許多種之長喙殼菌真菌類真菌可稱之為藍染真菌 (blue stain fungi)，因為其深 色之菌絲，會在寄主植物之邊材上造成藍、灰、甚至黑色之變化。其利用儲存於 邊材射髓 (ray parenchyma) 中之營養，因為不會分解纖維素、木質素、半纖維素，
所以並不會破壞樹木之結構，從外觀上可以在樹木之邊材及樹皮部位觀察到藍染 之現象。雖然大部分造成樹木藍染的長喙殼菌類真菌並不會造成植物之病害，但 少數亦會致病，造成維管束 (導管及假導管) 的阻塞 (Kirisits & Offenthaler, 2002) 甚至在高的接種濃度下，亦能造成樹皮壞疽、甚至樹木之死亡。此類病害屬於維 管束變色 (vascular stain)，非維管束萎凋，此類病原即是指致病力強之長喙殼菌 類真菌，包括 Ceratocystis polonica、C. laricicola、C. rufipenni、Leptographium wingfield、Ophiostoma minus 等 (Kirisits et al., 2002)。
長喙殼菌類真菌的演替
然而三個論述可以反駁此說法 (Six & Wingfield, 2010)，其一、可以造成樹木死亡 之小蠹蟲，其族群中並非每一個體都會攜帶共生之真菌，在縱使沒有攜帶具共生 真菌的情況下 (或有攜帶低致病力之真菌)，小蠹蟲也能對樹木有致死能力，顯示 植物的防禦機制在沒有真菌存在下，也能被小蠹蟲克服，所以小蠹蟲是可以不需 要真菌來消耗防禦機制的。其二、如果共生真菌確實能幫助小蠹蟲克服植物之防 禦機制，在共生關係的演化上，必定趨向“大部分之小蠹蟲個體皆具有致病力之共 生真菌”，因為那些不具有共生真菌之小蠹蟲是無法在活體植物立足的；然事實卻 不然，許多小蠹蟲與真菌共生的關係上，僅有部分 (甚至少部份)
的小蠹蟲個體身上帶有致病力之真菌，顯示出真菌對小蠹蟲來說，並非必要 的因子。其三、就真菌致病的歷程而言，若真菌是隨著小蠹蟲於繁殖鑽孔階段才 進入植物，以真菌生長緩慢之速度，根本來不及誘發植物之防禦能力來協助小蠹 蟲之入侵植物；在這同時，若果真有誘發植物之防禦反應，實際上是會將同時存 在之小蠹蟲防禦在外的，反而不利於小蠹蟲。以上之論述即是反駁“共生真菌作為 消耗樹木防禦機制來幫助小蠹蟲”說法的理論基礎。然而此說法亦不能一以概之，
對於那些羽化飛出樹幹後需要有一段熟成取食期之小蠹蟲種類，在侵入樹幹繁殖 前，其會暫時先棲息於樹梢幼嫩處 (Wood, 1982)，所以其所攜帶之菌種就明顯的 有足夠的時間，先削弱植物之防禦能力，來為後續小蠹蟲之鑽孔侵入鋪路。我們 相信此類真菌就有實際幫助昆蟲克服植物防禦機制之作用。然而大部分之小蠹蟲 明顯的並沒有因其所攜帶之真菌而獲得好處，所以可以推測真菌是偶然的搭乘小 蠹蟲之“便車”而傳播的。另外有一種關係，小蠹蟲反而會因為其所攜帶之共生真 菌而有負面之影響，southern pine beetle (南方松甲蟲 Dendroctonus frontalis) 和 Ophiostoma minus 之關係即是如此，此真菌若在樹木中生長量增加，就會使南方 松甲蟲之族群受到威脅而降低。有些種類之小蠹蟲，雖然也同樣是生長於樹皮內 側，但其身體構造上特化出儲菌器 (mycangium) 之攜菌構造 (Six, 2003)，對於此 共生關係，小蠹蟲就絕對的 (obligate) 需依賴其所共生的真菌才得以生存 (取食 此真菌，主要作為必需營養的補充)，小蠹蟲即是明顯獲益的一方。
然小蠹蟲 Tomicus piniperda 和真菌 Ophiostoma wingfieldii 共生，但族群中只有 少數個體會攜帶真菌 (Solheim & Långstöm, 1991)。有些種類族群中多數之個體會 攜帶真菌，但不同之個體可能會攜帶不同之共生菌，因為其共生菌的真菌種類皆 不只一種。
Ophiostoma、Ceratocystiopsis、Grosmannia 和小蠹蟲之關係 此類菌和小蠹蟲之共生關係緊密，也即是其傳播主要是依賴小蠹蟲。只有少 數種類和小蠹蟲之共生關係較為薄弱，而經常是由空氣、雨水、或其他昆蟲所攜 帶 (Krokene & Solheim, 1996; Stauffer et al., 2001)，如 Ophiostoma piceae 及 O.
piliferum。在專一性方面，有些種類專一性強，由特定之小蠹蟲所攜帶；而大多 數的種類專一性較低，同一種真菌會由不同之小蠹蟲攜帶至不同之寄主上。
Ceratocystis 和小蠹蟲之關係
此類真菌和小蠹蟲共生關係較不緊密，即經常都是藉由其他方式傳播，許多 種類甚至不需昆蟲之媒介，且專一性 低，但亦有少數種類具有高的專一性 (Harrington & Wingfield, 1998; Yamaoka et al., 1998)。
結 論
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Bark beetles are commonly associated with ophiostomatoid fungi. The devastating Dutch elm disease is the most notable example. The relationship between both partners is recognized as being symbiotic. Fungi benefit from this association to infect new host trees via bark beetles’ delivery. However, to bark beetles this association can be beneficial, neutral, or detrimental. For the beneficial effect, fungi pave the way for the bark beetles to invade trees by overwhelming host tree defenses.
This conception is being challenged due to the fact that some aggressive bark beetles can invade and kill trees without the virulent fungal companions. It suggests that there remain lots to be unveiled in their symbiotic relationships. Nevertheless, bark beetles are the carriers for many pathogenic ophiostomatoid fungi. Therefore clarification of the relationship between them will be valuable in the prevention and control of plant diseases caused by them.