Populations of pea aphids, Acyrthosiphon pisum Harris (Hemiptera:
Aphididae), can be kept below the economic threshold by their natural enemies
if these are present early and in sufficient numbers. Natural enemies include
parasitoids, predators, and diseases that reduce pest populations.
Predators
of pea aphids include ladybird beetles (adults and larvae), syrphid fly larvae,
and damsel bugs. These predators catch and eat pea aphids of all ages and
sizes. They are classified as generalists because they also prey on other
insect species.
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| The many faces of the adult harlequin ladybeetle (aka multicoloured Asian ladybeetle) (Photo: ©Entomart) |
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| Harlequin ladybeetle larva (Photo: cc by-sa Quartl) |
Pea aphids
are attacked by several species of parasitoid, including Aphidius ervi Haliday (Hymenoptera: Aphidiidae: Aphidiinae). Female
parasitoids lay individual eggs inside aphid nymphs. After hatching, the
parasitoid larva consumes its host, eventually killing it. The parasitoid
pupates inside the dead or mummified aphid before a new adult parasitoid emerges.
Aphid mummies look bloated and discoloured compared to healthy adult aphids. Parasitism
rates can be estimated by counting the number of aphid mummies on five host
plants at five locations within a field.
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| Aphidius ervi parasitoid (Photo: cc by Penny Greeves) |
For more
information about the predators and parasitoids of pea aphids, visit the Insect of the Week page or consult Field Crop and Forage Pests and their Natural Enemies in Western
Canada: Identification and Management Field Guide.
To learn more about some of the natural enemies
fighting pests in background for free, go to www.fieldheroes.ca
or follow @FieldHeroes on Twitter.
Blog post submitted by Dr. Meghan Vankosky. Follow her at @Vanbugsky.