Parasitoid Lysiphlebus Testaceipes Research Articles

Increase in Importance of Aphelinus nigritus (Howard) on Winter Crops in Oklahoma Coincides with Invasion of Sugarcane Aphid on Sorghum in Oklahoma

Aphid parasitoids on the Southern Great Plains provide important pest suppression services in summer and winter crops. The primary parasitoids Lysiphlebus testaceipes (Cresson), Aphelinus nigritus (Howard), and Diaretiella rapae (McIntosh) use multiple aphid host species on multiple crops in agricultural landscapes and historically, L. testaceipes has been the most abundant and arguably most important. However, after the sugarcane aphid, Melanaphis sacchari (Zehntner), infested sorghum (Sorghum bicolor (L.) Moench) on the Southern Plains, A. nigritus increased in abundance and impact on this summer crop. We hypothesized that A. nigritus also would be more abundant in fields of winter wheat (Triticum aestivum L.) and winter canola (Brassica napus L.) in the region following the sugarcane aphid. From 2016-2019, we documented aphid parasitoid abundance and percentage of parasitism in Oklahoma winter crops during late fall and early spring using a standardized sentinel aphid deployment retrieval and rearing approach. Unexpectedly, A. nigritus was relatively abundant during Fall 2016, parasitizing as many as 5.4% of sentinel aphids in winter wheat fields which was more than the typically dominant parasitoid L. testaceipes. However, percentage of parasitism by A. nigritus decreased during the study. Our results suggested that abundance of A. nigritus mirrored those of sugarcane aphids in the region, and the temporary presence of the parasitoid in winter crops reflected dynamics at a landscape level.

Population dynamics and species composition of maize field parasitoids attacking aphids in northeastern China

Maize, Zea mays L., is the most abundant field crop in China. Aphids are the most economically damaging pest on maize, particularly in the maize agri-ecosystems of Jilin Province, northeastern China. Parasitic wasps are important natural enemies of aphids, but limited information exists about their species composition, richness and seasonal dynamics in northeastern China. In this study, the population dynamics of maize aphids and parasitoid wasps were assessed in relation to each other during the summer seasons of two consecutive years, 2018 and 2019. We selected maize fields in the Changchun, Songyuan, Huinan and Gongzhuling areas of Jilin Province. Four species of aphids were recorded from these maize fields: Rhopalosiphum padi (L), Rhopalosiphum maidis (Fitch), Aphis gossypii Glover and Macrosiphum miscanthi (Takahashi). The dominant species in each of the four areas were R. maids (Filch) and R. padi in Changchun, R. padi in Songyuan, A. gossypii and R. padi in Huinan, and A.gossypii and R. padi in Gongzhuling. We delineated a species complex made up of primary parasitoids and hyperparasitoids associated with maize aphids. The primary parasitoids Lysiphlebus testaceipes, Binodoxys communis and Aphelinus albipodus together formed approximately 85.3% of the parasitoid complex. Pachyneuron aphidis, Phaenoglyphis villosa, Syrphophagus taeniatus and Asaphes suspensus made up the hyperparasitoids. Of the primary parasitoids, L. testaceipes was the dominant species (81.31%). Of the hyperparasitoid group, P. villosa was the dominant species (68.42%). Parasitism rates followed the fluctuation of the aphid population. The highest parasitic rate was observed during the peak period of cotton aphids. In this paper, the occurrence dynamics and dominant species of aphids and the dynamics of parasitic natural enemies of aphids in maize fields in Jilin Province are, for the first time, systematically reported. This study provides important information for the establishment and promotion of aphid biological control in maize fields.

Silicon-induced changes in plant volatiles reduceattractiveness of wheat to the bird cherry-oat aphid Rhopalosiphum padiand attractthe parasitoid Lysiphlebus testaceipes.

Silicon (Si) supplementation is well-known for enhancing plant resistance to insect pests, however, only recently studies revealed that Si accumulation in the plant not only confers a mechanical barrier to insect feeding, but also primes jasmonic acid-dependent defenses. Here, we examined whether Si supplementation alters wheat volatile emissions that influence the bird cherry-oat aphid (Rhopalosiphum padi) olfactory preference and the aphid parasitoid Lysiphlebus testaceipes. Even though Si accumulation in wheat did not impact aphid performance, we found that R. padi preferred constitutive volatiles from–Si wheat over those emitted by +Si wheat plants. In Y-tube olfactometer bioassays, the parasitoid was attracted to volatiles from +Si uninfested wheat, but not to those from–Si uninfested wheat. +Si and–Si aphid-infested plants released equally attractive blends to the aphid parasitoid; however, wasps were unable to distinguish +Si uninfested plant odors from those of aphid-infested treatments. GC-MS analyses revealed that +Si uninfested wheat plants emitted increased amounts of a single compound, geranyl acetone, compared to -Si uninfested wheat, but similar to those emitted by aphid-infested treatments. By contrast, Si supplementation in wheat did not alter composition of aphid-induced plant volatiles. Our results show that changes in wheat volatile blend induced by Si accumulation mediate the non-preference behavior of the bird cherry-oat aphid and the attraction of its parasitoid L. testaceipes. Conversely to the literature, Si supplementation by itself seems to work as an elicitor of induced defenses in wheat, and not as a priming agent.

The influence of aphid-produced honeydew on parasitoid fitness and nutritional state: A comparative study

Honeydew is a sugar-rich resource excreted by many hemipteran species and is a key food source for other insect species such as ants and parasitoid wasps. Here, we evaluated the nutritional value of 14 honeydews excreted by 13 aphid species for the generalist aphid parasitoid Lysiphlebus testaceipes to test a series of hypotheses concerning variation in the nutritional value of honeydew. There was a positive correlation between the body sugar content of honeydew-fed parasitoids and their longevity. This information is valuable for biological control researchers because it demonstrates that the nutritional state of honeydew-fed parasitoids in the wild can indicate their fitness, independently of the honeydew source they have fed on.Although the carbohydrate content and longevity of L. testaceipes differed greatly among the different honeydews, we did not find a significant effect of aphid or host plant phylogeny on these traits. This result suggests that honeydew is evolutionarily labile and may be particularly subject to ecological selection pressures. This becomes apparent when considering host aphid suitability: Schizaphis graminum, one of the most suitable and commonly used hosts of L. testaceipes, produced honeydew of the poorest quality for the parasitoid whereas Uroleucon sonchi, one of the few aphids tested that cannot be parasitized by L. testaceipes, excreted the honeydew with the highest nutritional value. These data are consistent with the hypothesis that hemipterans are subject to selection pressure to minimize honeydew quality for the parasitoids that attack them.

Landscape Context Affects Aphid Parasitism by Lysiphlebus testaceipes (Hymenoptera: Aphidiinae) in Wheat Fields.

Winter wheat is Oklahoma's most widely grown crop, and is planted during September and October, grows from fall through spring, and is harvested in June. Winter wheat fields are typically interspersed in a mosaic of habitats in other uses, and we hypothesized that the spatial and temporal composition and configuration of landscape elements, which contribute to agroecosystem diversity also influence biological control of common aphid pests. The parasitoid Lysiphlebus testaceipes (Cresson; Hymenoptera: Aphidiinae) is highly effective at reducing aphid populations in wheat in Oklahoma, and though a great deal is known about the biology and ecology of L. testaceipes, there are gaps in knowledge that limit predicting when and where it will be effective at controlling aphid infestations in wheat. Our objective was to determine the influence of landscape structure on parasitism of cereal aphids by L. testaceipes in wheat fields early in the growing season when aphid and parasitoid colonization occurs and later in the growing season when aphid and parasitoid populations are established in wheat fields. Seventy fields were studied during the three growing seasons. Significant correlations between parasitism by L. testaceipes and landscape variables existed for patch density, fractal dimension, Shannon's patch diversity index, percent wheat, percent summer crops, and percent wooded land. Correlations between parasitism and landscape variables were generally greatest at a 3.2 km radius surrounding the wheat field. Correlations between parasitism and landscape variables that would be expected to increase with increasing landscape diversity were usually positive. Subsequent regression models for L. testaceipes parasitism in wheat fields in autumn and spring showed that landscape variables influenced parasitism and indicated that parasitism increased with increasing landscape diversity. Overall, results indicate that L. testaceipes utilizes multiple habitats throughout the year depending on their availability and acceptability, and frequently disperses among habitats. Colonization of wheat fields by L. testaceipes in autumn appears to be enhanced by proximity to fields of summer crops and semi-natural habitats other than grasslands.

Potencial de Aclepias curassavica L. (Apocynaceae) en el control biológico de plagas


 
 
 Para conocer el potencial de Asclepias curassavica L. en el manejo de plagas, del 01 de enero al 28 de diciembre de 2012, se estableció un estudio en una plantación de limón “persa” Citrus latifolia en Emiliano Zapata, Villamar, Michoacán, México. Una sección (tratamiento) incluyó la planta A. curassavica y la otra se mantuvo sin esa especie (testigo). Muestreos semanales documentaron especies y número de depredadores, fitófagos, parasitoides, y niveles de parasitismo en áfidos. Toxoptera aurantii, Aphis spiraecola, Diaphorina citri y Phyllocnistis citrella, fueron las principales plagas. Sus mayores poblaciones ocurrieron en el segundo semestre del año y coincidieron con los principales periodos de brotación del cultivo. Los principales enemigos naturales observados en A. curassavica fueron las familias Coccinellidae, Syrphidae, Chamaemyiidae, Chrysopidae y el parasitoide Lysiphlebus testaceipes. Los Coccinellidos predominaron durante el primer semestre del año, mientras que los otros grupos fueron frecuentes durante todo el año. Los resultados muestran una reducción de 46.3% en las poblaciones de áfidos de los cítricos donde se establecieron Asclepias; sin embargo, las poblaciones de D. citri se incrementaron 77%. Probablemente el mayor biocontrol de áfidos favoreció la disponibilidad de nichos vacíos (brotes vegetativos) y consecuentemente las poblaciones del psílido. La amplia diversidad de enemigos naturales registrados en A. curassavica sugiere un alto potencial de la planta para utilizarse en la regulación y estabilidad de la entomofauna de los agroecosistemas, más que en el control de plagas específicas.
 
 

Host plants and aphid hosts influence the selection behaviour of three aphid parasitoids (Hymenoptera: Braconidae: Aphidiinae)

Aphis fabae and Myzus persicae (Hemiptera: Aphididae) are insect pests that damage sugar beet and bean crops. Both are responsible for losses in yield and transmission of viral diseases, and may be present on the same host at the same time. Three parasitoid species, Aphidius colemani, Lysiphlebus testaceipes and Lysiphlebus fabarum (Hymenoptera: Braconidae: Aphidiinae) have the potential to be used as biological control agents against at least one of these species of aphids. As a first step prior to the implementation of a biological control program, our aim was to understand the host selection behaviour of the parasitoids, particularly when both aphids are present. We recorded the host acceptance (number of insertions of the ovipositor / number of antennal contacts), suitability (number of mummies / the number of insertions of the ovipositor) and emergence (number of adults emerging from mummies) of these three aphid parasitoids when parasitizing the two aphids. We also analyzed the effect of the host plant on the host preference of the parasitoid. Females of each parasitoid species (n = 15) were exposed to 20 aphids of A. fabae or M. persicae, or a mixture of these two species of aphids, for 15 min, on a leaf disc of each of the two host plants, sugar beet and bean. Higher host acceptance and suitability were recorded for A. colemani attacking both species of aphid: A. fabae (43 and 46%) and M. persicae (43 and 46%) on beet and bean plants respectively, compared to L. testaceipes and L. fabarum. L. testaceipes and L. fabarum showed a clear preference for A. fabae. L. fabarum accepted M. persicae on both plants only when it was mixed with A. fabae, probably due to a confusion effect. We found that the host plant played a significant role in host acceptance, host suitability. We conclude that A. colemani is the better of the three parasitoids studied for the biological control in bean, and particularly, sugar beet crops.

Laboratory and field studies to evaluate the potential of an open rearing system of Lysiphlebus testaceipes for the control of Aphis craccivora in Argentina

The aim of this work was to examine, both in the field and in the laboratory, ecological aspects of selected plant–aphid–parasitoid interactions to evaluate their potential for the open rearing of the parasitoid Lysiphlebus testaceipes (Cresson) (Hymenoptera: Aphidiinae) for the control of Aphis craccivora (Koch) (Hemiptera: Aphididae) in alfalfa agroecosystems. To this end quantitative samplings of parasitoids and aphids were made fortnightly in three alfalfa crop fields and their spontaneously vegetated edges, in Rafaela (Santa Fe, Argentina), during three years (2009–2011). Three sink webs based on L.testaceipes, on a per-year basis, were constructed to assess the strength of the interactions established by aphids and parasitoids, the host ranges of alternative aphid species, and the tendencies in parasitoid host use across years. In the laboratory, emergence rates, parasitism rates, larval and pupal development times, and adult lifespan of L. testaceipes were analyzed by means of choice tests, including the alternative and the target aphid species in the assays. About 84 % of adults of L. testaceipes obtained in the samples came from Aphis nerii (Boyer de Fonscolombe), an innocuous aphid species only associated with plants of the genus Araujia Brotero (Apocynaceae). Based on our results, the system proposed has many features that support its feasibility to be used as an open rearing system of L. testaceipes: unrisky alternative aphid, easy reproduction of the banker plant and similar suitability of innocuous and pest aphid species for the parasitoid to oviposit and complete their development without noticeably preference for specific hosts.

Bioenergy Crops and Natural Enemies: Host Plant-Mediated Effects of Miscanthus on the Aphid Parasitoid Lysiphlebus testaceipes

Miscanthus spp. are biofuel crops that are triggering growing interest worldwide due to their numerous agronomic advantages. Though breeding programs take into account usual key plant traits of agronomic interest (e.g., biomass production, adaptation to broader climatic range), they generally overlook plant attributes relating to pest and pathogen resistance and even more those that may favor or improve the combined use of biological control agents of pests. A recent study showed that the parental species, Miscanthus sacchariflorus and, to a lesser extent, Miscanthus sinensis, were less suitable and acceptable host plants for the corn leaf aphid Rhopalosiphum maidis, one of the main pests of Miscanthus × giganteus in the USA, than the hybrid M. × giganteus. In the present laboratory study, we investigated the host plant-mediated effects of these three miscanthus species on various life history traits of the aphid parasitoid Lysiphlebus testaceipes. A clear host plant effect was shown on aphid size and, consequently, on parasitoid fitness parameters. High plant resistance to aphids was shown to be more detrimental to the parasitoid than partial resistance, with M. sacchariflorus being the least suitable host plant to both aphid and parasitoid development. Selection of partial resistance, such as the one exhibited by M. sinensis, should then be preferred to support efficient aphid regulation by parasitoids. This study provides the first contribution to the evaluation of bottom-up effects of a biofuel crop on beneficial insects. It also underlines the need to conduct additional research when considering the implementation of new biomass crops.

Intimate Rendezvous in a Tritrophic Context? Nothing but the Girls for MaleLysiphlebus testaceipes

In insects, mating often occurs after natal dispersal, and hence relies on a coevolved combination of sexual communication and movement allowing mate encounter. Volatile sex pheromones are widespread, generally emitted by females and triggering in-flight orientation of conspecific males. In parasitoid wasps, unmated females can start laying unfertilized eggs via parthenogenesis so that host patches could serve as sites of rendezvous for mating. Males could therefore use cues associated with host patches to focus their search on females that have successfully found oviposition sites. We hypothesized that in parasitoids exploiting herbivorous hosts, sex pheromones, and herbivore-induced plant volatiles (HIPV) should act in synergy, triggering male orientation toward ovipositing females. We tested this hypothesis with the aphid parasitoid Lysiphlebus testaceipes. Results from both field and laboratory experiments show that males are strongly attracted to virgin females, but that volatiles from aphid-infested plants have no effect on male orientation, neither has a cue, nor in interaction with the female sex pheromone. The absence of synergy between sex pheromones and HIPV contrasts with results on other species and raises interesting questions on mating systems and sexual selection in parasitoid wasps.

Aphid honeydew quality as a food source for parasitoids is maintained in Bt cotton.

Bt-transgenic cotton has proven to be highly efficient in controlling key lepidopteran pests. One concern with the deployment of Bt cotton varieties is the potential proliferation of non-target pests. We previously showed that Bt cotton contained lower concentrations of insecticidal terpenoids as a result of reduced caterpillar damage, which benefited the aphid Aphis gossypii. It is thus important that non-target herbivores are under biological control in Bt cotton fields. The induction or lack of induction of terpenoids could also influence the quality of aphid honeydew, an important food source for beneficial insects. We therefore screened A. gossypii honeydew for cotton terpenoids, that are induced by caterpillars but not the aphids. We then tested the influence of induced insect-resistance of cotton on honeydew nutritional quality for the aphid parasitoid Lysiphlebus testaceipes and the whitefly parasitoid Eretmocerus eremicus. We detected the cotton terpenoids gossypol and hemigossypolone in A. gossypii honeydew. Although a feeding assay demonstrated that gossypol reduced the longevity of both parasitoid species in a non-linear, dose-dependent manner, the honeydew was capable of sustaining parasitoid longevity and reproduction. The level of caterpillar damage to Bt and non-Bt cotton had no impact on the quality of honeydew for the parasitoids.These results indicate that the nutritional quality of honeydew is maintained in Bt cotton and is not influenced by induced insect resistance.

Effects of Milkweed Host Species on Interactions between Aphis nerii (Hemiptera: Aphididae) and Its Parasitoids

The oleander aphid, Aphis nerii Boyer de Fonscolombe, feeds on members of the Apocynaceae family. In Kentucky, A. nerii colonizes several Asclepias species and Cynanchum laeve. The prevalence of milkweeds and A. nerii in Kentucky ecosystems allow natural enemies, including the primary parasitoid Lysiphlebus testaceipes, to utilize this aphid as a resource. The efficacy of L. testaceipes when utilizing A. nerii reared on different host plant species was studied in the field and in the laboratory. In the laboratory, the time until first host contact and the number of ovipositional attempts by L. testaceipes did not vary among aphids from different host plant species. However significantly more aphids were mummified and more parasitoids successfully emerged from aphids on C. laeve than from aphids on tested Asclepias species. The successful emergence rates of L. testaceipes from A. nerii colonizing four species of milkweed were also determined in a naturally infested field plot. While no significant differences were detected in 2009, significantly more L. testaceipes emerged in 2010 from A. nerii mummies collected from C. laeve than from mummies on A. syriaca and A. incarnata with numbers emerging from mummies on A. tuberosa being indistinguishable from those on C. laeve or A. syriaca. Five hyperparasitoid species were also recovered from A. nerii mummies over a two year period. A comparison of hyperparasitoid emergence among A. nerii mummies collected from four species of milkweed found that with the exception of one species during 2009, emergence rates did not differ significantly among aphid host plants. Our results suggest that parasitoid development may be affected by aphid host plant and that adverse effects of A. nerii on L. testaceipes are less severe when aphids develop on C. laeve compared to tested Asclepias species.

Host selection and parasitism behavior of Lysiphlebus testaceipes: Role of plant, aphid species and instar

The aphid parasitoid Lysiphlebus testaceipes is a potentially valuable biological control agent of Aphis gossypii a major worldwide pest of cotton. One means of increasing the abundance of a biological control agent is to provide an alternative host habitat adjacent to cropping, from which they can provide pest control services in the crop. Host selection and parasitism rate of an alternative host aphid, Aphis craccivora by L. testaceipes were studied in a series of experiments that tested its host suitability relative to A. gossypii on cotton, hibiscus and mungbean. Host acceptance, as measured by number of ovipositions was much greater in A. craccivora compared to A. gossypii, while more host aphids were accepted on mungbean than cotton. When given a choice L. testaceipes attacks more 4th instar and adult stages (63% and 70%, respectively) of both hosts than 2nd instar nymphs (47%). In a switching (host choice) experiment, L. testaceipes preferentially attacked A. craccivora on mungbean over A. gossypii on cotton. Observations of parasitoid contact with A. gossypii cornicle secretion suggest it provides a useful deterrent against parasitoid attack. From these experiments it appears L. testaceipes has a preference for A. craccivora and mungbean compared to A. gossypii and cotton, in this respect using A. craccivora and mungbean as alternative habitat may not work as the parasitoid is unlikely to switch away from its preferred host.

Honeydew as a source of nutrition for Lysiphlebus testaceipes (Cresson) (Hymenoptera: Braconidae): effect of adult diet on lifespan and egg load

AbstractParasitoid survival and fecundity is generally enhanced with access to carbohydrate food sources. In many agricultural ecosystems, there is often a scarcity of suitable carbohydrates for parasitoids. This study compared the suitability of aphid honeydew and buckwheat nectar as diet for the aphid parasitoid Lysiphlebus testaceipes. Wasp lifespan and egg load were both increased with access to carbohydrates, but no differences were detected between the various carbohydrates diets tested. As aphid honeydew is a sufficient source of nutrition and L. testaceipes is a short‐lived species, adding additional sources of carbohydrates like floral nectar strips to the agricultural landscape is unlikely to significantly increase the biological control exerted by L. testaceipes.

Effect ofIsaria fumosorosea(Hypocreales: Cordycipitaceae) andLysiphlebus testaceipes, (Hymenoptera: Braconidae) on the Brown Citrus Aphid: Preliminary Assessment of a Compatibility Study

Recently, a strain of Isaria fumosorosea Wize (.Ifr) (= Paecilomyces fumosoroseus [Luangsa-ard et al. 2005]), (Hypocreales: Cordycipitaceae) was discovered in a Florida citrus grove infecting the Asian citrus psyllid, Diaphorina citri Kuwayama (Meyer et al. 2008). Also, laboratory studies have demonstrated that Ifr may be effective against several commercially important pests of citrus (Poprawski et al. 1999; Avery et al. 2009; Hoy et al. 2010; Hunter et al. 2011). Therefore, the use of Ifr (PFR 97TM 20% WDG, Certis USA, Columbia, Maryland), approved in 2011 by EPA for use in commercial citrus, may offer a potential tool for balancing citrus pest management with consum er demands for organic citrus produce. The brown citrus aphid (BCA), Toxoptera citri cidus Kirkaldy (=T. citricida [Nieto Nafria et al. 2005]), (Hemiptera: Aphididae) was discovered in Florida in 1995 and is recognized as a serious pest of citrus capable of vectoring citrus triseza virus (Halbert & Brown 1996; Michaud 1998; Roy & Brlansky 2009). Under optimal conditions, na tive natural enemies provide good management of BCA, although these are easily disrupted by insecticide applications (Michaud 1998; 2002). Presently, the aphid's population is managed in part by the parasitoid Lysiphlebus testaceipes Cresson (Hymenoptera: Braconidae) (Evans & Strange 1997). This generalist aphid parasitoid Lysiphlebus testaceipes, native to Florida and the Americas, is an effective biocontrol agent of BCA (Evans & Strange 1997). The objectives of our study were to assess the impact of Ifr on the mor tality of BCA populations as well as the parasit ism and emergence rates of L. testaceipes. BCA and Carrizo citrus (a trifoliate hybrid: Washington navel x trifoliate orange) were ob tained from the Sub-Tropical Insect Research Unit, USDA Horticulture Research Laboratory in Fort Pierce, Florida. For the experiment, 5 car rizo citrus seedlings (25-30 cm tall) were placed in each of four separate nylon mesh-covered cages (35 x 35 x 35 cm) and each infested with 4 alate BCA (20 per cage). A second infestation was made after 9 days. Cages were maintained in a growth room at 24.0 ± 1 °C, 45.0 ± 1 % RH and 16:8 h (L:D) photoperiod. Two weeks later, 10 L. testa ceipes adults were added to two of the cages. After an additional 4 days, one cage with and without L. testaceipes was treated with Isaria fumosoro sea (Ifr) suspension (PFR 97TM 20% WDG) at 107 CFU/ml using Nalgene® (Nalge Nunc Interna tional, Rochester, NY) aerosol sprayer. The ger mination of PFR 97TM blastospores was 96% using the technique of Avery et al. 2009. The remaining 2 cages were sprayed with an equal volume of wa ter. Parasitoids were temporarily removed from all cages prior to spraying to eliminate potential drowning and were replaced with an additional 5 to compensate for handling stress. Two replicates of the same study were conducted on different dates.

Effects of Verticillium lecanii (Zimm.) Viegas on Toxoptera citricida Kirkaldy (Homoptera: Aphididae) and its parasitoid Lysiphlebus testaceipes Cresson (Hymenoptera: Braconidae)

The preponderance of susceptible sour orange (Citrus aurantium L.) rootstock has facilitated the spread of Citrus tristeza virus (CTV) in Trinidad and Tobago. CTV is transmitted by the brown citrus aphid Toxoptera citricida (Kirkaldy), which establishes large colonies on new flushes of citrus plants. As the colonies become highly populated, winged (alate) aphids are produced which can migrate to uninfected neighbouring citrus trees and hence transmit CTV. In the present study different concentrations of the entomopathogenic fungus Verticillium lecanii (Zimm) Viegas in water-based formulations were applied to T. citricida and the pathogenic effects were analysed. Bioassays were also conducted on the major parasitoid Lysiphlebus testaceipes Cresson to test the pathogenic effects of V. lecanii on mortality and the percent emergence from mummies. The LC<sub>50</sub> values for T. citricida and L. testaceipes were 2.26 × 10<sup>10</sup> spores/ml and 1.09 × 10<sup>9</sup> spores/ml, respectively. Statistical analyses indicated that there was no significant difference between the two LC<sub>50</sub> values. At the highest concentration (1.49 × 10<sup>9</sup> spores/ml) percent mortality peaked at 78.9% after 12 days and 1.95 × 10<sup>9</sup> spores/ml, mortality of L. testaceipes reached 95.1% after 6 days. Emergence of L. testaceipes at the highest concentration of 1.95 × 10<sup>9</sup> spores/ml was 57.8%.

Interaction between the aphid parasitoid Lysiphlebus testaceipes (Hymenoptera: Aphidiidae) and its hyperparasitoid Syrphophagus africanus (Hymenoptera: Encyrtidae)

The interactions between the cowpea aphid Aphis craccivora Koch, its parasitoid Lysiphlebus testaceipes Cresson and hyperparasitoid Syrphophagus africanus Gahan were assessed in the laboratory. Host age preference for hyperparasitism was evaluated using parasitized aphids of different ages (i.e. 1, 2, 3, 4, 5 and 6 days old and mixed ages). We studied the influence of the hyperparasitoid on the parasitism efficiency of L. testaceipes, the effect of host age on some biological parameters of S. africanus, and its hyperparasitism based on aggregated or isolated mummies. The presence of S. africanus significantly affected aphid parasitism by L. testaceipes (21.2 ± 3.6 vs 36.6 ± 4.5%). Except for 1-day-old hosts, S. africanus successfully parasitized hosts of all tested ages, with preference for newly formed mummies (39.16 ± 3.31% parasitism in 5-day-old hosts). The development time of immature stages of the S. africanus progeny was significantly affected by host age. The sex ratio of the hyperparasitoid progeny was largely female biased and did not vary with host age. Syrphophagus africanus females from live parasitized aphids produced more offspring (36.55 ± 6.28 vs 25.00 ± 7.16) and lived longer (21.09 ± 1.57 vs 10.88 ± 2.31 days) than those from mummy hosts. Hyperparasitism rates were higher on aggregated mummies than on dispersed ones (36.00 ± 2.86 vs 20.66 ± 4.00%).

Aphids and their natural enemies in vegetable agroecosystems in Benin

This study was undertaken to provide new knowledge on biodiversity of aphids and their complex of natural enemies in vegetable agroecosystems in Benin. During a 2-year survey (2007/2008 to 2008/2009), aphid species, their host plants and natural enemies were identified from samples collected from 29 vegetable and 22 weed species at 30 vegetable production sites across Benin. A total of 82% of the vegetable species and 12% of the weed species were infested with aphids. Aphis gossypii Glover infested a wide range of the vegetables and occurred on 62% of the species, while Aphis craccivora Koch, Aphis spiraecola Patch, Lipaphis erysimi (Kalt.), Myzus persicae (Sulzer) and Toxoptera odinae (Van de Goot) were collected from a limited number of vegetables, each with a frequency occurrence ranging from 3 to 28%. The weeds Commelina benghalensis L. and Euphorbia hirta L. were common alternative weed hosts for aphids. Common natural enemies were the predators Cheilomenes propinqua (Mulsant), Cheilomenes sulphurea (Olivier) and Ischiodon aegyptius (Wiedemann), the obligate entomopathogen Neozygites sp., and the parasitoids Lysiphlebus testaceipes (Cresson) and Aphelinus ficusae Prinsloo & Neser. Lysiphlebus testaceipes was usually the only primary parasitoid on aphids across the sites and its common host was A.gossypii. From parasitized mummies, five species of hyperparasitoids were collected, the most abundant being Syrphophagus africanus (Gahan). These are the first records of L.testaceipes,S.africanus andA. spiraecola from West Africa. These findings provide baseline knowledge on the aphid fauna of Benin and contribute information for use in the development of sustainable vegetable pest management strategies in the country.

Occurrence of Lysiphlebus testaceipes parasitizing Aphis gossypii in watermelon in the State of Rio Grande do Norte, Brazil

This is the first report of the parasitoid Lysiphlebus testaceipes (Cresson) as a biological control agent of the aphid Aphis gossypii Glover in watermelon crop in Vale do Açu, RN. It was observed that near the harvest, almost all collected aphids were mummified, and after analyzing the emerged parasitoids, the parasitoid L. testaceipes was identified. Therefore, in the future, this species may be included in A. gossypii integrated management programs.

Seasonal Abundance of Resident Parasitoids and Predatory Flies and Corresponding Soybean Aphid Densities, with Comments on Classical Biological Control of Soybean Aphid in the Midwest

Seasonal abundance of resident parasitoids and predatory flies, and corresponding soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), densities were assessed in soybean fields from 2003 to 2006 at two locations in lower Michigan. Six parasitoid and nine predatory fly species were detected in 4 yr by using potted plants infested with soybean aphid placed in soybean fields. The parasitoid Lysiphlebus testaceipes Cresson (Hymenoptera: Braconidae) and the predatory flies Aphidoletes aphidimyza Rondani (Diptera: Cecidomyiidae), and Allograpta obliqua Say (Diptera: Syrphidae) were most numerous. Generally, L. testaceipes was more abundant late in the soybean growing season, but it also occurred during soybean vegetative growth; A. obliqua was more abundant during vegetative growth; and A. aphidimyza was common throughout the season. Soybean plants were visually inspected to estimate densities of soybean aphid, mummified aphids, and immature predatory flies. From 2003 to 2006, parasitism rates were inversely correlated with aphid density: percentage of parasitism was always very low (< or = 0.1%) at high aphid densities (> 100 aphids per plant), and higher parasitism, up to 17%, was observed at very low aphid densities (< 1 aphid per plant). Populations of immature predatory flies, particularly A. aphidimyza, generally increased in soybean fields with increasing soybean aphid populations, but aphids always outnumbered immature flies by 100-21,000-fold when flies were detected. Rearing field-collected aphid in 2006 substantiated that parasitism varied widely, with parasitism in most cases < 10%. Based on findings of low parasitism and predation, positive response to changing aphid densities by predatory flies but not parasitoids, early season abundance primarily of predatory flies, and past findings on these taxa's diversity and abundance, we discuss the potential use of exotic parasitoids and predatory flies to enhance soybean aphid biological control.