De­struc­tive spruce bud­worm be­ing mon­i­tored

The last out­break, decades ago, saw 50 mil­lion cu­bic me­tres of wood lost


There hasn’t been a ma­jor out­break of spruce bud­worm in the prov­ince for more than 30 years, but that doesn’t mean the prov­ince isn’t keep­ing an eye on them.

“Bud­worm is one of our ma­jor for­est pests,” said Dan Lav­i­gne, su­per­vi­sor of in­sect and dis­ease con­trol with the Depart­ment of Nat­u­ral Re­sources in Cor­ner Brook.

Be­cause of that, the depart­ment con­ducts an­nual sur­veys to mon­i­tor the spruce bud­worm pop­u­la­tion in the prov­ince. Lav­i­gne said this is in ad­di­tion to mon­i­tor­ing for other for­est pests like the hem­lock looper, bal­sam fir sawfly and spruce beetle.

Lav­i­gne said the last out­break of bud­worm in the prov­ince started in the early 1970s and didn’t col­lapse un­til the mid to late 80s. At the time it was es­ti­mated that 90 per cent of spruce and fir forests in the prov­ince were in­fested by the bud­worm.

“Dur­ing the out­break there’s an es­ti­mate that we lost 50 mil­lion cu­bic me­tres of wood (spruce and fir) to the spruce bud­worm,” said Lav­i­gne.

Trees weaken and die

The bud­worm feeds on both new and old fo­liage and most of the dam­age to trees oc­curs when the bud­worm are in the lar­val or cater­pil­lar stage. Af­ter three to five years the trees start to weaken and die off.

The main method used to track the bud­worm pop­u­la­tion is a pheromone trap­ping sur­vey where plas­tic traps con­tain­ing a syn­thetic lure are placed in trees. The lure is sim­i­lar to the scent emit­ted by fe­male bud­worm moths when they are ready to mate.

“The num­ber of moths that we catch from year to year gives us some in­di­ca­tion as to what’s hap­pen­ing with our pop­u­la­tions.”

Lav­i­gne said the depart­ment has a net­work of 100 lo­ca­tions across the is­land in spruce-fir forests where pheromone trap­ping oc­curs an­nu­ally. Within the last cou­ple of years the depart­ment has been record­ing an in­crease in the num­ber of male bud­worm moths caught in those traps. He said the aver­age has gone from 19 per trap in 2011 to 34 in 2012.

Two ar­eas on the west coast in the area of Gros Morne National Park ac­tu­ally saw trap catches of 500 and 200 moths. Lav­i­gne said those ar­eas were then sub­ject to weekly mon­i­tor­ing.

The re­sults showed an in­crease in catches and then a sud­den drop and this sug­gested some dis­per­sal event may have oc­curred to bring the moths, which can travel hun­dreds of kilo­me­tres, to the area. He noted, how­ever, that the lo­cal pop­u­la­tion is not a level that would pre­dict any kind of de­fo­li­a­tion.

Lav­i­gne said in ar­eas with high trap catches the depart­ment will do fol­lowup branch sam­pling to look for eggs and lar­vae.

This sur­vey­ing has yet to find any egg masses on the is­land. He said the depart­ment will also do aerial sur­vey­ing to look for dam­age to forests from the air.

Lav­i­gne said the depart­ment uses the in­for­ma­tion it gath­ers in a re­ac­tive way.

“The branch sam­pling that we do will tell us if we start get­ting above a cer­tain thresh­old of egg masses on our branch sam­ples then we know that we’re gonna ex­pect mod­er­ate to se­vere de­fo­li­a­tion in those ar­eas.”

He said from that they will look at the im­pact that will have on forests in the area, and noted a nor­mal out­break lasts about 10 years and a se­vere one 15 years. If the im­pact is above a cer­tain thresh­old, he said govern­ment may de­cide it is nec­es­sary to take some pro­tec­tive mea­sure which would in­volve a con­trol pro­gram us­ing an in­sec­ti­cide like BT.

Con­di­tions in Labrador are a lit­tle dif­fer­ent than on the is­land. Lav­i­gne said an out­break of spruce bud­worm was first de­tected in the Goose Bay area in 2006-07. Last year, the in­sect caused 30,000 hectares of mod­er­ate to se­vere de­fo­li­a­tion in that area.

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