Endophytic Insect Research Articles

Antagonism of the endophytic insect pathogenic fungus Metarhizium robertsii against the bean plant pathogen Fusarium solani f. sp. phaseoli

The antagonism of bean (Phaseolus vulgaris) root rot fungus Fusarium solani f. sp. phaseoli by the endophytic insect pathogenic fungus Metarhizium robertsii was investigated in vitro and in vivo. Dual cultures on Petri dishes showed antagonism of M. robertsii against F. solani. A relative inhibition of c. 60% of F. solani growth was observed in these assays. Cell-free culture filtrates of M. robertsii inhibited the germination of F. solani conidia by 83% and the inhibitory metabolite was heat stable. Beans plants colonized by M. robertsii, then exposed to F. solani, showed healthier plant growth and lower disease indices compared with plants not colonized by M. robertsii. These results suggest that the endophytic insect pathogenic fungus M. robertsii could also be utilized as a biocontrol agent against certain plant root pathogens.

How to be a fig wasp down under: The diversity and structure of an Australian fig wasp community

Endophytic insects and their parasitoids provide valuable models for community ecology. The wasp communities in inflorescences of fig trees have great potential for comparative studies, but we must first describe individual communities. Here, we add to the few detailed studies of such communities by describing the one associated with Ficus rubiginosa in Australia. First, we describe community composition, using two different sampling procedures. Overall, we identified 14 species of non-pollinating fig wasp (NPFW) that fall into two size classes. Small wasps, including pollinators, gallers and their parasitoids, were more abundant than large wasps (both galler and parasitoid species). We show that in figs where wasps emerge naturally, the presence of large wasps may partly explain the low emergence of small wasps. During fig development, large gallers oviposit first, before and around the time of pollination, while parasitoids lay eggs after pollination. We further show that parasitoids in the subfamily Sycoryctinae, which comprise the majority of all individual NPFWs, segregate temporally by laying eggs at different stages of fig development. We discuss our results in terms of species co-existence and community structure and compare our findings to those from fig wasp communities on other continents.

Endophytic Colonization by Brazilian Strains of <i>Bacillus thuringiensis</i> on Cabbage Seedlings Grown <i>in Vitro</i>

Bacillus thuringiensis is a very important bacterium used as a biological control agent of agricultural pests. It may be isolated from soil, water, plants and dead insects. Three Brazilian B. thuringiensis strains that present high activity to Lepidoptera pests were inoculated in the seeds of cabbage in order to study the penetration and endophytic colonization of this entomopathogen in cabbage using scanning electron microscopy. The ability of B. thuringiensis to colonize endophytic seedlings was verified by the presence of vegetative cells, spores and crystals of the four Brazilian B. thuringiensis strains in different parts of cabbage seedlings. The observation of B. thuringiensis structure on roots, shoots and leaves of cabbage revealed colonization predominantly on roots. The colonization was shown on the surface, near the stomata and inside stomata pores. The mechanism of penetration of B. thuringiensis probably occurs through openings and injuries in roots and then moves through the xylem until reaching the leaves. The endophytic colonization of B. thuringiensis did not affect the germination of seeds and initial seedling development. The strains labeled with radioisotopes were inoculated on cabbage and were detected inside the plant. This article demonstrates for the first time the ability of B. thuringiensis to colonize cabbage seedlings that are important to control the cryptic pest as P. xylostella and others endophytic insect’s pests.

The first record of endophytic insect oviposition from the Tartarian of European Russia

The first endophytic oviposition in a plant leaf from the Tatarian of European Russia (Isady locality) is formally described as Paleoovoidus rasnitsyni, sp. nov. This find supplements considerably the data on plant-insect interaction recorded in this locality.

Bacteria in oral secretions of an endophytic insect inhibit antagonistic fungi

Abstract1. Colonisation of host trees by an endophytic herbivore, the spruce beetle,Dendroctonus rufipennis, is accompanied by invasion of its galleries by a number of fungal species. Four of these associated species were identified asLeptographium abietinum,Aspergillus fumigatus,Aspergillus nomius, andTrichoderma harzianum.2. TrichodermaandAspergillussignificantly reduced spruce beetle survival and reproduction in controlled assays.3. A previously undescribed behaviour was observed, in which spruce beetle adults exuded oral secretions, especially within fungus‐pervaded galleries.4. These oral secretions inhibited the growth of fungi exceptA. nomius, and disrupted the morphology of the latter. Administration of these secretions indicated a dose‐dependent inhibitory effect.5. Oral secretions cultured on microbiological media yielded substantial bacterial growth.6. Filter‐sterilised secretions failed to inhibit fungal growth, evidence that the bacteria are responsible for the antifungal activity.7. Nine bacterial isolates belonging to the Actinobacteria, Firmicutes, Gammaproteobacteria, and Betaproteobacteria taxa were obtained from the secretions.8. Bacterial isolates showed species‐specific inhibitory activity against the four fungi antagonistic to spruce beetle. The bacterium with the strongest fungal inhibition activity was the actinomyceteMicrococcus luteus.9. The production of bark beetle secretions containing bacteria that inhibit fungal growth is a novel finding. This suggests an additional level of complexity to ecological associations among bark beetles, conifers, and microorganisms, and an important adaptation for colonising subcortical tissue.

Bacteria Associated with the Guts of Two Wood-Boring Beetles: <I>Anoplophora glabripennis</I> and <I>Saperda vestita</I> (Cerambycidae)

Commensal microorganisms have significant impacts on the health of many insect hosts. Little is known, however, about the structure of commensal bacterial communities associated with the Cerambycidae, despite the important roles this large family of herbivorous endophytic insects plays in ecosystem processes, economic losses to ornamental and forest trees, and biological invasions. We analyzed the bacterial commensal communities of the exotic Asian longhorned beetle, Anoplophora glabripennis, and the native linden borer, Saperda vestita, by randomly sequencing 16S rRNA gene fragments from bacterial DNA extracted directly from the gut of larvae. The 16S rRNA gene sequences sampled from S. vestita were derived entirely from the γ-Proteobacteria phylum of Bacteria. In contrast, the gut of A. glabripennis larvae contained members of the α-Proteobacteria, β-Proteobacteria, γ-Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes. A better understanding of insect-microbe interactions may lead to new strategies to reduce the effects of these pest species.

Endophytic insect communities of two prairie perennials (Asteraceae: Silphium spp.)

Little is known of the biology of most insects that are endemic to prairie ecosystems of North America, with the exception of large and conspicuous species. In particular, species that are sequestered within plant tissues are commonly overlooked. In this paper, we assess the biodiversity of endophytic insects that inhabit stems of Silphium laciniatum L. and S. terebinthinaceum Jacquin (Asteraceae), endemic plants of tallgrass prairies. Endophytic herbivores, gall wasps Antistrophus rufus Gillette and A. minor Gillette (Hymenoptera: Cynipidae) and stem-boring larvae of the beetle Mordellistena aethiops Smith (Coleoptera: Mordellidae) were attacked by 10 species of natural enemies. We report new host plant associations for herbivores, and new host insect associations for parasitoids. The two plant species differed significantly in their densities of gall wasps and the vertical dispersion of galls within stems. Interactions within and between trophic levels attest to the biodiversity of endophytic insect communities, and the specialized nature of these insects suggests they are highly vulnerable to habitat conservation practices that involve destruction of dead vegetation.

Impact of prescribed burning on endophytic insect communities of prairie perennials (Asteraceae: Silphium spp.)

Prescribed burning currently is used to preserve endemicity of plant communities in remnant tallgrass prairies. Although some types of arthropods benefit from changes in plant communities brought about by burning, other species that are endemic to prairies may be threatened. Because they inhabit the ‘fuel layer’ of prairies, endophytic insects would seem particularly susceptible to this management tactic. In this paper, we assess the impact of prescribed burning on endophytic insect communities inhabiting stems of Silphium laciniatum L. and S. terebinthinaceum Jacquin (Asteraceae), endemic prairie plants. Populations of these insects were decimated by burning, with mortality approaching 100% in most cases. Their populations nevertheless began to rebound within a single growing season, with densities moderately but significantly reduced 1 year after the burn. Even when a prairie remnant was completely incinerated, plant stems were recolonized by insects within one growing season. Our findings suggest that sufficient numbers of endophytic insects survive burns in remains of Silphium to recolonize burned areas the following year.

Effects of Nutrient Enrichment on Growth and Herbivory of Dwarf Red Mangrove (Rhizophora Mangle)

The objectives of this study were to determine responses by red mangrove (Rhizophora mangle) and its primary consumers to nutrient enrichment, to determine if nutrient limitation is responsible for the dwarf plant form of red mangrove, and to evaluate four competing hypotheses for the relation of nutrient status and invertebrate herbivory. In a factorial-designed experiment, I fertilized 48 dwarf trees along gradients of tidal elevation and water depth at Twin Cays, an intertidal mangrove island in Belize, Central America, and measured plant growth responses and herbivory for 2 yr. At the end of year- 2, I compared biomass accumulation and analyzed plant tissue for chemical and structural composition. Dwarf red mangrove trees on this tidal island responded quickly and grew vigorously when treated with P and NPK fertilizers. Leaf number, leaf area, branching, shoot length, and aerial root production increased dramatically over 2 yr. N-fertilized trees grew very slowly and their responses were not different from Control trees. N-fertilized and Control trees changed little over 2 yr. Some responses to phosphorus-containing fer- tilizers vary by water depth and tidal elevation, but physicochemical factors do not explain the differences in growth responses. I conclude that phosphorus availability is a major factor limiting red mangrove growth at my study site in the interior of Twin Cays. Herbivory by two specialized, endophytic insect species (Ecdytolopha sp., which feeds in apical buds, and Marmara sp., which mines stem periderm) increased in P- and NPK-fertilized trees compared to N-fertilized and Control trees. Twice as many apical buds were damaged or destroyed and the frequency of mines increased by 6-8 fold. However, fertilization had no effect on feeding rates and standing damage by a leaf-feeding guild of generalist herbivores or on the frequency of shoots killed by stem borers. Herbivory by the two specialists was not related to C:N ratios, but it was inversely related to concentrations of phenolic com- pounds. Neither nutrient ratios nor concentrations of phenolics affected rates of herbivory by the generalist folivores. Although sclerophylly of red mangrove leaves decreased in P- and NPK-fertilized trees but not in N-fertilized and Control trees, there was no relationship between leaf toughness and herbivory by generalist folivores. These data suggest that sclerophylly in oligotrophic ecosystems may be an adaptive mechanism related to nutrient conservation, and that it is associated with red mangrove survival in phosphorus-deficient soil rather than an adaptation to herbivory.