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Natural Controls for MPB
Flys, Wasps and Woodpeckers
A number of biological agents can affect populations of MPB. This includes insects, nematodes, and birds. The list below details many of these agents. The natural enemies are likely most important in limiting or controlling populations in the endemic phase. In outbreak phase, natural enemies appear less able to exert sufficient limit on the population.
The most important predator of MPB is another insect, Medeterra aldrichii, a type of fly. It feeds on MPB eggs and larvae. It will often feed on a larva for a short time and then feed on a second larva without completely eating the first.
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Medeterra sp. Adult |
Medeterra sp. Larva |
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www.bugwood.org |
A second predatory insect of PMB is known as the red-bellied clerid or Enoclerus sphegeus. Both the larva and adult of this insect feed on larvae and adult MPB. |
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Enoclerus sphegeus Adult |
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An important parasite of MPB is a braconid wasp known as Coeloides dendroctoni. This wasp lays its eggs on developing MPB larvae in June as the MPB larvae are reaching maturity. Each wasp larva feeds on a MPB larva. |
| Coeloides dendroctoni Adult | |
scf.rncan.gc.ca |
Another group of predators of MPB is
woodpeckers. They concentrate on trees with large larvae, especially over the winter. Common woodpecker predators include the three-toed woodpecker, hairy woodpecker, and downy woodpecker. In
addition to larvae, woodpeckers and other birds are known to consume
MPB adults during the flight period. Although they can consume large
numbers of beetle larvae, during outbreaks they are believed to have
an insignificant effect on MPB populations. |
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| Three-toed woodpecker on ponderosa pine |
Bark flaking on lodgepole pine from woodpeckers |
| www.fwp.mt.gov |
K. Gibson, USDA Forest Service |
The most significant natural control of mountain pine beetle when it is in outbreak is weather. The occurrence of very cold temperatures at the right time can have a major impact on larval survival under the bark. Although it had been believed that a single low temperature for a prolonged period of time would result in mortality of MPB, it has been found that that is too simple an understanding. What has been found is that cold tolerance varies within a season, among seasons, and among geographic locations depending on local climate. Beetles build up materials in their bodies that reduce the risk of ice formation. These materials develop over time as the larvae are exposed to increasingly colder temperatures during the winter. This process of becoming acclimated to cold is driven by daily changes in temperature. Sudden drops in temperature, especially in early and late winter, have the greatest impact on MPB mortality. Gradual cooling, even to very low temperatures, has little effect.
