Weevils in Native Plant Seed Production
Bob Hammon
Colorado State University
Tri River Area Extension
Grand Junction CO
Why Weevils?
Presentation goals
If it’s a weevil, it’s probably a pest
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Identify adult & larval weevils
Life history of some damaging weevils
Sampling options for weevils
Developing management plans for weevils
What is a Weevil?
• Snout beetles
• 3 families
• Curculionidae
– Largest family of beetles
• now includes bark beetles
Sweet clover weevil
– 3000 species 500 genera in North America
– Almost all are plant feeders
• Living and dead plants
– Larvae feed within (sometimes upon) plant tissues
– Adults drill holes in fruits, nuts, stems, roots
Weevil larvae
• Legless grub
with distinct
head capsule
• Rarely moves
far from feeding
site
True Weevils
Curculionidae
The Yucca Weevil
• Distinct snout
• much variation of form
• Antennae arise from ~ middle of snout
• Huge size variation – 1 mm – 1 inch+
• Many “play dead” when disturbed
• Most have narrow host range
Weevils as Biocontrol Agents
• Tamarisk
• Coniatus splendidulus (leaf buds & foliage)
• Thistles:
• Larunus planus (seeds)
• Baris subsimilis (crown/root),
• Rhynocillus conicus (seeds)
The Penstemon
Crown Borer
Barus sp.
• Restricted
to SW Co?
• Can be devastating to
stands
• Unknown species?
• Control is difficult
• Once damage is
apparent, control is
impossible
PCB Adult
• About 3/16” long
• Adults present in fall
& early spring
– found in feeding cells
within roots
– Abundant on torn-out
plants in disked field
• Eggs laid in spring??
– eggs are unknown
PCB Larvae
• Found in Jun/Jul/Aug
• Inside roots/crowns
near soil surface
– up to 3” deep
• Pupation within
feeding cell
• Destructive sampling
is necessary
Penstemon Crown Borer Pupa
Pupation occurs during
the late summer/ early fall
The pupa is found within
the feeding chamber
Beetle pupae are
coarctate – the
appendages are free from
the body – looks like a
white mummified adult
Managing the Penstemon Borer
Stage
Egg
Season
Spring
Larva
SpringSummer
Pupa
Fall
Adult
Fall
Spring
Location
On plant??
below soil??
tunnels within
underground
portion of plant
within feeding
chamber
overwinters within
plant, moves in
spring mobile
Management
spring applied
nematodes?
foliar
insecticide in
spring
Penstemon Crown Borer
Management
• Monitor weevils in spring
– suction sampler?
– sweep net?
– sacrifice plants?
• If found, use adulticide
(pyrethroid) in spring
– Before egg laying!
• Check native plants in
area
Straight Snouted Weevils
Brentidae
• Elongated, forward pointing snout
• 150+ North American species
• Larvae bore into stems, seeds &
other plant parts
• Hollyhock weevil adults feed on
leaves & buds
•Larvae feed on seeds
• Beetles fall from plant when
disturbed
Sphaeralcea Weevil(s)
Anthonomus sphaeralciae Fall
• Specialist on
Sphaeralcea
• Easily found in
sweep samples
• Present during
bloom
• Infested 25% of
flowers in samples
at Hotchkiss CO
Sphaeralcea Weevil Eggs
Eggs are placed
under calyx after
adult weevil chews
oviposition hole
Flowers with eggs
can be sight
identified by the
stunted or
shriveled petals
Sphaeralcea Weevil egg scar
Sphaeralcea Weevil Larvae
Larvae feed on
developing ovaries
The flower falls off and
damage is not seen later
in the season
Larval life span is short –
probably less than 2
weeks
The larva is more
elongate than a
curculionid. There
is a distinct hgead
and no legs
We don’t know if there is
a second generation
The Hidden Damage
Larval feeding causes
flowers & immature
seeds to abort.
There is no damaged
seed visible
Impact is low yield of
indeterminate cause!!
Managing the Sphaeralcea Weevil
• Adults are easily found with a sweep net
– Regular samples beginning at late bud
• If found, take a decision quickly
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Thresholds???
How many flowers can you lose?
How much compensation for lost flowers?
How many eggs per weevil?
• Sprays need to be bee-friendly
Bee Friendly Insecticide Applications
• Pre bloom sprays using pyrethroids
• Night time applications during bloom
– Use “flash” insecticides w/ no residual
– Dibrom is used in seed alfalfa
– Moisture must be monitored!
• Moisture + insecticides = dead bees
Lomatium Seed Weevil
Smicronyx sp.
Taking a Life History SWAG
Smicronyx fulvus: Red sunflower seed weevil
Smicronyx sordidus: Gray sunflower seed weevil
• Eggs laid late bud to early bud growth stage
• Females need pollen to mature eggs
– Monitor with DEET, sweep net in Lomatium??
• Larvae are internal developing seed feeders
– Lomatium has small seed: different life history?
• Pupation in soil after larvae drop from plant
– Larvae emerging in storage will die!
Managing Smicronyx in Lomatium
• Monitor with sweep net or DEET
– Treatment thresholds?????????
– How valuable is the seed?
• Adult control at (pre?) / early bloom
– Bee impact is major concern!!!!!
• Soil treatment of larva / pupa
– Nematodes
– Long term
– Must consider native population source
Seed Weevils aka Seed Beetles
Chrysomelidae: Bruchinae aka Bruchidae
• Small beetles, < 5mm long
• Elytra shortened
• not covering tip of abdomen
• Snout not well-developed
• Usually dull gray or brown
• Larvae feed/pupate in seeds
• Eggs laid on developing
fruits or pods
• Bruchids, especially Acanthoscelides can be expected in many legumes
• some generalists, others may be species specific
• Losses in Hedysarum boreale have approached 75%
• Undescribed Acanthoscelides species
HEBO Seed Weevil
Acanthoscelides sp. (fraterculus?)
Seed weevil damage
Managing Seed Weevils
• Management must be
preventative
• Once egg is laid, control is
impossible
• Monitor for adults
• First bud – bloom
• Pre bloom cleanup spray
• Monitoring throughout bloom
period
• Sweep nets work well
• Nocturnal behavior?
Sweep Nets
Cheap & Easy – No excuses!
Heavy Duty
Sweep Net
• Gemplers
• Ben Meadows
• Bioquip
• Many others
Weevils in Legume Seeds
Dalea ornata Astragalus filipes Hedysarum boreale Lupinus argenteus
Bruchidae
Acanthoscelides
aureolus
daleae
fraterculus
oregonensis
pullus
Brentidae
Apion
amaurum
oedorhycum
Curculionidae
Tychius
semisquamosus
tectus
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Other plants to watch for weevils
• All legumes
– Curculionids, Bruchids
• Composites
– Stem and seed boring curculionids
• Prunus & other Rosaceae stone fruits
– Seed feeding curculio
• Malvaceae
– Seed feeding Brentidae
Seed Production Pests
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Western Colorado Insects Web Site
http://wci.colostate.edu/seed_production
Pesticides for seed production
Plant species pages
Bob Hammon
Colorado State University
Tri River Area Extension
Grand Junction CO
bob.hammon@mesacounty.us
(970) 244-1838