Canadian Forest Service Publications
Does spruce budworm (Lepidoptera: Tortricidae) rearing diet influence larval parasitism? 2013. Seehausen, M.L.; Régnière, J.; Bauce, É. Can. Entomol. 145:539-542.
Issued by: Laurentian Forestry Centre
Catalog ID: 35381
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Artificial diet is commonly used to rear the spruce budworm, Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae), in the laboratory. While its effect on spruce budworm performance is relatively well studied, no information exists about the influence of rearing diet on larval parasitism. In this study, spruce budworm larvae reared in the laboratory on artificial diet or balsam fir, Abies balsamea (Linnaeus) Miller (Pinaceae), foliage were introduced in the field to compare parasitism. Additionally, a laboratory choice test was conducted with the larval parasitoid Tranosema rostrale (Brischke) (Hymenoptera: Ichneumonidae). No significant influence of spruce budworm rearing diet on parasitism in the field was found. However, in the laboratory, T. rostrale attacked significantly more foliage-fed larvae. We conclude that even if initial differences in parasitism may exist between diet-fed and foliage-fed larvae in the laboratory, spruce budworm larvae reared on artificial diet can be used in field studies investigating parasitism of wild spruce budworm populations without concern that the food source would affect parasitism.
Plain Language Summary
The spruce budworm (SBW) is a native insect pest whose outbreaks constitute the most significant natural disturbance affecting balsam fir stands in Canada. Budworm parasitoids play a vital role in maintaining SBW populations at endemic levels between outbreaks. One of these parasitoids, the wasp Tranosema rostrale, uses its stinger to lay an egg under the skin of SBW larvae. The wasp larva produced from this egg will feed on the internal tissues of its host.
To measure the levels of parasitism by T. rostrale in endemic SBW populations, researchers use a technique called "sentinel larvae", which consists of rearing SBW larvae on artificial food in a laboratory setting before exposing them to parasitoids in the forest.
The question addressed by this study is whether the use of this artificial food, as compared with balsam fir foliage, affects the probability of the SBW being attacked by T. rostrale. In the field, diet did not have an effect on parasitism levels. In the laboratory however, a much higher number of foliage-reared larvae were attacked by the wasp.
Despite this preference for foliage-reared larvae in the laboratory, the researchers concluded that larvae reared on the artificial diet could be used to determine levels of parasitism in the field, without the risk of biasing the results.