Plusiinae

Larvae are distinguished from geometrid loopers (true loopers) by possessing three pairs of prolegs rather than two. This trait, combined with the looping gait, separates Plusiinae from both geometrids and other noctuid larvae with five pairs of prolegs. Adults may be distinguished from other noctuids by a combination of wing venation and genitalic characters, though specific identification often requires dissection. Larvae of some economically important species (e.g., Chrysodeixis includens, Rachiplusia nu) are difficult to distinguish in the field and require examination of spinneret shape for conclusive identification.

Habitats are diverse and generally associated with host plant availability. Many species occupy agricultural landscapes, particularly soybean fields, alfalfa, and other legume crops. Some species occur in natural and semi-natural habitats including grasslands, open woodlands, and disturbed areas. Dry conditions appear to favor population increases in some pest species, while moist conditions promote fungal pathogens that suppress larval numbers.

Worldwide distribution with species on all continents except Antarctica. Major pest species such as Chrysodeixis includens occur in the Americas from the United States through Brazil. Rachiplusia nu is distributed across South America in Argentina, Bolivia, Brazil, Chile, Paraguay, Peru, and Uruguay. Other species occur throughout Europe, Asia, Africa, and Australia.

Activity patterns vary by species and latitude. In temperate regions, adults are typically active from spring through fall with multiple generations. In subtropical and tropical regions, activity may occur year-round with population peaks corresponding to crop phenology. In Argentina, Rachiplusia nu infestations tend to occur during the reproductive stages of soybean growth.

Larvae are primarily folivorous, feeding on leaves of diverse plants. Many species are polyphagous. Documented hosts include soybean (Glycine max), alfalfa (Medicago sativa), sunflower (Helianthus annuus), flax (Linum usitatissimum), and various wild and cultivated legumes. Young larvae typically feed on lower leaf epidermis between veins, producing 'window paning' damage; older larvae consume entire tissues while avoiding major veins, resulting in skeletonized foliage.

• Glycine max - larval food plantmajor pest host for multiple species
• Medicago sativa - larval food plantearly season host for some species
• Helianthus annuus - larval food plantheavily attacked in drier regions
• Linum usitatissimum - larval food plantearly season host
• Vitis spp. - larval food planthost for some species

Complete metamorphosis with egg, larva, pupa, and adult stages. Eggs are typically laid on the undersides of leaves. Larvae pass through multiple instars, with young stages feeding superficially and older stages consuming entire leaf tissues. Pupation occurs in soil or leaf litter. Multiple generations per year occur in favorable climates.

Adults are nocturnal and visit flowers for nectar, often hovering rather than landing. Larvae exhibit characteristic looping locomotion due to reduced proleg number. When disturbed, some larvae may drop from foliage on silken threads. Feeding damage patterns are distinctive: young larvae produce window-pane damage by consuming only lower epidermis between veins, while older larvae skeletonize leaves by consuming all tissue except major veins.

Larvae function as primary consumers in both natural and agricultural ecosystems. As significant defoliators of leguminous plants, they influence plant productivity and can alter community composition in outbreak conditions. They serve as prey for diverse natural enemies including parasitoid wasps, predatory insects, and birds. Some species are hosts for parasitoid wasps used in biological control programs.

Several species are major agricultural pests causing significant economic damage to soybean, particularly in the Americas. Chrysodeixis includens (soybean looper) is a primary pest in the southeastern United States and Brazil. Rachiplusia nu is the dominant plusiine pest of soybean in Argentina, with increasing importance of C. includens in northern regions. Control challenges include pesticide resistance in C. includens and misidentification of similar larval species leading to control failures. The subfamily has been extensively studied for development of artificial diets for laboratory rearing.

• GeometridaeLarvae also loop, but geometrids possess only two pairs of prolegs versus three in Plusiinae; geometrid larvae lack prolegs on abdominal segment 3
• Noctuidae (other subfamilies)Other noctuid larvae typically have five pairs of prolegs and do not exhibit looping locomotion
• Chrysodeixis includens vs. Rachiplusia nuLarvae are morphologically similar and difficult to distinguish in the field; conclusive separation requires examination of spinneret shape or subtle color differences (R. nu tends toward smoky-blue, C. includens toward yellow-green)

Larvae are often misidentified as geometrid 'loopers' due to similar locomotion, but the three pairs of prolegs in Plusiinae versus two in Geometridae is a definitive distinction. The common name 'looper' is applied to both groups, causing confusion. Larvae of closely related pest species (particularly C. includens and R. nu) are frequently misidentified in regions where they co-occur, leading to inappropriate pesticide applications due to differing susceptibilities.

• Noctuidae
• agricultural pest
• soybean pest
• looper
• defoliator
• Lepidoptera
• Plusiinae

• BugGuide
• Wikipedia
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• Noctuidae | Beetles In The Bush | Page 3
• ID Challenge #14 | Beetles In The Bush
• This Artificial Diet May Make Insect Rearing Easier