Integrated Pest Management Guide

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BLACKHEADED FIREWORM, Rhopobota naevana (Hübner)

Pest Status: This insect is one of the major pests of cranberry in British Columbia.

Life cycle and feeding habits: This insect overwinters in the egg stage. Overwintering eggs are yellow, about 0.5 mm (less than 1/16 inch) in diameter, and are found on the underside of cranberry leaves. Hatching of this first generation usually begins in late April, reaches a peak in early May and is completed by early June.

Newly hatched larvae burrow into the leaf near the egg, then move up to the growing tip of uprights or runners. Larvae may tunnel into unopened buds or web together the terminal leaves of uprights with silk and feed inside this shelter or "tent". Each larva may make five or six tents before it pupates. After a feeding period of 3-5 weeks, fully grown larvae, which are about 8 mm (1/3 inch) long with a shiny black head, go into the pupal stage in the trash layer or within their tents. Larvae have three pairs of front legs and five pairs of hind legs.

The first adults usually appear in late May or early June. This first flight of moths lasts until July. During this time, the male and female moths (6 mm (1/4 inch) long) can be seen flying among the vines. Most mating occurs in late afternoon and evening. Eggs are laid on the underside of cranberry leaves. These second-generation eggs begin hatching in late June or early July. In addition to making tents, larvae larva feed on uprights and runners directly and may burrow into the developing fruit.

When the larval population is high and injury is severe, damaged plant tissue dries out and appears scorched as if by fire. Following pupation, moths of the second generation are present from late July through September. Although most eggs laid by second-generation moths will not hatch until the next spring, a third generation of larvae may be seen in August and September if temperatures remain warm. These third-generation larvae are injurious to fruit. In warm years, moths of the third generation may be seen flying as late as December on dry-pick farms .

Monitoring: Monitoring for this pest begins by looking for larvae (worms) in late April. Look closely at runner tips and buds along warm edges of beds for small tents and frass made by newly hatched larvae (about 1.5 mm (1/16 inch) long). One to 2 weeks after larvae are seen, more extensive monitoring can be done by "visual sweeps": crouching down to examine areas of about 0.18 square metres (2 square feet). When searching visually, examine the edges of the bed and known "hot spots" (areas of previous infestation) first, doing at least 10 visual sweeps per acre (25 per hectare).

Regardless of actions taken in spring for larvae, pheromone traps for monitoring moth flight should be placed in fields in mid-May. A minimum of three traps should be placed on farms of 4 hectares (10 acres) or less. On larger farms, one trap per 2 hectares (5 acres) is recommended. When placing lures in traps, use disposable gloves and keep gloves from touching any other part of the trap. Check traps weekly by counting the number of fireworm moths, then scraping them off the sticky floor of the trap or replacing the sticky bottom or insert of the trap if necessary. Change lures after 6 weeks and before the second flight of moths. Ten days to 2 weeks after the greatest number (peak) of moths is caught or 3 weeks after first catch, begin checking field edges and known "hot spots" for larvae. It is helpful to map the location of fireworm larvae.

Control: An insecticide treatment is recommended if an average of one larva per visual sweep is found. Most larvae should be 3 - 6 mm (1/8 to 1/4 inch) long when insecticide is applied. During bloom, do not apply insecticides that are toxic to bees.

The need for insecticide application may be reduced or eliminated by using 3M Sprayable Pheromone for Mating Disruption of Blackheaded Fireworm. This product interferes with moth communication and prevents most male fireworm moths from finding and mating with females. Sprayable pheromone should be applied at the label rate at or just before first moth catch in pheromone traps. Two or three applications at intervals of 2.5 - 3 weeks should reduce mating of the first flight of moths. As or just before the second flight begins, applications of sprayable pheromone should begin again, and continue at intervals of 2.5 - 3 weeks until flight ends. During the first year of sprayable pheromone use, insecticide applications against fireworm larvae should continue as usual. During the second and subsequent years, it should be possible to reduce or eliminate summer applications of insecticide against fireworms. Sprayable pheromone is not toxic to mammals or beneficial insects like bees.

"Decoy-female" pheromone traps are used to track the efficacy of sprayable pheromone. The lures placed in these traps estimate the number of male fireworm moths that can locate one female fireworm moth. These lures should be stored in a freezer and replaced in traps every 3 weeks. Decoy-female traps should be placed in the beds the day after the first application of sprayable pheromone. The recommended number of traps is: a minimum of three traps on farms of 8 hectares (20 acres) or less; five traps on farms of 8 - 40 hectares (20 - 100 acres); and 10 traps for farms greater than 40 hectares (100 acres). If application is done by chemigation, place one trap close to the area where the pheromone is first delivered and one in the area receiving the spray last. It is also important to avoid putting traps in areas known as fireworm "hot spots".

Regular pheromone traps (= monitoring or IPM traps) are also required in fields to track the flight pattern and peak catch. Decoy-female traps and IPM traps should be placed at least 37 metres (120 feet) apart. Monitoring for fireworm moths in both kind of traps should be done once a week during the flight periods.

A tiny parasitic wasp, Trichogramma sibericum (Sorokina) , is sometimes found in beds not treated with insecticides. These tiny wasps are well-adapted to parasitize fireworm eggs.

The tachinid Hemisturmia tortricis (Coq.), a beneficial parasitic insect, has been reared from blackheaded fireworm larvae collected from unmanaged farms and farms seldom treated with insecticide.

A granulosis virus is also known to infect blackheaded fireworm larvae on unmanaged cranberry farms. Infected larvae become sluggish, flaccid, and liquid as they succumb to the virus.


Blackheaded fireworm eggs


Blackheaded fireworm larva	Blackheaded fireworm moth


"Tent" made by fireworm larva	Damage associated with mature fireworm larvae