Dectes sayi

Dillon & Dillon, 1953

Soybean Stem Borer

Dectes sayi is a stem-boring longhorn (: Lamiinae) to North America. Described by Dillon and Dillon in 1953, this is closely related to the more economically notorious Dectes texanus but is distinguished by morphological features including a more protruding and smaller lower lobe. The are internal feeders within the stems of herbaceous plants, particularly favoring common ragweed ( artemisiifolia) over soybean, though it will utilize soybean when available. The species is named in honor of Thomas Say, the 19th-century regarded as the 'Father of .'

Dectes sayi 296215079 by Jackson Kusack. Used under a CC0 license.

Dectes sayi 296215060 by Jackson Kusack. Used under a CC0 license.

Dectes sayi 43268279 by Philip Stepnowski. Used under a CC BY 4.0 license.

Pronunciation

How to pronounce Dectes sayi: //ˈdɛk.teɪs ˈseɪ.aɪ//

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Identification

Distinguished from the congeneric Dectes texanus by two facial characters: the is distinctly more protruding, and the lower lobe of the is smaller, creating the impression of 'tall .' are longhorn with longer than the body. are legless, -like, with small and abdominal that resemble an accordion; full-grown larvae reach 1/2 to 5/8 inch in length.

Images

Habitat

Agricultural fields and natural areas supporting herbaceous plants, particularly those in the Asteraceae and Fabaceae . develop internally within the pith of host stems.

Distribution

Broadly distributed across the United States and Canada. GBIF records confirm presence in Manitoba, Ontario, and Québec, Canada, with wider distribution throughout North America.

Seasonality

are active during summer months. overwinter within girdled stems at or near ground level, pupating in spring.

Diet

feed internally within stems of plants, tunneling through pith tissue. feed on tissues including leaf and stems.

Host Associations

common ragweed - preferred artemisiifolia; this is 'much happier' boring in ragweed than soybean
soybean - occasional Glycine max; known to bore in stems but less preferred than ragweed
cocklebur - Xanthium sp.
sunflower - Helianthus sp.

Life Cycle

. Females lay on or near plants, typically in leaf . hatch and bore into stems, tunneling downward through the pith to the base of the . Mature larvae the inside of the stem at or just above ground level, then move below this girdle to overwinter in an insulated chamber packed with fibrous . occurs in spring, with emerging the following summer.

Behavior

Larval stem-boring involves tunneling through pith, causing internal damage without external signs until girdling occurs. Mature exhibit girdling behavior prior to , severing the internal stem structure and predisposing plants to . are weak fliers with localized .

Ecological Role

on wild Asteraceae, primarily common ragweed. Agricultural pest of soybean, though less damaging than Dectes texanus due to stronger preference for alternative .

Human Relevance

Minor agricultural pest of soybean, occasionally causing stem and yield loss. Often confused with the more damaging Dectes texanus. Cultural practices including , destruction of , and good weed control (particularly of ragweed) help manage . No chemical control recommendations are currently available; early harvest is the primary management strategy to reduce lodging losses.

Similar Taxa

Dectes texanusCongeneric with overlapping range and distribution; distinguished by less protruding , larger lower lobe, and greater economic impact on soybean; are pale gray versus the facial structure differences in D. sayi

Misconceptions

Often confused with Dectes texanus and lumped under the 'soybean ,' which properly applies to both . The name 'soybean stem borer' is misleading for D. sayi given its preference for common ragweed over soybean.