Insects Associated with Alfalfa Seed Production

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Integrated pest management | Guide to pest insects | Guide to beneficial insects

This field guide was prepared to enable growers of seed alfalfa to quickly identify their pest and beneficial insects.

The important distinguishing features are indicated on the plates by arrows. These features can be readily seen with a hand lens or magnifying glass.

Economic thresholds are based on the average number of insects captured in five 90^o sweeps. (Figure 1).

Figure 1. How to make a sweep

Integrated pest management

Alfalfa seed growers must manage the insect pest populations to obtain increased seed production while simultaneously protecting pollinators and other beneficial insects. Towards this end, an alfalfa integrated pest management program has been established.

The major goal of this program is to combine biological, chemical and cultural pest insect control methods with management practices that allow the beneficial insect populations to increase.

Guide to Pest Insects

Immature lygus bug (nymph) Description up to 4 mm in length usually light green with black spots on the back (arrow) nymph stage 1, 2, 3 - no wing pads (top row, Figure 2) nymph stage 4, 5 - wing pads (middle row, Figure 2) nymph stages scamper from net absence of cornilles (contrast with aphids) Damage feed on buds suck juice out of developing seeds Evidence buds turn white flowers drop no bloom seeds brown and papery thin Generation 2-3 generations per year Economic threshold nymph stage 1, 2, 3 - fifteen per sweep bud and bloom - nymph stage 4, 5 - two or three per sweep after bloom - nymph stage 4, 5 - four per sweep	Figure 2. Lygus bugs
Adult lygus bug Description 4-5 mm in length brown lygus - pale yellow to brown with darker brown, black and red markings green lygus - pale green with some portions bright green last two segments of antennae of equal length and the same color a distinctive "V" mark on the back body shorter and broader than alfalfa plant bug (bottom row, Figure 2) Damage feed on buds suck juice out of developing seeds Evidence buds turn white flowers drop no bloom seeds brown and papery thin Generation 2-3 generations per year Economic threshold bud and bloom - 2-3 per sweep after bloom - 4 per sweep
	Lygus
Immature alfalfa plant bug (nymph) Description up to 5 mm in length usually dark green no spots on the back nymph stage 1, 2, 3 - no wing pads (top row, Figure 3) nymph stage 4, 5 - wing pads (rows 2, 3, Figure 3) nymph stages walk from net antennae with last segment enlarged and dark (arrow) absence of cornicles (contrast with aphids) Damage feed on buds suck juice out of developing seeds inject toxin Evidence buds turn white flowers drop no bloom seeds brown to black and papery thin Generation 1-2 generations per year Economic thresholds nymph stage 1, 2, 3 - fifteen per sweep bud and bloom - nymph stage 4, 5 - two or three per sweep after bloom - nymph stage 4, 5 - four per sweep Adult alfalfa plant bug Description 8-9 mm in length yellowish-green segments two and three of antennae of equal length, dark areas on three and four body long and thin (bottom row, Figure 3) Damage feed on buds suck juices out of developing seeds Evidence buds turn white flowers drop no bloom seeds brown to black and papery thin Generation 1-2 generations per year Economic threshold bud and bloom - 2-3 per sweep after bloom - 5 per sweep	Figure 3. Alfalfa plant bug. The insect in the top row centre is a lygus bug inserted for comparison.
Immature pea aphid (nymph) Description up to 3 mm in length light to dark green soft-bodied, pear-shaped cornicles on abdomen (arrow) (middle row, Figure 4) remain in net Damage suck juice from plants stunt growth Evidence honeydew on leaves Generation several generations per year young born alive, resembling adult Economic threshold 150-200 per sweep	Figure 4. Pea aphid
Immature alfalfa weevil (larva) Description up to 8 mm in length head capsule black instar 1, 2 - light brown to brown (top row, Figure 5) instar 3, 4 - green with white line down middle of back (middle row, Figure 5) worm-like (actually legless) Damage feed on developing buds feed on leaves stunt growth Evidence "shot holes" in leaves field has a silvery sheen no bloom Generation 1 generation per year Economic threshold 20 per sweep Adult alfalfa weevil Description 3-5 mm in length spring adults - dark grey to black summer adults - dark brown with a conspicuous dark stripe extending 3/4 way down middle of back weevil-like (bottom row, Figure 5) Damage feed on buds feed on leaves stunt growth Evidence large holes in leaves no bloom field has silvery sheen Generation 1 generation per year Economic threshold not known	Figure 5. Alfalfa weevil
Guide to Beneficial Insects
Immature damsel bug (nymph) Description up to 8 mm in length greyish resemble adults (top row, Figure 6) Benefit and prey feed on aphids, immature lygus and plant bugs will sometimes feed on small alfalfa weevil larvae Generation 1 generation per year Adult damsel bug Description 8 mm in length greyish brown (bottom row, Figure 6) Benefit and prey feed on aphids, immature lygus and plant bugs will sometimes feed on small alfalfa weevil larvae Generation 1 generation per year	Figure 6. Damsel bug
Immature ladybird beetle (larva) Description up to 12 mm in length marked with blues, blacks, oranges somewhat flattened resemble small "alligators" (top row, Figure 7) Benefit and prey voracious appetite will consume about 25 aphids per day Generation several generations per year Adult ladybird beetle Description 4 to 6 mm in length usually red, orange or yellow wings covered with different arrangements of black spots (bottom row, Figure 7) Benefit and prey consumes up to 25 aphids per day must consume 120 aphids before egg laying will consume three aphids for each egg laid deposits about 1,500-1,700 eggs during the summer Generation several generations per year	Figure 7. Ladybird beetle
Immature green lacewing (larva) Description up to 9 mm in length usually mottled grey with yellowish grey larvae "alligator like" with distinct sickle-shaped mandibles (jaws) that pierce and suck juice from their prey (top row, plate 8) Benefit and prey feed on aphids, immature lygus and plant bugs Generation 1 generation per year Adult green lacewing Description up to 20 mm in length wingspan over 30 mm in length entirely green (bottom row, Figure 8) long antennae four delicate, lacy wings pungent odor when caught Benefit and prey feed on aphids and other soft-bodied insects also feed on honeydew, plant nectar and pollen Generation 1-2 generations per year	Figure 8. Green lacewing
Immature minute pirate bug (nymph) Description up to 2 mm in length nymph stage 1, 2, 3 - yellowish to reddish orange nymph stage 4, 5 - black and white and resemble adult body somewhat flattened (top row, Figure 9) Benefit and prey feed on aphids and other small soft-bodied insects Generation 3-4 generations per year Adult minute pirate bug Description 1.5-2 mm in length black and white head with a very prominent beak (bottom row, Figure 9) Benefit and prey feed on aphids, mites and other small soft-bodied insects Generation 3-4 generations per year	Figure 9. Minute pirate bug
Immature common syrphid fly (larva) Description up to 8 mm in length color varies from brown to yellowish or green with white lines down back. Distinguished from alfalfa weevil larva by not having a black head capsule (see immature alfalfa weevil) slug-like, rounded at rear, pointed at front (top row, Figure 10) spiny hair-like structures on body Benefit and prey 400 aphids consumed by larva during its developmental period Generation several generations per year Adult common syrphid fly Description 4-6 mm in length abdomen marked with yellow, black or white bands flies like a mini-helicopter, hovering over flowers resembles small bee or wasp (bottom row, Figure 10) Benefit and prey larvae feed on aphids adults feed on honeydew, plant nectar and pollen Generation several generations per year	Figure 10. Common syrphid fly
Immature big-eyed bug Description up to 5 mm in length buff grey or blackish very large eyes and buff color distinguishes them from lygus and alfalfa plant bug nymphs. Resembles adult. Benefit and prey feed on aphids, immature lygus and alfalfa plant bugs Generation 2-3 generations per year
Adult big-eyed bug Description 3-5 mm in length mostly buff grey or blackish very prominent large eyes (Figure 11) Benefit and prey feed on aphids, immature lygus and alfalfa plant bugs Generation 2-3 generations per year	Figure 11. Adult big-eyed bug

Prepared by:

B.D. Schaber
Agriculture Canada
Lethbridge Research Station, Lethbridge, Alberta

Source: Agdex 121/620-1.

For more information about the content of this document, contact Scott Meers.
This document is maintained by Jennifer Rutter.
This information published to the web on May 1, 1986.