Microbiomes of willow-galling sawflies: effects of host plant, gall type, and phylogeny on community structure and function

While free-living herbivorous insects are thought to harbor microbial communities composed of transient bacteria derived from their diet, recent studies indicate that insects that induce galls on plants may be involved in more intimate host–microbe relationships. We used 16S rDNA metabarcoding to survey larval microbiomes of 20 nematine sawfly species that induce bud or leaf galls on 13 Salix species. The 391 amplicon sequence variants (ASVs) detected represented 69 bacterial genera in six phyla. Multi-variate statistical analyses showed that the structure of larval microbiomes is influenced by willow host species as well as by gall type. Nevertheless, a “core” microbiome composed of 58 ASVs is shared widely across the focal galler species. Within the core community, the presence of many abundant, related ASVs representing multiple distantly related bacterial taxa is reflected as a statistically significant effect of bacterial phylogeny on galler–microbe associations. Members of the core community have a variety of inferred functions, including degradation of phenolic compounds, nutrient supplementation, and production of plant hormones. Hence, our results support suggestions of intimate and diverse interactions between galling insects and microbes and add to a growing body of evidence that microbes may play a role in the induction of insect galls on plants.

Plant galls recorded from Guanacaste Conservation Area-Costa Rica as an integrated concept of a biological database

Galling insects are specialist herbivorous that have the ability of manipulating plant tissue to form complex biological structures called galls. Even though different organisms have the ability to induce galls in plants, insect galls have the highest degree of structural complexity. The main goal of this study was to obtain a preliminary systematic record of plant gall morphotypes from the Guanacaste Conservation Area in Costa Rica and integrate the information into a biological database. Plant gall morphotypes were recorded, characterized and deposited into a specialized herbarium established as a reference for the inventory. Moreover, organisms associated with gall morphotypes were included in the inventory when it was possible to obtain and identify them. Galls were collected in the rainy season over a period of three years. In total, we recorded forty-four families, seventy genera, and eighty-seven host plant species. One hundred thirty-one morphotypes of plant galls were identified in the Guanacaste Conservation Area. The family with the highest number of gall morphotypes was Fabaceae (8.4%). Leaves were the organ with the largest number of galls (71%), followed by stems (17.6%), and apical buds (6.9%). The predominant gall shape was globular (25.2%), followed by discoid (18.3%). Fifty-nine percent of the galls had a glabrous texture, which was most common on leaves, with 77%. One hundred twenty of our field records (91.6%) of plant galls were new morphotypes not only for Costa Rica but also the world. As a consequence of this research and considering the prospect of future increases in new gall records (and associated organisms), we proposed having the biological entities resulting from the inventory placed in a cecidiarium. This repository represents a standardized and comprehensive way to manage the data and biological materials associated with the plant galls. We also suggest a nomenclature for standardizing gall morphotype registries and identifications. This work is the first and most detailed inventory of plant galls carried out thus far in the Guanacaste Conservation Area.

A novel family of secreted insect proteins linked to plant gall development

In an elaborate form of inter-species exploitation, many insects hijack plant development to induce novel plant organs called galls that provide the insect with a source of nutrition and a temporary home. Galls result from dramatic reprogramming of plant cell biology driven by insect molecules, but the roles of specific insect molecules in gall development have not yet been determined. Here we study the aphid Hormaphis cornu, which makes distinctive “cone” galls on leaves of witch hazel Hamamelis virginiana. We found that derived genetic variants in the aphid gene determinant of gall color (dgc) are associated with strong downregulation of dgc transcription in aphid salivary glands, upregulation in galls of seven genes involved in anthocyanin synthesis, and deposition of two red anthocyanins in galls. We hypothesize that aphids inject DGC protein into galls, and that this results in differential expression of a small number of plant genes. Dgc is a member of a large, diverse family of novel predicted secreted proteins characterized by a pair of widely spaced cysteine-tyrosine-cysteine (CYC) residues, which we named BICYCLE proteins. Bicycle genes are most strongly expressed in the salivary glands specifically of galling aphid generations, suggesting that they may regulate many aspects of gall development. Bicycle genes have experienced unusually frequent diversifying selection, consistent with their potential role controlling gall development in a molecular arms race between aphids and their host plants.One Sentence SummaryAphid bicycle genes, which encode diverse secreted proteins, contribute to plant gall development.

The mechanism of plant gall induction by insects: revealing clues, facts, and consequences in a cross-kingdom complex interaction

Galls are defined as modifications of the normal developmental design of plants, produced by a specific reaction to the presence and activity of a foreign organism. Although different organisms have the ability to induce galls in plants, insect-induced galls are the most elaborate and diverse. Some hypotheses have been proposed to explain the induction mechanism of plant galls by insects. The most general hypothesis suggests that gall formation is triggered by the action of chemical substances secreted by the gall inducer, including plant growth regulators such as auxins, cytokinins, indole-3-acetic acid (IAA), and other types of compounds. However, the mode of action of these chemical substances and the general mechanism by which the insect could control and manipulate plant development and physiology is still not known. Moreover, resulting from the complexity of the induction process and development of insect galls, the chemical hypothesis is very unlikely a complete explanation of the mechanism of induction and morphogenesis of these structures. Previous and new highlights of insect gall systems with emphasis on the induction process were analyzed on the basis of the author’s integrated point of view to propose a different perspective of gall induction, which is provided in this article. Due to the extraordinary diversity of shapes, colors, and complex structures present in insect galls, they are useful models for studying how form and structure are determined at the molecular level in plant systems. Furthermore, plant galls constitute an important source of material for the study and exploration of new chemical substances of interest to humans, due to their physiological and adaptive characteristics. Considering the finely tuned control of morphogenesis, structural complexity, and biochemical regulation of plant galls induced by insects, it is proposed that an induction mechanism mediated by the insertion of exogenous genetic elements into the genome of plant gall cells could be involved in the formation of this kind of structure through an endosymbiotic bacterium.

RESISTANCE OF SOME NEW CLONES OF EUCALYPTUS TO INSECTS CAUSES GALL IN MOUNT MUTIS, NTT

Eucalyptus (Eucalyptus spp.) is a fast-growing tree native in Australia, Papua, and Eastern part of Indonesia. It is valued for its timber, oil, gum, and resin, and as an ornamental tree. Many eucalyptus clones have been developed and planted for timber production in Sumatera. Several galls caused by insects are known as serious pests of eucalyptus and can reduce the quality and quantity of the timber production. This study was aimed to identify the gall inducers and describe the galls that formed on the eucalyptus clones which planted in Mt. Mutis, East Nusa Tenggara Province. The research was conducted from October 2017 to July 2018. A total of 855 seedlings consisting of 57 clones and 15 plants for each clone were planted in Mt. Mutis. Observations of the gall symptoms were done biweekly on each plant. Gall symptoms were directly observed and identified, included the form, size, location, color, and insect that caused the gall. There were four types of gall forms were recorded. One type of gall caused by Ophelimus sp. (Hymenoptera: Eulophidae) which similar to the gall recorded in Sumatera and Java. The other three gall forms were never been reported in Indonesia. The insects that associated with galls were Hymenoptera and Diptera orders. The type of gall that mostly found in the eucalyptus clones was the big clustered leaf gall caused by Fergusonina sp. (Diptera: Fergusoninidae). There are only two clones which are included as susceptible clones based on the type of gall formed, C35 and C53. There were 27 eucalyptus clones with no gall infestations which were considered as the good candidate of resistance eucalyptus clones to the gall infestations.

INFLUENCE OF PHYTONCIDE PROPERTIES OF OAK PLANTATIONS ON THE GROWTH AND DEVELOPMENT OF OAK GALLFLIES IN COPPICE OAK FOREST IN URBAN GREEN BELT OF VORONEZH

The article is devoted to research on the effect of phytoncide properties of oak grown in plantations of forest and park area of Voronezh on the growth and development of oak gallflies. The aim is to study the oak pests - oak gallflies - small flying insects. The female of gall wasps makes injection on an oak leaf using the ovipositor and lays eggs in the wound, which is beginning to develop, and the next underlying cells and tissues begin to form sheet "nut" or plant gall. Soon the larva hatches from the egg and begins to work its jaws. All larval development occurs in the gall. It turns out that from the time of laying the egg and then the larva during all the time of its development are in close proximity to the plant tissues and phytoncides. So, oak leaf tissue is not toxic to the larvae of gallflies. Meanwhile, it is well known that volatile phytoncides of oak leaves are poisonous to many microorganisms including the very resistant, for example, for the dysentery bacillus. When laying eggs in the leaf tissue insects necessarily hurt it. Namely wound leaf increases the "production" of phytoncides, but it remains without consequences for the insect to adapt to phytoncides of oak leaves. This adaptation of some insects to poisonous phytoncides affects equally scientists. One of the major reasons of sanitary and hygienic influence of the forest is the antimicrobial effect of the volatile, which secrete plant organizations as they play an important role in chemical interaction of plants in phytocenoses, that was proved by the works of N. G. Kholodny, A. L.Kholodny, A. L. Chesovennaya (1987) – the number of phytoncides and their activity in one and the same species varies with conditions of oak forest location