User:Stephaniestamp/sandbox

Lee:

- Types of trees affected is very short. Do you know if specific species of trees are being targeted or does it depend on where beetles are located/found?

- There's nothing written under the chemical defense. If you aren't going to expand it, I think it might be better to get rid of it.

= Blue stain fungus symbiosis =

Fungal species with known symbiont roles
The term blue stain fungi refers to any fungus with dark pigmentation, primarily blue but may be more grey-ish, that stains the wood in which it is inoculated. The fungi that are responsible for the effects of the blue staining fungus belong to the family Ophiostomataceae, of Ascomycota, with some belonging to the genus Grosmannia (specifically Grosmannia clavigera), Ophiostoma, and Ceratocystis.

Beetle species with known associations
The beetles associated with blue staining fungi, commonly referred to as bark beetles, belong to the Scolytinae family with many belonging to the genus Dendroctonus. The mountain pine beetle (Dendroctonus ponderosae) is one of the most prolific and widespread insects that is associated with blue stain fungi, while ambrosia beetle s maintain a close relationship but with their own specific type, the ambrosia fungus.

Characteristics of beetles
While not always being associated with a type of fungus, all beetles that fall under the heading of bark beetle use trees as a means for reproduction. Depending on the species, either the male or female will burrow through the bark and create egg galleries within the tree. Once the eggs are laid, they will hatch and the beetles will then overwinter as larvae, feeding not on the bark but on the slightly more nutritious phloem tissue. Once a tree is not able to produce any more phloem tissue, the beetles (and fungus) must move on to a new host.

Beetle as a fungal vector
Because the perpetuation of the symbiosis depends on the inoculation of new host trees by successive beetle generations, the fungus has developed a dependence on the transportation provided by the insect. The mountain pine beetle acts as a vector for the Ophiostoma fungus, increasing access to new hosts. The fungus does not create any reproductive structures to disperse spores, making the beetle an essential part of the fungal reproductive cycle.

Physiological connections/structures
Beetles associated with the blue stain fungal strains have often been found to have anatomical structures that appear to be specific to supporting this symbiosis. Some species exhibit integumental invaginations known as as mycangium, which are sac-like structures located on the distal end of the main mouthpart, known as the maxillary cardines. Other species lack these sac-like mycangia but have structures located on their exoskeleton, such as pits, that function to transport fungi and so can be considered mycangia.

Several studies have employed different methods to explore the purpose of these structures, including the use of electron microscopy for visual confirmation as well as procedures to culture the fungi in the lab based on the contents of the mycangium. There has been evidence of bacterial cohabitants inside the mycangium as well, which may imply another layer of symbiosis and/or competition.

Fungal benefits to beetle
The fungi may aid the beetle in stifling tree defenses and conditioning phloem (e.g. detoxifying tree defense chemicals) in order to facilitate brood development. There is other research suggesting that the fungus overstimulates the tree's defense mechanisms, oftentimes triggering a hypersensitive response, causing the tree to lose valuable resources in the attempt to protect itself. The exhaustion of tree defenses allows for complete invasion of the tree's sapwood and phloem tissues.

There has also been research suggesting that the fungus modifies the generally nutrient-poor phloem tissue, or provides complimentary vitamins, proteins or sterols to supplement the larval diet.

Some blue stain fungi have been observed to be very pathogenic, and may even kill their host in the absence of their beetle vector.

Types of trees affected
There are a number of trees that may be colonized by blue stain fungi, including lodgepole pine, Norway spruce, jack pine, and tree hybrids. It appears that the fungi/beetle symbiosis is not species specific in terms of host selection.

Host choice by beetle
The host site is selected by either a male or female beetle (which varies with genus ) and in most cases the beetles will seek a diseased or dying tree. There are several theories for how the insects select their host tree, such as the long range detection of volatile chemicals usually released by dying trees (known as primary attraction), and another where pheromones produced by beetles are detected close range, after the beetle has landed on the tree. Bark beetles then release an aggregation pheromone to alert and attract conspecifics, an area of study that has been receiving increasing interest in recent years.

Fungal inoculation
The inoculation process begins in midsummer, with the emergence of adult beetles searching for tree hosts. Sexually immature adult beetles acquire fungal spores just prior to dispersing from the natal host when, shortly before emerging, they feed on thick layers of spores that commonly line the galleries in which the larvae pupate. After locating a suitable host, a beetle will chew through the inner bark of the tree in order to create the egg galleries. The fungus is carried by the beetle, and introduced into the tree tissue upon tunneling. The fungus is initially confined to the beetle frass of the egg galleries but then spreads, first proliferating in sapwood rays and systematically breaching successive layers of phloem with hyphae until they penetrate the primary cell walls of the ray parenchyma cells to infiltrate the pith layer. Fungal hyphae then proceed to breach the tracheid s, after which they grow in a longitudinal fashion.

Fungal effects on trees
Due to the infiltration of the phloem and sapwood by the hyphae, the tree begins to suffer water stress and essentially starvation as its water conducting network is blocked by the fungal mycelium. The tracheids are also blocked by the germinating fungal spores, making nutrient transfer very difficult for the tree. The characteristic color, from which the blue stain fungus gets its name, is the result of staining of the sapwood due to the dark pigmentation of the hyphae themselves, and can also be a slight grey color depending on the fungus type. The discoloration of wood due to a fungal inoculation specifically is known as spalting.

Mechanical defenses
Upon detection of a burrowing beetle, the conifer tree may release a heavy resin flow from the wound, a process known as resinosis in order to fend off attack. The resin is thick and viscous, slowing down and possibly entombing the beetle attempting to penetrate the bark to access the layers underneath. The production and use of calcium oxalate crystals has also been seen to mechanically impede the movement of beetles within the phloem, and it is thought that the tough physical structure physically restricts the insects.

Chemical defenses
Chemical defenses employed by trees against beetles include the manufacture of phenolic compunds, common plant defenses against herbivory, which require a metabolic change in the phloem parenchyma cells. Infected trees have also been observed to produce enzymes such as protein-based chitinases and glucanases that can degrade the chitonous exoskeletons of the beetles, as well as toxic porins and lectins, all of which impede the ability of the beetle to metabolize the substrate.

Economic importance
Because the staining of the wood caused by the fungi is not removable, many stands of lumber lose a considerable amount of value as the discoloration is not desirable to most consumers. However, as a preventative measure to staining, boards may be inoculated with a colorless mutant fungus Ophiostoma piliferum to prevent discoloration from the blue variant. The structural integrity of the wood is not affected and the dark coloration is purely cosmetic as the blue stain fungus does not cause decay of lignin or cellulose.

Effects of climate change
Increased frequency of higher temperatures and more frequent droughts during the last 25 years has resulted in a steady increase in bark beetle outbreaks as milder winters allow for the beetles to skip the overwintering process and continue to reproduce and spread to new hosts. Not only do the numbers of beetles increase, but their range does as well, potentially putting the beetles in contact with tree stands with no previous interactions with the beetles, making them more susceptible to being overwhelmed before their defenses can be triggered.

Watershed effects
As a result of large amounts of dying pines, the mountain pine beetle, coupled with its fungal symbiont, may be driving changes in hydrological effects such as annual water yield, peak and low flows, groundwater levels and soil moisture, and these effects have been postulated to possibly last as long as 60-70 years. Other studies have seen a rapid increase of groundwater levels in previously pine-dominated areas, coupled with the premature replacement of 'summer soil' (dry and firm) with 'winter soil' (wetter, less firm), making the operation of large forestry equipment difficult to nearly impossible before the freezing of the soil in the winter months.