Bertha armyworm (Mamestra confgurata) is native to North America and belongs to a group of insects referred to as "climbing cutworms." Also included in this group are the true armyworm and variegated cutworm. Bertha armyworm is one of the most important insect pests of canola in Canada. In most years, populations are kept low by unfavourable environmental conditions, parasites, predators, and diseases. But when natural regulators fail, populations increase dramatically causing widespread damage to a variety of broadleaf crops. Infestations may be localized or spread over millions of acres. In extreme situations, infestations of more than 1000 larvae per square metre have been reported while densities of 50 to 200 larvae per square metre may be common. Are crops of Saskatchewan at risk? Bertha armyworm occurs throughout Manitoba, Saskatchewan, Alberta and into the interior of British Columbia. Severe infestations can occur throughout most of this area but are usually limited to the parkland area of the Prairies and the Peace River region of British Columbia and Alberta. Failure to detect an infestation early could result in widespread crop destruction. Provided producers monitor their crops and detect the infestation early, widespread infestations over hundreds of thousands of acres can be controlled with available insecticides and application equipment. However, failure to detect infestations early may lead to temporary insecticide shortages, inadequate time to apply them, and unavoidable crop destruction. What plants are most at risk? Bertha armyworm feeds on a wide variety of cultivated crops and weeds. Only canola, rapeseed, mustard, quinoa, lamb's quarters and related plants are preferred as host plants. However, once the primary host plants have been consumed, hungry, nearly-mature larvae will feed on a variety of plants including alfalfa, beans, beets, cabbage, corn, flax, lentils, mustard, peas, potato, sweet­clover, tobacco, tomato, turnip, garden vegetables, flowers and a variety of weeds. To prevent unnecessary crop losses from bertha armyworm, it is important to know the bertha armyworm's life cycle, when and how to monitor, the population levels that warrant control, and the recommended insecticides. What is the life cycle of the insect? Bertha armyworms develop through four distinct stages: adult, egg, larva and pupa. In Canada, there is one complete generation per year. In warm years, some pupae may continue their development and emerge in late August or September. Life Cycle of Bertha Armyworm Adult Adult Bertha Armyworm The emergence of the adult moth from the overwintering pupae begins in early to mid June and continues until early August. The bertha armyworm moth has a wing span of about 38 mm (1.5 inches) and insect is active only at night. The forewing is predominantly gray, and flecked with patches of black, brown, olive and white scales. Near the middle of the forewing, toward the leading wing margin (front), there is a prominent, white, kidney­shaped marking defined with a ring of whitish scales. Near the tip of the forewing, there is a conspicuous white and olive­colored, irregular transverse marking that is characteristic of the species After emergence, the moths are strongly attracted to canola fields which are in bloom and secreting nectar. Adults mate within 5 days of emergence and lay their eggs on the preferred host plants. Each female moth will lay about 2150 eggs but numbers as high as 3500 eggs per female have been recorded. Egg Egg Stage - Bertha Armyworm eggs are laid in single­layered clusters of about 50 ­ 500 eggs on the lower surface of the host plant leaves eggs are sculptured, ridged and pinhead in size are white when first laid, but become darker as they develop at average temperatures, the eggs hatch within a week Larva Larval Stage - Bertha Armyworm The newly hatched bertha armyworm larvae are about 0.3 cm (1/l0 in ) long. They are pale green with a pale yellowish stripe along each side. The larvae difficult to see on the underside of leaves because of their size and color. Small larvae may drop off the leaves by a fine silken thread if disturbed. This behavior makes it difficult to distinguish small bertha armyworm larvae from those of the diamondback moth, which display a similar behavior. Large larvae may drop off the plants and curl up when disturbed, a defensive behavior typical of cutworms and armyworms. The larvae take approximately 6 weeks to complete their development, depending upon temperature. During this period, they moult five times and pass through six stages. As larvae mature, their colouration becomes variable; some larvae remain green, but many become brown or velvety black The larva at maturity will be about 4 centimetres (1.5 inches) long, and burrow into the ground and pupate. Crop damage is caused entirely by the larvae. It varies with the crop being fed upon, the plant's growth stage, the growth stage of the larvae and the number of larvae present. Small larvae feeding from the underside of the leaves chew irregularly shaped holes in the leaves but they usually cause little damage even when population levels are high. Crop damage accelerates rapidly once the larvae moult to the second last stage. These larvae are about 13 mm (0.5 inches) in length. Larvae in the last two larval stages eat about 80 to 90% of the plant material consumed. If the plants, especially canola, drop their leaves before the larvae are mature, the developing larvae will feed directly upon the seed pods. Seed pods may be "debarked". More commonly, the larvae chew holes into the seed pods and eat the seeds. At high population levels, the entire seed pod may be consumed. Even when the seed pods are only stripped of their outer green layer, this may contribute to crop losses through premature shattering. In flax, the larvae eat flowers and the developing bolls. But once the flax bolls are full size and start to ripen, larval feeding is usually limited to the calyx below the boll. Occasionally, larvae will feed on the green stems of ripening bowls causing them to drop off. Significantly crop damage usually occurs within a three week period between late July to late August depending on the season and where the crop is grown. Pupa Pupa Stage - Bertha Armyworm A pupa is a pod­like structure the bertha armyworm forms around itself to protect it while it transforms from the larval stage to the adult moth. Bertha armyworms survive the winter as pupae in the ground at depths of 5 to 16 cm (2 to 6 in.) Pupation usually begins in mid to late August. All larvae will have pupated by early to mid-September. If the autumn is unusually warm, some pupae may continue their development and emerge as moths in late August or September, only to perish when winter arrives. Pupae are reddish brown in color, about 0.5 to 1.8 cm (02 to 0.7 in.) in size and tapered with flexible, terminal abdominal segments. Bertha armyworm pupae are indistinguishable from other cutworm pupae. How is the pest managed? In most years, bertha armyworm is controlled naturally by biological or environmental factors. Environmental conditions have a significant impact on bertha armyworm populations, especially on the overwintering pupae. During harsh winters in snowfree fields, most bertha armyworm pupae perish. Bertha armyworm outbreaks appear to be favoured by snow accumulation which protects pupae from experiencing prolonged exposure to temperatures below ­10°C. The trend toward reduced tillage and stubble conservation will likely result in more snow accumulation on infested fields and favour bertha armyworm survival, especially in years with early snow fall. In addition, newly hatched larvae are especially vulnerable to inclement weather and diseases. Monitoring - It is important to monitor larvae numbers in each field. Adjacent fields may have very different larval densities, depending upon how attractive the crop was when the moths were laying their eggs. Adjacent crops may also have different sized larvae, depending on when the eggs were laid. For accurate larval estimates in a crop, samples are taken that are in at least three locations a minimum of 50 metres apart. The plants are beaten to dislodge the larvae. The plants are then pushed aside and a count is taken of the number of larvae in the square metre area. As few as 20 larvae per square meter can reduce canola yields by 1.16 bushels/acre. Adult populations can be monitored using traps which attract the male moths with pheromones or synthetic sex attractant. Changes in the number of moths collected by these traps correspond to the fluctuations in bertha armyworm larval populations. The higher the trap catches the more likely larval populations will exceed economic thresholds. Biological Control - There are a number of diseases and parasites attack the bertha armyworm including: a nuclear polyhedrosis virus, an ichneumonid wasp, and a tachinid fly. These natural enemies often do not destroy larvae until after considerable damage has occurred. These biological agents have their greatest impact on reducing the number of armyworm produced a year or two after the peak of an outbreak and are probably the reason that severe infestations only last 2 or 3 years. Their presence in a crop does not however, indicate that control measures are not warranted. Cultural Control - Manipulation of bertha armyworm populations by tillage, planting alternative crops, altering seeding dates, seeding different cultivars, effective weed control, early swathing, and fall cultivation are methods that may be used to reduce crop loss. Fall cultivation has been suggested as a way to kill bertha armyworm pupae. Fall cultivation minimizes the amount of snow trapped on a field and exposes pupae to sub­zero temperatures. Although this practice may be effective for individual fields, fall cultivation is not likely to be effective unless it is adopted by air producers since adult moths are strong flyers. Altering seeding dates may help to reduce bertha armyworm infestations. Also, Polish and Argentine type canola seeded on the same dates are likely to infested at different levels. Bertha armyworm infestations in flax, peas, lentils and sugar beets can be reduced with adequate weed control. Controlling lamb's quarters and wild mustard early prevents infestation because larvae first feed upon the weeds and then move onto crops after the weeds have been destroyed. Early swathing can be used to limit damage when the crop is very close to mature and weather conditions are warm and dry. The technique has merit if the crop is within a couple of days of normal swathing and the bertha armyworm population does not greatly exceed the economic threshold. However, problems may occur if larval populations are underestimated or the canola crop is swathed too early. High larval densities may result in serious damage to swaths because larvae will continue to feed either until they are mature or the crop dries to the point­where it is no longer acceptable as food. Once canola is swathed the option of controlling the population with insecticides is no longer possible and extensive damage may occur. Swathing the crop too early may also increase the number of green, unripened seeds and adversely affect seed quality and grade. Although cultural control practices have merit, most have not been thoroughly investigated. The precise effect of using a particular cultural control strategy is unknown and may vary from year to year. The best option is to select a combination of crops, varieties, and seeding dates that will minimize the risk of crop loss. Chemical control - Chemical control is the producers last line-of-defence against the bertha armyworm. For the best results, an insecticide should be applied as soon as economic thresholds are reached and before the larvae have damaged the plants. If producers are to get the most value from an insecticide application it must be used in conjunction with an adequate monitoring program. Early detection of bertha armyworm larvae is critical if crop losses are to be minimized. An insecticide application is recommended when bertha armyworm larvae are abundant enough that they may consume crop valued in excess of the cost of controlling them. This is referred to as economic threshold. The economic threshold for bertha armyworm varies with the cost of the insecticide, the method of application, and the crop's value. Control is usually achieved with a single, well­timed application of any of the registered insecticides applied with aerial or high clearance ground equipment.