Toxoneuron nigriceps

(Viereck, 1912)

Toxoneuron nigriceps is a koinobiont endoparasitoid in the Braconidae. It is highly -specific to the tobacco budworm, Heliothis virescens, and historically provided substantial natural in agricultural systems. The exhibits complex host manipulation strategies including injection of , venom, and ovarian proteins during oviposition, followed by a distinctive postegression feeding phase where larvae exit the host to feed externally on liquefied tissues before .

Pronunciation

How to pronounce Toxoneuron nigriceps: //tɒkˈsoʊ.njuˌrɒn nɪˈɡrɪ.sɛps//

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Habitat

Tobacco agroecosystems; laboratory rearing conditions include temperature 29±1°C, 60±10% relative humidity, and 14:10 L:D .

Distribution

Documented from field studies in Georgia with historical rates of 50–100% in tobacco budworm ; specific 96% and 76% parasitism rates recorded in consecutive years.

Diet

during internal larval development (first through early third instar); liquefied host tissues during external postegression feeding phase in late third instar.

Host Associations

  • Heliothis virescens - primary tobacco budworm; highly -specific, normal development occurs only in this
  • Helicoverpa zea - non-oviposition attempted but developmentally unsuitable; females spend less time foraging than for H. virescens
  • Manduca sexta - non-oviposition attempted but developmentally unsuitable; females spend less time foraging than for H. virescens
  • Heliothis virescens prepupal tissue (unparasitized) - experimental accepted when presented but with reduced nutritional benefit compared to parasitized tissue

Life Cycle

to second instar and second to early third instar can be reared in artificial media; late third instar requires postegression tissue feeding to survive to . Egression from occurs after host to fifth instar. External tissue feeding lasts several hours (up to 4 hours), during which larvae nearly double in length and girth and change from bright green to dull whitish color. Pupation occurs within a cocoon spun in a small, partially enclosed chamber; larvae cannot form cocoons on open flat surfaces.

Behavior

Females exhibit differential searching , spending more time hovering and foraging for H. virescens than for non- H. zea and M. sexta. During postegression feeding, larvae anchor the end in the egression hole, curve to form a second hole in host , and feed on liquefied tissues; will feed on presented tissues even when normal behavior is disrupted.

Ecological Role

agent of Heliothis virescens, a serious pest of tobacco, cotton, soybean, and tomato; historically provided high degree of natural control with field rates up to 96%.

Human Relevance

Studied as a agent for agricultural pest management; mass-rearing protocols developed using artificial chambers (gelatin capsules and microtube rack wells recommended).

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