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» Pickleworm and melonworm can reduce the yield and marketability of squash fruit.
» Pickleworm and melonworm overwinter in southern Florida and can migrate northward and westward during the cucurbit cropping season.
» Integration of cultural and chemical strategies can be used to help manage pickleworm and melonworm on squash.
Pickleworm (Diaphania nitidalis) and melonworm (D. hyalinata) are related insects that feed on and damage cucurbit crops such as summer and winter squashes. Pickleworm can be one of the most destructive insects on squashes in areas where it is present. Melonworm also can be an important pest on squash, but it is usually not as economically damaging as pickleworm.1,2 These insects can also cause damage on cucumber and melon but rarely on watermelon. They are tropical insects and are found mostly in the Gulf states, including Florida, Georgia, and southern Texas, but commonly migrate into the Carolinas. They have been found as far west as Oklahoma and Nebraska, and pickleworms have been found as far north as Connecticut and Michigan.1,2,3
Figure 1. Pickleworm (A) adult and (B) larva. (A) Natasha Wright, Braman Termite & Pest Elimination, Bugwood.org, (B) Alton N. Sparks, Jr., University of Georgia, Bugwood.org.
LIFE CYCLE AND IDENTIFICATION
Pickleworm: Pickleworm can overwinter in central and southern Florida and maybe in south Texas.1,2 The life cycle is usually completed in about 30 days, with multiple generations per year in much of its range. As many as four generations per year occur in Georgia, and two to three generations per year are common in North Carolina. The larvae feed on cultivated and wild cucurbit species. Summer squashes are their preferred host and the crop most heavily damaged by pickleworms.3 Pickleworm moths have a 1-inch wingspan and an overall purplish hue. The wings are triangular and have a central semitransparent, yellow area surrounded by a dark brown border (Figure 1A). Bush-like appendages are present on the end of the abdomen. Adults fly mostly during the evening hours, three to five hours after sunset. Females produce pheromones that attract the males.1,2,3 Female pickleworm moths lay eggs on flower buds, flowers, and other areas of new growth. The eggs are very small (0.4 to 0.6 mm long), spherical to flattened, initially white but changing to yellow with age. Each female can lay 300 to 400 eggs, which usually hatch in four days.1,3 The larvae that emerge from the eggs are initially white with dark spots turning green and have an average length of 1/15th inch (1.6 mm) during the first instar. By the fifth instar, the larvae (caterpillars) are up to 1 inch (2.5 cm) long (Figure 1B). Larvae lose their spots and turn a pink to dark copper color before pupation.1,3 The larvae start feeding inside flower buds and flowers. They chew their way out, creating round exit holes, and migrate to fruit or other flower buds. They bore into fruit and feed from within. When ready to pupate, they exit the fruit, and pupate in leaf folds or dead leaf material. The pupal stage typically lasts eight to nine days, after which the next generation of adult pickleworm moths emerge.2.3 Melonworm: The melonworm also overwinters in south Florida and migrates northward as the growing season progresses, and it completes its lifecycle in about 30 days. Adult moths have white, iridescent wings with dark brown borders (Figure 2A) and brush-like appendages at the ends of their abdomens. Eggs are deposited on leaves, usually in groups of two to six. Larvae are colorless when they emerge from the eggs but turn green and develop two white stripes on the sides of their bodies as they mature (Figure 2B). Larvae typically feed on the undersides of leaves. Pupae form in leaf-folds.1,2,4
Figure 2. Melonworm (A) adult and (B) larva. (A) Mark Dreiling, Bugwood. org, (B) Alton N. Sparks, Jr., University of Georgia, Bugwood.org.
DAMAGE
Both pickleworm and melonworm larvae feed on cucurbit plants, and squashes are preferred hosts for both insect species. In regions where the insects overwinter (Florida and maybe Texas), damage to squash plants can occur early in the season. In regions where they do not overwinter, damage occurs later in the season, depending on when adult moths migrate into the area. In these regions, early-season crops may escape damage by these two caterpillar species.2 The most economically important damage caused by pickleworm results from larvae feeding within fruit, making the fruit unmarketable. However, feeding damage to blossoms can reduce potential fruit production by reducing fruit set. Small entry holes in the fruit are often filled with insect frass. Feeding injury on the fruit can allow the introduction of pathogens, resulting in the development of fruit rot.2,3,4 Melonworm larvae feed primarily on the leaves of cucurbits, and they can defoliate plants if populations are high. They usually feed on and remove the leaf’s interveinal areas, giving it a lace-like appearance. If leaf tissue is unavailable, the larvae can feed externally on fruit, resulting in the scaring of fruit surfaces.1,2,4
SCOUTING
Action (treatment) thresholds have not been established for either pickleworm or melonworm. However, scouting for these insects can help alert growers to their presence in the field. Moths fly at night, and the eggs of both species are very small and difficult to detect. So, scouting for these insects focuses on examining plant parts for damage and the presence of larvae. For pickleworm, look for damage and larvae on flower buds over two inches long. For melonworm, look for larvae and feeding damage on the undersides of leaves.1,2
MANAGEMENT
There appears to be some variation in the susceptibility of squash varieties to infestation by pickleworm and melonworm, most likely based on the plants being more or less preferred egg-laying sites. However, no true resistance to either insect has been identified in squash.2,3
In areas where the insects do not overwinter, planting early can help reduce the level of damage caused by pickleworm and melonworm. In areas where the insects can overwinter, the prompt removal of cucurbit crop debris after harvest and management of weed hosts, such as creeping cucumber and wild balsam apple, can help reduce population levels of the insects in the following season.1,2,3 Floating row covers may help prevent egg laying on squash plants, but the application and removal times are critical for effectiveness. The row covers need to be in place before egg laying begins, and the covers must be removed to allow for pollination. It is possible to remove the row covers early in the day to allow pollinators to access the flowers but then recover the plants in the evening before the adult moths become active. However, this may only be feasible for small-area plantings. Row covers may be more effective against melonworm than pickleworm.1,2,3
If pickleworm or melonworm moths are present, applying insecticides can help reduce crop damage and yield losses due to these insects. Fruit must be protected before pickleworm larvae begin to burrow into them, because the cover provided by the fruit itself will protect the larvae from most insecticides. For melonworm, insecticides need to reach the undersides of leaves where the larvae are feeding. Larvae are most effectively managed when they are young.1,3 Care should be taken to protect pollinators and other beneficial insects from insecticide applications. Applying insecticides late in the day can help minimize the harm to honeybees because they are most active in the crop in the morning and early afternoon. Using insecticides with little residual activity can also be less harmful to pollinators.
Natural enemies have not been shown to provide adequate control of pickleworm or melonworm on squash where there is a zero tolerance for fruit infestation. The entomopathogenic nematode Steinernema carpocapsae has been shown to provide some suppression of pickleworm injury on squash. However, they can be challenging apply in such a way that they are effective. Bt-based insecticides may also provide some level of suppression if applied before larvae start to feed, and repeated applications may be needed.2,3
SOURCES
1 Elsey, K. and Webb, S. 2017. Pickleworm and melonworm. In Keinath, A., Wintermantel, W., and Zitter, T. (Eds.) Compendium of Cucurbit Diseases and Pests, Second Edition. The American Phytopathological Society. St. Paul. MN.
2 Zehnder, G. 2011. Biology and management of pickleworm and melonworm in organic curcurbit production systems. eOrganic. https://eorganic.org/node/5320. 3 Capinera, J. 2017. Pickleworm. Featured Creatures. UF IFAS.
3 Capinera, J. 2017. Pickleworm. Featured Creatures. UF IFAS. https://entnemdept.ufl.edu/creatures/veg/pickleworm.htm#:~:text=Pickleworm%20may%20damage%20summer%20and
their%20development%20without%20entering%20fruit.
4 Salgado, L., Huval, F., Reagan, T., and Carlton, C. Diaphania nitidalis and Diaphania hyalinata, pickleworm and melonworm moths (Lepidoptera: Crambidae). Bug Biz, LSU Ag Center. https://www.lsuagcenter.com/articles/page1619562097942#:~:text=Melonworm%20 adults%20remain%20within%20the,the%20heat%20of%20the%20day.
Websites verified 11/28/20231
ADDITIONAL INFORMATION
For additional agronomic information, please contact your local seed representative. Performance may vary, from location to location and from year to year, as local growing, soil and environmental conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on their growing environment. The recommendations in this article are based upon information obtained from the cited sources and should be used as a quick reference for informationabout vegetable production. The content of this article should not be substituted for the professional opinion of a producer, grower, agronomist, pathologist and similar professional dealing with vegetable crops.
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5911_279851 Published 11/09/2023