Insect Gallers and Their Plant Hosts: From Omics Data to Systems Biology.

Gall-inducing insects are capable of exerting a high level of control over their hosts' cellular machinery to the extent that the plant's development, metabolism, chemistry, and physiology are all altered in favour of the insect. Many gallers are devastating pests in global agriculture and the limited understanding of their relationship with their hosts prevents the development of robust management strategies. Omics technologies are proving to be important tools in elucidating the mechanisms involved in the interaction as they facilitate analysis of plant hosts and insect effectors for which little or no prior knowledge exists. In this review, we examine the mechanisms behind insect gall development using evidence from omics-level approaches. The secretion of effector proteins and induced phytohormonal imbalances are highlighted as likely mechanisms involved in gall development. However, understanding how these components function within the system is far from complete and a number of questions need to be answered before this information can be used in the development of strategies to engineer or breed plants with enhanced resistance.

New Gall-Forming Insect Model, Smicronyx madaranus: Critical Stages for Gall Formation, Phylogeny, and Effectiveness of Gene Functional Analysis.

The molecular mechanisms underlying insect gall formation remain unclear. A major reason for the inability to identify the responsible genes is that only a few systems can be experimentally validated in the laboratory. To overcome these problems, we established a new galling insect model, Smicronyx madaranus. Our manipulation experiments using nail polish sealing and insecticide treatment revealed an age-dependent change in gall formation by S. madaranus; adult females and larvae are responsible for gall induction and enlargement, respectively. Furthermore, it has been suggested that substances released during oviposition and larval feeding are involved in each process. Phylogenetic analysis showed that gall-forming weevils, including S. madaranus, belong to two distinct lineages that utilize different host plants. This may indicate that gall-forming traits evolved independently in these Smicronyx lineages. The efficacy of RNA interference (RNAi) in S. madaranus was confirmed by targeting the multicopper oxidase 2 gene. It is expected that the mechanisms of gall formation will be elucidated by a comprehensive functional analysis of candidate genes using RNAi and the S. madaranus galling system in the near future.

Vascular implications of Dasineura sp. galls' establishment on Peumus boldus stems.

Some chewing larvae are capable of inducing galls in the host vascular cylinder, e.g. Dasineura sp. (Cecidomyiidae) on Peumus boldus stems. Due to the medicinal and economic importance of P. boldus, the anatomical and functional implications of establishment of Dasineura sp. on P. boldus stems were investigated. We asked if establishment of Dasineura sp. in P. boldus stems induces abnormalities at the cellular and organizational level of the vascular system that increase during gall development in favour of the hydric status of the gall. Anatomical alterations induced in the stems during gall development were determined. Cytohistometric analyses in mature galls were compared to non-galled stems, and water potential and leaf area of non-galled stems were compared with galled stems. Dasineura sp. establishes in the vascular cambium, leading to delignification and rupture of xylem cells, inhibiting formation of phloem and perivascular sclerenchyma. Gall diameter increases together with larval feeding activity, producing a large larval chamber and numerous layers of nutritive tissue, vascular parenchyma, and sclerenchyma. These anatomical alterations do not affect the leaf area of galled stems but favour increased water flow towards these stems. The anatomical alterations induced by Dasineura sp. in P. boldus stems guarantee water and nutrient supply to the gall and larva. After the inducer exits stems, some host branches no longer have vascular connections with the plant body.

Grape Phylloxera Genetic Structure Reveals Root-Leaf Migration within Commercial Vineyards.

Depending on their life cycle, grape phylloxera (Daktulosphaira vitifoliae Fitch) leaf-feeding populations are initiated through asexually produced offspring or sexual recombination. The vine's initial foliar larvae may originate from root-feeding phylloxera or wind-drifted foliar larvae from other habitats. Though some studies have reported phylloxera leaf-feeding in commercial vineyards, it is still unclear if they are genetically distinct from the population structure of these two sources. Using seven SSR-markers, this study analyzed the genetic structure of phylloxera populations in commercial vineyards with different natural infestation scenarios and that of single-plant insect systems that exclude infestation by wind-drifted larvae. We saw that during the vegetation period, phylloxera populations predominately go through their asexual life cycle to migrate from roots to leaves. We provided evidence that such migrations do not exclusively occur through wind-drifted foliar populations from rootstock vines in abandoned thickets, but that root populations within commercial vineyards also migrate to establish V. vinifera leaf populations. Whereas the former scenario generates foliar populations with high genotypic diversity, the latter produces population bottlenecks through founder effects or phylloxera biotype selection pressure. We finally compared these population structures with those of populations in their native habitat in North America, using four microsatellite markers.

Microbial Inoculants Differentially Influence Plant Growth and Biomass Allocation in Wheat Attacked by Gall-Inducing Hessian Fly (Diptera: Cecidomyiidae).

Beneficial root microbes may mitigate negative effects of crop pests by enhancing plant tolerance or resistance. We used a greenhouse experiment to investigate impacts of commercially available microbial root inoculants on growth and biomass allocation of wheat (Triticum aestivum L. [Cyperales: Poaceae]) and on survival and growth of the gall-inducing wheat pest Hessian fly, Mayetiola destructor (Say). A factorial design was used, with two near-isogenic wheat lines (one susceptible to Hessian fly, the other resistant), two levels of insect infestation (present, absent), and four inoculants containing: 1) Azospirillum brasilense  Tarrand et al. (Rhodospirillales: Azospirillaceae), a plant growth-promoting bacterium, 2) Rhizophagus intraradices (N.C. Schenck & G.S. Sm.) (Glomerales: Glomeraceae), an arbuscular mycorrhizal fungus, 3) A. brasilense + R. intraradices, and 4) control, no inoculant. Larval feeding stunted susceptible wheat shoots and roots. Plants had heavier roots and allocated a greater proportion of biomass to roots when plants received the inoculant with R. intraradices, regardless of wheat genotype or insect infestation. Plants receiving the inoculant containing A. brasilense (alone or with R. intraradices) had comparable numbers of tillers between infested and noninsect-infested plants and, if plants were susceptible, a greater proportion of aboveground biomass was allocated to tillers. However, inoculants did not impact density or performance of Hessian fly immatures or metrics associated with adult fitness. Larvae survived and grew normally on susceptible plants and mortality was 100% on resistant plants irrespective of inoculants. This initial study suggests that by influencing plant biomass allocation, microbial inoculants may offset negative impacts of Hessian flies, with inoculant identity impacting whether tolerance is related to root or tiller growth.

A new species of Youngomyia Felt from Brazil and new morphological data on Youngomyia pouteriae Maia (Insecta, Diptera, Cecidomyiidae)

Abstract Youngomyia matogrossensis Proença & Maia a new species of Cecidomyiidae (Insecta: Diptera) that induces cylindrical hairy galls on leaves of Pouteria torta (Mart.) Radlk. (Sapotaceae) is herein described and illustrated (larvae, pupal exuviae, male and female). The galler, gall and host plant were collected at Parque Nacional da Chapada dos Guimarães, in the state of Mato Grosso (Brazil). New morphological data and photographs of pupal exuviae, male and female of Youngomyia pouteriae Maia, 2001 are also provided.

Insect galls of Itamonte (Minas Gerais, Brazil): characterization and occurrence / Galhas de insetos de Itamonte (Minas Gerais, Brasil): caracterização e ocorrência

Three sites of Itamonte (Minas Gerais) were investigated for insect galls from September, 2011 to July, 2012, seasonally. One-hundred and one morphotypes of insect galls were recorded on 63 species of host plant (45 genera and 23 families). Melastomataceae was the most galled plant family, followed by Asteraceae and Myrtaceae. Galls were recorded on leaves, stems, buds, and aerial roots. Leaves were the most galled plant organ. The gall morphotypes were characterized according to their shape, color, pubescence, and number of internal chambers. Globose and fusiform galls were the most frequent. The majority was glabrous and one-chambered. The gallers comprised three insect orders: Diptera (Cecidomyiidae and Tephritidae), Hemiptera, and Lepidoptera. Cecidomyiidae were the most frequent galling taxa. Parasitoids (Hymenoptera) were obtained from six morphotypes (ca. 6% of the total). The results are compared to those of other Brazilian insect gall inventories. As there is no previous gall inventory in Itamonte, all records presented here are new.

Três localidades de Itamonte (Minas Gerais) foram investigadas para galhas de inseto no período de setembro, 2011 a julho, 2012, sazonalmente. Cento e um morfotipos de galhas de inseto foram registrados em 63 espécies de plantas hospedeiras (45 gêneros e 23 famílias). Melastomataceae, Asteraceae e Myrtaceae foram as famílias de planta com maior riqueza de galhas. As galhas foram encontradas em folhas, caules, gemas e raízes aéreas. As folhas foram o órgão vegetal com maior incidência de galhas. Os morfotipos foram caracterizados em relação è forma, coloração, pubescência e número de câmaras internas. Galhas globosas e fusiformes foram as mais frequentes. A maioria era glabra e unilocular. Os galhadores incluíram três ordens de insetos: Diptera (Cecidomyiidae and Tephritidae), Hemiptera e Lepidoptera. Os Cecidomyiidae foram o táxon galhador mais frequente. Parasitóides (Hymenoptera) foram obtidos de seis morfotipos de galhas (cerca de 6% do total). Os resultados são comparados com outros inventários de galhas no Brasil. Como não havia inventário prévio de galhas em Itamonte, todos os registros apresentados são novos.

Duas novas espécies de Lopesia Rübsaamen (Diptera, Cecidomyiidae) do Brasil, com chave para as espécies / Two new species of Lopesia Rübsaamen (Diptera, Cecidomyiidae) from Brazil, with an identification key of species

Lopesia erythroxyli Rodrigues & Maia e Lopesia maricaensis Rodrigues & Maia, duas novas espécies de Cecidomyiidae que induzem galhas cônicas em gemas de Erythroxylum ovalifolium Peyr (Erythroxylaceae) e enrolamentos da borda da folha de Protium brasiliense (Spr.) Engl. (Burseraceae), são descritas e ilustradas (larva, pupa, macho, e fêmea) baseado em material do Rio de Janeiro, Brasil. Uma chave de segregação para as espécies conhecidas de Lopesia é dada.

Lopesia erythroxyli Rodrigues & Maia and Lopesia maricaensis Rodrigues & Maia, two new species of Cecidomyiidae that induce conical galls on bud of Erythroxylum ovalifolium Peyr (Erythroxylaceae) and on marginal leaf roll of Protium brasiliense (Spr.) Engl. (Burseraceae), are described and ilustrated (larva, pupa, male, and female) based on material from Rio de Janeiro, Brazil. A key to the known species of Lopesia is given.