Andrew Polaszek

Do differences in food web structure between organic and conventional farms affect the ecosystem service of pest control

While many studies have demonstrated that organic farms support greater levels of biodiversity, it is not known whether this translates into better provision of ecosystem services. Here we use a food-web approach to analyse the community structure and function at the whole-farm scale. Quantitative food webs from 10 replicate pairs of organic and conventional farms showed that organic farms have significantly more species at three trophic levels (plant, herbivore and parasitoid) and significantly different network structure. Herbivores on organic farms were attacked by more parasitoid species on organic farms than on conventional farms. However, differences in network structure did not translate into differences in robustness to simulated species loss and we found no difference in percentage parasitism (natural pest control) across a variety of host species. Furthermore, a manipulative field experiment demonstrated that the higher species richness of parasitoids on the organic farms did not increase mortality of a novel herbivore used to bioassay ecosystem service. The explanation for these differences is likely to include inherent differences in management strategies and landscape structure between the two farming systems.

Encarsia parasitoids of Bemisia tabaci (Hymenoptera: Aphelinidae, Homoptera: Aleyrodidae): a preliminary guide to identification.

A key is provided for the recognition of previously described Encarsia species which are known to attack the tobacco whitefly, Bemisia tabaci (Genna-dius). 28 nominal species are included, of which type material has been examined for 22. Eight new synonymies are proposed: Encarsia aleyrodis (Mercet) and E. partenopea Masi are both synonymized with E. inaron (Walker); E. bemi-siae (Ishii) is synonymized with E. transvena (Timberlake); E. citri (Ishii) is synonymized with E. strenua (Silvestri), E. angelica Howard and E. deserti Rivnay & Gerling are both synonymized with E. luteola Howard; E. perspicuipennis (Girault) is synonymized with E. quaintancei (Howard); E. tabacivora Viggiani is synonymized with E. pergandiella Howard. E. hispida De Santis is removed from synonymy with E. meritoria Gahan. A lectotype is designated for E. porteri (Mercet). The known distributions and alternative hosts of Encarsia species attacking B. tabaci are provided as well as references to biology and notes on their use in biological control.

A revision of the Chinese species of Encarsia Förster (Hymenoptera: Aphelinidae): parasitoids of whiteflies, scale insects and aphids (Hemiptera: Aleyrodidae, Diaspididae, Aphidoidea)

The species of Encarsia Forster (Hymenoptera: Aphelinidae) known from China are revised. This study is based largely on newly-collected material from Fujian and Guangdong provinces in mainland China, and from the island of Taiwan. A total of 76 species are treated, including 29 new species, one new combination and 16 new records for China. All species are fully described or diagnosed, and illustrated. Three new specific synonymies are proposed and two lectotypes are designated. Four species are described from males only, three belonging to the perflava-group (ancistrocera, echinocera, viggianii), having modified antennae, and one (magnivena) in the strenua-group having very unusual fore wings. A key to the Chinese species of Encarsia, based largely on females, is provided.

Utilisation of wild gramineous plants for management of cereal stemborers in Africa

Field trials in Kenya demonstrated that the forage grass, Sorghum vulgare sudanense (Sudan grass) attracted greater oviposition by stemborers than cultivated maize, resulting in significant increase in maize yield. On the other hand, the non-host forage plant, Melinis minutiflora (molasses grass), when inter-cropped with maize, repelled gravid stemborer females from ovipositing on maize, resulting in significant reduction in stemborer infestation. Using these trap- and repellent gramineous plants, a novel pest management approach based on a ’push-pull’ or stimulo-deterrent diversionary strategy is being developed where stemborers are repelled from the food crop and are simultaneously attracted to a discard or trap crop. The plant composition and permanence of habitat surrounding maize fields also influence the abundance of natural enemies that invade agroecosy stems once a pest population is present. It may be advantageous to promote the growth of native Gramineae and other wild plants which minimise, or even suppress, population growth of pests during non-cropping seasons, but still provide a suitable habitat for natural enemies.RésuméDes essais de terrain au Kenya ont prouvé que l’herbe fourragère, Sorghum vulgare sudanense (herbe du Soudan) attirait plus de foreurs de tiges pour la ponte que le maïs cultivé, entraînant une augmentation significative de la récolte de maïs. D’autre part, la plante fourragère non-hôte, Melinis minutiflora (herbe mélasse), une fois en culture mixte avec le maïs, empêchait des foreurs de tiges femelles gravides de pondre sur le maïs, ce qui réduisait significativement l’infestation du maïs par les foreurs de tiges. L’utilisation de ces plantes graminées pièges et répulsives, une approche nouvelle du contrôle des ravageurs basée sur une strategie diversionniste de ’pousse-tire’ ou de ’stimulation-déterrence’ est en train d’être dévelopée là où les foreurs de tiges sont repoussés loin des cultures de consommation et sont simultanément attirés vers une plante rebut ou piège. La composition botanique et la permanence de l’habitat entourant les champs de maïs influencent aussi l’abondance des ennemis naturels qui envahissent des agroécosystèmes dès qu’une population de ravageurs est présente. Il serait avantageux de promouvoir la croissance des graminées indigènes et d’autres plantes sauvages qui minimisent ou même inhibent la croissance des populations des ravageurs durant les saisons de jachère, tout en assurant un habitat favorable pour les ennemis naturels.

Egg parasitism in Aphelinidae (Hymenoptera: Chalcidoidea) with special reference to Centrodora and Encarsia species

Aphelinidae are all insect parasitoids, and most species are associated with nymphal stages of Homoptera: Sternorrhyncha, either as primary parasitoids or hyperparasitoids. The occurrence of egg parasitism in aphelinids has been recorded in eight of the 38 valid genera and these records are reviewed; it is particularly common in the genus Centrodora , which is shown to be the most polyphagous in the family. One species, C. darwini (Girault), is given special attention because of its occurrence in three recent surveys for biological control agents of crop pests. It is briefly redescribed, diagnosed, and shown to be the most polyphagous aphelinid known. A checklist of Australian Centrodora spp. is given, including the new combination Centrodora grotiusi (Girault) comb. n . The purported evidence for the classification of certain Encarsia spp. associated with eggs of Lepidoptera as ‘heterotrophic parasitoids’ is re-examined and dismissed.

Morphological and molecular taxonomic analysis of the Encarsia meritoria species-complex (Hymenoptera, Aphelinidae), parasitoids of whiteflies (Hemiptera, Aleyrodidae) of economic importance

Five closely related species of Encarsia, belonging to the luteola species‐group, are analysed taxonomically using morphological and molecular techniques. Four of these belong to the meritoria‐complex, and all species have a complicated taxonomic history of repeated misidentification and confusion. Morphological analysis is focused on morphometric characters of the female antennae using principal component and canonical discriminant analyses. DNA sequence data for the D2 region of 28S nuclear ribosomal genes were obtained for 13 populations of the luteola‐group, with a further seven population sequences being obtained from GenBank. The combination of morphological and molecular study enables us to resolve the complex to a large extent, and to correct the previous confusion surrounding this group of species. Two species —E. californica and E. dispersa— are described as new. A proposal to place E. brasiliensis (Hempel) in synonymy with E. hispida DeSantis (the more recently described taxon) is presented. A lectotype is designated for E. haitiensis Dozier. Diagnoses or descriptions, and illustrations, of all included species are provided to facilitate the identification of females belonging to this complex. All known data concerning hosts and geographical distribution are presented.

Morphometric and molecular analysis of the Encarsia inaron species-group (Hymenoptera: Aphelinidae), parasitoids of whiteflies (Hemiptera: Aleyrodidae)

Several series of host-reared specimens of an Encarsia species, initially thought to be the cosmopolitan Encarsia inaron (Walker), were collected in the Azores Islands (Portugal). Subsequent morphometric analysis supported the presence of two species: E. inaron and a new species, described herein as Encarsia estrellae Manzari & Polaszek sp. n. Encarsia estrellae was reared from Aleyrodes singularis Danzig, A. ?singularis, and Bemisia sp. afer-group on several host plants. In addition, the D2 region of the 28S rDNA gene was sequenced in eight individuals belonging to these species, as well as single representatives of two closely related and one distantly related species. Phylogenetic analysis of these DNA sequences, together with 23 additional Encarsia sequences retrieved from the European Molecular Biology Laboratory (EMBL) and GenBank databases, further supported the specific status of E. estrellae, and the placement of E. dichroa (Mercet) in the E. inaron species-group. Additionally, E. inaron is redescribed and some taxonomic problems in the E. inaron species-group are discussed.

The effects of two species of hymenopterous parasitoid on the reproductive system of the pea aphid, Acyrthosiphon pisum

Two cultures of first instar pea aphids, Acyrthosiphon pisum (Harris) (Homoptera: Aphididae), were subjected to parasitization by Ephedrus plagiator (Nees) and Aphidius ervi Haliday (Hymenoptera: Braconidae) respectively, and a third culture, of fourth instar pea aphids, was subjected to parasitization by E. plagiator. Significant parasitogenic effects on the reproductive system occurred within 24 h of exposure to parasitoids in the form of reductions in both embryo number and the size of the largest embryo, and degenerative changes in the embryos themselves. No evidence was found of direct feeding by the larvae on the hosts tissues, until just before larval pupation. The largest embryos of some fourth instar aphids escaped the effects of parasitization probably because they had developed a resistant cuticle by the time of oviposition by the parasitoid. Results suggested that embryonic degeneration was an indirect effect of parasitization due to starvation, interference with the aphids hormone levels, or both.

Taxonomy of the Telenomus busseolae species-complex (Hymenoptera: Scelionidae) egg parasitoids of cereal stem borers (Lepidoptera: Noctuidae, Pyralidae)

Morphological studies of different populations of what was previously considered to be a single species, Telenomus busseolae Gahan, revealed a complex of three distinct species. A total of four species were found to belong to this complex, all of which are egg parasitoids of stem boring Lepidoptera belonging to the closely related noctuid genera Busseola and Sesamia , with a single record from the pyralid stem borer genus Coniesta . All these host genera are of major economic importance as cereal pests. Two of the four Telenomus spp. are fully sympatric with regard to distribution, hosts and oviposition period. Two species, Telenomus isis and Telenomus nagarajae , are described as new.

Molecular and morphological diagnoses of five species of Trichogramma: biological control agents of Chrysodeixis chalcites (Lepidoptera: Noctuidae) and Tuta absoluta (Lepidoptera: Gelechiidae) in the Canary Islands

Prospecting for potential natural enemies of the invasive lepidopteran tomato pest Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) and the banana pest Chrysodeixis chalcites (Esper) (Lepidoptera: Noctuidae) on the Canary Islands archipelago, where no Trichogramma species were previously recorded, has led to the discovery of five distinct species. T. achaeae Nagaraja & Nagarkatti, T. bourarachae Pintureau & Babault, T. euproctidis (Girault) and T. evanescens Westwood are relatively widespread species. The fifth is close to T. brassicae Bezdenko, but differs sufficiently in the sequence of the ITS2 region of ribosomal RNA to warrant further investigation as a species probably new to science. Each species is treated in detail in order to facilitate identification in future using molecular and/or morphological characters, or a combination of both. All species are newly recorded for the Canary Islands, and the distribution of each within the islands and elsewhere is provided. Known host records are given within the Canary Islands and elsewhere. The most common species found, T. achaeae, is already being used in biological control programmes against T. absoluta in mainland Spain and field trials are ongoing to evaluate its effectiveness as a biological control agent of C. chalcites in banana crops.