとなった。しかし、Liriomyza 属ハモグリバエで認められた発育遅延は、プピコルニスヒメコバチの抑圧能力を低下させると考えられた。一方、今回明らかとなった夏休眠は、生物的防除資材としてのプピコルニスヒメコバチの常温長日条件での長期保存を可能にするものであり、ナモグリバエを含めたハモグリバエ類の生物的防除での有効利用の道を開くものと期待される。