Identification of volatile compounds involved in host location by Anthonomus grandis (Coleoptera: Curculionidae).

Na publicação: Maria C. Blassioli-Moraes

Identificação e avaliação em campo do feromônio sexual de uma população brasileira de Spodoptera cosmioides

O objetivo deste trabalho foi identificar o feromônio sexual de Spodoptera cosmioides e avaliar se existe atração cruzada em Spodoptera sp. (Lepidoptera: Noctuidae). Extratos de glândulas de S. cosmioides foram analisados por GC-FID e GC-MS. A ação dos compostos encontrados nas glândulas foi avaliada por meio de bioensaios em túnel de vento e eletrofisiologia. Em campo, testaram-se diferentes armadilhas feromonais: com feromônio comercial de S. frugiperda; com acetato de (9Z)-9-tetradecenila (Z9-14:OAc) e acetato de (9Z,12E)-9,12-tetradecadienila (Z9,E12-14:OAc); com duas fêmeas de S. cosmioides; e controle com hexano. Quatro acetatos foram identificados nas glândulas de fêmeas de S. cosmioides como Z9-14:OAc, Z9,E12-14:OAc, (11Z)-acetato de hexadecenila e acetato de hexadecila (16:OAc), mas somente os dois primeiros acetatos induziram resposta eletrofisiológica nas antenas de machos de S. cosmioides. Nos bioensaios em túnel de vento, machos de S. cosmioides e S. frugiperda responderam em maior número à mistura de coespecíficos; no entanto, houve atração cruzada, uma vez que 47% dos machos de S. frugiperda e 25% dos machos de S. cosmioides responderam à mistura heteroespecífica. Nos experimentos em campo, S. frugiperda e S. cosmioides mostraram o mesmo padrão de resposta observado nos bioensaios em túnel de vento. Em resumo, os componentes do feromônio sexual de S. cosmioides são Z9-14:OAc e Z9,E12-14:OAc, que são importantes para conferir espécie-especificidade do feromônio, e há atração cruzada entre S. cosmioides e S. frugiperda mediada por feromônios.The objective of this work was to identify the sex pheromone of Spodoptera cosmioides and to evaluate whether there is pheromone cross-attraction in Spodoptera sp. (Lepidoptera: Noctuidae). Spodoptera cosmioides gland extracts were analyzed by GC-FID and GC-MS. Wind tunnel and electrophysiology experiments were conducted to evaluate the role of gland compounds. In the field, different pheromone traps were tested: S. frugiperda commercial lure; (9Z)-9-tetradecenyl acetate (Z9-14:OAc) and (9Z,12E)-9,12-tetradecadienyl acetate (Z9,E12-14:OAc) trap; two females of S. cosmioides trap; and hexane control trap. Four acetates were identified in the S. cosmioides female gland extracts as Z9-14:OAc, Z9,E12-14:OAc, (11Z)-11-hexadecenyl acetate (Z11-16:OAc) and hexadecyl acetate (16:OAc), but only the first two acetates induced electrophysiological responses from S. cosmioides male antennae. In wind tunnel experiments, S. cosmioides and S. frugiperda males responded more strongly to conspecific blends; however, there was some cross-attraction, as 47% males of S. frugiperda and 25% males of S. cosmioides responded to heterospecific blends. In field experiments, S. frugiperda and S. cosmioides showed the same response pattern as observed in the wind tunnel bioassays. In summary, the sex pheromone components of S. cosmioides are Z9-14:OAc and Z9,E12-14OAc; they are important for conferring species specificity, and there is pheromone-mediated cross attraction between S. frugiperda and S. cosmioides

Variability in herbivore-induced defence signalling across different maize genotypes impacts significantly on natural enemy foraging behaviour

‘Smart’ plants that release volatile defence compounds in response to pest damage, and which recruit beneficial natural enemies, offer an opportunity for exploiting biological control in future crop protection strategies. Using six maize genotypes, Zapalote Chico (‘landrace’), Mirt2A, Sintético Spodoptera (SS), L3, and two commercial hybrids BRS 4103 and BRS 1040, the aim of this work was to evaluate maize responses to larval damage from the fall armyworm Spodoptera frugiperda, a major maize pest in Brazil, and the ability of the egg parasitoid Telenomus remus to respond to HIPVs induced by S. frugiperda damage. Y-tube olfactometer bioassays with T. remus showed preferential responses to the S. frugiperda-induced volatiles of SS and BRS 4103 compared to constitutive volatiles of the same genotypes, but to none of the other genotypes tested. Chemical analysis of maize volatile extracts showed that SS produced more volatile compounds in response to S. frugiperda damage, followed by BRS 4103. In addition, higher levels of mono, homo-, or sesquiterpenes, together with green leaf volatiles (GLVs) were the most attractive blend for T. remus; however, there was no attraction when only GLVs were produced in higher levels. In summary, these results show that volatile defence signalling produced by maize plants due to S. frugiperda damage varies significantly depending on maize genotype and this variability influences T. remus foraging behaviour

Tremulatory and abdomen vibration signals enable communication through air in the stink bug Euschistus heros.

Communication by substrate-borne mechanical signals is widespread among animals but remains one of their least understood communication channels. Past studies of vibrational communication in insects have been oriented predominantly to communication during mating, showing that species- and sex-specific vibrational signals enable recognition and localization of potential mates on continuous solid substrates. No special attention has been paid to vibrational signals with less obvious specificity as well as to the possibility of vibrational communication across substrates that are not in physical contact. We aimed to reinvestigate emission of the aforementioned vibrational signals transmitted through a plant in the stink bug Euschistus heros (Pentatomidae: Pentatominae) and to check whether individuals are able to communicate across adjecent, physically separated substrates. We used laser vibrometry for registration of substrate-borne vibrational signals on a bean plant. Using two bean plants separated for 3 to 7 cm between two most adjacent leaves, we investigated the possibility of transmission of these signals through air. Our study showed that males and females of E. heros communicate using tremulatory, percussion and buzzing signals in addition to the previously described signals produced by vibrations of the abdomen. Contrary to the latter, the first three signal types did not differ between sexes or between pentatomid species. Experiments with two physically separated plants showed significant searching behaviour and localization of vibrational signals of an E. heros male or a female, in response to abdominal vibration produced signals of a pair duetting on the neighbouring plant, in comparison to control where no animals were on the neighbouring plant. We also confirmed that transmission through air causes amplitude and frequency decay of vibrational signals, which suggests high-amplitude, low-frequency tremulatory signals of these stink bugs their most plausible way of communication across discontinuous substrates

Attraction of telenomus podisi to volatiles induced by euschistus heros in three different plant species

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Specialized natural enemies that forage for polyphagous hosts need to locate hosts on different plants. Telenomus podisi (Hymenoptera: Platygastridae) is a stink bug egg parasitoid with a preference for Euschistus heros (Hemiptera, Pentatomidae), a polyphagous species. The aim of this study was to evaluate the induction of defences in three E. heros host plants: maize (Zea mays), sunflower (Helianthus annuus) and pigeon pea (Cajanus cajan). We hypothesized that E. heros damage to these three plants enhances the attraction of the parasitoid T. podisi as has been observed in other systems. Using Y-tube olfactometer bioassays, we tested parasitoid responses to combinations of the following odour sources: clean air, undamaged plants and plants damaged by stink bug feeding. Volatiles were collected by means of dynamic headspace collection and analysed by gas chromatography coupled to mass spectrometry. T. podisi did not distinguish odours from undamaged plants against air for any of the three plant species. For maize, the parasitoid preferred the odour from herbivore-damaged plants over both clean air and undamaged plants. For sunflower, the parasitoid only preferred the odour of herbivore-damaged plants over the odour of undamaged plants. For pigeon pea, no preferences were observed. Quantitative differences in the volatile profile of damaged and undamaged plants were observed in each plant species. We conclude that sunflower and maize plants, when damaged by E. heros, release volatiles that attract the parasitoid T. podisi; the parasitoid appears to use a different blend composition to distinguish herbivore-damaged plants of each species.Specialized natural enemies that forage for polyphagous hosts need to locate hosts on different plants. Telenomus podisi (Hymenoptera: Platygastridae) is a stink bug egg parasitoid with a preference for Euschistus heros (Hemiptera, Pentatomidae), a polyph105419428CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)sem informaçãoThis work received financial support from the Conselho Nacional de Desenvolvimento Científico e Tecnológico— CNPq, through a studentship to AMD, as well as grants from Embrapa, CNPq and FAP-DF. MP was supported by a FAEPEX PAPDIC grant from UNICAM

Architecture of bean plants (<i>Phaseolus vulgaris</i> L.) and experimental setup.

<p>Structure and dimensions of bean plants used, and experimental setup in airborne inter-plant communication experiments (below). See text for detailed description of experimental procedures.</p

Spectral characteristics of vibrational signals before and after transmission through air.

<p>Frequency spectra (A) (one pulse), sonograms (B) (10 s sequence) and oscillograms (C) (10 s sequence) of abdomen vibration produced signals, recorded simultaneously from the plant where insects were singing (lower traces) and from the neighbouring plant (upper traces). The two plants were separated by an approximately 3 (left) or 6 (right) cm air gap.</p

Parameters of vibrational signals produced by mechanisms other than abdomen vibration.

<p>n = the number of signals analysed, N = the number of individuals analysed, where N is not specified then N = 1. Data are shown as mean ± SD when differences in parameter values between individuals were not significant and as minimal and maximal values when differences in parameter values between individuals were significant. For percussion signals we indicate the statistical test used to compare parameters of signals emitted as independent sequences (I) and parameters of signals emitted as a response to other vibrational emissions (R).</p