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Insects (Maine Cranberries) - Blackheaded Fireworm

Order: Lepidoptera || Family: Tortricidae
Scientific Name: Rhopobota naevana (Hübner)

photo showing a Blackheaded Fireworm larva (photographed June 18th in central Maine) Blackheaded Fireworm larva (photographed May 27th in central Maine) photo showing 3 empty eggs (blackheaded fireworm eggs that have previously hatched) photo showing several cranberry leaves damaged by Blackheaded Fireworm larvae (larvae feed by skeletonizing the leaves) Photo of a damaged cranberry leaf (damaged by Blackheaded Fireworm) next to a healthy, undamaged leaf 2nd photo showing two cranberry leaves damaged by Blackheaded Fireworm larvae (larvae feed by skeletonizing the leaves) photo showing a cranberry tip occupied by a Blackheaded Fireworm larva (photographed June 22nd in central Maine) Cranberry tips pulled together and occupied by a Blackheaded Fireworm larva (photographed June 22nd in central Maine) photo showing another example of 3 or 4 cranberry tips pulled and webbed together by a Blackheaded Fireworm larva (some frass is also visible in this picture) A cranberry tip with obvious damage from something (happens to be due to a Blackheaded Fireworm larva hidden inside the tip) photo of a cranberry bed with a noticeable dark area that is an area that was ravaged by Blackheaded Fireworm larvae (2nd-generation larvae) (photographed August 20th - downeast Maine) photo showing a pair of Blackheaded Fireworm pupae (photographed June 21st central Maine) picture of a Blackheaded Fireworm moth in the palm of a person's hand Photo of a single Blackheaded Fireworm moth (picture taken June 22nd - central Maine)

photos by C. Armstrong


Adults / Moths: Adults (see last two pictures above) are very small, only about 1/4-inch in length, dark in color, with alternating light and dark gray-brown bands on their forewings. They are active at dusk, and can be seen hovering freely just above the vines. They will occasionally fly during the day if it is cloudy and warm or if they are disturbed. Female moths begin laying eggs within a day of emergence from their pupae. By early to mid-July, a second generation of caterpillars begins, and this leads to a 2nd-generation of moths that emerge and lay a new generation of eggs.  In some years, a third generation may be possible, but generally these are the eggs that subsequently overwinter before hatching into 1st-generation larvae the following May.

Eggs: Eggs oviposited by the final generation of moths overwinter and begin to hatch in May (average over the years puts the first hatching at around May 22nd for most of Maine).  The hatching period may continue for 3 to 6 weeks, depending on vine density and weather. Eggs laid by the ensuing moths begin to hatch usually in mid-July (sometimes end of June in warmer summers or in warmer locations like southern Maine and Massachusetts). Each egg is laid singly on the underside of the cranberry leaves and has a flat, disklike shape. They are extremely small (1/32-inch in diameter) and yellow in color.

Larvae (mid to late May until mid to late-June, and again starting generally in mid to late July when a 2nd-generation begins): The damaging stage of the blackheaded fireworm is the larval stage. Larvae are green-yellow or pale yellow, and their heads are black and shiny (see photos above). When mature (2 to 3 weeks after hatching), they measure roughly 1/3-inch in length. There are two separate generations of larvae (maybe even three) each season, and the 2nd generation is the more damaging one since their numbers are normally much greater and the plants are developing their fruit at that time.

Monitoring and Control: In addition to sweep-net scouting, spend some time visually scanning for upright tips with terminal leaves that have been webbed tightly together!  Break off any tip of that sort, and carefully tease apart the terminal leaves.  If a small larva suddenly squirms out, wriggling backwards and possibly right across your hand and down to the ground (often attached to a strand of silk)…and if this happens before you’ve even blinked, then you’ve probably encountered a fireworm larva. You should then sweep, if you haven’t already, to see if you pick up any in your net.  They do not get picked up in sweeps very easily, so if you average even one larva per 25 sweeps, you may well be justified in taking action (depending on your history with this pest, your expected crop value, etc.). View the Maine Cranberry Pest Management Guide for the most current recommended Action Threshold (AT) to consider using (traditional AT is 1 to 2 per 25 sweeps), and for a list of control materials.  Infestations of 2nd-generation larvae are far more dangerous, because their numbers are much higher, especially, of course, if any 1st-generation populations are left uncontrolled.  Infestations of both generations are usually patchy, at least at first, and larvae tend to be more numerous along edges. Spot-treatment is desirable in such cases. Sweepnet-Captured First Dates for 1st-generation larvae (Average First Date = May 22nd): 6/12/06, 5/25/07, 5/14/08, 5/14/09, 5/16/13, 5/20/14 (See also Degree Days and/or the Pest Reports pages for keeping up with Maine’s first detection of 1st-generation fireworm larvae)

Pheromone Traps: If you like using traps, can find someone still manufacturing them, and are comfortable with them, monitoring for the fireworm moths with traps should begin around June 1st or a bit later in colder Springs. Change the lure every 3 weeks, and use at least 1 trap per 10 acres (don’t place traps close to each other). Place them on the upwind side of the bog so the wind will carry the scent over the bog. Also, one should begin searching for larvae on the bed(s) a week after the first moths are seen in the trap(s) because there may not necessarily be any larvae on your bed.  It is possible the moths captured (which are males only) came from wild stands of cranberries, and the female moths could still be located only in those other locations and might not necessarily migrate to your site. Only the males are attracted to the traps, so you would not be contributing to an infestation of your site by virtue of using the traps.  Therefore, the presence of moths in the traps may not always mean you will see larvae at your site later on, which is why scouting for larvae is so very important.

Cranberry questions? Contact Charles Armstrong, Cranberry Professional. University of Maine Cooperative Extension || Pest Management Unit || 17 Godfrey Drive || Orono, ME 04473-3692 || Tel: 207.581.2967 [email:]


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