Luigi Iodice

Host-locating response by the aphid parasitoid Aphidius ervi to tomato plant volatiles

Abstract The blend of volatile compounds emitted by tomato plants (Solanum lycopersicum) infested with the potato aphid (Macrosiphum euphorbiae) has been studied comparatively with undamaged plants and aphids themselves. Aphid-infested plants were significantly more attractive towards Aphidius ervi than undamaged plants and aphids themselves. Oriented response towards host-damaged plant, from which aphids were removed just before running the bioassay, did not differ from that recorded for infested plants. Collection of the volatiles and analysis by gas chromatography revealed only quantitative differences between uninfested and aphid-infested plants. Nine compounds, α-pinene, (Z)-3-hexen-1-ol, α-phellandrene, limonene, (E)-β-ocimene, p-cymene, methyl salicylate, (E)-β-caryophyllene and an unknown compound, were emitted at higher levels from aphid-infested plants than from undamaged control plants, whilst no differences were noted for hexanal, 6-methyl-5-hepten-2-one, and humulene (=α-caryophyllene). Synthetic standards of these compounds were tested in wind tunnel bioassays and all elicited a significant increase in oriented flight and landings on the target by the aphid parasitoid Aphidius ervi. (E)-β-caryophyllene resulted the most attractive towards female wasps. These results corroborate the hypothesis that the volatiles produced by the plant in response to aphid attack derive from both jasmonic and salicylic acid pathways, and are exploited by A. ervi as olfactory cues to locate its hosts.

Electrophysiological and behavioural responses of Aphidius ervi (Hymenoptera: Braconidae) to tomato plant volatiles

Flight responses of the aphid parasitoid Aphidius ervi to tomato volatiles have recently demonstrated that different plant stresses can lead to increases in attractiveness for this parasitoid. For example, infestation of tomato plants by the aphid Macrosiphum euphorbiae results in the overexpression of defensive genes, as well as the release of volatile compounds that attract aphid parasitoids. Here, we determine which of the induced compounds elicit a significant electrophysiological response from parasitoid antennae. Compounds shown to be detected at the antennal level were then tested at a range of doses in a wind tunnel assay. A significant electroantennogram response was demonstrated for three compounds, (8S,9R)-(E)-caryophyllene, methyl salicylate, and (Z)-3-hexen-1-ol, over four concentrations. These compounds proved to be significantly attractive in the wind tunnel at a rate not always proportionally dependent upon the dose. The practical implications of these findings are discussed in the framework of sustainable control for pest aphids in agriculture.

Molecular and chemical mechanisms involved in aphid resistance in cultivated tomato

*An integrated approach has been used to obtain an understanding of the molecular and chemical mechanisms underlying resistance to aphids in cherry-like tomato (Solanum lycopersicum) landraces from the Campania region (southern Italy). The aphid-parasitoid system Macrosiphum euphorbiae-Aphidius ervi was used to describe the levels of resistance against aphids in two tomato accessions (AN5, AN7) exhibiting high yield and quality traits and lacking the tomato Mi gene. *Aphid development and reproduction, flight response by the aphid parasitoid A. ervi, gas chromatography-mass spectrometry headspace analysis of plant volatile organic compounds and transcriptional analysis of aphid responsive genes were performed on selected tomato accessions and on a susceptible commercial variety (M82). *When compared with the cultivated variety, M82, AN5 and AN7 showed a significant reduction of M. euphorbiae fitness, the release of larger amounts of specific volatile organic compounds that are attractive to the aphid parasitoid A. ervi, a constitutively higher level of expression of plant defence genes and differential enhancement of plant indirect resistance induced by aphid feeding. *These results provide new insights on how local selection can offer the possibility of the development of innovative genetic strategies to increase tomato resistance against aphids.

Biology and monitoring of Dryocosmus kuriphilus on Castanea sativa in Southern Italy

1 The cynipid gall wasp Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae) is an invasive wasp in Europe and is one of the major pests of chestnuts worldwide. An investigation of this cynipid was started in Campania, Southern Italy, in 2008, with the aim of providing guidelines for its sustainable control. 2 The number of larvae/gall increased in the second year of colonization relative to the first one but thereafter decreased in the third year of colonization, whereas the volume of the galls after the initial increase in the second year of colonization became stable. Adult emergence generally peaked between the middle of June and July. 3 The only reliable method for assessing the presence of the pest at its earliest stage was through dissecting the buds because oviposition scars on the buds tended to disappear during the winter. 4 Yellow traps were shown to be an effective method for assessing the emergence of cynipid adults and could potentially be used to time chemical applications in those cases in which this control method is feasible. 5 No correlation was recorded between the relative durations of the final stages (pupae, pharate adults and emergence). 6 Possible control strategies for this invasive pest are discussed.

Interactions between Bt-expressing tomato and non-target insects: the aphid Macrosiphum euphorbiae and its natural enemies.

Bacillus thuringiensis Berliner toxins are highly specific in terms of insect pest targeted. For example, Cry3Bb is active against Coleoptera. As a consequence, in the framework of using genetically modified plants expressing different Bt toxins in sustainable agriculture, there is a growing interest about the impact of these crops on the environment and on non-target organisms. The effects of genetically modified Bt-tomato plants expressing the toxin Cry3Bb on the aphid Macrosiphum euphorbiae (Thomas) and its natural enemies, the generalist predator Macrolophus caliginosus Wagner and the endoparasitoid wasp Aphidius ervi Haliday, were assessed under laboratory conditions. No significant differences between performance of M. euphorbiae were observed on genetically modified tomato plants (line UC82Bt) with respect to their near-isogenic control line (line UC82). Immunoassays did not detect Cry3Bb protein in M. euphorbiae developing on Bt-expressing tomato plants. Similarly, no significant differences were found on the longevity and prey consumption of M. caliginosus when fed aphids reared on UC82Bt or on UC82. Moreover, the genetic modification did not affect the attractiveness of uninfested tomato plants toward A. ervi. It is therefore concluded that Cry3Bb-expressing tomato plants did not show any acute adverse effects on the biological parameters of the non-target herbivore M. euphorbiae or its natural enemies, M. caliginosus and A. ervi, under laboratory conditions.

Interactions between tomato volatile organic compounds and aphid behaviour

Abstract In the tritrophic system consisting of tomato, Solanum lycopersicum (L.), the aphid Macrosiphum euphorbiae (Thomas) and its natural enemy, the parasitoid Aphidius ervi (Haliday), it has been shown that the release of volatile organic compounds following aphid attack is responsible for attracting aphid parasitoids in wind tunnel experiments. The main compounds involved in these multitrophic interactions have been characterized and quantified. In this work, the possible activity of such compounds on plant direct defences against the aphid M. euphorbiae was assessed in laboratory tests. The selected compounds were applied to uninfested tomato plants, either by evaporation or contact, and performance of aphids, in terms of plant acceptance, fixing behaviour and aphid development, calculated in standard conditions. The results showed that two compounds, namely methyl salicylate and cis-hex-3-en-1-ol, alter aphid performance. These two compounds have been reported to be those eliciting the best response by A. ervi in terms of flight behavior (wind tunnel bioassay) and antennal stimulation (EAG bioassay).

Foraging activity of bumblebees (Bombus terrestris L.) on Bt-expressing eggplants

A greenhouse experiment was setup to study foraging behavior of the bumblebee Bombus terrestris L. on Cry3Bb-expressing genetically modified (GM) eggplants and their near-isogenic control. Commonly, more bumblebees visited GM eggplants compared to near-isogenic control, but this difference was only marginally significant. The mean length of feeding bouts was similar on the two treatments. Neither the number of flowers produced nor their size could explain bumblebees’ tendency to prefer GM eggplants. Volatile compounds were extracted from five plants per genotype and separated using gas chromatography. Thirteen compounds were identified and five of them appeared significantly more abundant in GM eggplants. Six of the identified compounds [(+)-limonene, Z-jasmone, p-cymene, α-pinene, methyl-salicilate, and (−)-limonene] were tested in electrophysiological bioassays with antennas detached from young bumblebees, and a response was recorded in all six cases. Experimental results indicate that pollination activity of bumblebees is compatible with this GM eggplant event as a food source and that chemical cues may have an important role in plant identification. The implications for environmental risk assessment of GM plants are discussed.

Effects of cold storage on Thripobius javae (=T. semiluteus) (Hymenoptera: Eulophidae)

Abstract Thripobius javae (Girault) was introduced in 1995 from Israel into Italy to control the greenhouse thrips, Heliothrips haemorrhoidalis (Bouché). Following introduction, successive augmentative releases of this parasitoid gave unsatisfactory and contradictory results, mainly due to the difficulty in synchronising its availability in sufficient number at the time of release. Efficient storage of this biological control agent could improve its current production and use. The effects of different sets of storage techniques at a single temperature and with a combination of different temperatures and instars on several fitness traits (residual developmental time to adult emergence after the end of storage, pupal mortality, longevity with and without hosts and progeny of emerged adults) were evaluated in order to determine the best conditions for storing the parasitoid. For the pupal stage, increasing storage up to 14 days, at 10°C, gave only a moderate reduction (33%) of a modified composite quality index of its fitness. In contrast, when adults were stored for more than 10 days, at 15°C, residual longevity and progeny were reduced significantly. A combination of two temperatures (10 and 15°C) for pupal storage and a combination of pupal (10°C) and adult (15°C) storage had detrimental effects on parasitoid fitness. Temperatures of storage lower than 15 and 10°C had detrimental effects on adults and pupae, respectively.