Étude comportementale et écologie chimique de la recherche d'un partenaire sexuel chez le puceron de la pomme de terre, Macrosiphum euphorbiae (Thomas) (Homoptera : Aphididae)

Afin d’utiliser les phéromones sexuelles dans les programmes de lutte intégrée des espèces nuisibles d’insectes, il est essentiel d’identifier les composés chimiques phéromonaux et de comprendre adéquatement la biologie reproductive des espèces considérées. Cette thèse porte sur l’étude de ces deux thèmes chez le puceron de la pomme de terre, Macrosiphum euphorbiae (Homoptera: Aphididae), un insecte nuisible pour l’agriculture à l’échelle mondiale. Les femelles sexuées vierges du puceron de la pomme de terre émettent leur phéromone sexuelle afin d’attirer les mâles conspécifiques. Lorsque soumisent à des températures froides, elles expriment ce comportement à un plus jeune âge que dans des conditions plus chaudes. En laboratoire, pour tous les régimes thermiques, une grande différence était observée au niveau du comportement d’appel en fonction de l’âge (i.e., les vieilles femelles appelaient plus tôt après l’ouverture des lumières et passaient plus de temps à appeler). Toutefois, sur le terrain, compte tenu des effets des faibles températures, des vents élevés et de la pluie sur l’activité des femelles en appel, les changements liés à l’âge étaient beaucoup moins prononcés. La phéromone sexuelle libérée par les femelles de M. euphorbiae a été identifiée comme étant un mélange de deux monoterpenoïdes, le nepetalactol (I) et la nepetalactone (II). Ces deux composés étaient présents dans un rapport de 4:1 à l’émergence des femelles. Ce ratio a changé avec l’âge, les femelles les plus âgées libérant un mélange au rapport de 2:1. Des proportions semblables de mâles de M. euphorbiae ont répondu aux mélanges synthétiques des rapports de 3:1, 4:1 et 5:1 et aux femelles vierges en appel. Cependant, les mâles mettaient plus de temps pour atteindre une source de phéromone synthétique que des femelles en appel. Le comportement des mâles face aux femelles sexuées en appel a été étudié dans des bioessais en laboratoire et sur le terrain. En laboratoire, les mâles détectaient la phéromone et s’orientaient vers la source mais ne volaient pas contre le vent lorsqu'ils étaient exposés à une source de phéromone. Par contre, ils rejoignaient la source si un pont était présent entre la source de phéromone et les cages de relâche pour leur permettre de marcher contre le vent. Sur le terrain, les comportements d'appel des femelles et de marche des mâles ont été étudiés pour différentes vitesses de vent inférieures à 5 m/s. Les femelles appelent jusqu’à une vitesse de 4 m/s mais le comportement de vol des mâles était inhibé à des vélocités supérieures à 2 m/s. Tel qu’observé en laboratoire, les mâles marchaient vers la source à des vitesses de vent élevées. Toutefois, contrairement aux résultats de laboratoire où les mâles atteignaient tous la source en marchant, 30% des mâles volaient contre le vent et se posaient sur la source. L'étude détaillée des patrons de vent a démontré qu'en présence de vent, les mâles marchaient vers la source, mais s'envolaient et progressaient vers l'avant lorsqu'une accalmie temporaire du vent se présentait.In order to use insect sex pheromones in integrated management programme of pest species, it is essential to have the correct identification of the chemical composition of pheromones and a solid understanding of the reproductive biology for the species in question. In this thesis, I examined the two aspects in the potato aphid, Macrosiphum euphorbiae (Homoptera: Aphididae), an agricultural pest of importance worldwide. Virgin female oviparae of the potato aphid release sex pheromone to attract conspecific males. At cooler temperatures females express this behavior at a younger age that at warmer ones. Under all constant temperature regimes in the laboratory there was a significant change in calling behavior as a function of age, with older females calling sooner after the “lights on” signal and spending more time calling. However, under field conditions the age related changes were much less evident due to the effects of low temperatures, high winds and rain on female calling activity. The sex pheromone emitted by calling females of M. euphorbiae was identified as a mixture of two monoterpenoids nepetalactol (I) and nepetalactone (II). The two components were present in a 4:1 ratio in the young females, but this changed with age and older females released a 2:1 ratio. A similar proportion of M. euphorbiae males responded to 3:1, 4:1, and 5:1 synthetic blends and to calling virgin, although the time taken to reach the source was less when conspecific females were used. Males’ behaviour to the calling females was examined in the laboratory and field bioassays. In the laboratory, males detected and oriented themselves to the source but did not fly upwind when exposed to calling females or appropriate lures, and only reached the source if there was a bridge available between the release cage and pheromone source allowing them to walk upwind. Under field conditions female calling, and male walking behavior were observed under variable wind speeds < 5m/s, but male flight behavior was inhibited at variable winds > 2m/s. In contrast to laboratory results where males only reached the source by walking, nearly 40% of males reaching the source did so by flying. A detailed examination of the wind patterns showed that in the presence of wind males walked towards the source but would take flight and make forward progress when there was a temporary lull in the wind

EFFECT OF DIFFERENT LIGHT SPECTRA ON FECUNDITY OF EPHESTIA KUEHNIELLA ZELLER (LEPIDOPTERA: PYRALIDAE)

This paper examines the effects of different light spectra on the number of eggs of Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) as a general host of biological control agents. Six distinct spectra of light, ranging from 395 nm to 625 nm, were examined in laboratory conditions. Green and red spectra with ranges of 520-525 nm and 620-625 nm caused the highest and the lowest numbers of eggs, respectively. Additionally, the effects of time on the mean egg load of E. kuehniella were also found to be significant at five days. The implications of the current results are discussed below and suggest that the application of a green spectrum in insectariums could help in increasing egg production

New Chalcididae (Hymenoptera: chalcidoidea) of economic importance from Iran

International audienceThree Chalcididae, namely Brachymeria ceratoniae Delvare sp. nov., Proconura persica sp. nov. and Psilochalcis ceratoniae Delvare sp. nov., are described from Iran. They were all reared from the carob moth Apomyelois ceratoniae (Lepidoptera: Pyralidae), the main pest of Ceratonia siliqua. Invreia subita Nikol'skaya, 1960 is formally transferred to the genus Psilochalcis. A lectotype is designated for Brachymeria confalonierii Masi, 1929

Fertility life table parameters, COI sequences and Wolbachia infection in populations of Trichogramma brassicae collected from Chilo suppressalis

Trichogramma wasps are frequently applied in the biological control of Chilo suppressalis (Walker), which causes economic damage to rice in Iran. A survey was carried out to collect local Trichogramma brassicae Bezdenko populations from C. suppressalis eggs in the northern Iran. Fertility life tables were constructed and the mitochondrial cytochrome oxidase subunit I (COI) sequences were determined to estimate the genetic distance between populations. Also, the prevalence of Wolbachia and its effect on host fitness was determined. Thirteen populations of T. brassicae were sampled in which two were infected by Wolbachia. Results revealed biological and molecular differences between populations collected from a single host species in a relatively small geographic region. A significant positive effect of Wolbachia infection was found in the host fitness such as net reproductive rate and intrinsic rate of increase. The genetic relationship among populations is discussed in the context of historical wasp releases in the rice fields of northern Iran

Does Wolbachia infection affect decision-making in a parasitic wasp?

International audienceVarious physiological effects of Wolbachia infection have been reported in invertebrates, but the impact of this infection on behavior and the consequences of these behavioral modifications on fitness have rarely been studied. Here, we investigate the effect of Wolbachia infection on the estimation of host nutritive resource quality in a parasitoid wasp. We compare decision-making in uninfected and Wolbachia-infected strains of Trichogramma brassicae Bezdenko (Hymenoptera: Trichogrammatidae) on patches containing either fresh or old host eggs. For both strains, fresh eggs were better hosts than older eggs, but the difference was smaller for the infected strain than for the uninfected strain. Oviposition behavior of uninfected wasps followed the predictions of optimal foraging theory. They behaved differently toward high- vs. low-quality hosts, withmore hosts visited andmore ovipositions, fewer high-quality hosts used for feeding or superparasitism, and a sex ratio that was morebiased toward females in patches containing high-quality hosts than in patches containing low-quality ones. Uninfected wasps also displayed shorter acceptance and rejection times in high-quality hosts than in hosts of lower quality. In contrast, infected wasps were less efficient in evaluating the nutritive quality of the host (fresh vs. old eggs) and had a reduced ability to discriminate between unparasitized and parasitized hosts. Furthermore, they needed more energy and therefore engaged in host feeding more often. This study highlights possible decision-making manipulation by Wolbachia, and we discuss its consequences forWolbachia fitness

Differential expression of heat shock proteins and antioxidant enzymes in response to temperature, starvation, and parasitism in the Carob moth larvae, Ectomyelois ceratoniae (Lepidoptera: Pyralidae).

Insects face diverse biotic and abiotic stresses that can affect their survival. Many of these stressors impact cellular metabolism, often resulting in increased accumulation of reactive oxygen species (ROS). Consequently, insects will respond to these stressors by increasing antioxidant activity and increased production of heat shock proteins (HSPs). In this study, the effect of heat, cold, starvation, and parasitism by Habroacon hebetor wasps was examined in the carob moth, Ectomyelois ceratoniae, to determine which responses were common to different stresses. For all stressors, malondialdehyde levels increased, indicative of oxidative stress in the insects. The activity of two antioxidant enzymes, superoxide dismutase (SOD) and catalase (CAT), increased with each stress, suggesting that these enzymes were serving a protective role for the insects. Heat (46°C for 100 min) and cold (-15°C for 30 min) treatments caused significant mortalities to all developmental stages, but pretreatments of moderate heat (37°C for 10 min) or cold (10°C for 10 min) induced thermotolerance and reduced the mortality rates when insects were subsequently exposed to lethal temperatures. Quantitative RT-PCR confirmed that heat and cold tolerance were associated with up-regulation of two HSPs, HSP70 and HSP90. Interestingly, HSP70 transcripts increased to a greater extent with cold treatment, while HSP90 transcripts increased more in response to high temperatures. RNA interference (RNAi)-mediated knockdown of either HSP70 or HSP90 transcripts was achieved by injecting larvae with dsRNA targeting each gene's transcripts, and resulted in a loss of acquired thermotolerance in insects subjected to the heat or cold pretreatments. These observations provide convincing evidence that both HSP70 and HSP90 are important mediators of the acquired thermotolerance. Starvation and parasitism by wasps caused differential expression of the HSP genes. In response to starvation, HSP90 transcripts increased to a greater extent than HSP70, while in contrast, HSP70 transcripts increased to a greater extent than those of HSP90 during the first 48 h of wasp parasitism. These results showed the differential induction of the two HSPs' transcripts with variable stresses. As well as, heat, cold, starvation, and parasitism induce oxidative stress, and antioxidant enzymes likely play an important role in reducing oxidative damage in E. ceratoniae

Identification of bioactive plant volatiles for the carob moth by means of GC-EAD and GC-Orbitrap MS

The aim of this study was to validate a workflow that allows structural identification of plant volatiles that induce a behavioral response in insects. Due to the complexity of plant volatile emissions and the low levels at which these bioactive components tend to occur, gas chromatography-electroantennography (GC-EAD) was applied as the prime differentiator technique, i.e., to indicate particular peaks of interest in the chromatogram. In a next step, the analysis was repeated under identical conditions using GC-Orbitrap mass spectrometry (MS). Combining electron impact (EI) ionization and chemical ionization (CI) with the superior spectral resolution and mass accuracy of the technique enabled straightforward identification of these unknowns, with high confidence in a minute amount of time. Moreover, because of the intrinsic sensitivity of the technique, components that occur at trace amounts but may induce disproportional large behavioral responses are evenly well-identified. We were able to positively identify beta-caryophyllene as a bioactive compound in female carob moths. Behavioral attraction was negatively correlated with the amount of beta-caryophyllene in host fruits. In an oviposition experiment on filter paper, beta-caryophyllene was stimulated in the range of 40-100 ng, while concentrations above 200 ng inhibited oviposition