Acceptance and suitability of four lepidopteran stemborers for the development of the pupal parasitoid Xanthopimpla stemmator (Hymenoptera: Ichneumonidae)

Xanthopimpla stemmator (Thunberg), a solitary endoparasitoid of lepidopteran stemborer pupae, was recently imported into East Africa as a candidate biological control agent of gramineous stemborers. Suitability of Busseola fusca Fuller, Chilo partellus (Swinhoe), Eldana saccharina (Walker) and Sesamia calamistis Hampson, for the development of X. stemmator was studied in the laboratory. One- to 6-day-old laboratory reared pupae of the four stemborer species were exposed to naïve X. stemmator females. All host pupae and ages were acceptable for oviposition. The parasitoids inflicted multiple probe wounds on 67.8% of pupae exposed. B. fusca, C. partellus and S. calamistis were equally suitable with 56.4, 59.4 and 52.3%, respectively, of probed pupae leading to emergence of adult parasitoids. E. saccharina was less suitable with only 22.6% of probed pupae producing parasitoids. Emergence of parasitoids did not differ significantly across the six pupal ages for B. fusca and S. calamistis, but varied for C. partellus and E. saccharina. No parasitoids emerged from 6-day-old E. saccharina pupae. Realized fecundity of females reared on the four stemborer pupae showed that fewer progeny were produced by females emerging from E. saccharina than females reared on the other three stemborer species. Eldana saccharina may be a poor host for X. stemmator in Kenya, but this parasitoid is a potential candidate for biological control of B. fusca, C. partellus and S. calamistis.     

Multiparasitism by the pupal parasitoids, Xanthopimpla stemmator (Hymenoptera: Ichneumonidae) and Pediobius furvus (Hymenoptera: Eulophidae) on two African cereal stemborers, Chilo partellus (Lepidoptera: Crambidae) and Busseola fusca (Lepidoptera: Noctuidae)

The outcome of multiparasitism by two pupal parasitoids, the exotic solitary ichneumonid Xanthopimpla stemmator and the indigenous gregarious eulophid Pediobius furvus, was studied using the invasive crambid stem borer Chilo partellus and the indigenous noctuid Busseola fusca as hosts. Two parasitism sequences were observed, where X. stemmator oviposited before P. furvus, and vice versa. In addition, the effect of time between first and second parasitism on parasitoid emergence, development, sex ratio, and number of offspring was assessed. For most treatments, time interval between parasitism had no significant effect on the percentage if pupae producing either P. furvus or X. stemmator. In general, X. stemmator outcompeted P. furvus irrespective of the order of oviposition, time interval between ovipositions and host species. Further studies, especially on host finding capacity of the two parasitoid species are required to determine the competitiveness of the two species under field conditions.     

Species diversity and distribution of lepidopteran stem borers in South Africa and Mozambique

Country‐wide surveys of lepidopteran stem borers in wild host plants were undertaken between 2006 and 2009 in South Africa and 2005 and 2010 in Mozambique. A total of 4438 larvae were collected from 65 wild host plants in South Africa and 1920 larvae from 30 wild host plants in Mozambique. In South Africa and Mozambique, 50 and 39 stem borer species were recovered, respectively, with four new species and two new genera among noctuids. Less than 5% of the total number of species collected are considered to be economically important in Africa. These species were Busseola fusca (Fuller) (Noctuidae), Chilo partellus (Swinhoe) (Crambidae) and Sesamia calamistis Hampson (Noctuidae). Data from this study and others in East Africa on the very low abundance of stem borers in wild host plants question the putative role of wild host plants as reservoir for stem borer pests. One new host plant family (Prioniaceae), as well as 24 and 13 wild hosts from South Africa and Mozambique respectively, was added to the list of known hosts in Africa.     

水稻螟虫神经肽PBAN及其受体序列的生物信息学分析

【目的】性信息素合成激活肽(PBAN)是控制昆虫产生性信息素的激素,本文旨在分析水稻螟虫神经肽PBAN及其受体的序列。【方法】通过t Blastn同源检索从水稻螟虫基因组和转录组数据库中鉴定水稻螟虫PBAN神经肽及其受体序列,在此基础上进行序列比对及系统发生分析。【结果】发现二化螟Chilo suppressalis、三化螟Tryporyza incertulas和大螟Sesamia inferens的PBAN成熟肽序列均含有33个氨基酸残基,其C端五肽序列完全相同,3种水稻螟虫PBAN多肽相似度为54.55%~63.64%;发现二化螟PBAN受体3个异构体全长氨基酸序列(PBANR-A、PBANR-B和PBANR-C),均含有7个跨膜区域。【结论】进化树分析发现不同昆虫PBAN神经肽及其受体存在一定的保守性和多样性,并且在进化树上的位置几乎与昆虫系统发育分类一致,推测PBAN神经肽和PBAN受体在昆虫系统进化过程中可能存在协同进化现象。本研究为水稻螟虫PBAN神经肽及其受体的结构和功能分析提供基础。     

A Retrospective Analysis of the Establishment and Dispersal of the Introduced Australian Parasitoids Xanthopimpla rhopaloceros (Krieger) (Hymenoptera: Ichneumonidae) and Trigonospila brevifacies (Hardy) (Diptera: Tachinidae) within New Zealand

Two Australian parasitoids, Xanthopimpla rhopaloceros (Krieger) and Trigonospila brevifacies (Hardy), were introduced to New Zealand to control the light-brown apple moth (Epiphyas postvittana Walker). Dispersal by the parasitoids has since occurred naturally and with the aid of releases in fruit-growing areas. The present geographical range of the parasitoids includes all the North Island and some offshore islands to latitude 41 20 S. X. rhopaloceros is also present to latitude 41 48 S in the South Island. Comparisons of these distributions with those in Australia indicate that climatic conditions may have played a major role in the areas of establishment of both species in New Zealand. The mean winter temperature may be a limiting factor in the dispersal of T. brevifacies and X. rhopaloceros in New Zealand. Other factors that have probably aided the successful dispersal of the parasitoids include the wide distribution of host Tortricidae and the occurrence of tortricid host plants. The areas of New Zealand that appear suitable for further colonization by T. brevifacies include northern areas of the South Island, and both parasitoids could disperse further into suitable climate areas of the east and west coasts of the central South Island. The rate of dispersal for X. rhopaloceros was estimated at 13-24 km/year, and for T. brevifacies at 8-15 km/year.     

Interspecific competition between Xanthopimpla stemmator Thunberg and Dentichasmias busseolae Heinrich (Hymenoptera: Ichneumonidae), pupal parasitoids attacking Chilo partellus (Lepidoptera: Crambidae) in East Africa

Interspecific competition between Xanthopimpla stemmator and Dentichasmias busseolae was studied using pupae of the invasive crambid stemborer Chilo partellus as the host. While X. stemmator is an old association, D. busseolae formed a relatively new association with C. partellus in East Africa. Two different time intervals between parasitism (0 and 48 h) and two parasitoid sequences [i.e., X. stemmator before D. busseolae (Xs–Db) and D. busseolae before X. stemmator (Db–Xs)] were chosen. In addition, the parasitoids’ performance on pupae in maize stems and ears was assessed. For both X. stemmator and D. busseolae, there was no difference in foraging time between unparasitized pupae and pupae previously parasitized by the other species, indicating that the two species were not capable of interspecific host discrimination. In the Xs–Db sequence, the time interval between parasitism did not have an influence on the percentage of pupae producing either parasitoid species. By contrast, in the Db–Xs sequence, the percentage of pupae producing X. stemmator was almost 8 times higher in the 0-h than the 48-h interval, while for D. busseolae it was the reverse. In the 0-h interval, X. stemmator outcompeted D. busseolae irrespective of whether it parasitized first or second, while in the 48-h interval, the parasitoid parasitizing first won. While D. busseolae successfully searched for and parasitized pupae in both stems and ears, parasitism of pupae in ears by X. stemmator was negligible. It was concluded that the two species could co-exist because they partly exploit different ecological niches.     

Host preference of the facultative hyperparasitoidTetrastichus howardi (Hym.: Eulophidae)

Tetrastichus howardi (Olliff) preferred the lepidopteran hosts,Chilo partellus (Swinhoe) (Pyralidae) andHelicoverpa armigera (Hübner) (Noctuidae) to their parasitoids,Xanthopimpla stemmator (Thunberg) (Hymenoptera: Ichneumonidae) andPalexorista laxa (Curran) (Diptera: Tachinidae). IfT. howardi had previously experienced parasitising a certain host, its preference for that host increased, but not significantly. When reared on a certain host, the preference for that host increased.T. howardi showed no preference to any particular age of its hosts.T. howardi was able to discriminate between parasitised and unparasitised hosts, initially preferring parasitised hosts, but two days later preferring unparasitised hosts.     

Preference and performance of the hyperparasitoid Syrphophagus aphidivorus (Hymenoptera: Encyrtidae): fitness consequences of selecting hosts in live aphids or aphid mummies

Abstract.  1. Theoretical models predict that ovipositional decisions of parasitoid females should lead to the selection of the most profitable host for parasitoid development. Most parasitoid species have evolved specific adaptations to exploit a single host stage. However, females of the aphid hyperparasitoid Syrphophagous aphidivorus (Mayr) (Hymenoptera: Encyrtidae) display a unique and atypical oviposition behaviour by attacking either primary parasitoid larvae in live aphids, or parasitoid pupae in dead, mummified aphids.
2. In the laboratory, the correlation between host suitability and host preference of S. aphidivorus on the host Aphidius nigripes Ashmead parasitising the aphid Macrosiphum euphorbiae (Thomas) was investigated.
3. The relative suitability of the two host stages was determined by measuring hyperparasitoid fitness parameters (survival, development time, fecundity, sex ratio, and adult size of progeny), and calculating the intrinsic rate of population increase ( r _m). Host preference by S. aphidivorus females and the influence of aphid defence behaviour on host selection was also examined.
4. Hyperparasitoid offspring performance was highest when developing from hosts in aphid mummies and females consistently preferred this host to hosts in parasitised aphids. Although aphid defensive behaviour may influence host selection, it was not a determining factor. Ecological and evolutionary processes that might have led to dual oviposition behaviour in S. aphidivorus are discussed.     

Host suitability and preference studies of Trichogramma cordubensis (Hymenoptera: Trichogrammatidae)

Studies of host suitability and preferences of Trichogramma cordubensis Vargas and Cabello (Hymenoptera: Trichogrammatidae) were performed with eggs of six Lepidoptera (Noctuidae) species: Thysanoplusia orichalcea Fabricius, Peridroma saucia (Hübner), Xestia c-nigrum L., Phlogophora meticulosa (L.), Noctua pronuba (L.), and N. atlantica (Warren). Host suitability was studied by analysing separately the effects of the attacked host species and the influence of the rearing host species on different biological parameters of T. cordubensis. Host preference was analysed by offering eggs of two host species simultaneously to a single female wasp without previous oviposition experience (dual-choice tests). Results show that P. saucia, followed by P. meticulosa were the least suitable hosts for T. cordubensis, since on these species the preimaginal development of the parasitoids was significantly longer and, the number of parasitized eggs as well the number of offspring per female were significantly lower. Contrarily, T. cordubensis parasitized at a higher rate the eggs of the endemic non-target species, N. atlantica. Dual choice tests showed that the option of the first host to be accepted by the wasp was random; however, the mean number of parasitized eggs differed significantly when two host species were offered simultaneously to T. cordubensis, always being the host species with heavier eggs the most parasitized.     

Biology of Tetrastichus howardi (Olliff) (Hymenoptera: Eulophidae): A facultative Hyperparasitoid of stem borers

The biology of the parasitoid Tetrastichus howardi, which was introduced from the Philippines into South Africa for the biological control of the stem borer Chilo partellus, was studied in the laboratory. On average, a T. howardi female produced 101 progeny (92% females) which developed in 4.3 hosts. The upper threshold temperature for development was around 33°C, the minimum threshold was calculated as 12.8°C and the thermal constant as 239.8 day‐degrees. With hosts, females lived 23.6 and males 16.7 days. T. howardi was found to be a facultative hyperparasitoid with a very wide host range. As a primary parasitoid, it developed in pupae of various Lepidoptera as well as Coleoptera and Hymenoptera and as a hyperparasitoid in dipteran and hymenopteran parasitoids. A linear relation was found between the number of emergent parasitoids and the volume of the host from which they emerged. Preference tests indicated that T. howardi preferred to parasitize the phytophagous insects C. partellus and Heliothis armigera, over their parasitoids Xanthopimpla stemmator and Palexorista laxa. The host selection of inexperienced T. howardi females was different from the experienced parasitoids. When given a choice, females showed preference for the host species they were allowed to parasitize previously and the host species from which they had been reared. The use of facultative hyperparasitoids in biological control in general and against stem borers in South Africa in particular is discussed.     

烟粉虱成虫对黄瓜叶龄的喜好性及与后代发育适合度间的关系

在室内采用笼罩和发育测定方法,研究了烟粉虱成虫对黄瓜叶龄的喜好性及其与后代生长发育、存活之间的关系,同时调查了叶毛密度与成虫喜好性之间的相关关系。结果表明(1)烟粉虱成虫比较喜欢在黄瓜植株的中部叶片取食和产卵。(2)叶龄对烟粉虱的存活率没有显著影响,对烟粉虱的发育历期只在卵期和若虫四龄期表现出显著影响,对其他龄期或整个世代均没有显著影响。(3)叶毛密度随着叶龄的增大而顺次显著减小;在接虫初始阶段,烟粉虱成虫的叶片选择性与叶毛密度成显著负相关关系,但72h后具有中等叶毛密度的叶片上的成虫数量和着卵量均显著高于叶毛密度较大或较小的叶片。研究结果对培育抗烟粉虱的黄瓜品种和改进烟粉虱的防治措施具有一定指导意义。     

Regulatory processes and population cyclicity in laboratory populations ofAnagasta kühniella (Zeller) (lepidoptera: Phycitidae) V. Host finding and parasitization in a “small” universe by an entomophagous parasite,Venturia canescens (Gravenhorst) (Hymenoptera: Ichneumonidae)

Summary Host finding by the entomophagous parasite,Venturia canescens (Grav.), parasitizingAnagasta kühniella (Zeller) was studied. Studies utilizing fixed densities and dispersion patterns of the hosts where no choice of density groupings was offered showed that within the experimental conditions used, host density relationships were more important than dispersion. Decreasing the time hosts were exposed to a parasite from 72 hours to 24 hours did not alter the overall parasitization. In both cases progressively less hosts were parasitized as host density increased, which exemplified aHolling-type of response. However, when host densities were varied within the same universe, independent of dispersion patterns, and the parasites were given a “choice” of host densities to attack, an increasing percentage of hosts in the higher host density groups were parasitized; thus a density-dependent behavioral response was exhibited. These studies were conducted as a partial fulfillment in the Ph. D. program of one of us (B. M. Matsumoto) and form a part of a broad investigation into the processes operating in the dynamics of arthropod populations under grants toC. B. Huffaker from the U. S. Public Health Service, National Institutes of Health and the U. S. Department of Agriculture.     

Ovipositional response ofVenturia canescens (Grav.) (Hymenoptera: Ichneumonidae) to various host and parasite densities

Summary Ovipositional response inVenturia canescens (Grav.) parasitizingAnagasta kühniella (Zeller) is analyzed for all combinations of five parasite densities (2, 5, 10, 25, and 50), four host densities (25, 50, 100, and 200), and three floor area universe sizes (76 cm², 160 cm², and 345 cm²). Over this range, no mutual interference (as measured by decreasing parasite fecundity) was observed, althoughNicholson’s area of discovery decreased significantly with parasite density increase as a result of a non-Poisson distribution of parasite eggs; use of this parameter is therefore not a suitable means of determining if mutual interference is present. Other parameters studied, and for which significant correlations were obtained, include mean parasite eggs per host, percentage parasitization, percentage of parasite eggs wasted, and negative binomialk approximations. This study was conducted as part of a broad investigation into the processes operating in the dynamics of arthropod populations under a grant toC. B. Huffaker by the U.S. Public Health Service, National Institutes of Health.     

Host recognition byPimpla instigator F. (Hymenoptera: Ichneumonidae): Preferences and learned responses

This study identifies some previously unreported tactile and visual cues used by the pupal parasitoid Pimpla instigatorF. (Ichneumonidae) to recognize potential hosts. Paper cylinders were presented to the wasps as simple models of lepidopteran pupae. Acceptance of these models was evaluated by determining the frequency with which the wasps punctured the cylinders with their ovipositors. The length of the cylinders did not influence acceptance of the models; however, both surface texture and structural modifications to the ends of the cylinder did affect the frequency of punctures. Smooth cylinders were punctured more often than roughened cylinders, and cylinders with closed ends were frequently punctured, whereas open-ended cylinders were consistently rejected. The wasps also discriminated between blue and yellow cylinders and could be trained to associate blue or yellow with the presence of hosts. Preferences were established during a single 90- min training period and persisted for at least 4 days following training.     

Studies on the horizontal migration of dipterous stem borers (Oscinella spp.) in direct drilled Italian ryegrass

The distance stem boring dipterous larvae e.g. Oscinella frit L. migrate in direct drilled Italian ryegrass (Lolium multiflorum) was investigated. First, adjacent contrasting swards of Italian ryegrass or Cocksfoot (Dactylis glomerata) were grown which were, respectively, expected to be either infected with large populations of larvae or likely to be free of larvae. Sampling revealed that these expectations were realised. Swards were then desiccated by herbicide, and subsequently direct drilled with Italian ryegrass. Over 50% of the larvae in original, infested part of the sward migrated to infest tillers of the newly sown ares. The distance larvae migrated was gauged by assessing how far they were found from the perimeter of a previously uninfested area which had been reseeded. Most larvae migrated 20 cm or less, but a small proportion appeared to migrate several metres, apparently passing many suitable host tillers as they did so.deceased September 1989     

Effect of wasp size, physiological state, and prior host experience on host-searching behavior in a parasitoid wasp (Hymenoptera: Ichneumonidae)

Host-searching behavior in insects generally varies among individuals. A number of physiological and environmental factors can be involved in such individual variation. Here, a series of behavioral observations were made to highlight the importance of physiological state (i.e., number of mature eggs a female carries, amount of nutrient reserves, etc.) and learning state (i.e., prior host experience) on host-approaching behavior of parasitoids. Itoplectis naranyae (Hymenoptera: Ichneumonidae), a solitary endoparasitoid wasp attacking lepidopteran pupae and prepupae, was used as a test insect. The results show that female wasps with experience ovipositing on hosts 2 days before the test found hosts more quickly than did naïve wasps. Prior experience of host odor itself did not affect host-finding behavior, however. A single oviposition was enough for wasps to shorten time to find a host; additional experience had no significant effect on the efficiency of searching. The number of mature eggs a female carried had no effect on the time required to find a host regardless of prior host experience. The size of wasps, instead, was a significant factor when wasps had no prior host experience, and larger wasps found hosts more rapidly than did smaller wasps. Searching activity was not affected by how many hosts a female wasp had fed on before testing.     

Host Age Choice for Oviposition in Pauesia juniperorum (Hymenoptera: Braconidae: Aphidiinae) and its Effect on the Parasitoid's Biology and Host Population Growth

Pauesia juniperorum has been selected as a potential agent for the biological control of Cinara cupressivora, an important introduced pest of conifers in Africa. As part of the pre-introductory assessment studies, selection of different host age categories for oviposition was studied in choice and no choice experiments. The duration of development and adult size of parasitoid progeny developing in different host age categories were compared. The effects of parasitism on survival and reproduction of five categories of the apterous morph of the host ranging in age from 3-15 days was also studied. The age of hosts had a significant influence on the degree with which different categories were parasitized. Host defensive behaviour, which increased with age, influenced the outcome of attempts by the parasitoid to oviposit. The effect was greater in older hosts, but in young hosts their small size was more important in enabling aphids to escape parasitism. The duration of development decreased while adult size increased with age of hosts. This demonstrated that fitness attributes of P. juniperorum were affected by larval ontogeny with older/larger hosts being more optimal. The ability of the parasitoid to exploit hosts of varying age was suggestive of a high degree of phenotypic plasticity which is potentially of adaptive value. Hosts parasitized before they were 9-days-old became mummies without reproducing. Those that were 9 days or older achieved part of their reproductive capacity before dying. Thus, the impact of P. juniperorum is markedly reduced when attacking older hosts.     

小峰熊蜂访花偏爱性

传粉昆虫在访花时,通常会表现出对某一类型花的偏爱性。本研究利用人工制作的大小、颜色、形态和气味不同的9种类型的花来研究小峰熊蜂Bombus hypocrita的访花偏爱性。结果表明：当增加花的大小、形态、气味等附加特征数时,小峰熊蜂的偏爱性程度与花朵附加特征数有显著相关性（P<0.01）。当花朵颜色由2种增加到4种,熊蜂对紫色花的偏爱性程度降低,但花朵颜色的种类与小峰熊蜂的访花偏爱性没有相关性（P>0.05）,花颜色的种类对熊蜂访紫色花的偏爱性影响不大。大小为5 cm的紫花被访次数（108±9次）明显高于大小为3 cm的紫花被访次数（40±4次）（P<0.01）,说明熊蜂明显喜欢访大花瓣的紫花。完全盛开的紫花被访次数（129±13次）显著高于刚绽放的花被访次数（26±3次）（P<0.01）,说明熊蜂喜欢访盛开的紫花。柠檬味的紫花被访次数（63±8次）明显低于草莓味的紫色花被访次数（88±2次）（P<0.05）,说明熊蜂喜欢访草莓味的花朵。     

Intraspecies competition in a field population ofGregopimpla himalayensis (Hymenoptera: Ichneumonidae) parasitic onMalacosoma neustria testacea (Lepidoptera: Lasiocampidae)

Intraspecies competition in a field population of Gregopimpla himalayensis (Hym.: Ichneumonidae) parasitic on the prepupae of Malacosoma neustria testacea (Lep.: Lasiocampidae) was investigated. The parasite oviposits the sufficient number of progeny (5 individuals/0.1 g dry weight of host) to exhaust a single host in a single attack. However, at the intensity less than 22–26 individuals/0.1 g d.w. of host, all individuals can emerge, i.e. density-dependent mortality does not occur. Within this range of intensity, survival of parasite larvae is guaranteed by diminution in body size and decreasing sex ratio. In contrast, total biomass of parasites showed a peak at 5 individuals/0.1 g d.w. of host at which a single host is exhausted. Above the intensity of 22–26, extraordinary minute individuals appeared and they died before maturation. If intraspecies competition play a role in regulation of G. himalayensis population in the field, the process is usually not through density-dependent mortality but through decreasing reproductive rate caused by decrease in the sex ratio, adult longevity and fecundity.