Pollen beetle – adult C. Noronha, AAFC

Hosts

Canola and oilseed rape (Brassica spp.), mustards (Brassicogethes), bittercress (Sinapis spp.), rockcress (Arabis spp.), wild radish (Raphanus spp.) and dogmustard (Erucastrum spp.). Not known to be established in Western Canada but present in Nova Scotia, PEI, and Quebec.

Pollen beetle, Bronzed blossom Brassicogethes viridescens (Fabricius)

Identification

ADULTS: 2–2.5 mm long elongate-oval body with orange-yellow mouthparts and legs; metallic green to blue or brownish-red elytra (wing covers); antennae are clubbed (last segments swollen) with yellowish basal segments.

Coleoptera

MATURE LARVAE: 4 mm long, grayish white with black head; twp small black spots on top of each abdominal segment.

Life Cycle

Adults overwinter in the soil under plant debris and can aggregate in nearby forested areas. They become active when air temperature reaches about 15°C in the spring. They will fly up to 3 km in search of host plants that are in bud through bloom stage. Female can lay up to 250 oval white eggs during their life span in small clusters of 2-3 eggs in the developing buds. Eggs hatch after about 12 days and larvae enter developing flower buds to feed. Larvae have two instars over 20-30 days before dropping to the ground to pupate in the soil. Adults emerge after about 4 weeks and feed on the pollen of other host plants before seeking overwintering sites in late summer. One generation per year.

Feeding Damage

ADULTS: Feed on buds, developing flower parts, and pollen of crop hosts; also feed on pollen of several non-crop hosts in the spring and prior to overwintering. LARVAE: First insar larvae feed inside buds on pollen and second instar feed on pollen in open blossoms. Seed production can be reduced up to 70% by larval and adult feeding damage. Plants may compensate but seed is smaller and less mature at harvest (green seed).

Similar Species

The rape pollen beetle (Brassicogethes aeneus) closely resembles B. viridescens in life cycle, appearance and damage. However, B. aenus adults are mainly shiny black with a hint of metallic green, legs are black and the basal antennal segments are not yellow. It also emerges about 2-3 weeks earlier in the spring as it becomes active at 11°C..

Monitoring/Scouting During canola bud development and bloom (stages 3 and 4), at 5- to 7-day intervals, count the number of beetles on the budding shoots of 10 plants along five transects (at least 30 m long) from the crop margin towards the centre. Divide the total beetles observed by the number of shoots sampled to determine average beetles/ shoot. Also calculate the number of plants/m2 for each transect.

Larva beetle – larva C. Noronha, AAFC

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Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and Management Field Guide

PESTS Economic Threshold

None have been developed for Western Canada. In Denmark, the threshold is 0.2 – 3 beetles per plant depending on precipitation (lower threshold for lower moisture). In Britain the threshold varies according to budding shoot density (from 7 beetles/shoot at 70 plants/m2 to 25 beetles/ shoot at 30 plants/m2.

Pollen beetle – clutch of eggs C. Noronha, AAFC

Management Options

BIOLOGICAL: Ground beetles are reported as predators of both adults and larvae. In Britain parasitic wasps cause up to 50% larval mortality in unsprayed crops. CULTURAL: Eliminate potential infestations sources/alternate hosts such as volunteer canola and mustards. Pollen beetle – damage C. Noronha, AAFC

Coleoptera

CHEMICAL: None registered in Canada.

Pollen beetle in canola C. Noronha, AAFC

Descriptions of Field Crop Pests

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Field Crop and Forage Pests and their Natural Enemies in Western Canada IDENTIFICATION AND MANAGEMENT FIELD GUIDE

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