Insecticidal Metabolites from Fusarium avenaceum, a Fungus Associated with Foliage of Abies balsamea Infested by Spruce Budworm, Choristoneura fumiferana

Abstract

Hyphae from cultures of Fusarium avenaceum, a fungus associated with spruce budworm-infested balsam fir foliage, were toxic to spruce budworm larvae when ingested. The toxic principle isolated from hyphal extracts was identified as enniatin complex, rich in enniatin A/A 1 . A minor F. avenaceum product, ergosterol peroxide, caused damage to spruce budworm cell cultures, but did not display toxicity in feeding assays at the range of concentrations tested. Ecological implications of the presence of insecticidal fungi on the foliage of spruce budworm host-trees are addressed.The spruce budworm, Choristoneura fumiferana (Clemens), is a phytophagous insect, whose principal hosts are balsam fir, Abies balsamea (L.) Mill., and three spruce, Picea species, which together dominate the coniferous forests of eastern North America. Populations of the insect periodically irrupt to epidemic proportions, resulting in widespread destruction of susceptible host trees, with major ecological and recently, economic consequences. The outbreaks are followed by dramatic declines of the insect populations, and there is evidence indicating that, at least during the last two centuries, these oscillations have occurred quite regularly with a frequency of 30-40 years (]_, 2). A detailed understanding of the processes that cause the collapse of an epidemic spruce budworm population is a desideratum for both the ecologist and the forest manager, and intensive research on natural spruce budworm mortality factors is being conducted in several laboratories. The study described in this report originated in a suggestion that fungi colonizing the foliage of the spruce budworm 1 s host trees might produce toxic metabolites, adversely affecting the insects and possibly contributing to the decline of an outbreak population (E. Eveleigh, T. Royama, Canadian Forestry Service -Maritimes; D. B. Strongman, N. Whitney, Univ. of New Brunswick, unpublished discussions, 1984). This hypothesis receives some support from a growing literature on plant-fungal interactions that result in protection of the plant against the depredation of phytophagous insects and other herbivores (3,-6).

Potential Use of Fusarium Isolates as Biological Control Agents: Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) Case Study

“…The entomopathogenic effect of the Fusarium species has been reported by investigators on certain insect species, such as the greenhouse whitefly, Trialeurodes vaporariorum (Westwood) (Homoptera: Aleyrodidae) [49], the spruce budworm, Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae) [50], the wheat stem sawfly, Cephus cinctus (Norton) (Hymenoptera: Cephidae) [51] and eggs and larvae of the tobacco cutworm, Spodoptera litura (F.) (Lepidoptera: Noctuidae) [52]. As reviewed by da Silva Santos et al [53], the most frequently reported entomopathogenic Fusarium species lay between four species complexes of Fusarium incarnatum-equiseti, F. fujikuroi, F. solani, and F. oxysporum.…”

The first report on entomopathogenic effect of Fusarium avenaceum (Fries) Saccardo (Hypocreales, Ascomycota) against rice weevil (Sitophilus oryzae L.: Curculionidae, Coleoptera)

“…As a plant pathogen, it can cause serious diseases to the plants it attacks, such as seed borne diseases of legumes (Kelloc et al, 1978), stem and root rot diseases in various pasture legumes (McGee & Kellock, 1974;Lamprecht et al, 1988;Satyaprasad et al, 2000), head blight of wheat (Kang et al, 2005). However, the entomopathogenic effect of this fungus has been recently reported by a few investigators on certain insect species, such as the greenhouse whitefly, Trialeurodes vaporariorum, spruce budworm, Choristoneura fumiferana, and wheat stem sawfly, Cephus cinctus, (Strunz & Strongman, 1988;Eleonora-Rojas et al, 2003;Sun, 2008). Our strain of F. avenaceum has demonstrated a high level of entomopathogenic effect against S. oryzae adults, and the direct spraying of the adult weevils with the fungus conidial suspension gave the highest mortality percentage compared to the other types of treatment or the Control.…”

“…Fusarium avenaceum was one of the entomopathogenic species of Fusarium that has been isolated from a number of insect species, and its pathogenicity to insects has been demonstrated in few species, such as greenhouse whitefly, Trialeurodes vaporariorum (Eleonora-Rojas et al, 2003), spruce budworm, Choristoneura fumiferana, (Strunz & Strongman, 1988) and wheat stem sawfly, Cephus cinctus, (Sun, 2008). To the best of our knowledge, no reports are yet available on the entomopathogenic activity of F. avenaceum against S. oryzae or any other coleopteran insects of stored grain.…”