Plastic cup traps equipped with light-emitting diodes for monitoring adult Bemisia tabaci (Homoptera: Aleyrodidae)

Equipping the standard plastic cup trap, also known as the CC trap, with lime-green light-emitting diodes (LED-plastic cup trap) increased its efficacy for catching Bemisia tabaci by 100%. Few Eretmocerus eremicus Rose and Zolnerowich and Encarsia formosa Gahan were caught in LED-plastic cup traps. The LED-plastic cup traps are less expensive than yellow sticky card traps for monitoring adult whiteflies in greenhouse crop production systems and are more compatible with whitefly parasitoids releases for Bemisia nymph control.     

烟粉虱及海氏桨角蚜小蜂对中国番茄黄化曲叶病毒感染烟草的嗅觉反应

双生病毒可通过调控寄主植物促进媒介昆虫烟粉虱种群增长,然而病毒侵染植物后是否通过调控植物挥发物来影响烟粉虱及其天敌的嗅觉反应还未见报道。【目的】本文旨在研究烟草植株感染中国番茄黄化曲叶病毒(Tomato yellow leaf curl China virus,TYLCCNV)后对烟粉虱Bemisia tabaci(Gennadius)及其重要寄生性天敌海氏桨角蚜小蜂Eretmocerus hayati(Zolnerowich and Rose)嗅觉反应行为的影响。【方法】利用Y形嗅觉仪方法,我们测试了烟粉虱及海氏桨角蚜小蜂对带毒植株、健康植株及烟粉虱危害植株的选择偏好性。【结果】烟粉虱及海氏桨角蚜小蜂选择携带TYLCCNV病毒的烟草显著多于健康烟草植株,但烟草被病毒与烟粉虱共同侵染时,烟粉虱对带毒烟草的选择仍显著多于无毒植株,而寄生蜂虽然仍较多选择带毒植株,但无显著差异。【结论】这些结果表明烟粉虱及海氏桨角蚜小蜂偏好选择携带TYLCCNV病毒的烟草,但这种偏好作用在烟粉虱取食共同危害时有一定程度的减弱。本研究首次报道了双生病毒侵染植物可增加烟粉虱及其天敌对植物的选择作用,并就其功能及机制进行了讨论。     

海氏桨角蚜小蜂对两种生物型烟粉虱的功能反应研究

本文报道海氏桨角蚜小蜂Erelmocerus hayati在室内对不同寄主密度下的B型和Q型烟粉虱Bemisiatabaei寄生和取食情况,并比较了该蜂对两种生物型烟粉虱功能反应的差异。结果表明,海氏桨角蚜小蜂对两种生物型烟粉虱的寄生率和致死率可分别达到60％和70％以上,平均每日最大致死量可达40头烟粉虱若虫。该蜂对两种生物型烟粉虱的功能反应曲线符合Holling Ⅱ型,随寄主密度的增加对烟粉虱若虫的寄生和致死数量均增加直至达到每日最大致死数量,而寄生率和致死率则随寄主密度的增加而显著下降。该蜂对两种生物型烟粉虱的功能反应没有显著的差异。     

Host-parasite interactions between whiteflies and their parasitoids

There is relatively little information available concerning the physiological and biochemical interactions between whiteflies and their parasitoids. In this report, we describe interactions between aphelinid parasitoids and their aleyrodid hosts that we have observed in four host-parasite systems: Bemisia tabaci/Encarsia formosa, Trialeurodes vaporariorum/E. formosa, B. tabaci/Eretmocerus mundus, and T. lauri/Encarsia scapeata. In the absence of reported polydnavirus and teratocytes, these parasitoids probably inject and/or produce compounds that interfere with the host immune response and also manipulate host development to suit their own needs. In addition, parasitoids must coordinate their own development with that of their host. Although eggs are deposited under all four instars of B. tabaci, Eretmocerus larvae only penetrate 4th instar B. tabaci nymphs. A pre-penetrating E. mundus first instar was capable of inducing permanent developmental arrest in its host, and upon penetration stimulated its host to produce a capsule (epidermal in origin) in which the parasitoid larva developed. T. vaporariorum and B. tabaci parasitized by E. formosa initiated adult development, and, on occasion, produced abnormal adult wings and eyes. In these systems, the site of parasitoid oviposition depended on the host species, occurring within or pressing into the ventral ganglion in T. vaporariorum and at various locations in B. tabaci. E. formosa's final larval molt is cued by the initiation of adult development in its host. In the T. lauri-E. scapeata system, both the host whitefly and the female parasitoid diapause during most of the year, i.e., from June until the middle of February (T. lauri) or from May until the end of December (E. scapeata). It appears that the growth and development of the insects are directed by the appearance of new, young foliage on Arbutus andrachne, the host tree. When adult female parasitoids emerged in the spring, they laid unfertilized male-producing eggs in whiteflies containing a female parasitoid [autoparasitism (development of male larvae utilizing female parasitoid immatures for nutrition)]. Upon hatching, these male larvae did not diapause, but initiated development, and the adult males that emerged several weeks later mated with available females to produce the next generation of parasitoid females. Thus, the interactions that exist between whiteflies and their parasitoids are complex and can be quite diverse in the various host-parasitoid systems.     

Shifting preference between oviposition vs. host-feeding under changing host densities in two aphelinid parasitoids

Destructive host-feeding is common in hymenopteran parasitoids. Such feeding may be restricted to host stages not preferred for oviposition. However, whether this is a fixed strategy or can vary according to resource levels or parasitoid needs is less clear. We tested the trade-off between host feeding and oviposition on two whitefly parasitoids under varying host densities. Females of two aphelinid parasitoids, Eretmocerus hayati and Encarsia sophia were exposed to nine different densities of their whitefly host, Bemisia tabaci, in single-instar tests to identify their functional response. Mixed-instar host choice tests were also conducted by exposing whiteflies at four densities to the parasitoids. We hypothesized that the parasitoid females can detect different host densities, and decide on oviposition vs. host-feeding accordingly. The results showed that both Er. hayati and En. sophia females tended to increase both oviposition and host-feeding with increased host density within a certain range. Oviposition reached a plateau at lower host density than host-feeding in Er. hayati, while En. sophia reached its oviposition plateau at higher densities. At low densities, Er. hayati parasitized most on first and second (the optimal ones), and fed most on third nymphal instars (the suboptimal one) of the whitefly host as theory predicts, while at high densities, both parasitism and host-feeding occurred on first and second instars which are preferred for oviposition. En. sophia parasitized most on third and fourth (the optimal ones), while fed on first instars (the suboptimal one) at low densities, and utilized third and fourth instars for both at high densities. In conclusion, oviposition vs. host-feeding strategy of parasitoid females was found to vary at different host densities. The balance between reserving optimal hosts for oviposition or using them for host-feeding depended on parasitoid life history and the availability of host resources.     

利用黄板监测烟粉虱及其寄生蜂的种群动态

研究了黄板不同放置高度、不同时间内对日光棚室内番茄上烟粉虱Bemisia tabaci(Gennadius)及其寄生蜂种群的诱集监测效果。结果表明,在同一时间内以黄板上部与植株顶部持平的高度悬挂的黄板对烟粉虱和蚜小蜂的诱集效果最好,其次是以黄板上部与植株中部持平的高度悬挂的黄板,当黄板的底部高出植株顶部30 cm时对烟粉虱及其蚜小蜂的诱集效果最差。在5~10月份,随着季节的变化,同一位置的黄板对烟粉虱及蚜小蜂的诱集数量逐渐增加。调查发现,番茄上烟粉虱的寄生蜂主要为桨角蚜小蜂属EretmocerusHaldeman和恩蚜小蜂属EncarsiaF erster,2个属的蚜小蜂在季节上呈互补之势,因此总体上蚜小蜂对烟粉虱的寄生率在5~10月之间呈不断上升的趋势。     

Augmentative biological control of whiteflies using transplants

Field studies showed that transplants can be used to move parasitoids into fields of commercially grown cantaloupe, Cucumis melo (Cucurbitaceae), and augment parasitism of sweet potato whitefly, Bemisia tabaci biotype B (= Bemisia argentifolii) (Homoptera: Aleyrodidae). Methods were developed to inoculate cantaloupe seedlings with newly imported Eretmocerus spp. (Hymenoptera: Aphelinidae), then transfer plants into both organic and conventional fields of cantaloupe in the desert growing region of southeastern California. Several obstacles to inoculating banker plants with an adequate number of parasitized whiteflies were overcome and numbers of parasitoids per transplant increased. In 1999 the use of banker plants was compared to a standard hand-release method and a no-release control in a replicated study at an organic farm. Augmentation through releases of parasitoids increased parasitism over that in the no-release controls (p <0.05). Banker plants increased the proportion of parasitized whiteflies more than the hand-release method (0.21 vs. 0.08). During a region-wide demonstration spring 2000, plots receiving banker plants significantly increased parasitism over paired control plots at seven commercial farms of cantaloupe. Parasitism in banker plant treated plots in 2000 was higher in organic fields (seasonal average =0.30) than conventional ones (seasonal average =0.06). Differences may be due to the use of imidacloprid, a systemic insecticide, in conventional fields for whitefly control. Over the 2-year study, however, releases of parasitoids did not consistently reduce densities of B. tabaci. Only in late season at some sites in 2000 were whitefly densities lower in release plots than paired controls. Most of the parasitoids recovered and identified from plots receiving parasitoids were the same as those released, Eretmocerus spp. (ex. Ethiopia M96076), and E. hayati(M95012, ex. Pakistan).     

海氏桨角蚜小蜂对不同龄期“Q”烟粉虱的取食和寄生反应

【背景】近年来＂Q＂烟粉虱在我国快速扩张,已成为农业生产上的一种重要入侵害虫。由于化学农药的大量使用,＂Q＂烟粉虱已对多种农药产生高抗药性,保护和利用天敌昆虫对其进行控制具有重要意义。【方法】本文在室内研究了近年引入我国的海氏桨角蚜小蜂对不同龄期＂Q＂烟粉虱若虫的取食和寄生能力。【结果】各龄期的＂Q＂烟粉虱若虫均可被海氏桨角蚜小蜂取食和寄生。在48h内,寄生蜂取食1、2、3、4龄烟粉虱若虫的数量分别为10.7、6.4、6.7、5.0头,呈现随龄期增大取食数量下降的趋势;海氏桨角蚜小蜂对不同龄期烟粉虱若虫的寄生能力存在明显差异,其更偏好寄生2、3龄若虫（25.4和27.5头）,其次是1龄若虫（22.1头）,而寄生4龄粉虱的数量最低（16.5头）。【结论与意义】寄主龄期对海氏桨角蚜小蜂的取食和寄生能力具有显著影响。综合来看,该寄生蜂表现出对＂Q＂烟粉虱较好的生物防治潜能,是防治烟粉虱的理想寄生性天敌昆虫。     

Parasitoid Mark-Release-Recapture Techniques-- II. Development and Application of a Protein Marking Technique for Eretmocerus spp., Parasitoids of Bemisia argentifolii

In this study, we validate and apply techniques for marking and capturing small parasitoids of the silverleaf whitefly, Bemisia argentifolii Bellows & Perring [ = B. tabaci (Gennadius), strain B] for mark-release-recapture (MRR) studies. The marker is the purified protein, rabbit immunoglobulin G (IgG), which was applied externally by topical spray or internally by feeding. Marked parasitoids were then assayed using a sandwich enzyme-linked immunosorbent assay (ELISA) for the presence of the protein marker using an antibody specific to rabbit IgG. Virtually all of the externally marked Eretmocerus sp. (Ethiopia, M96076) (98.0%) contained enough rabbit IgG to be easily distinguished from unmarked parasitoids, regardless of the amount of protein applied or the post-marking interval. A field MRR study was then conducted to examine the dispersal characteristics of E. emiratus Zolnerowich & Rose. Parasitoids marked externally and internally with protein were released on three separate trial dates into the center of a cotton field bordered by cantaloupe and okra. Overall, a total of 1388, 637, and 397 marked and unmarked wasps were captured in suction traps during each trial, respectively with the majority of parasitoids captured between 0600 and 0800 h. Furthermore, even though we released an equal proportion of males to females, our traps consistently contained more males. Our results suggest that there are gender-specific differences in the dispersal behavior of E. emiratus . Almost 40% of the captured parasitoids collected during the three release trials were positively identified for the presence of the protein marker. The distribution of the marked parasitoids revealed two distinct patterns. First, almost all of the marked parasitoids recaptured in the cotton plot were in suction traps at or adjacent to the     

Effects of planting pattern of collards on resistance to whiteflies (Homoptera: Aleyrodidae) and on parasitoid abundance

Fourteen collard entries, Brassica oleraceae L., Acephala group, were evaluated for resistance to natural populations of Bemisia argentifolii Bellows & Perring in replicated field plots in Charleston, SC. Glossy-leaf phenotypes ('SC Glaze', 'SC Landrace,' 'Green Glaze') were the most resistant collard entries and had fewer whiteflies than the nonglossy, open-pollinated cultivars. Also, two F1 hybrid cultivars with normal, nonglossy leaves ('Blue Max' and 'Top Bunch') were resistant. In laboratory experiments, there were no differences in the intrinsic rate of growth (rs) of B. argentifolii populations on either glossy or nonglossy collard phenotypes. Over a 2-yr period, there were no differences in the abundance of whiteflies on the glossy phenotype of Green Glaze when it was planted in solid 20-plant plots or when it was alternated (every other plant) with the nonglossy phenotype of Green Glaze. In a similarly designed experiment, there was no difference in the resistance of Blue Max in either solid or mixed planting scheme compared with the susceptible 'Morris Heading'. Higher numbers of whiteflies and parasitoids (primarily Eretmocerus spp.) were collected on yellow sticky cards in the solid plantings of the nonglossy phenotype of Green Glaze than were collected in the solid plantings of the glossy Green Glaze phenotype. Counts on sticky cards in the mixed plots were intermediate. These data show that planting pattern of collard entries is relatively unimportant in the deployment of these sources of host plant resistance. The data also suggest that nonpreference is the primary mode of resistance to whiteflies for certain collard entries.     

Monitoring adult Eretmocerus mundus, Encarsia lutea and Bemisia tabaci with yellow sticky traps in cotton Gossypium hirsutum

Abstract:  The efficiency of yellow sticky traps for estimating adult population dynamics of Bemisia tabaci (Genn.) (Hom., Aleyrodidae) and its parasitoids Eretmocerus mundus Mercet, Encarsia lutea (Masi) (Hym., Aphelinidae) was examined in cotton in choice and no-choice studies in Çukurova, Turkey in 2004 and 2005. In the no-choice study, traps were suspended individually on the third, fifth or eighth main stem node branches from the tops of cotton plants. For the choice study, three traps were suspended on the same individual node branches on different plants. Trap captures were counted weekly. Mean (±SE) numbers of B. tabaci captured on traps were higher in no-choice (max.: 697.8 ± 55.6) compared with choice (max.: 533.3 ± 47.4) studies each year. Population fluctuation patterns of E. mundus and E. lutea adults were similar to those of adult B. tabaci on traps with low weekly mean numbers occurring initially and increasing to peak levels in mid-August, then decreasing in later weeks of the studies. The relationship between weekly mean numbers of B. tabaci and E. lutea was greater than the relationship between B. tabaci and E. mundus . Mean numbers of E. mundus and E. lutea on traps were higher at the third main stem nodes than traps suspended on the fifth or eighth node. Mean numbers of E. lutea pupae were usually higher than E. mundus from the first sampling date throughout the end of the growing season on leaves. The relationship between parasitoid pupae and adults captured in traps is discussed.     

Variation in the Bemisia tabaci s. l. species complex (Hemiptera: Aleyrodidae) and its natural enemies leading to successful biological control of Bemisia biotype B in the USA

Parasitoids of the Bemisia tabaci (Gennadius) species complex collected in Spain and Thailand were evaluated as biological control agents of B. tabaci biotype B in cole crops in Texas, USA. Parasitoids were identified by morphological and RAPD-PCR analyses. The most abundant parasitoid from Spain was Eretmocerus mundus Mercet with apparent field parasitism of 39-44%. In Thailand, Encarsia formosa Gahan, E. transvena Timberlake, E. adrianae Lopez-Avila, Eretmocerus sp. 1 and sp. 2 emerged, with apparent field parasitism of 1-65%. Identification and molecular classification of B. tabaci associated with parasitoid collections and in the release site in Texas were accomplished using morphological traits and nucleotide sequence comparison of the mitochondrial cytochrome oxidase I gene (COI) (700-720 bp). Collections of B. tabaci from Thailand grouped separately from B types from Arizona and Florida and the target B type from Texas, USA, a cluster from India, and other New World B. tabaci. The Spanish B. tabaci host of E. mundus which was laboratory and field-tested to achieve biological control of the B type was most closely related to non-B type B. tabaci populations from Spain and Sudan, the latter which formed a second group within the larger clade that also contained the B type cluster. Laboratory tests indicated that E. mundus from Spain parasitized more B. tabaci type B than did Eretmocerus spp. native to Texas and other exotic parasitoids evaluated. Eretmocerus mundus from Spain also successfully parasitized B. tabaci type B when field-released in a 0.94 million ha test area in Texas, and has significantly enhanced control of B. tabaci type B in California, USA. In contrast, parasitoids from Thailand failed to establish in the field in Texas, collectively suggesting a positive correlation between the centres of diversity of compatible parasitoid-host complexes.     

Mating and host density affect host feeding and parasitism in two species of whitefly parasitoids

Abstract The parasitoids in the genera of Encarsia and Eretmocerus (Hymenoptera: Aphelinidae) are important biological control agents of whiteflies, and some of them not only parasitize hosts but also kill them with strong host‐feeding capacity. Two whitefly parasitoid species, Encarsia sophia and Eretmocerus melanoscutus were examined to determine if mating and host density affected their host feeding and parasitism. The whitefly host, Bemisia tabaci, was presented to these two wasp species in densities of 10, 20, 30, 40, 50 and 60 third‐instar nymphs per clip cage. Mated whitefly parasitoid females fed on more hosts than unmated females under a range of host densities (under all six host densities for En. sophia; under the densities of 40 nymphs or more for Er. melanoscutus). Meanwhile, mated females parasitized more whitefly nymphs than unmated females under all host densities for both species. With increase of host density, mated or unmated Er. melanoscutus females killed more hosts by host feeding and parasitism. Mated En. sophia females killed more hosts by host feeding with increase of host density, whereas unmated females did not parasitze whitefly nymphs at all. Our results suggest that only mated female parasitoids with host‐feeding behavior should be released in crop systems to increase their bio‐control efficiency.     

Impact of Eretmocerus eremicus (Hymenoptera: Aphelinidae) on open-field Bemisia tabaci (Hemiptera: Aleyrodidae) populations

The effect of three different release rates (1×, 10×, and 20× the recommended rate of 25,000/ha) of Eretmocerus eremicus Rose and Zolnerowich on Bemisia tabaci (Gennadius) populations found in open-field cantaloupe, Cucumis melo L., was evaluated against populations in untreated control plots. Parasitoids were released from a point source in the center of each of nine treatment plots. Whitefly population growth, encompassing all developmental stages, and rates of parasitism were monitored within a 10-m annulus surrounding the center point in all 12 plots over a 52-d period. The rates of B. tabaci population increase during this time were equivalent regardless of the parasitoid release rate. Whitefly densities were not limited in any of our treatment plots when compared to those found in the control plots. Moreover, mean rates of parasitism did not increase with time nor did they differ among the three treatments or control plots (7.9 ± 6.5%). Finally, estimated rates of parasitism were density-dependent responding positively to increasing host numbers. The ineffectiveness of this parasitoid in controlling whitefly populations in the field may be due to its high propensity to disperse at low host densities or to influxes of immigrating whiteflies. Hence, the use of E. eremicus alone is not an efficient means to reduce whitefly populations in melon crops in the southwestern United States.     

Intraguild predation of Serangium parcesetosum (Coleoptera: Coccinellidae), on whitefly Bemisia tabaci (Homoptera: Aleyrodidae) parasitized by Eretmocerus mundus (Hymenoptera: Aphelinidae)

We studied intraguild predation of Serangium parcesetosum on Eretmocerus mundus, both natural enemies of Bemisia tabaci, on eggplant under laboratory conditions. Fourth instar and adult predators attacked parasitized and unparasitized hosts equally if immature parasitoids were larvae, but avoided predating on parasitized hosts containing pupae.     

基于SCAR标记技术的丽蚜小蜂快速识别

丽蚜小蜂Encarsia formosa Gahan作为温室粉虱Trialeurodes vaporariorum Westwood和烟粉虱Bemisia tabaci (Gennadius)等粉虱类害虫的优势寄生蜂而备受关注。针对丽蚜小蜂体型微小, 难以与其他同域近缘种寄生蜂快速、 准确区别的问题, 本研究采用SCAR (sequence characterized amplified region, 特异性扩增区域)标记技术, 筛选出一对丽蚜小蜂特征片段扩增引物(EFZZF/EFZZR), 其扩增片段的大小为287 bp。种特异性检验结果表明, 该对引物只对丽蚜小蜂的基因组DNA具有扩增能力, 对其近缘种属寄生蜂如浅黄恩蚜小蜂Encarsia sophia (Girault & Dodd)、 海氏桨角蚜小蜂Eretmocerus hayati Zolnerowich & Rose、 本地未知种桨角蚜小蜂Eretmocerus sp.、 蒙氏桨角蚜小蜂Eretmocerus mundus Mercet、 刺粉虱黑蜂Amitus hesperidum Silvertri不具有扩增效果, 对丽蚜小蜂的寄主包括不同生物型 (B型、 Q型、 ZHJ 1型和ZHJ 2型)的烟粉虱、 温室粉虱以及我国最常见的黑刺粉虱Aleurocanthus spiniferus (Quaintanca)等亦不具有扩增能力。同时, 该检测技术灵敏度高, 对成虫的最低检出阈值为7.812 ng/μL (相当于1/1 600头成虫)。研究结果对丽蚜小蜂的种类识别、 寄主谱的确定及其有效利用具有重要意义。     

Compatibility of Insect Growth Regulators with Eretmocerus eremicus (Hymenoptera: Aphelinidae) for Whitefly (Homoptera: Alyerodidae) Control on Poinsettias: II. Trials in Commercial Poinsettia Crops

The efficacy and cost of reduced release rates of the parasitoid Eretmocerus eremicus Rose and Zolnerowich (Hymenoptera: Aphelinidae) when combined with application of the insect growth regulator buprofezin were compared to those of a higher parasitoid release rate used alone for whitefly control (Homoptera: Aleyrodidae) on poinsettia (Euphorbia pulcherrima Willd. ex Koltz.). The trial was conducted in seven greenhouses in Methuen, Massachusetts from August through December 1997 and employed commercial poinsettia production practices. Two whiteflies species, Trialeurodes vaporariorum (Westwood) and Bemisia argentifolii Bellows and Perring (= Bemisia tabaci [Gennadius] strain B), were present. Three treatments were examined: (1) E. eremicus used alone at a release rate of three females per plant per week (two greenhouses); (2) E. eremicus at an intermediate release rate of two females per plant per week, combined with mid-season use of buprofezin (two applications, spaced 1 week apart, applied in weeks 9 and 10) (two greenhouses); and (3) E. eremicus at a low release rate of one female per plant per week, combined with mid-season use of buprofezin, applied as in treatment 2 (two greenhouses). In addition, observations were made in one additional greenhouse at the site, in which the grower used pesticides for whitefly control. Prior to the start of the trial, cuttings used for all treatments experienced some pesticide use, first abamectinduring rooting and later buprofezin at potting to reduce whitefly numbers, which were initially very high. At harvest, densities of live whitefly nymphs were not statistically different among the biological control treatments, indicating that a low parasitoid release rate combined with buprofezin was as effective as a higher release rate of the parasitoid used alone. Nymphal densities in separate market samples (based on smaller sample sizes) showed differences among treatments, but all treatments, including the low parasitoid release rate + buprofezin maintained densities of live nymphs + pupae at or below approximately two per leaf, a level commercially acceptable in local markets. Control costs per single-stemmed poinsettia plant were $1.18 for the high parasitoid release treatment, $0.75 for the treatment of weekly releases of two female parasitoids per plant per week + buprofezin, $0.38 for the treatment of releases of one female parasitoid per plant per week + buprofezin, and $0.14 for the chemical control greenhouse.     

Biology of a thelyotokous biotype of Eretmocerus mundus (Hymenoptera: Aphelinidae) on Bemisia tabaci (Homoptera: Aleyrodidae)

Abstract Thelyotokous biotype of Eretmocerus mundus Mercet (Hymenoptera: Aphelinidae), a parasitoid of Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae), was recently recorded in northern Iran. Reproductive biology of this biotype was studied as part of an evaluation of its potential for biological control of B. tabaci. The parasitoid deposited more eggs under 2nd and 3rd nymphal instars than 1st or 4th instars. Adult females fed honey, with no access to whitefly nymphs, lived significantly longer (13.6 ± 4.7 d) than those given access to nymphs, but not fed honey (7.6 ± 2.21 d). Lifetime fecundity averaged 81.7 ± 26.9 female progeny per female parasitoid, ranging from 11–132. Daily fecundity, measured as the number of whitefly nymphs parasitized by per female each day for 10 d, averaged 18.06 ± 3.95 for the first 6 d of life, and then declined to < 11. Developmental time from oviposition to parasitoid emergence was significantly shorter in the 3rd instar of the host (15.9 ± 1.06 d) than in the 1st instar (18.7 ± 2.3 d), but not in the 2nd instar (16.4 ± 1.3 d).     

Effect of whitefly parasitoids on the cuticular lipid composition of Bemisia argentifolii (Homoptera: aleyrodidae) nymphs

Experiments were conducted to determine the effects of whitefly parasitoids on the cuticular lipid composition of the silverleaf whitefly, Bemisia argentifolii Bellows and Perring [=sweetpotato whitefly, Bemisia tabaci (Gennadius), Biotype B] nymphs. The cuticular lipids of B. argentifolii nymphs that had been attacked by parasitic wasps, either Eretmocerus mundus Mercet or Encarsia pergandiella Howard, were characterized by capillary gas chromatography and CGC-mass spectrometry and the results compared with the cuticular lipids of unparasitized nymphs. Previous studies with B. argentifolii nymphs had shown that wax esters were the major components of the cuticular lipids with lesser amounts of hydrocarbons, long-chain aldehydes, and long-chain alcohols. No appreciable changes in lipid composition were observed for the cuticular lipids of E. pergandiella-parasitized nymphs as compared to unparasitized controls. However, the cuticular lipids from nymphs parasitized by E. mundus contained measurable quantities of two additional components in their hydrocarbon fraction. Analyses and comparisons with an authentic standard indicated that the two hydrocarbons were the even-numbered chain length methyl-branched alkanes, 2-methyltriacontane and 2-methyldotriacontane. The occurrences and possible functions of 2-methylalkanes as cuticular lipid components of insects are discussed and specifically, in regard to host recognition, acceptance, and discrimination by parasitoids. Published 2000 Wiley-Liss, Inc.     

Functional response,host stage preference and interference of two whitefly parasitoids

The functional responses of two parasitoids, Eretmocerus hayati Zolnerowich & Rose and Encarsia sophia Girault & Dodd, of whitefly Bemisia tabaci Gennadius Middle East‐Asia Minor 1 were studied under laboratory conditions. In addition, the influence of host density and host stage on the competitive interactions between the two parasitoids, and biological control effect on whitefly were evaluated. In the functional response study, adult parasitoids were tested individually, with a conspecific or heterospecific competitor. Both Er. hayati and En. sophia exhibited a type II response to increasing host density, whether a conspecific or heterospecific competitor was present or not. Difference of searching rates and handling times between treatments suggested interference interactions existed between two parasitoid species. In the host stage preference study, two parasitoid species were jointly tested. Er. hayati had a competitive advantage over En. sophia when provided young host instars (first and second instar), whereas no advantage was found on old host instars (third and fourth instar). The biological control effect of Er. hayati and En. sophia in different introductions varied with host density. However, the effect of host instar on host mortality was not significant. These findings provide information for the practice of biological control and give better insight into how parasitoid species may coexist in diverse environments.