Stefano Colazza

Insect oviposition induces volatile emission in herbaceous plants that attracts egg parasitoids

SUMMARY The egg parasitoid Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae) responded to synomones emitted by leguminous plants induced by feeding and oviposition activity of the bug Nezara viridula (L.) (Heteroptera: Pentatomidae). This was shown by laboratory bioassays using a Y-tube olfactometer. Broad bean leaves (Vicia faba L.) damaged by feeding activity of N. viridula and on which host egg mass had been laid produced synomones that attracted T. basalis. By contrast, undamaged leaves or feeding-damaged leaves without eggs did not attract wasp females. French bean plants (Phaseolus vulgaris L.) also emitted attractive synomones when they were damaged by host feeding and carrying egg masses. Thus, release of feeding- and oviposition-induced synomones does not seem to be plant-specific. Synomone production was shown to be a systemically induced plant physiological response to feeding damage and oviposition. Also, parts of the plant that were left undamaged and did not carry host eggs emitted attractive synomones when other parts of the plant were damaged by feeding and carrying eggs. Furthermore, wasps were not attracted by N. viridula egg masses offered alone or combined with damaged broad bean leaves. Thus, the attractiveness of feeding-damaged leaves carrying eggs is due to induction by feeding and oviposition rather than due to a combined effect of attractive volatiles released from eggs and damaged leaves. The production of synomones was influenced by the age of the host egg mass, because feeding-damaged leaves bearing egg masses attracted the parasitoid until the eggs were ∼72-96 h old but not once the larvae had hatched from the eggs (∼120 h old). These results show that annual plants are able to produce synomones as a consequence of feeding and egg mass oviposition by a sucking insect.

Identification of volatile synomones, induced by Nezara viridula feeding and oviposition on bean spp., that attract the egg parasitoid Trissolcus basalis.

Bean plants (Vicia faba L. and Phaseolus vulgaris L.) damaged by feeding activity of Nezara viridula (L.) (Heteroptera: Pentatomidae), and onto which an egg mass had been laid, produced volatiles that attracted the egg parasitoid Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae). Extracts of volatiles of broad bean and French bean plants induced by adults of N. viridula as a result of their feeding activity, oviposition activity, and feeding and oviposition activity combined were analyzed by gas chromatography–mass spectrometry (GC–MS), and tested in Y-tube olfactometer bioassays as attractants for T. basalis females. In extracts from undamaged leguminous plants, green-leaf volatiles were absent or scarcely detected, and monoterpenes and sesquiterpenes were present at trace levels. No significant differences were detected in the profiles of volatiles of undamaged plants, and undamaged plants on which bugs were allowed only to lay eggs. In contrast, feeding and oviposition by adults of N. viridula induced in both leguminous plants a significant increase in terpenoids such as linalool, (E)-β-caryophyllene, (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene, and (3E)-4,8-dimethyl-1,3,7-nonatriene, which was induced only in French bean plants. Quantitative comparisons revealed increased levels of (E)-β-caryophyllene in extracts from feeding-damaged plants with N. viridula egg masses compared to feeding-damaged plants without egg masses. In Y-tube olfactometer bioassays, T. basalis females were attracted by extracts of both leguminous plants only when N. viridula adults were allowed to feed and oviposit upon them. Fractionation of extracts of volatiles from broad bean plants with N. viridula feeding damage and egg masses yielded two fractions, but only the fraction containing (E)-β-caryophyllene was attractive to the egg parasitoid. These findings indicate that N. viridula feeding and oviposition induce leguminous plants to produce blends of volatiles that are characterized by increased amounts of (E)-β-caryophyllene, and these blends attract female T. basalis. The role of (E)-β-caryophyllene as a potential synomone for T. basalis is discussed.

The Egg Parasitoid Trissolcus basalis uses n-nonadecane, a Cuticular Hydrocarbon from its Stink Bug Host Nezara viridula, to Discriminate Between Female and Male Hosts

Contact kairomones from adult southern green stink bugs, Nezara viridula (L.) (Heteroptera: Pentatomidae) that elicit foraging behavior of the egg parasitoid Trissolcus basalis (Wollaston) were investigated in laboratory experiments. Chemical residues from tarsi and scutella of N. viridula induced foraging by gravid female T. basalis. Residues from body parts of female N. viridula elicited stronger responses than those from the corresponding body parts of males. Deproteinized tarsi still elicited searching responses from wasps, indicating that the kairomone was not proteinaceous. Hexane extracts of host cuticular lipids induced searching responses from T. basalis, with a strong preference for extracts from female hosts. Extracts consisted primarily of linear alkanes from nC19 to nC34, with quantitative and qualitative differences between the sexes. Extracts of female N. viridula contained more nC23, nC24, and nC25 than the corresponding extracts from males, whereas nC19 was detected only in extracts from males. Direct-contact solid phase microextraction (DC-SPME) of N. viridula cuticle and of residues left by adult bugs walking on a glass plate confirmed gender-specific differences in nC19. Trissolcus basalis females responded weakly to a reconstructed blend of the straight-chain hydrocarbons, suggesting that minor components other than linear alkanes must be part of the kairomone. Addition of nC19 to hexane extracts of female N. viridula significantly reduced the wasps’ arrestment responses, similar to wasps’ responses to hexane extracts of male hosts. Overall, our results suggest that a contact kairomone that elicits foraging by T. basalis females is present in the cuticular lipids of N. viridula, and that the presence or absence of nC19 allows T. basalis females to distinguish between residues left by male or female hosts. The ecological significance of these results in the host location behavior of scelionid egg parasitoids is discussed.

A comparative analysis of patch-leaving decision rules in a parasitoid family

The proximate behavioural rules adopted by parasitoid females to manage their foraging time on patches of hosts were studied, under standardized laboratory conditions, in different species (and populations) of the Trichogrammatidae (Hymenoptera) family. Seventeen species/populations were compared and the behavioural mechanisms adopted by the females were identified by means of a Coxs proportional hazards model. On average, females increased their patch-leaving tendency each time a healthy host was attacked and each time a parasitized host was rejected. Strong variation was observed in these patch-leaving mechanisms among the different species. Moreover, the interspecific variation in these two behavioural mechanisms showed a significant positive correlation, and this correlation remained significant when the phylogenetic relationship between the strains was controlled with the use of phylogenetic comparative methods. The adaptive and evolutionary meanings of these results are probably related to the ecological features and distribution patterns of the hosts attacked by the species/populations compared.

Response of Egg Parasitoid Telenomus busseolae to Sex Pheromone of Sesamia nonagrioides

The olfactory cues involved in the host-finding behavior of Telenomus busseolae Gahan, a solitary egg parasitoid of the corn stalk borer, Sesamia nonagrioides (Lefebvre), were studied. The female wasp was attracted to odors from calling virgin females of S. nonagrioides in a Y-tube olfactometer. No response was elicited by noncalling virgin female moths and/or mated female moths. A four-component commercially available sex pheromone of the corn borer was also tested, as were the individual components of the mixture. T. busseolae respond to the whole blend [(Z)-11-hexadecenyl acetate, (Z)-11-hexadecenol, (Z)-11-hexadecenal, and dodecyl acetate in the ratio of 8.5:1:1:2]. Z11–16:OH was the only compound that elicited no significant activity. These results suggest that the sex pheromone released by the host female S. nonagrioides is used by T. busseolae as an indirect cue to locate egg masses of this host.

Chemical and Physical Signals Mediating Conspecific and Heterospecific Aggregation Behavior of First Instar Stink Bugs

We investigated cues that mediate the aggregation behavior of immature pentatomid bugs by using nymphs of six different pentatomid bug species (Nezara viridula, Acrosternum hilare, Chlorochroa ligata, Chlorochroa sayi, Thyanta pallidovirens, and Euschistus conspersus). When first instars of any two species were put together in a Petri dish, they readily formed heterospecific aggregations similar to their natural conspecific aggregations. The chemical profiles of first and second instar nymphs of each species were determined by solvent extraction with pentane, followed by GC–MS analysis. Immature bugs of the different species had some compounds in common, and some that were more species specific. Within a species, there were distinct differences in the profiles of compounds extracted from first and second instars. Bugs did not aggregate around untreated polysulfone beads (1 mm diam) that were glued together in groups approximating bug egg masses, suggesting that tactile cues alone were insufficient to induce aggregation. Furthermore, when tested over a range of doses, groups of polysulfone beads treated with crude whole-body extracts of bugs did not induce or maintain aggregations. However, first instar N. viridula nymphs did respond to beads treated with two of the three major components of bug extracts. 4-Oxo-(E)-2-decenal induced significant aggregations at two doses, whereas tridecane, the major component in extracts from all six species, did not, and (E)-2-decenal was repellent. The repellence of (E)-2-decenal may explain why we and previous researchers were unable to induce aggregations of first instar N. viridula using whole-body extracts.

Olfactory response of two aphid parasitoids, Lysiphlebus testaceipes and Aphidius colemani, to aphid-infested plants from a distance

The role of volatile stimuli in the host‐searching behaviour of the two parasitoid species Lysiphlebus testaceipes Cresson and Aphidius colemani Viereck (Hymenoptera: Braconidae) was studied in relation to the host Aphis gossypii Glover (Homoptera: Aphididae) on cucumber plants, Cucumis sativa L. (Cucurbitaceae). Experiments were carried out in the laboratory in a wind tunnel, exposing individual parasitoids to signals from three sources simultaneously: (1) a complex of cucumber plants, Cucumis sativa, and A. gossypii; (2) uninfested cucumber plants; and (3) dummy cardboard plants. The flight response of the female parasitoids was considered oriented when they landed on plants and non‐oriented when the females landed elsewhere (tunnel floor, sides, or top). Results showed that the proportion of oriented flights was significantly higher than non‐oriented flights. A comparison between the two wasp species suggested that A. colemani females may be better able to locate plants than L. testaceipes, as the proportion of females that made an oriented flight was higher in this species. For females of both wasp species which made an oriented flight, landing was more often observed on real plants (i.e., with no difference between infested and uninfested plants), than on dummy plants. A description of the flight behaviour of the two parasitoid species is presented. One difference between the species was that flight duration was higher in L. testaceipes than in A. colemani. This work shows that the two parasitoid species respond to stimuli from the host‐plants of A. gossypii in a similar way to parasitoids of aphid pests in other crops.

Inter and intra-guild interactions in egg parasitoid species of the soybean stink bug complex

Abstract – The objective of this research was to evaluate the parasitism behavior of Telenomus podisiAshmead, Trissolcus basalis (Wollaston) e Trissolcus urichi Crawford (Hymenoptera: Scelionidae) oneggs of Nezara viridula L., Euschistus heros F., Piezodorus guildinii Westwood and Acrosternumaseadum Rolston (Heteroptera: Pentatomidae), in no choice and multiple choice experiments. For allparasitoid species, the results demonstrated the existence of a main host species that maximizes thereproductive success. The competitive interactions among the parasitoid species were investigated inexperiments of sequential and simultaneous release of different combinations of parasitoid pairs on thehosts N. viridula, E. heros and A. aseadum. Exploitative competition was observed for egg batches atthe genus level ( Telenomus vs. Trissolcus) and interference competition at the species level ( T. basalisvs. T. urichi). Trissolcus urichi was the most aggressive species, interfering with the parasitism ofT. basalis. Generally, T. basalis showed an opportunistic behavior trying to parasitise eggs after T. urichihad abandoned the egg batch. The selection of parasitoid species for use in augmentative biologicalcontrol programs should take into account the diversity of pentatomids present in soybean in additionto the interactions among the different species of parasitoids.Index terms: parasitism, host-parasite relations, biological competition, pest control methods.Interacoes inter-guilda e intra-guilda entre especies de parasitoides de ovosque atacam o complexo de percevejos da sojaResumo – O objetivo desta pesquisa foi avaliar o comportamento de parasitismo de Telenomus podisiAshmead, Trissolcus basalis (Wollaston) e Trissolcus urichi Crawford (Hymenoptera: Scelionidae)em ovos de Nezara viridula L., Euschistus heros F., Piezodorus guildinii Westwood e Acrosternumaseadum Rolston (Heteroptera: Pentatomidae), em experimentos de multipla escolha e sem escolha dehospedeiros. Todas as especies de parasitoides testadas demonstraram possuir um hospedeiro quemaximizou a sua capacidade reprodutiva. As interacoes competitivas entre especies de parasitoidesforam investigadas mediante experimentos de liberacao sequencial e simultânea de diferentescombinacoes de pares de especies de parasitoides em N. viridula, E. heros e A. aseadum. Competicaopor exploracao foi observada a nivel de genero ( Telenomus vs. Trissolcus) e competicao por interferenciaa nivel de especie (T. basalis vs. T. urichi). A especie mais agressiva foi T. urichi, interferindo noparasitismo de T. basalis. Geralmente, T. basalis apresentou um comportamento oportunista tentandoparasitar os ovos apos T. urichi ter abandonado os lotes de ovos. A selecao de especies de parasitoidespara uso em programas de controle biologico aumentativo deve considerar a diversidade depentatomideos presentes na soja, alem das interacoes entre as especies de parasitoides que serao liberadas.Termos para indexacao: parasitismo, relacao parasita-hospedeiro, competicao biologica, metodos decombate as pragas.

Source of the host marking pheromone in the egg parasitoid Trissolcus basalis (Hymenoptera: Scelionidae)

After oviposition, Trissolcus basalis females always mark the hosts surface, depositing host marking substances for herself and to warn other ovipositing females. The perception of these host marking substances, probably through the antennae, can induce the female to leave and seek healthy hosts. Parasitoid females exposed to conspecific parasitized egg masses left the host egg masses significantly more often than when exposed to non-parasitized egg masses. More egg mass leaving behavior also was observed when the egg masses were treated with Dufours gland secretion but not when treated with secretion from the common oviducts. The common oviduct has a secretory epithelium that produces electron-dense vesicles, probably containing proteinaceous substances. The secretory cells of the accessory gland, Dufours gland, contain electron-lucid vesicles, whose secretion appears to be a lipid similarly to that found in pheromone secreting glands. Ultrastructural and behavioral evidence suggests that Dufours gland is the host marking pheromone source.

Responses of Rhynchophorus ferrugineus adults to selected synthetic palm esters: electroantennographic studies and trap catches in an urban environment

BACKGROUND The red palm weevil (RPW), Rhynchophorus ferrugineus Olivier, accidentally introduced into the European countries facing the Mediterranean basin, is becoming the most serious pest for ornamental palms in the urban environment. In the present work, tests were conducted on the electroantennogram (EAG) and behavioural responses of RPW adults to five selected synthetic palm esters, ethyl propionate, ethyl butyrate, ethyl isobutyrate, ethyl lactate and ethyl acetate, to assess the application of a mass trapping technique in an urban environment. RESULTS In the laboratory, EAG bioassays on RPW adults with the synthetic palm esters showed: (1) positive dose-dependent responses; (2) differences among the treatments; (3) a greater response to ethyl propionate; (4) a higher sensitivity of female antennae compared with male antennae. In the urban environment, RPW behavioural responses, evaluated over six biweekly observations on pheromone- and molasses- baited traps, showed that more adults were caught by traps supplemented with ethyl propionate and ethyl acetate than by traps supplemented with only ethyl propionate. Similar catches were recorded in the traps supplemented with ethyl propionate or ethyl acetate. CONCLUSION This study supports the application of the mass trapping implemented with synthetic palm esters as a potential tool for the management of RPW populations to protect ornamental palms in urban environments.