Plusiina
Plusiina is a subtribe within the Plusiinae of the . Members are commonly known as or semiloopers due to their distinctive larval . The subtribe includes economically significant agricultural pests such as Rachiplusia nu and Chrysodeixis includens, which cause damage to soybean and other . are characterized by having three pairs of and a looping gait, distinguishing them from true geometrid loopers which possess only two pairs.
Pronunciation
How to pronounce Plusiina: //pluˈsiː.ɪ.nə//
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Identification
are distinguished from true geometrid () by possessing three pairs of rather than two. Within Plusiina, identification often requires examination of the shape—Rachiplusia nu has a differently shaped spinneret than Chrysodeixis includens. Field identification is complicated by similar larval appearance between species; R. nu older larvae tend to show darker coloration and thoracic asperites not apparent in C. includens. require genitalic dissection or molecular methods for reliable species-level identification.
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Habitat
Associated with agricultural and natural supporting their plants. In Argentina, found in the Humid Pampas region and expanding northeastern provinces, particularly in soybean-growing areas. Dry conditions appear to favor increases in some .
Distribution
Widely distributed across the Americas. Rachiplusia nu occurs in Argentina, Bolivia, Brazil, Chile, Paraguay, Peru, and Uruguay. Chrysodeixis includens is established in the southeastern United States, Brazil, and has appeared with increasing frequency in northern Argentina. The subtribe as a whole has a predominantly New World distribution.
Diet
feed on a range of plants including soybean, sunflower, alfalfa, and flax. Young larvae feed on lower leaf between , creating "window pane" damage; older larvae consume entire tissue while avoiding veins, resulting in skeletonized foliage. A single larva can consume more than 100 cm² of soybean foliage.
Host Associations
- Glycine max - larval soybean, major agricultural
- Helianthus annuus - larval sunflower, heavily attacked in drier western regions of Córdoba Province, Argentina
- Medicago sativa - larval alfalfa, early season for Rachiplusia nu
- Linum usitatissimum - larval flax, early season for Rachiplusia nu
Life Cycle
with , , , and stages. Eggs are laid primarily on undersides of leaves. Larvae progress through multiple , with feeding damage increasing substantially in later stages. Specific details of sites and adult longevity are not well documented in available sources.
Behavior
exhibit characteristic looping due to reduced number compared to typical . of at least some (e.g., Chrysodeixis includens) hover at flowers during dusk rather than landing. are laid on leaf undersides where larvae begin feeding immediately after hatching.
Ecological Role
Significant defoliators in agricultural . Larval are suppressed by under moist conditions. Serve as for including Cotesia vanessae, which has been investigated as a agent.
Human Relevance
Major agricultural pests, particularly of soybean production in South and North America. Rachiplusia nu is the primary plusiine affecting soybean in Argentina, while Chrysodeixis includens is a major pest in the southeastern United States and Brazil. Control failures occur due to misidentification and differing susceptibilities between —C. includens has developed to multiple pesticides. The subtribe has been subject to extensive research on artificial rearing diets, with the McMorran diet successfully supporting development of multiple species.
Similar Taxa
- GeometridaeTrue with only two pairs of and similar looping ; distinguished by proleg count and
- Helicoverpa zeaLarval coloration and body form can appear similar, but H. zea typically has a prominent black spot above the second pair of true legs and different arrangement
Misconceptions
Frequently misidentified as due to shared "" and similar larval movement. The subtribe name Plusiina is sometimes confused with the Plusia or the Plusiinae in general. of Rachiplusia nu and Chrysodeixis includens are often misidentified in areas of sympatry due to superficial similarity and difficulty of field-diagnostic characters.
More Details
Taxonomic History
The subtribe Plusiina was established within Plusiinae to accommodate a group of sharing derived larval characteristics. historically placed in Pseudoplusia have been transferred to Chrysodeixis following synonymization by Goater et al. (2003) and formal acceptance in North fauna by Lafontaine and Schmidt (2010).
Laboratory Rearing
Members of Plusiina are among the most frequently reared in laboratory settings. The McMorran artificial diet, developed in 1965 and modified with linseed , supports development of numerous . In one study, 39 noctuid species including multiple Plusiina members were successfully reared on this diet, facilitating research on and .