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 • 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 Season Location Management Egg Spring On plant?? below soil?? Larva Spring- tunnels within spring applied Summer underground nematodes? portion of plant Pupa Fall within feeding chamber Adult Fall overwinters within foliar Spring plant, moves in insecticide in spring mobile 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 We don’t know if there is elongate than a a second generation curculionid. There is a distinct hgead and no legs 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 – 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 X daleae X fraterculus X X oregonensis X pullus X Brentidae Apion amaurum X oedorhycum X Curculionidae Tychius X semisquamosus X tectus X 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 • 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 [email protected] (970) 244-1838.