Effect of temperature on the reproductive biology of Peristenus spretus (Hymenoptera: Braconidae), a biological control agent of the plant bug Apolygus lucorum (Hemiptera: Miridae)

Peristenus spretus Chen et van Achterberg (Hymenoptera: Braconidae), a parasitoid of the plant bug Apolygus lucorum (Hemiptera: Miridae), has been studied for use in augmentative biological control in China. Under laboratory conditions, we explored the development, survival, age-specific and potential lifetime fecundity, oviposition period and progeny sex ratio of P. spretus reared at six constant temperatures (15°C, 19°C, 23°C, 27°C, 31°C, 35°C) on the second instar nymphs of A. lucorum. At 15°C, male and female P. spretus took 48.7 ± 0.3 and 52.5 ± 0.3 days to complete their immature development, while developmental time was reduced by more than half at 23°C and 27°C. The parasitoid can only develop to the larval stage at 31°C and neither larva nor pupa survived at 35°C. The estimated lower developmental threshold of the immature stage was 7.3°C. When parasitoid adults were exposed at 15°C, females laid 90% of their eggs at first 19 days of oviposition and had an extended reproductive life. In contrast, females held at 27°C laid most of their eggs (90%) in their first of 10 days of oviposition and had shorter longevity. The highest potential lifetime fecundity of P. spretus was 671.2 ± 34.7 SE eggs produced over 23.4 ± 1.4 SE days at 23°C. At 15°C, 19°C and 23°C, sex ratios of reared parasitoids were male-biased, but at 27°C there was no male bias.     

Detection of European Peristenus digoneutis loan in mirid populations in southern Ontario

Lygus spp. Hahn (Hemiptera: Miridae) are serious pests of a wide variety of economically important crops in North America. A European parasitoid, Peristenus digoneutis Loan (Hymenoptera: Braconidae), released in the northeastern USA for the biological control of Lygus, has successfully established in nine states and in eastern Canada, including southeastern Ontario, southern Quebec and Nova Scotia. To determine the extent to which P. digoneutis has dispersed and established in mirid populations in Ontario, a single-step multiplex PCR assay, designed to differentiate European species P. digoneutis and P. relictus from native North American Peristenus species, was used to identify parasitoid larvae dissected from field-collected Miridae. A total of 222 parasitoid larvae were analysed with the multiplex assay. Most (172) were identified as members of the P. pallipes Curtis complex; however, three from the Niagara region were identified as P. digoneutis. Specimens that did not amplify using the Peristenus multiplex PCR assay were screened with a PCR primer set designed to detect Leiophron (Hymenoptera: Braconidae) species, and most were confirmed to be Leiophron larvae. This study confirms the presence of P. digoneutis species in southern Ontario, and is another example of the utility of molecular methods for the detection of newly introduced or dispersed parasitoids. The presence of exotic P. digoneutis in southern Ontario may expedite future releases to augment already-established populations. Following such releases, the Peristenus multiplex PCR assay will be a useful component of post-release studies to evaluate the success of the biological control programme for Lygus plant bugs in Canada.     

Does host plant influence parasitism and parasitoid species composition in Lygus rugulipennis? A molecular approach

Lygus Hahn plant bugs (Hemiptera: Miridae) are serious pests of a wide variety of economically important crops in North America. European Peristenus digoneutis Loan and P. relictus Ruthe (Hymenoptera: Braconidae) are being considered for release in Canada as part of a classical biological control program for Lygus. The attractiveness of different host plants to European Peristenus has not been addressed, but may be an important consideration prior to parasitoid release. Lygus rugulipennis Poppius nymphs were collected in the Northern Temperate Atlantic (NTA) ecoregion on red clover (Trifolium pratense L.; Fabaceae) and chamomile (Matricaria recutita L.; Asteraceae), and in the Western European Broadleaf Forest (WEBF) ecoregion on red clover and alfalfa (Medicago sativa L.; Fabaceae). Parasitism levels and parasitoid species were determined using a multiplex PCR assay for P. digoneutis, P. relictus, and P. pallipes Curtis. Mean parasitism levels in L. rugulipennis were 45-49% in the NTA ecoregion and 25-32% in the WEBF ecoregion. However, in neither ecoregion were parasitism levels and parasitoid species compositions significantly different in nymphs from different host plant species. Furthermore, multiparasitism was low despite the fact that P. digoneutis and P. relictus share the same host species.     

PCR-based,rapid diagnosis of parasitism of Lygus spp. (Hemiptera: Miridae) by Peristenus relictus (Hymenoptera: Braconidae)

Several species of Lygus (Heteroptera: Miridae: Mirini) are serious crop pests in North America where their parasitism rate by native nymphal parasitoids is generally lower than in Europe. Peristenus relictus (Ruthe) (formerly P. stygicus Loan) (Hymenoptera: Braconidae: Euphorinae) is the predominant nymphal parasitoid of several Lygus spp. in the warm Mediterranean region and has been a candidate for introduction against Lygus hesperus Knight and L. lineolaris (Palisot de Beauvois) in the southern US. We report a rapid, sensitive, and specific PCR-based assay for diagnosis of P. relictus immature stages within Lygus nymphs that entails three steps: DNA extraction, PCR of the partial mitochondrial COI gene, and agarose gel electrophoresis. The PCR-based methodology is species-specific because the target DNA of other sympatric, congeneric species was not amplified with use of the primers developed for P. relictus diagnosis. The sensitivity of the PCR method, assessed through spike tests, was established by the detection of a ratio of 1:10,000 P. relictus DNA to Lygus DNA. Molecular diagnosis of parasitism of field collected nymphs is achievable in one day, eliminating the need to rear nymphs to obtain adult parasitoids for morphological identification.     

Overwintering strategies and cold hardiness of two aphid parasitoid species (Hymenoptera: Braconidae: Aphidiinae)

The role of winter diapause in two aphid parasitoid species, Aphidius ervi Haliday and Aphidius rhopalosiphi DeStefani-Peres (Hymenoptera: Braconidae: Aphidiinae), in host synchronization and the induction of cold hardiness was investigated. Parasitoids were reared during three successive generations on Sitobion avenae Fabricius, at 15 degrees C under a photoperiod of 9 h light 15 h dark. Although these conditions are known to be strongly diapause inducing, neither parasitoids showed an incidence of diapause above 65% over the three generations; the rest of the population underwent quiescence. In both parasitoid species, diapausing mummies exhibited greater cold hardiness than non-diapausing mummies, resulting in significantly lower supercooling points (SCP) and in a higher survival rate during long-term exposures at 0 and -10 degrees C. The induction of increased cold hardiness in parasitoids was thus associated with the diapause state. SCPs of third instar larvae of S. avenae were similar to those of non-diapausing mummies of both parasitoid species, but significantly higher than those of diapausing mummies. The effect of winter climate on the stability of the host-parasitoid interaction is discussed.     

Parasitism of the Wheat Stem Sawfly (Hymenoptera: Cephidae) in Montana

The wheat stem sawfly,Cephus cinctusNorton (Hymenoptera: Cephidae) was first found in wild grasses and soon became an economically important pest of wheat after cultivation began in the northern Great Plains. Of the species of parasitoids that attackC. cinctusin wild grasses, onlyBracon cephi(Gahan) andB. lissogasterMuesebeck (Hymenoptera: Braconidae) have been found in wheat. Levels of parasitism vary between wheat-producing regions in Montana. Parasitism levels were increased by releasing individuals from a region with high levels of parasitism into a region where parasitism levels were low. This suggests that there has been unequal rates of parasitoid adaptation from wild grasses to wheat in different regions of Montana.     

Functional response and mutual interference of Peristenus spretus (Hymenoptera: Braconidae), a parasitoid of Apolygus lucorum (Heteroptera: Miridae)

Peristenus spretus Chen & van Achterberg (Hymenoptera: Braconidae) is a solitary endoparasitoid, which is considered for augmentative biological control of Apolygus lucorum Meyer-Dür (Heteroptera: Miridae) in Chinese cotton fields. Since the association of P. spretus with A. lucorum was only recently discovered, the biology of the parasitoid remains unknown. In order to understand its reproductive biology, the mutual interference and functional response of P. spretus were investigated by altering either the parasitoid or the host density while keeping the other constant. In both experiments, the effects of parasitoid and host densities on parasitism, superparasitism, progeny production and sex ratio were assessed. P. spretus exhibited a Holling type II functional response to changing host densities, indicating that parasitism increases with increasing host density until the parasitoid reaches its maximum reproductive capacity. The model suggested that a single P. spretus female could parasitise a maximum of 88 nymphs per day or four nymphs per hour. Increasing the wasp-nymph ratio from 1:10 to 1:80 significantly increased the offspring production more than fivefold from ±5.8 to ±35.6; further increasing the host densities (above 80 nymphs) did not significantly increase offspring production. Strong mutual interference of foraging P. spretus females occurred only at high parasitoid densities. Parasitoids foraging alone produced an average progeny of 33.4, whereas parasitoids foraging in groups of 16 produced only 2.6. The optimal wasp-nymph ratio for mass-rearing P. spretus is 4:100, given that resources of parasitoids and nymphs are unlimited.     

Hymenopteran parasitoids of diamondback moth (Lepidoptera: Ypeunomutidae) in northern Thailand

Larvae of the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Ypeunomutidae), cause severe economic damage to cabbage, Brassica oleracea L. variety capitata (Brassicaceae) and related vegetables in Thailand. Overuse of broad-spectrum insecticides for diamondback moth control is a serious problem and has obscured the contributions of indigenous parasitoids. Our objectives were to identify indigenous diamondback moth parasitoids in northern Thailand and to assess their potential for natural control. Six parasitoid species were reared from diamondback moth larvae and pupae collected in 1990 and in 2003-2004. These included the larval parasitoid Cotesia plutellae Kurdjumov (Braconidae), a larval-pupal parasitoid Macromalon orientale Kerrich (Ichneumonidae), and pupal parasitoids Diadromus collaris Gravenhorst (Ichneumonidae) and Brachymeria excarinata Gahan (Chalcididae). Single specimens of Isotima sp. Forster (Ichneumonidae) and Brachymeria lasus Walker (Chalcididae) also were reared from diamondback moth hosts. C. plutellae was the dominant larval parasitoid and was often reared from host larvae collected from fields sprayed regularly with insecticides; parasitism ranged from 14 to 78%. Average parasitism by M. orientale was only 0.5-6%. Parasitism of host pupae by D. collaris ranged from 9 to 31%, whereas B. excarinata pupal parasitism ranged from 9 to 25%. An integrated pest management (IPM) protocol using simple presence-absence sampling for lepidopterous larvae and the exclusive use of Bacillus thuringiensis (Bt) or neem resulted in the highest yields of undamaged cabbage compared with a control or weekly sprays of cypermethrin (local farmer practice). IPM programs focused on conservation of local diamondback moth parasitoids and on greater implementation of biological control will help alleviate growing public concerns regarding the effects of pesticides on vegetable growers and consumers.     

Chinese species of the genus Prochiloneurus Silvestri with description of a new species(Hymenoptera: Encyrtidae)

Four species of the genus Prochiloneurus Silvestri, belonging to the family Encyrtidae of Hymenoptera, are reported from China. Among them, P. stenopterus sp. nov., which is reared as the hyperparasitoid of Phenacoccus solenopsis Tinsley(Hemiptera: Pseudococcidae), an invasive mealybug to China, is reported as new to science. A key of the genus is provided for the recognition of the females of Chinese species. Notes on the parasitoid and hyperparasitoid of the mealybug Phenacoccus solenopsis are provided.     

Effect of continuous rearing on courtship acoustics of five braconid parasitoids,candidates for augmentative biological control of <Emphasis Type="Italic">Anastrepha</Emphasis> species

The courtship acoustics of five species of parasitoid wasps (Hymenoptera: Braconidae), potential candidates for augmentative biological control of Anastrepha (Schiner) species (Diptera: Tephritidae), were compared between recently colonized individuals and those continuously reared 70–148 generations. During courtship, males of these parasitoid species fan their wings and produce a series of low amplitude pulses. The first series of 15 or more continuous courtship pulses was used to measure the pulse duration, frequency, and interpulse interval (IPI) from the beginning, middle, and end of the pulse series. Each parameter was compared between young and old colonies, and among species. Several differences in courtship acoustics were detected in colonies that had been continuously reared. The pulse duration at the end of the pulse series was longer in old colonies for Doryctobracon crawfordi (Viereck) (Hymenoptera: Braconidae), but shorter for old colonies of Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae). The IPI of the middle pulse was shorter in old colonies of Opius hirtus (Fischer) (Hymenoptera: Braconidae), and was also shorter at the last pulse for old colonies of both Utetes anastrephae (Viereck) (Hymenoptera: Braconidae) and D. longicaudata. The duration of the middle pulse distinguished the three native species, and separated the two introduced species from each other. We discuss our findings in light of their biological and applied implications, particularly those dealing with quality control of mass-reared parasitoids.     

Parasitoid Wasps in Flower Heads of Asteraceae in the Brazilian Cerrado: Taxonomical Composition and Determinants of Diversity

This study provides the first survey of the parasitoid fauna reared in flower heads of Asteraceae in the Brazilian cerrado. We investigated the relative importance of herbivore richness and plant species commonness to differences in parasitoid species richness among the plant species. A total of 15,372 specimens from 192 morphospecies belonging to 103 genera of Hymenoptera were reared from the flower heads of 74 Asteraceae species. Chalcidoidea and Ichneumonoidea were the most common superfamilies, with Eulophidae and Braconidae as the main families of parasitoid wasps. Singletons and doubletons accounted for 45% of total parasitoid species richness. The number of parasitoid species per plant species ranged from 1 to 67, and the variation in parasitoid species richness among plants was mainly explained by the number of sites in which the plants were recorded. This study shows that there is a highly diversified fauna of Hymenoptera parasitoids associated with flower heads of Asteraceae in the Brazilian cerrado. Our findings suggest that the accumulation of parasitoid species on plants is mainly determined by the regional commonness of plant species rather than the number of herbivore species associated with the plants.     

Biological control of Lygus lineolaris by Peristenus spp. in strawberry

Peristenus digoneutis Loan (Hymenoptera: Braconidae) was introduced to the US for biological control of the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois) (Hemiptera: Miridae), and has since spread through much of the northeast. The purpose of this study was to determine if P. digoneutis and a native congener, Peristenus pallipes (Curtis), parasitize L. lineolaris in strawberry (where it is a key pest), and what factors relate to parasitism levels. During 1997–1999 we monitored parasitism on 17 strawberry farms in 14 counties in eastern and western New York State. We found that in eastern NY (where P. digoneutis has been established since the early 1990s), overall mean parasitism was 19.7% (ranging from 0 to 70%), mostly by P. digoneutis. Mean parasitism was significantly lower (12.3%, ranging from 0 to 58%) in western NY (where P. digoneutis was first recorded in 1999), and was mostly by P. pallipes. P. pallipes parasitism was significantly lower in eastern than western NY, suggesting the potential for competitive interaction with P. digoneutis. The insecticide regime of a farm was an important factor influencing parasitism rate, which was 5- to 6.5-fold higher on organic or casually sprayed farms than on intensely treated farms, though pest density under these three regimes was not significantly different. L. lineolaris density, and parasitism rate in nearby alfalfa and abandoned fields were also significant factors for parasitism in strawberry.     

Does rearing an aphid parasitoid on one host affect its ability to parasitize another species?

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Preliminary inventory of parasitoids associated with fruit flies in mangoes,guavas, cashew pepper and wild fruit crops in Benin

Fruit flies are pests of great economic importance due to their quarantine pest status and losses recorded in West Africa. An inventory of parasitoids associated with fruit flies in mangoes, guavas, cashew, pepper and major wild fruit crops was carried out in northern-central Benin in 2005, 2006, and 2008. Tephritid parasitoids reared from field-collected fruits belonged to three families: Braconidae (97.2%), Eulophidae (1.6%) and Pteromalidae (1.2%). Fopius caudatus (Szépligeti) accounted for 73.8% of all the parasitoids and therefore was the most abundant and widely distributed parasitoid. The parasitism rate was 7.7%, with the highest recorded in wild fruit crop habitat. Ceratitis cosyra (Walker) (77%) was the fly host most commonly reared from fruits that produced F. caudatus. The recently introduced pest Bactrocera invadens Drew Tsuruta and White was rarely parasitized and only by Pachycrepoideus vindemmiae (Rondani) (Hymenoptera: Pteromalidae) at this time. This is the first report of the inventory of one native parasitoid species from B. invadens in Africa, especially in West Africa.     

PERMANENT GENETIC RESOURCES: Polymorphic microsatellite loci for Diachasma alloeum (Hymenoptera: Braconidae)

Here, we report the isolation of 21 novel primers for amplification of microsatellite loci in Diachasma alloeum (Hymenoptera: Braconidae). Diachasma alloeum is a larval parasitoid of the apple maggot fly (Rhagoletis pomonella), which is an economically significant agricultural pest species and a textbook example of sympatric speciation via host-plant shifting. These microsatellite markers will prove useful both for assessing genetic relationships between different host-associated populations of D. alloeum, as well as for future R. pomonella biological control programmes. We also report the cross-species amplification of several loci for Diachasmimorpha mellea and Diachasma ferrugineum, parasitoids of R. pomonella and R. cingulata, respectively.     

Field collection of egg parasitoids of Pentatomidae and Scutelleridae in Northwest Italy and their efficacy in parasitizing Halyomorpha halys under laboratory conditions

The invasion of Halyomorpha halys (Stål) (Hemiptera: Pentatomidae) has caused severe economic damage in crops in North America and Europe, motivating research to identify its natural enemies, both in native and invaded areas. In its Asian native range, the main natural enemies are egg parasitoids, among which the most effective are Trissolcus japonicus (Ashmead) and Trissolcus mitsukurii (Ashmead) (Hymenoptera: Scelionidae) in China and Japan, respectively. In Europe, biology, host range, and impact of most native scelionid species are not well‐known. The present study aimed to investigate (1) presence and abundance of scelionid species that parasitize native Pentatomidae and Scutelleridae eggs in Northwest Italy, and (2) their ability to develop on H. halys eggs. During 4‐year field surveys, egg masses were collected and reared until bug nymph or adult parasitoid emergence. Then, the obtained scelionid females were tested for their ability to parasitize H. halys eggs in laboratory no‐choice experiments. Egg masses of all collected bug species were parasitized, and Telenomus spp. (Hymenoptera: Scelionidae), Trissolcus belenus (Walker), and Anastatus bifasciatus (Geoffroy) (Hymenoptera: Eupelmidae) were the most common parasitoids. In the laboratory, Trissolcus kozlovi Rjachovskij was the only species to significantly produce offspring from fresh H. halys eggs, whereas all tested Trissolcus species significantly induced host egg abortion (non‐reproductive effects). This study provides knowledge of the parasitoid species associated with native bugs, and represents a starting point to investigate the intricate interactions between native and exotic parasitoids recently found in northern Italy. These egg parasitoids could potentially be effective biocontrol agents of H. halys.     

Taxonomic Composition of Hymenopteran Parasitoid Assemblages from Agromyzid Leaf-miners Sampled in Central Argentina

This paper deals with the taxonomic composition of parasitoid assemblages reared from agromyzid leaf-miners of 28 species collected in Cordoba, Central Argentina. The relative representation of each parasitic family was estimated, taking into consideration their species richness and abundance. Sample size affected the total species richness in each complex, and also that of Eulophidae and Pteromalidae, indicating that not only size but also taxonomic structure of parasitic assemblages are influenced by sampling effort. 3 superfamilies and 5 families of Hymenoptera Parasitica were represented, with Eulophidae (Chalcidoidea) specifically and numerically dominant both in the total community of parasitoids and in the parasitic assemblages of individual hosts. Chrysonotomyia, Chrysocharis (Eulophidae), Halticoptera (Pteromalidae) and Phaedrotoma (Braconidae) were the most relevant genera in terms of number of species and number of specimens reared. The parasitoids obtained from samples taken in agroecosystems differed from the global spectrum of taxa mainly by showing a numerical dominance of Braconidae, despite a noticeable specific impoverishment of this family.     

Ecological and morphological characteristics of endoparasitoids on Elcysma westwoodii (Vollenhoven) (Lepidoptera: Zygaenidae)

Six species of insect endoparasitoids were identified from Elcysma westwoodii, which is the most damaging lepidopteran pest of Prunus yedoensis. From Hymenoptera, two species were identified: a species in Braconidae and Charops striatus in Ichneumonidae. From Diptera, there were four species in Tachinidae: Compsilura concinnata, Exorista sp., Pales sp. and Tachinidae spp. The parasitic ratio was 4.86% (45 of 926 larvae). The hymenopterans were parasitic on 31 individuals of E. westwoodii (68.9%) and the dipterans were parasitic on 14 individuals (31.1%). It was found that parasitoids from the larvae of E. westwoodii were all either endoparasitoids or larval parasitoids. However, Exorista sp. of Tachinidae was found to be either a larval parasitoid or larval-pupal parasitoid. Additionally, all the identified parasitoids were solitary parasitoids, as only one parasite occurred in a larva of E. westwoodii. Because the larva of E. westwoodii eats and molts after it is parasitized, all the parasitoids were identified as koinobionts. There were no big differences in morphological characteristics and life histories between C. striatus and C. concinnata. However, for Exorista sp. and Pales sp., males took 3–5 days longer to emerge from their pupae and had remarkably longer body lengths than females.     

A survey of hymenopteran parasitoids of forest macrolepidoptera in the central Appalachians

In 1995 and 1996, we conducted a study of the hymenopteran parasitoids of macrolepidopteran larvae in the George Washington National Forest (GWNF), Augusta County, Virginia, and the Monongahela National Forest (MNF), Pocahontas County, West Virginia. Macrolepidopteran larvae were collected from canopy foliage and from under canvas bands placed around tree boles. A total of 115 macrolepidopteran species and 5,235 individual larvae were reared. Forty-two percent (2,221) of the larvae were gypsy moth, Lymantria dispar (L.) (Lymantriidae). A total of 43 primary and secondary (hyperparasitoid) hymenopteran parasitoid species were reared from 46 macrolepidopteran species. Hymenopteran families represented included Ichneumonidae (23 species), Braconidae (19), Eulophidae (6), Perilampidae (1), and Trigonalidae (1). We reared 41 and 28 parasitoid species from the GWNF and the MNF, respectively, with 19 species reared from both forests. Many parasitoid species were collected infrequently, suggesting that they are relatively rare on the sampled hosts. The introduced species Cotesia melanoscela (Ratzeburg) (Braconidae), and Euplectrus bicolor (Swederus) (Eulophidae) were among the most commonly reared parasitoids, the latter reared from native hosts. The four most commonly reared native parasitoids were Meteorus hyphantriae, Riley (Braconidae), Microplitis near hyphantriae (Ashmead) (Braconidae), Aleiodes preclarus Marsh & Shaw, and Euplectrus maculiventris (Westwood) (Eulophidae). A total of 53 new hymenopteran parasitoid-macrolepidopteran host records were documented. Results from this study will be used to evaluate long-term treatment effects of regional applications of Bacillus thuringiensis kurstaki, and the gypsy moth fungus Entomophaga maimaiga Humber, Shimazu & Soper on hymenopteran parasitoids of macrolepidopteran larvae.     

Systematic mass rearing and release ofMicroctonus hyperodae (Hym.: Braconidae,Euphorinae), a parasitoid of the argentine stem weevilListronotus bonariensis (Col.: Curculionidae) and records of its establishment in New Zealand

The method whereby equal numbers of seven ecotypes of the parasitoidMicroctonus hyperodae Loan (Hymenoptera: Braconidae, Euphorinae) were reared and released is described along with the reasons for doing so. This was achieved by variably intense rearing effort depending on the number of founder females in that particular ecotype. The parasitoid was released in three regions of New Zealand as a control agent of theListronotus bonariensis Kuschel (Col.: Curculionidae), a severe pest of New Zealand pastures. It was later recovered from all three regions.