The Effects of Aphid Traits on Parasitoid Host Use and Specialist Advantage

Specialization is a central concept in ecology and one of the fundamental properties of parasitoids. Highly specialized parasitoids tend to be more efficient in host-use compared to generalized parasitoids, presumably owing to the trade-off between host range and hostuse efficiency. However, it remains unknown how parasitoid host specificity and host-use depends on host traits related to susceptibility to parasitoid attack. To address this question, we used data from a 13-year survey of interactions among 142 aphid and 75 parasitoid species in nine European countries. We found that only aphid traits related to local resource characteristics seem to influence the trade-off between host-range and efficiency: more specialized parasitoids had an apparent advantage (higher abundance on shared hosts) on aphids with sparse colonies, ant-attendance and without concealment, and this was more evident when host relatedness was included in calculation of parasitoid specificity. More traits influenced average assemblage specialization, which was highest in aphids that are monophagous, monoecious, large, highly mobile (easily drop from a plant), without myrmecophily, habitat specialists, inhabit non-agricultural habitats and have sparse colonies. Differences in aphid wax production did not influence parasitoid host specificity and host-use. Our study is the first step in identifying host traits important for aphid parasitoid host specificity and host-use and improves our understanding of bottom-up effects of aphid traits on aphid-parasitoid food web structure

Aphids and parasitolds on willows and poplars in southeastern Europe (Hornoptera : Aphidoidea; Hymenoptera : Braconidae, Aphidiinae)

Aphid and aphid parasitoid associations on willows (Salix spp.) and poplars (Populus spp.) in southeastern Europe are reviewed. In total 13 aphid parasitoid species were reared from aphids on these plants. The specific parasitoid complex of Acyrthosiphon cf. malvae (Mosley) on Salix retusa and the aphids and parasitoids composition on willows and poplars are discussed. The most frequently sampled and the most abundant parasitoid species in poplar aphid-aphid parasitoid associations was Adialytus salicaphis Fitch. Furthermore, Lysiphlebus confusus Tremblay & Eady was the most abundant species collected on willow-feeding aphids, whereas A. salicaphis, Euaphidius cingulatus (Ruthe) and Binodoxys heraclei (Haliday) were the most frequently sampled parasitoid species on willows. Trophic connections between aphids and parasitoids associated with willow agroecosystems are also discussed. A key for the identification of aphid parasitoids associated with aphids on willows and poplars in southeastern Europe is provided

Insecticidal effect of NeemAzal against three stored-product beetle species on rye and oats

The insecticidal effect of the azadirachtin-based insecticide, NeemAzal, was examined against adults of Rhyzopertha dominica (F.), Sitophilus oryzae (L.), and Tribolium confusum Jacquelin du Val in rye, whole oats, and peeled oats. The insecticide was applied at three dose rates, which were equivalent to 50, 100, and 200 ppm of azadirachtin A. Adults of the above-mentioned species were exposed to the treated grains at 25 degrees C and 65% RH, and mortality was assessed after 24 h, 48 h, 7 d, and 14 d of exposure. Then, all adults were removed, and the treated substrate remained at the same conditions for an additional 45 d. After this interval, the grains were checked for progeny production. In all species and commodities tested, mortality increased with the increase of dose and exposure interval, except for T. confusum on whole and peeled oats. For R. dominica, NeemAzal was more effective on oats than on rye and peeled oats. In contrast, at rates >= 100 ppm, azadirachtin was equally effective against S. oryzae on whole rye and oats, where mortality was 100% after 7 and 14 d of exposure, respectively. NeemAzal was not very effective against T confusum where adult mortality was low, even after 14 d of exposure at the highest rate. For all species, significantly less progeny were recorded in the treated grains than in the untreated grains, with the exception of T confusum on oats where offspring was significantly reduced only at the highest rate

Toxicity Of Some Terpenoids Of Essential Oils Of Xylopia Aethiopica From Cameroon Against Sitophilus Zeamais Motschulsky

The acute toxicity of essential oils from the whole fruit (EF) or from the fibres of the fruit (FF) of the local aromatic plants Xylopiα αethiopicα Dunal (Annonaceae) collected in north Cameroon was evaluated on Sitophilus zeαmαis adults. A concentration of 1 ml of essential oil per 100 g of maize seeds was tested to determine weevil mortality after 24 h of exposure. Under these conditions, the essential oil derived from both EF and FF of X. αethiopicα led to 100% mortality. In a second step, proportions of active compounds present in the oil of both EF and FF of X. αethiopicα were quantified. The toxicity of the four main compounds was tested against S. zeαmαis: α-pinene, β-pinene, -3-carene and terpinen-4-ol according to their proportion in the essential oil of the concerned plant part. β-pinene and terpinen-4-ol were responsible for 50% of the mortality at the proportion found in EF and FF essential oils respectively. When mixed, a synergic effect of the compounds was observed that restored the mortality percentage observed for the crude oil. It appears that X. αethiopicα essential oil could be a potential source of natural and low-cost insecticide to control storage pests

Singing on the wings! Male wing fanning performances affect female willingness to copulate in the aphid parasitoid Lysiphlebus testaceipes (Hymenoptera: Braconidae: Aphidiinae)

Lysiphlebustestaceipes(Hymenoptera:Braconidae:Aphidiinae)isageneralist endoparasitoid attacking more than 100aphid species. In L. testaceipes, wing fanning is a main male courtship display evoked by a female-borne sex pheromone. However, no information is available on the characteristics and behavioral role of male fanning during courtship in this parasitoid. Here, the courtship behavior of a wild strain of L. testaceipes wasquantifiedandthemalewingfanningperformanceswereanalyzedthroughhigh-speed video recordings and examined in relation to mating success. Courtship sequence of wild L.testaceipesdidnotsubstantiallydifferfromthatpreviouslyreportedforotherpopulations mass reared on aphids. We observed that the male courtship duration did not affect mating success.However,videoanalysisrevealedthatthemalesproducinghigh-frequencyfanning signals achieved higher mating success over those that display low-frequency fanning. Wing fanning before successful and unsuccessful courtship differed in amplitude of wing movements and alignment toward the mate, highlighting that frontal courtship positively influencethefemalematingdecisions.Thisstudyincreasesknowledgeonsexualbehavior inakeyparasitoidofaphids,highlightingtheimportanceofwingfanningamongtherange ofsensorymodalitiesusedinthesexualcommunicationofL.testaceipes.Fromapractical point of view, this information is useful in L. testaceipes-based biocontrol strategies, since it can help to establish parameters for quality checking of mass-reared wasps over time

Insecticidal efficacy of diatomaceous earth against Sitophilus oryzae (L.) (Coleoptera : Curculionidae) and Tribolium confusum du Val (Coleoptera : Tenebrionidae) on stored wheat: influence of dose rate, temperature and exposure interval

Laboratory experiments were conducted in order to assess the insecticidal effect of a diatomaceous earth formulation (Silicosec(R), Biofa GmbH, Germany) against Sitophilus oryzae and Tribolium confusum on stored wheat. Adults of the two species were exposed on wheat treated with diatomaceous earth at four dose rates: 0.25, 0.5, 1 and 1.5 g/kg of wheat, respectively. For each dose rate, the treated wheat was placed at 22degreesC, 25degreesC, 27degreesC, 30degreesC and 32degreesC. Dead adults were counted after 24 and 48 h, 7 and 14 d of exposure. After the 14-d interval, the live adults were removed and placed for 7 d in untreated wheat (in the case of S. oryzae) or untreated flour (in the case of T confusum), and the production of F-1 was recorded. For both species, dose rate, temperature and exposure interval significantly affected mortality (P<0.001). Mortality was higher at longer exposure intervals. The efficacy of SilicoSec against S. oryzae increased with temperature, but for T confusum mortality was lower at 32degreesC, compared to 30degreesC, for 24 and 48 h exposure intervals. Tribolium confusum proved less susceptible to SilicoSec than S. oryzae. In general, the rates of 1 and 1.5g/kg of wheat provided a satisfactory level of protection against the two species examined. For S. oryzae, F-1 emerged only at 22degreesC, in wheat treated with 0.25 or 0.5 g/kg. However, for T confusum, F-1 were recorded at 22degreesC for 0.5 g/kg and at 22degreesC, 25degreesC, 27degreesC and 30degreesC for 0.25 g/kg. (C) 2004 Elsevier Ltd. All rights reserved