Trichogramma egg parasitism of Helicoverpa armigera on short‐duration pigeonpea intercultured with sorghum

Abstract

The levels of egg parasitism by Trichogramma spp. (Hymenoptera: Trichogrammatidae) on populations of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) were recorded on sorghum (Sorghum bicolor L.) and on two flushes of flowers on short‐duration pigeonpea (Cajanus cajan L.). H. armigera oviposition was concentrated on the early flowering stage of sorghum and the flowering and early podding stages of both flushes of pigeonpea. Parasitism on sorghum increased rapidly as egg density increased and reached a peak of 74.6%. Parasitism on pigeonpea was concentrated on H. armigera eggs laid on the first flush of pigeonpea flowers with a maximum of 69.2%. These high levels of parasitism on pigeonpea coincided with the period of parasite activity on sorghum. The levels of parasitism then declined rapidly and only very low levels were detected on a second flush of flowers. This rapid decline resulted in the overall egg mortality caused by Trichogramma on pigeonpea to be low, with a maximum of 7.8% caused by parasitism, compared to 34.4% on sorghum. The pattern of parasitism suggests that a transfer of parasites occurred from sorghum to pigeonpea. The rapid decline of parasitism on the pigeonpea indicates that parasite populations cannot be sustained on pigeonpea once the influx from sorghum stops. The results are discussed in terms of a possible method of encouraging the transfer of parasites from sorghum to short‐duration pigeonpea by producing a more continuous cropping environment.

Trichogramma egg parasitism of Helicoverpa armigera on pigeonpea and sorghum in southern India

“…Helicoverpa armigera was attracted to sorghum throughout anthesis with the peak egg density coinciding with the 50% flowering stage, as has been reported earlier (Parsons, 1940;Duffield, 1994). The sticky trap catches show that Trichogramma spp.…”

“…There was no detectable movement of Trichogramma spp. from sorghum into pigeonpea as has been suggested by Duffield (1994). In a single season trial, Duffield reported high parasitism levels of eggs collected from pigeonpea when H. armigera was ovipositing simultaneously in both crops.…”

“…In this cropping system, Trichogramma spp. have been reported to parasitize up to 69% of H. armigera eggs collected from pigeonpea during one season (Duffield, 1994). The author suggested that parasitoids moved from sorghum into pigeonpea.…”

Insect Pests of Pigeonpea and Their Management

“…No reliable or comprehensive life table study that evaluated the role and impact of natural enemies of any insect pest on pigeonpea has been published. An attempt was made to increase the impact of natural enemies on short-duration pigeonpea by intercropping with short-duration sorghum (17). The mechanism behind this strategy was that synchronized flowering times would facilitate the transfer of natural enemies from sorghum to pigeonpea.…”

Oviposition Behaviour and Reproductive Performance of Trichogramma australicum Girault (Hymenoptera: Trichogrammatidae) Reared in Artificial Diet

“…Trichogramma species have been widely used as biocontrol agents in inoculative release programs against many lepidopteran pests, but programs involving inundative releases of Trichogramma species have given varying results (Neil and Specht 1990;Rawat and Pawar 1991;Andow and Prokrym 1991;Ashraf et al 1993;Duffield 1994). Mass production of Trichogramrna is needed to effectively apply inundative control methods.…”