Effects of local vegetation and plantation age for the parasitoid Asecodes mento– a biocontrol agent in organic strawberry fields

Abstract The parasitoid Asecodes mento (Walker, 1839) (Hymenoptera: Eulophidae) is the most important biocontrol agent of the strawberry leaf beetle Galerucella tenella (L.) (Coleoptera: Chrysomelidae) in northern Europe. Here, I investigated whether natural parasitism in organic strawberry plantations was affected by the presence of the alternative host plant meadowsweet (Filipendula ulmaria), and whether parasitism rates differed between plantations of different ages (6 to 79 years). I also investigated whether parasitoid brood size, body size and sex ratio differed between the two host plants in the field. Parasitism was very low (0%) in newly established plantations and increased to a plateau (～40%) in fields where strawberries had been grown for approximately 20 years or longer. Such an extended colonization process is unacceptable for commercial growers. It would thus be desirable to find a method to catalyze parasitoid population buildup in young plantations. Parasitoid brood sizes were larger in beetles collected from meadowsweet, while body size and sex ratio did not differ between parasitoids collected from the two plants. These findings suggest that meadowsweet can export parasitoids to neighboring strawberry fields. Although this is a possibility, I did not find any significant differences in parasitism rates between isolated strawberry fields and fields adjacent to meadowsweet stands, indicating that effects of local vegetation are small on parasitism rates. Releasing parasitoids in newly established strawberry plantations may be a better strategy for quickly obtaining high parasitism than intercropping with meadowsweet.     

入侵害虫椰心叶甲的研究进展

近30年来,椰心叶甲Brontispa longissima(Gestro)在亚太椰子产区扩散蔓延,成为棕榈植物上主要害虫。2002年,该害虫入侵我国海南并暴发成灾。化学防除是控制椰心叶甲危害的首要措施,其中包括挂药包等农药缓释技术,而生物防治是控制该虫扩散蔓延的经济有效措施。从感病椰心叶甲虫体上分离的微生物杀虫剂绿僵菌Metarhizium anisopliae被我国和其他多个国家应用。椰心叶甲天敌寄生蜂的引进利用是可持续控制该害虫发生的重要措施。幼虫寄生蜂椰甲截脉姬小蜂Asecodes hispinarum和蛹寄生蜂椰心叶甲啮小蜂Tetrastichus brontispae是椰心叶甲的两种重要天敌。2004年,椰甲截脉姬小蜂和椰心叶甲啮小蜂被引入到我国,经扩繁释放后,取得了良好的控害效果,其中有些地区的椰甲截脉姬小蜂寄生率可达90%,椰心叶甲啮小蜂寄生率可达100%。连续放蜂,且椰心叶甲种群有合适虫龄被寄生蜂寄生是控害效果的关键。气候等生态因子也可能是影响寄生蜂控制靶标害虫效果的因素,应进一步加强研究。论文最后提出了未来椰心叶甲防控的研究的方向。     

椰心叶甲寄生蜂——椰甲截脉姬小蜂的生物学特性

椰甲截脉姬小蜂Asecodes hispinarum Boucek是椰心叶甲Brontispa longissima（Gestro）幼虫的重要内寄生蜂,2004年3月从越南引进到海南省。在实验室条件下,对椰甲截脉姬小蜂的形态、发育、繁殖、寄生潜能等生物学特性进行了初步研究。结果表明,椰甲截脉姬小蜂在24℃±2℃,RH 75%±10%条件下,卵期平均为2.8天,幼虫期6.7天,蛹期(含预蛹期)7.5天;成蜂在没有营养补充的情况下,平均存活2.5天。椰甲截脉姬小蜂的寿命受温度和补充营养的影响,雌蜂寿命长于雄蜂寿命。雌蜂平均怀卵量为43粒,产卵高峰期在交配后的12 h内。椰甲截脉姬小蜂对椰心叶甲4龄幼虫的功能反应属 HollingⅡ型,随自身密度的增加其寄生效果呈下降的趋势。     

椰甲截脉姬小蜂野外种群与实验种群差异性比较

通过随机抽样,比较了椰甲截脉姬小蜂Asecodes hispinarum Bou(c)ek林间种群与室内种群的雌雄比、出蜂量、未出蜂量、怀卵量的差异.t检验表明这些参数在2个种群间均存在显著的差异.野外种群和室内种群雌蜂比例分别占81.63%±2.54%和65.34%±1.80%,出蜂量分别是(25.13±1.17)头...     

引进天敌椰甲截脉姬小蜂防治椰心叶甲的可行性探讨

从2 0 0 2年海南省首次在海口市发现新入侵害虫椰心叶甲Brontispalongissima(Gestro)以来,现该虫已蔓延到海南省的1 1个市县。从地理纬度、气候条件、寄主分布范围等自然条件来看,椰心叶甲也完全有可能向高纬度的临近省份扩散。直接影响到种植业及旅游业的健康发展,因此防治该虫迫在眉睫。通过海南省的生态条件,椰心叶甲的寄主和天敌特点综合分析,认为引进天敌椰甲截脉姬小蜂Asecodeshispinarum防治该害虫是经济有效的方法。     

Factors affecting the parasitism rate and the number and sex ratio of offspring of Asecodes hispinarum Bouček (Hymenoptera: Eulophidae), a biological control agent of Brontispa longissima (Gestro) (Coleoptera: Chrysomelidae)

To optimise the production of Asecodes hispinarum Bou?ek (Hymenoptera: Eulophidae), a parasitoid of coconut leaf beetle, Brontispa longissima (Gestro) (Coleoptera: Chrysomelidae), some of the factors affecting rates of parasitism, number of offspring produced per host and sex ratio of A. hispinarum were investigated. The numbers and sex ratio of A. hispinarum offspring per host reduced significantly at extreme low humidity (30% relative humidity [RH]), but there was no significant effect on parasitism. Photoperiod had no significant effects on any of the life traits tested. A. hispinarum was able to reproduce via arrhenotoky, and while increasing the proportion of female parents increased the number of parasitoids produced, the proportion of female offspring decreased. Older females showed a lower rate of parasitism than young females, however, maternal age did not affect the number or the sex ratio of offspring. Increasing the number of hosts offered to a pair of parasitoids significantly increased the number of parasitised hosts but decreased the parasitism rate while the sex ratio of progeny was not affected. Present work showed that to maximise the production of female parasitoids, a parasitoid/host ratio of 1:1, using one-day old A. hispinarum at a female/male ratio of 3:1 and RH of at least 55% is recommended.     

Selection by parasitoid females among closely related hosts based on volatiles: Identifying relevant chemical cues

Parasitoid fitness is influenced by the ability to overcome host defense strategies and by the ability of parasitoid females to select high‐quality host individuals. When females are unable to differentiate among hosts, their fitness will decrease with an increasing abundance of resistant hosts. To understand the effect of mixed host populations on female fitness, it is therefore necessary to investigate the ability of female parasitoids to select among hosts. Here, we used behavioral assays, headspace volatile collection, and electrophysiology to study the ability of Asecodes parviclava to use olfactory cues to select between a susceptible host (Galerucella calmariensis) and a resistant host (Galerucella pusilla) from a distance. Our studies show that parasitoid females have the capacity to distinguish the two hosts and that the selection behavior is acquired through experiences during earlier life stages. Further, we identified two volatiles (α‐terpinolene and [E]‐β‐ocimene) which amounts differ between the two plant–herbivore systems and that caused behavioral and electrophysiological responses. The consequence of this selection behavior is that females have the capacity to avoid laying eggs in G. pusilla, where the egg mortality is higher due to much stronger immune responses toward A. parviclava than in larvae of G. calmariensis.     

三种农药亚致死剂量对椰甲截脉姬小蜂功能反应的影响

测定了氯氰菊酯、啶虫脒和椰甲清3种杀虫剂亚致死剂量对椰甲截脉姬小蜂Asecodes hispinarumBoucˇek寄生椰心叶甲Brontispa logissima(Gestro)功能反应的影响。结果表明:亚致死剂量杀虫剂没有改变椰甲截脉姬小蜂功能反应模型的基本结构,但影响到了模型的各项参数。药剂处理后椰甲截脉姬小蜂的最大日捕食量降低,处理猎物时间延长,搜寻效应减弱。氯氰菊酯和啶虫脒的处理后瞬时攻击率减小,但椰甲清处理后瞬时攻击率高于对照。可见,在亚致死剂量下,氯氰菊酯和啶虫脒对椰甲截脉姬小蜂的寄生作用存在不良影响,椰甲清(30%杀虫单+15%啶虫脒)可提高其瞬时攻击率但减弱其搜索效应。     

Natal origin affects host preference and larval performance relationships in a tritrophic system

Many insects face the challenge to select oviposition sites in heterogeneous environments where biotic and abiotic factors can change over time. One way to deal with this complexity is to use sensory experiences made during developmental stages to locate similar habitats or hosts in which larval development can be maximized. While various studies have investigated oviposition preference and larval performance relationships in insects, they have largely overlooked that sensory experiences made during the larval stage can affect such relationships. We addressed this issue by determining the role of natal experience on oviposition preference and larval performance relationships in a tritrophic system consisting of Galerucella sagittariae, feeding on the two host plants Potentilla palustris and Lysimachia thyrsiflora, and its larval parasitoid Asecodes lucens. We firstly determined whether differences in host‐derived olfactory information could lead to divergent host selection, and secondly, whether host preference could result in higher larval performance based on the natal origin of the insects. Our results showed that the natal origin and the quality of the current host are both important aspects in oviposition preference and larval performance relationships. While we found a positive relationship between preference and performance for natal Lysimachia beetles, natal Potentilla larvae showed no such relationship and developed better on L. thyrsiflora. Additionally, the host selection by the parasitoid was mainly affected by the natal origin, while its performance was higher on Lysimachia larvae. With this study, we showed that the relationship between oviposition preference and larval performance depends on the interplay between the natal origin of the female and the quality of the current host. However, without incorporating the full tritrophic context of these interactions, their implication in insect fitness and potential adaptation cannot be fully understood.     

椰甲截脉姬小蜂在中国的适生性分布

研究极端温度对椰甲截脉姬小蜂Asecodes hispinarum Bouek存活的影响。在2℃、33℃和36℃恒温条件下放置48h后,该蜂羽化率较对照来说大大降低,基本上不能羽化;而在0℃和39℃恒温条件下即使只放置24h,该蜂全部死亡。在该实验的基础上,结合其它生态学特性的研究结果,利用地理信息系统ARC VIEW3.2分析预测该虫在我国的可能适宜分布范围。结果表明:椰甲截脉姬小蜂在我国的最适宜分布范围在16.53°~19.1°N,108.61°~112.33°E,只集中在海南省的南部;适宜分布范围大体在20.03°~24.27°N,101.98°~117.65°E,集中在海南、广东、广西、云南和福建5省;潜在分布范围大体在23.3°~33.4°N,98.5°~122.1°E,主要集中在西南、华东、华中等地区的172个县。