Réflexion sur l'utilisation des auxiliaires entomophages contreDiprion pini [Hym. Diprionidae]

Résumé Le problème de la lutte biologique en forêt, par utilisation d'entomophages indigènes, est discuté dans le cas d'un hyménoptère, le diprion du pin,Diprion pini L. Des études de dynamique des populations montrent que le schéma de progression spatiale des populations de cet insecte dans le sud du Bassin Parisien semble se renouveler à chaque pullulation. De plus les parasites représentent un véritable “facteur clé”. Leur incidence varie notamment de génération en génération: en faible nombre au début d'une gradation, ils ne peuvent alors en empêcher le développement; mais ensuite leur multiplication assure une régression brutale du ravageur. Dans ces conditions, des interventions assez peu onéreuses et faciles à réaliser, comme de simples transports de matériel parasité pourraient être efficaces; elles supposent toutefois le développement d'un foyer initial d'infestation. En revanche l'élevage d'espèces régulatrices commeAchrysocharella ruforum Krausse etPleolophus basizonus Grav. permettrait d'assurer la préservation permanente des massifs forestiers.

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Summary The spatial pattern of insect populations progression in southern “Bassin Parisien”, showed by population dynamics studies, seems to happen again for every outbreak. Parasites are moreover a true “key-factor”. Their effect is quite different from one generation to another one; scarce at the beginning of an outbreak, they cannot stop its evolution; but then, their increase allows a brutal collape of the pest. In such a case, cheap and easily achieved operations as simple carryings of parasited insects may be efficient, but they need the development of a first infestation focus. In return breeding of regulating species asAchrysocharella ruforum Krausse andPleolophus basizonus Grav. would be able to sure forest stands permanently.

     

Survey and phylogenetic analysis of culturable microbes in the oral secretions of three bark beetle species

In a recent study, we reported a previously undescribed behavior in which a bark beetle exuded oral secretions containing bacteria that have antifungal properties, and hence defend their galleries against pervasive antagonistic Hyphomycete fungi. Actinobacteria, a group known for their antibiotic properties, were the most effective against fungi that invade the spruce beetle galleries. In the present study, we describe the isolation and identification of microorganisms from oral secretions of three bark beetles (Coleoptera: Curculionidae: Scolytinae): the spruce beetle, Dendroctonus rufipennis Kirby, the mountain pine beetle, Dendroctonus ponderosae Hopkins, and the pine engraver, Ips pini Say. Bacteria isolated from these three species span the major bacterial classes α-, β-, and γ-Proteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria, except for D. ponderosae , which yielded no α-proteobacteria or Bacteroidetes isolates. Spruce beetles and pine engraver beetles had similar numbers of α-proteobacteria isolates, but pine engravers yielded twice as many Bacteroidetes isolates as spruce beetles. In contrast, mountain pine beetles yielded more isolates in the β- and γ-proteobacteria than spruce beetles and pine engravers. The highest percentage of Actinobacteria was obtained from spruce beetles, followed by pine engravers and mountain pine beetles. All of the fungal isolates obtained from the three beetle species were Ascomycetes. The greatest fungal diversity was obtained in spruce beetles, which had nine species, followed by pine engravers with five, and mountain pine beetles with one.     

Species of the genus Mastrus Förster (Hymenoptera, Ichneumonidae) of China with descriptions of two new species parasitizing sawflies (Hymenoptera)

Four species of Mastrus Förster, 1869 are reported from China. Two, Mastrus nigrus Sheng & Zeng, sp. n. reared from Arge pullata (Zaddach) and Mastrus rugotergalis Sheng & Zeng, sp. n. reared from Diprion jingyuanensis Xiao & Zhang, are new to science. One, Mastrus deminuens (Hartig, 1838), is a parasitoid of Pachynematus itoi Okutani. A key to species of Mastrus Förster known in China is provided.     

水溶性phellinus多糖PS1的分离提取及免疫活性研究

目的：从Phellinus pini子实体中提取分离到一种水溶性多糖纽分PS1,并对其免疫活性进行初步研究。方法：先进行热水提取,DEAE-纤维素离子交换树脂,sepharose CL-4B凝胶树脂分离纯化PS1,并利用GC色谱、FT-1R光谱进行组成成分分析,然后通过刚果红吞噬实验、脾脏B淋巴细胞增殖实验及免疫器官指数评价其免疫活性。结果：PS1为一种β型杂多糖,总糖含量70．36％,蛋白质含量4．69％,分子量为230kDa。糖类构成有鼠李糖、阿拉伯糖、木糖、甘露糖、半乳糖、葡萄糖,其摩尔比为2．14：2．36：0．44：4．28：5．17：85,61。多糖PS1能显著提高正常小鼠的脾指数和胸腺指数（P〈0．01）,免疫力低下小鼠的肝指数、胸腺指数也有提高,但效果不明显．PS1均能提高正常和免疫低下小鼠的巨噬细胞吞噬能力。此外。PS1能显著促进脾细胞体外增殖能力（P〈0．01）。结论：多糖PS1能显著提高机体的免疫能力。可作为一种生物效应调节剂应用于医药或保健食品领域。     

Interactions among intraspecific competition, emergence patterns, and host selection behaviour in Ips pini (Coleoptera: Scolytinae)

Abstract.  1. Variations in developmental conditions of bark beetles, particularly intraspecific competition, can induce morphological and physiological modifications in the offspring. It is hypothesised that intraspecific competition could also affect host selection behaviour. Such behavioural changes might be manifested in response to host (alpha-pinene) or beetle (verbenone) compounds.
2.  Ips pini were bred at different densities. The offspring were measured for size, weight, and lipid concentration, and then subjected to tunnelling bioassays in agar media amended with varying amounts of alpha-pinene or verbenone.
3. High parental colonisation densities reduced emergence time of parents and offspring. Increasing colonisation density and emergence time had a negative influence on offspring vigour, resulting in a reduction of the distance tunnelled by the beetles.
4. Both alpha-pinene and verbenone were repellent. Surprisingly, verbenone was also toxic at high concentrations, with its effect being greater on beetles arising from high densities. The repellent effect of these compounds did not vary according to colonisation density, but for both compounds, at a 1.5 mg g^–1 concentration, it increased with emergence time.
5. The consequences of varying vigour and behaviour in relation to developmental conditions and emergence patterns on population dynamics of I. pini are discussed.     

The significance of background odour for an egg parasitoid to detect plants with host eggs

Scots pine has been shown to produce a volatile bouquet that attracts egg parasitoids in response to oviposition of the herbivorous sawfly Diprion pini. Previous analyses of headspace volatiles of oviposition-induced pine twigs revealed only quantitative changes; in particular, the sesquiterpene (E)-beta-farnesene was emitted in significantly higher quantities by oviposition-induced pine. Here we investigated whether (E)-beta-farnesene attracted the egg parasitoid Chrysonotomyia ruforum. We tested the behavioural response of C. ruforum females to different concentrations of (E)-beta-farnesene. Egg parasitoids did not respond to this sesquiterpene at either concentration tested. However, they did respond significantly to (E)-beta-farnesene when this compound was offered in combination with the volatile blend emitted from pine twigs without eggs. This response was dependent on the applied concentration of (E)-beta-farnesene. Further bioassays with other components [(E)-beta-caryophyllene, delta-cadinene] of the odour blend of pine were conducted in combination with the volatile blend from egg-free pine as background odour. None of the compounds tested against the background of odour from an egg-free pine twig were attractive to the egg parasitoid. These results suggest that the egg parasitoids responded specifically to (E)-beta-farnesene, but only when this compound was experienced in the 'right' context, i.e. when contrasted with a background odour of non-oviposition-induced pine volatiles.     

The effects of 20-hydroxyecdysone on breaking diapause of Diprion pini L. (Hym., Diprionidae)

Abstract .The pine sawfly, Diprion pini L, like almost all Diprionidae, has complex diapause phenomena which affect the prepupal stages (eonymph and pronymph) in the cocoon. Experiments using 20-hydroxyecdysone to break diapause of different populations of D. pini , were conducted. Doses of 2 and 10 μg/g of the hormone were injected into the insects in diapause, previously removed from their cocoons and placed in transparent capsules to observe their development. The experiments showed that 20-hydroxyecdysone may cause D. pini to resume development and may even totally break the diapause. However, this reactivation seemed to require large doses of 20-hydroxyecdysone. Moreover, the effects of applying this hormone varied according to the insect's origin, duration of the diapause maintenance and conditions of photoperiod and temperature present before and after the treatment. According to the cases, this resumption of development can affect a variable fraction of individuals and be more or less complete. It is suggested that the reaction to 20-hydroxyecdysone in standard conditions could be used to measure the intensity of the diapause of natural D. pini populations.     

Flight muscle changes in male pine engraver beetles during reproduction: the effects of body size, mating status and breeding failure

Abstract. In a pattern that is typical for bark beetles, the lateralis medius flight muscle of male pine engravers, Ips pini Say (Coleoptera: Scolytidae), was found to decrease four-fold in volume (from mean ± SE = 1.36 ± 0.06 × 10^?2 mm³ to 0.34 ± 0.06 × 10^?2 mm³) within five days of the initiation of breeding galleries, and then to regenerate gradually to functional capacity during subsequent weeks. Although there was considerable variation in the timing and extent of flight muscle regeneration in males, this variation was not a consequence of differences between small (length < 4.0 mm) and large (length ≥ 4.0 mm) males. Two subsequent experiments revealed that male pine engravers can control the timing of flight muscle regeneration. In the first experiment, the flight muscles of males that were denied mates degenerated within 5 days of gallery initiation, but then showed complete regeneration 5 days later. In the second experiment, mated males that were removed from their breeding galleries (to simulate breeding failure) also showed extensive muscle degeneration 5 days after gallery initiation, but then regenerated their flight muscles to functional capacity by the tenth day. The ability of males to regenerate their flight muscles in response to conditions at the gallery is probably adaptive because it allows them to fly in search of new breeding opportunities when they are unable to attract mates or when breeding attempts fail.     

Too close for comfort: effect of trap spacing distance and pattern on statistical inference of behavioral choice tests in the field

Behavioral choice tests provide a powerful and commonly used technique for evaluating the biological activity of chemical signals. Despite the widespread application of this approach, relatively few studies have evaluated a key assumption, that is, relative independence among treatments. Previous work has demonstrated that both the number of choices and their physical arrangement can affect the results of choice tests with leaf‐feeding insects in laboratory assays. Here, we consider another spatial component, the distance between treatments, in a field assay, using a bark beetle as our model. We used three geometries of trap arrangements, two spacing levels, and both ‘low activity’ lures and a ‘high activity’ lure in our behavioral assays. We found that proximity to an attractive treatment generated unexpectedly high trap catches at relatively non‐attractive treatments, even in the presence of a uniform treatment effect and relatively constant insect population size. Increases in traps baited with ‘low activity’ lures proximate to a highly attractive treatment ranged from 4 to 7× the catch observed in configurations with traps spaced wider apart. Moreover, even in the absence of ‘high activity’ lures, a lure catching less than one insect per day on average could obscure the effect of a control trap at proximate spacing. In our example, a spacing distance of 15 m appears to provide independence among traps used to sample the bark beetle Ips pini (Say) (Coleoptera: Curculionidae: Scolytinae), but 3 m does not. Our broader intent is to provide a useful approach to the design and evaluation of behavioral choice experiments in the field.