Disjunction between canola distribution and the genetic structure of its recently described pest,the canola flower midge (Contarinia brassicola)

Population genomics is a useful tool to support integrated pest management as it can elucidate population dynamics, demography, and histories of invasion. Here, we use a restriction site‐associated DNA sequencing approach combined with whole‐genome amplification (WGA) to assess genomic population structure of a newly described pest of canola, the diminutive canola flower midge, Contarinia brassicola. Clustering analyses recovered little geographic structure across the main canola production region but differentiated several geographically disparate populations at edges of the agricultural zone. Given a lack of alternative hypotheses for this pattern, we suggest these data support alternative hosts for this species and thus our canola‐centric view of this midge as a pest has limited our understanding of its biology. These results speak to the need for increased surveying efforts across multiple habitats and other potential hosts within Brassicaceae to improve both our ecological and evolutionary knowledge of this species and contribute to effective management strategies. We additionally found that use of WGA prior to library preparation was an effective method for increasing DNA quantity of these small insects prior to restriction site‐associated DNA sequencing and had no discernible impact on genotyping consistency for population genetic analysis; WGA is therefore likely to be tractable for other similar studies that seek to randomly sample markers across the genome in small organisms.     

瘿蚊科中国一新纪录属种记述(双翅目,瘿蚊科)

报道了瘿蚊科鼓瘿蚊亚科中国1新纪录属,即独瘿蚊属Asynapta Loew,1850及其中国1新纪录种,即戈氏独瘿蚊Asynapta groverae Jiang et Bu,nom nov.(山东:青岛).本种模式产地在印度,原置于Dicerura属,即Dicerura indi-ca Grover,后由定名人转入Cryptoneurus属,本文将其转入Asynapta属,是为新组合;但转入后,本种与Asynapta属中的原有种同名,成为一个次后同名,因此为本种命一新名.文中重新描述并图示该种的特征,补充和修正了原始描述中的不足.     

浙江端突瘿蚊属一新种记述(双翅目,瘿蚊科)

记述了采自浙江的端突瘿蚊属Epidiplosis 1新种,即长叉端突瘿蚊Epidiplosis furcata sp. nov..正模♂,浙江省西天目山,2000-07-19,墨铁路、刘涛灯诱.该新种与拟丝端突瘿蚊Epidiplosis simulifilifera Mo比较近似,与后者主要区别如下:1)抱器基节各具1叉状端瓣,阳具基侧突骨化,呈"T"形;2)下颚须第3节长约为宽的3.4倍;3)触角末鞭节的端结长为宽的2.5倍;4)体长1.16 mm.     

Plant quality effects on intraguild predation between Orius laevigatus and Aphidoletes aphidimyza

To understand the influence of plant quality on intraguild predation and consequently on the suppression of a shared prey population as well as on plant yield, the interactions between Aphis gossypii Glover (Hemiptera: Aphididae) (shared prey), Aphidoletes aphidimyza (Rondani) (Diptera: Cecidomyiidae) (intermediate predator), and Orius laevigatus Fieber (Hemiptera: Anthocoridae) (top predator) were investigated in 25‐day experiments on cucumber, Cucumis sativus L. (Cucurbitaceae) at various N fertilization levels (90, 150, and 190 p.p.m.) in microcosm set‐ups under greenhouse conditions. The final aphid population size was significantly affected by an interactive effect of N fertilization and predator application. Regardless of the N fertilization levels, O. laevigatus alone was more effective in aphid suppression than A. aphidimyza alone. In addition, the risk for aphids of being predated upon by both predators together was significantly reduced in the low and medium‐N fertilization levels, whereas it was additive in the high‐N fertilization treatment. The A. aphidimyza population was suppressed by O. laevigatus in both the 90 and 150 p.p.m. N treatments. However, there was no intraguild predation of O. laevigatus on A. aphidimyza at the 190 p.p.m. N level. Total plant yield depended on predator treatments and N fertilization levels, with the highest yield produced at the 150 p.p.m. N fertilization level in treatments with either O. laevigatus alone or with both predators together. Our results demonstrate that the weak asymmetric intraguild predation among A. aphidimyza and O. laevigatus does not influence the ability of both predators together to diminish bottom‐up effects on aphid populations and the yield losses associated with aphid infestations.     

Symbiont‐mediated phenotypic variation without co‐evolution in an insect–fungus association

Recent studies have shown that symbionts can be a source of adaptive phenotypic variation for their hosts. It is assumed that co‐evolution between hosts and symbionts underlies these ecologically significant phenotypic traits. We tested this assumption in the ectosymbiotic fungal associate of the gall midge Asteromyia carbonifera. Phylogenetic analysis placed the fungal symbiont within a monophyletic clade formed by Botryosphaeria dothidea, a typically free‐living (i.e. not associated with an insect host) plant pathogen. Symbiont isolates from four divergent midge lineages demonstrated none of the patterns common to heritable microbial symbioses, including parallel diversification with their hosts, substitution rate acceleration, or A+T nucleotide bias. Amplified fragment length polymorphism genotyping of the symbiont revealed that within‐lineage genetic diversity was not clustered along host population lines. Culture‐based experiments demonstrated that the symbiont‐mediated variation in gall phenotype is not borne out in the absence of the midge. This study shows that symbionts can be important players in phenotypic variation for their hosts, even in the absence of a co‐evolutionary association.     

Ovipositing females of a short‐lived gall midge take time to assess suboptimal grass seed heads

Abstract The short‐lived adult wheat midge Sitodiplosis mosellana deposits eggs on the seed head of various grasses close to the developing seeds on which larvae feed. The time taken to make egg‐laying decisions is investigated using three types of wheat Triticum aestivum seed heads. Young Roblin, Old Roblin and Young Key differ in their effects on ovipositing females (72%, 22% and 6% of eggs in choice tests, respectively) and effects on feeding larvae (75%, 25% and 5% larval survival, respectively). Within seconds of arriving, the female is able to distinguish Young Roblin from the two lower‐ranked types. However, the lower‐ranked types are not rejected at this time. Instead, all head types are examined before the female eventually flies away. On Young Roblin, probing with the ovipositor is the first behaviour that occurs. Thereafter probing and insertion of the ovipositor occupy most of the female’s time and behavioural transitions tend to be ‘progressive’, signalling a shift from low to high intensity examining. Differences between females visiting Old Roblin and Young Key are significant but take longer to emerge. On both, sitting is the first behaviour but, over the next 5–10 min, the female on Young Key exhibits more sitting, walking and ‘regressive’ transitions than the female on Old Roblin. It is suggested that, when the ovipositing female is short‐lived and incapable of controlled flight in all but essentially windless conditions, her behaviour is designed to thoroughly, rather than rapidly, examine a suboptimal host before abandoning it for the uncertain future of finding a better host.     

Changes in function and temporal variation in a guild of gall‐parasitoids across a temperature gradient in Australian subtropical rainforest

Parasitoids play an important role in ecosystem functioning through their influence on herbivorous insect populations. Theoretical and experimental evidence suggest that increased species richness can enhance and stabilize ecosystem function. It is important to understand how richness‐driven functional relationships change across environmental gradients. We investigated how temperature affected the relationship between parasitoid richness and parasitism rate in a guild of gall‐parasitoids along an elevational gradient. We collected galls at 15 sites along five elevational gradients (between 762 m and 1145 m asl) on six occasions over a year. A total of 1902 insects, including 1593 parasitoids, were reared from 12 402 galls. Parasitism rate increased significantly with temperature on all sampling occasions, except December and February. We found a significant, positive richness–parasitism relationship. This relationship, however, was weaker at higher elevations which may be linked to decreased functional efficiency of parasitoids at lower temperatures. Temporal variability in parasitism rate and parasitoid richness were significantly related, regardless of temperature. A stable functional guild of this kind may provide a more reliable ecosystem service under environmental changes.     

Gall size determines the structure of the Rabdophaga strobiloides host–parasitoid community

Abstract.  1. The relationship between gall size and mortality of the willow pinecone gall midge Rabdophaga strobiloides (Diptera: Cecidomyiidae) was examined by determining the fate of all galls in a 30-ha area in central Alberta, Canada over 4 years. It was found that gall size has a large effect on the type and intensity of mortality experienced by the gall midge, and consequently this factor has the potential to influence the dynamics of the host–parasitoid interaction through the creation of phenotypic refuges.
2. Total midge mortality ranged from 51% to 78% over the course of the study and was dominated by parasitism by Torymus cecidomyiae (Hymenoptera: Torymidae) and Gastrancistrus sp. (Hymenoptera: Pteromalidae) as well as predation by birds. Gall size had a strong, non-linear effect on the attack rates of each of these natural enemies.
3. Birds attacked the smallest size classes. Torymus cecidomyiae preferentially attacked medium diameter galls and thus avoided predation by birds in smaller galls. Gastrancistrus sp. preferentially attacked the largest galls and consequently suffered lower rates of predation by both T. cecidomyiae and birds.
4. This study emphasises the importance of understanding the interactions among mortality factors in order to describe adequately the susceptibility of R. strobiloides to parasitism and predation, and ultimately its population dynamics.     

Oviposition and larval performance of Rabdophaga terminalis on Salix spp. with special consideration to bud size of host plants

Females of the gall midge Rabdophaga terminalis (H. Loew) (Diptera: Cecidomyiidae) are very selective in their choice of host plants at oviposition. In preference trials, eggs were laid almost exclusively on S. alba and S. fragilis. One single oviposition occurred on S. viminalis but none on S. triandra, S. daphnoides or S. smithiana. Significantly more eggs were laid on S. alba than on S. fragilis. No differences were detected between clones of the same species regarding oviposition in laboratory trials. Within the species of S. alba, larger buds were preferred. However, this did not explain the preference of S. alba to S. fragilis. There was agreement between plant species selected by the females and survival of the larvae. No galls developed when eggs were transferred to species that were not oviposited on. There was no difference between S. alba and S. fragilis in larval growth, but after two weeks of development there was a significantly higher proportion of larvae in cocoons and pupae on S. alba. There was a negative linear relationship between weight of larvae and larval number per gall, indicating larval competition. The negative slope was steeper for S. alba than for S. fragilis when larvae were weighed after two weeks of development. There were some discrepancies between laboratory and field data on infestation of S. alba and S. fragilis. Higher infestation levels were related to denser stands in the field.

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Résumé Etude de la ponte et des performances larvaires de Rabdophaga terminalis (Diptera; Cecidomyiidae) sur plusieurs espèces de saules avec examen particulier de l'influence de la taille des bourgeons.La ponte et les performances larvaires de la cécidomyie galliforme, Rabdophaga terminalis (H. Loew) ont été étudiées sur plusieurs espèces et clones de saules cultivés en Suède. Les femelles sélectionnent avec soin les plantes hôtes lors de la ponte. Dans des essais préférentiels, les oeufs ont été pondus presque exclusivement sur S. alba et S. fragilis; une ponte a été observée sur S. viminalis et aucune sur S. triandra, S. daphnoïdes ou S. smithiana. Significativement plus d'oeufs ont été pondus sur S. alba que sur S. fragilis. Les essais au laboratoire n'ont pas permis de déceler des différences entre clones de la même espèce. Chez S. alba, les plus gros bourgeons étaient préférés, mais ceci ne permet pas d'expliquer la préférence pour S. alba par rapport à S. fragilis. Il y a coïncidence entre les plantes choisies par les femelles et al survie des larves; il n'y avait pas développement de galles quand des oeufs étaient transférés sur des espèces qui n'avaient pas reçu de pontes. La croissance larvaire sur S. alba et S. fragilis ne présentait pas de différences, mais après 2 semaines de développement il y avait significativement plus de larves en cocons et pupes sur S. alba. La corrélation entre le poids des larves et le nombre de larves par cellule était linéaire et négative, ce qui indique une compétition larvaire; la pente était plus raide pour S. alba que pour S. fragilis quand les larves étaient pesées au bout de 2 semaines de développement. Il y a eu quelques discordances entre les résultats au laboratoire et les données de terrain sur la contamination de S. alba et S. fragilis. Les plus fortes contaminations étaient observées à l'extérieur sur pépinières denses.