Did the introduction of maize into Europe provide enemy‐free space to Ostrinia nubilalis? Parasitism differences between two sibling species of the genus Ostrinia

We examined whether maize offers enemy‐free space (EFS) to its pest Ostrinia nubilalis, and may thereby have contributed to its divergence from the sibling species, Ostrinia scapulalis, feeding mainly on mugwort, when introduced into Europe five centuries ago. We collected Ostrinia larvae on maize (70 populations, 8425 individuals) and mugwort (10 populations, 1184 individuals) and recorded parasitism using both traditional (counting emerging parasitoids) and molecular methods (detection by specific polymerase chain reaction). The main parasitoid was Macrocentrus cingulum (Braconidae). On mugwort, parasitism was twice that on maize, and parasitoid‐related mortality was 8 times higher. This suggests that maize affords substantial EFS to Ostrinia feeding on it. The lower Mortality:Infestation ratio in maize suggests that O. nubilalis’ immune response might be stronger than that of O. scapulalis. If so, adapting to maize and diverging from O. scapulalis would decrease the impact of parasitism on O. nubilalis at both ecological and evolutionary levels.     

Using the literature to evaluate parasitoid host ranges: a case study of Macrocentrus grandii (Hymenoptera: Braconidae) introduced into North America to control Ostrinia nubilalis (Lepidoptera: Crambidae)

We propose a method for using the literature to evaluate host ranges of parasitoids that are candidates for biological control introductions. Data on the parasitoids that attack a given host species can be used as negative evidence concerning the candidate whose host range is being evaluated. By compiling studies for a variety of host species, one can delineate those taxa unlikely to be attacked by the candidate. Using a retrospective case study of a parasitoid introduced into North America, we describe (1) this approach to using the literature to evaluate host range and (2) how well predictions based on such an evaluation match actual host range. Based on the host range of Macrocentrus grandii in Eurasia as reported in the literature, we predicted that the species in the genus Ostrinia are the most likely hosts. Of native North American species, Ostrinia obumbratalis is the only non-target species likely to be attacked by M. grandii. The predicted host range for North America matched the actual host range found in the field. This suggests that a careful literature review could be used as an important source of data on host range of parasitoid species proposed for introduction into a new environment.     

Suitability of three Ostrinia species as hosts for Macrocentrus cingulum： A comparison of their encapsulation abilities

Two cornborer species, Ostrinia furnacalis （Lepidoptera： Crambidae） and O. nubilalis, are major corn pests in Asia and Europe, respectively. In both continents, the larval endoparasitoid Macrocentrus cingulum （Hymenoptera： Braconidae） develops on another, closely related stemborer, O. scapulalis, which feeds on mugwort and other dicotyledons. M. cingulum also emerges from O. furnacalis in Asia and （9. nubilalis in North America, but not from O. nubilalis in Europe. We assessed the ability of three populations of each of the three Ostrinia species to encapsulate foreign bodies of a size similar to that of a M. cingulum egg. We conclude that variations in encapsulation ability alone cannot account for the differences observed in the field between parasite emergence rates in these different host species and geographic areas.     

Effects of sugar feeding on carbohydrate and lipid metabolism in a parasitoid wasp

Lifetime patterns of carbohydrate and lipid metabolism were compared in starved and sucrose‐fed adults of the parasitoid Macrocentrus grandii (Goidanich) (Hymenoptera: Braconidae). As expected, sucrose‐fed individuals lived longer than did starved individuals. Macrocentrus grandii males and females eclosed with levels of simple storage sugars (presumably primarily trehalose) and glycogen that were below maximum levels recorded from sucrose‐fed parasitoids. Both of these nutrients dropped to very low levels in starved individuals within 4 days post‐emergence and were maintained at high levels in sucrose‐fed individuals throughout their lives. Lipid reserves at emergence represented the highest lipid levels for both sexes in the two diet treatments, with levels declining over the lifetimes of males and females from both diet treatments. Our results therefore suggest that dietary sucrose is used to synthesize trehalose and glycogen, but not lipids in M. grandii. Also, in contrast to the patterns observed for the simple sugars and glycogen, lipid levels in starved individuals did not drop below levels observed in sugar‐fed individuals. The average number of mature eggs carried by females at emergence was 33 and increased to approximately 85 in sucrose‐fed and 130 in starved females by the age of 5 d in the absence of hosts. The egg maturation rate was therefore higher in starved than in sugar‐fed females. Potential explanations for this unexpected result are discussed.     

螟长距茧蜂对植物挥发物质的行为反应

本文报道玉米螟Ostrinia furnacalis(Guenée)幼虫寄生蜂——螟长距茧蜂Macrocentrus Linearis(Ness)对植物挥发物质的行为反应.用嗅觉仪测定表明,雌蜂能被寄主植物(玉米、棉花)的挥发物质所吸引,但正常寄主植物的气味不能明显地引起雌蜂产卵管的刺探行为.然而,寄主幼虫损伤的寄主植物,即使不存在寄主幼虫,亦能明显地诱发雌蜂进行产卵管刺探.非寄主植物(黄豆、灰菜)的气味对雌蜂既无明显的吸引力,亦无特别的排斥作用.当把正常的和寄主幼虫损伤的寄主植物同时提供给雌蜂时,雌蜂明显地选择后者.在寄主植物和非寄主植物同时存在时,雌蜂明显地被寄主植物的气味所吸引.寄主植物的挥发物质能被乙醚抽提,抽提液滴加在滤纸上同样能诱发雌蜂触角搜索和敲打行为.     

Extraembryonic membrane of the polyembryonic parasitoid Macrocentrus cingulum Brischke (Hym., Braconidae) is essential for evasion of encapsulation

Abstract:  The wasp Macrocentrus cingulum (Hymenoptera) is an endoparasitoid that uses larvae of the Asian corn borer Ostrinia furnacalis as one of its hosts. The wasp is polyembryonic and a single wasp egg gives rise to several dozens of embryos. Earlier studies showed that the fibrous layer on the surface of M. cingulum eggs protects them from the immune system of the moth larvae. However, the way in which the embryos of the parasitoid avoid being encapsulated remained unknown. In this paper, we show that the evasion of encapsulation is mediated through the extraembryonic membrane. We also show that M. cingulum embryos developed normally in the larvae of O. furnacalis but were encapsulated when injected into the larvae of Helicoverpa armigera , which is not a host species for the wasp larvae. When the extraembryonic membrane was removed, either chemically using the enzyme dispase or mechanically using a dissecting needle, the 'unprotected' embryos were also encapsulated both in vivo and in vitro by the haemocytes of the normal host O. furnacalis . It was also shown that the extraembryonic membrane was labelled strongly with fluorescein isothiocyanate (FITC)-conjugated Helix pomatia ( H.p. ) lectin. This suggests that a chemical in, or on, the extraembryonic membrane, that helps the embryos of M. cingulum to avoid encapsulation, is possibly a glycodeterminant produced in the haemocoel of the wasp.     

健康和虫害的红松挥发物对赤松梢斑螟及其寄生蜂寄主选择行为的影响

摘要：为了研究红松球果害虫赤松梢斑螟Dioryctria sylvestrella及其寄生蜂的寄主趋向机理,本文用Y型嗅觉仪测定了赤松梢斑螟成虫及其寄生蜂长距茧蜂Macrocentrus sp,对红松健康和梢斑螟幼虫危害的球果、主梢及侧枝的昼夜行为反应;并用GC-MS分析了健康和虫害球果、主梢及侧枝昼夜所释放挥发物的组份及含量变化。结果表明,赤松梢斑螟处女雌蛾、交尾雌蛾和雄蛾在夜晚对健康球果及主梢有较强的趋性。雌雄长距茧蜂白天对虫害红松球果、主梢有较强的趋性。红松各部位挥发物成分及含量在健康与虫害、白天与夜晚之间存在显著差异,主要表现为单萜类物质相对含量显著变化,如α-蒎烯、莰烯、β-水芹烯、β-蒎烯、3-蒈烯、罗勒烯、β-月桂烯、柠檬烯,以及产生特异性倍半萜类挥发物,如乙酸龙脑酯、石竹烯等。其中红松各部位单萜类挥发物含量变化是影响赤松梢斑螟及其寄生蜂的寄主选择行为的主要原因;而特异性倍半萜单体或组合,是否能够作为产卵刺激剂,协同单萜类挥发物调控二者的产卵行为,还需要试验的进一步证明。     

寄生稻纵卷叶螟的长体茧蜂属—新种记述(膜翅目:茧蜂科:长体茧蜂亚科)

本文报道寄生稻纵卷叶螟幼虫的长体茧蜂属一新种:纵卷叶螟长体茧蜂 Macrocentruscnapholocrocis,sp.nov.     

螟长距茧蜂、玉米螟与春玉米间相互关系的初步研究

研究表明,螟长距茧蜂发生高峰期比玉米螟成虫高峰期大约推迟6-9天,与春玉米抽雄期相一致。玉米抽雄开花时绝大部分玉米螟幼虫处在易被螟长距茧蜂寄生的Ⅲ、Ⅳ龄。玉米开花后雄穗的形态结构和营养成分发生改变,致使幼虫下垂转移寻找更适宜的食物。螟长距茧蜂被取食玉米雄穗的玉米螟幼虫所吸引。其寄生与玉米螟幼虫的发育和玉米生育期密切相关。