Dectes texanus

LeConte, 1862

Dectes stem borer, Texas prick, soybean stem borer

Dectes texanus is a North longhorn (: Lamiinae) that has emerged as a significant agricultural pest of soybeans and sunflowers in the Midwestern and Great Plains regions of the United States. are characterized by longer than their bodies and a pale gray coloration. tunnel inside stems from July through October, then the stem base internally before , causing pre-harvest and yield losses. The has expanded its range and pest status dramatically since the 1980s, correlating with increased soybean acreage and adoption of no-till farming practices. Originally associated with wild including ragweed and cocklebur, it colonized cultivated soybeans approximately 50 years ago.

Dectes texanus P1250052a by
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Pronunciation

How to pronounce Dectes texanus: /ˈdɛk.tiːz tɛkˈseɪ.nəs/

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Identification

are pale gray approximately 9–10 mm in length with distinctly longer than the body. The is only slightly protruding, with a relatively large lower lobe of the —features that distinguish it from the Dectes sayi, which has a more protruding face and smaller lower eye lobe creating an impression of "tall ." are legless, -like, with a small and abdominal resembling an accordion; fully grown larvae reach 12–16 mm.

Images

Habitat

Agricultural fields, particularly soybean and sunflower ; also found in areas with wild plants including ragweed, cocklebur, and wild sunflower. Overwinters in the bases of host stalks below the soil .

Distribution

to eastern North America; established in at least 14 states. In Kansas, documented in 64 counties as of 2008 with range expansion from 5 counties in 1985. Highest occur in southwest and north-central Kansas; notably sparse in eastern Kansas despite extensive soybean acreage. Also present in Missouri, western Tennessee, Mississippi, Arkansas, and Texas.

Seasonality

Single per year. emerge late June through July, with extended period lasting through the growing season. laid in leaf ; tunnel and feed July through October. Larvae stems and overwinter from October through May, pupating May to June.

Diet

feed internally on pith of and stems. feed on of newly expanded plant tissue.

Host Associations

Glycine max - larval (primary host)soybean
Helianthus annuus - larval (primary host)cultivated sunflower
Helianthus spp. - larval wild sunflower
Ambrosia artemisiifolia - larval common ragweed
Xanthium spp. - larval cocklebur

Life Cycle

Single annually: inserted into pith of leaf , hatching in a few days; tunnel down petioles into main stems, feeding up and down the pith from late July through October; mature larvae the stem internally at or just above ground level (1–2 inches), then move below the girdle to pack around themselves and overwinter; occurs May to June in the soil or base; emerge late June through July, living several weeks.

Behavior

exhibit cryptic , spending most of their time tunneling inside stems. Mature larvae stems internally before , causing . are reasonably strong fliers capable of infesting fields within several miles but do not undergo long-distance ; they are weak fliers relative to some . involves male of females, with evidence for a female contact .

Ecological Role

Agricultural pest causing through stem and yield reduction. Some research suggests 10–15% yield reduction from tunneling activity alone. Serves as for including Zelia tricolor ().

Human Relevance

Significant economic pest of soybean and sunflower production in the Great Plains and Midwest. Management relies on cultural practices: early harvest to avoid losses, fall tillage to reduce , destruction of stubble, crop , and weed control to eliminate . No-till farming increases overwintering survival. Chemical control is not recommended due to cryptic larval habit; no elite soybean currently available though QTL for have been identified.

Similar Taxa

Dectes sayiCongeneric also found in soybeans; distinguished by more protruding , smaller lower lobe, and preference for common ragweed over soybean
Ataxia hubbardiAnother stem-borer in sunflowers; remain active through winter without girdling, do not cause significant damage
Mecas spp.Longhorn that sunflower stems; larger (approximately 12 mm), gray, with different girdling pattern (two girdles about one-third down stalk)

More Details

Population expansion

The has shown dramatic increase and range expansion since the 1980s. In Kansas, fields with >50% plants infested rose from 4% (1999) to 11% (2008). This correlates with expanded soybean acreage, increased no-till farming, and possibly climate factors.

Host plant resistance

Wild Helianthus annuus shows substantial to due to higher resin content, lower succulence, and tougher . These antixenotic properties have been inadvertently diminished in cultivated sunflower breeding.

Transcriptomic adaptations

feeding on soybean upregulate genes involved in oxidoreductase activity, polygalacturonase activity, P450s, and carboxylesterases—suggesting enhanced detoxification and -wall digestion capabilities compared to larvae on primary .

Genomic resources

GWAS studies have identified 3 QTL for reduced larval and 4 QTL for reduced girdled stems in soybean, with effects of 1–9% reduction, offering potential for breeding .