Synergy between parasitoids and pathogens for biological control of Helicoverpa armigera in chickpea

Abstract

The chickpea pod borer, Helicoverpa armigera H€ ubner (Lepidoptera: Noctuidae), is an important pest of many legume crops, including chickpea, Cicer arietinum L. (Fabaceae). We field-tested the efficacy of two pathogens, Helicoverpa armigera nucleopolyhedrosis virus (HaNPV) and Bacillus thuringiensis Berliner subsp. kurstaki (Btk), both alone and in combination with the parasitoid Habrobracon hebetor Say (Hh) (Hymenoptera: Braconidae), for control of H. armigera larvae in chickpea fields. A randomized complete block design was used at two sites, so that wasp release treatments at one site would not contaminate pathogen-only treatments at the other. Pathogens were applied when most pest larvae were in the second instar, and wasp releases were made 2 days later. Number of H. armigera larvae per plant, number of damaged pods, yield (kg ha À1 ), treatment cost (US$ ha À1 ), and benefit:cost ratio were all determined. Treatments separated significantly at 14 days after treatment, with the HaNPV+Hh and Btk+Hh treatments providing the best control, suggesting a synergistic impact of the wasp and the pathogens when applied together. These treatments also produced the fewest damaged pods, the highest yields, and the greatest yield increments in comparison to untreated controls. However, costs were also highest for these combined treatments, which reduced their net benefit in comparison to use of Hh or Btk alone, although more efficient mass production of the pathogens might make combined applications feasible. We conclude that both HaNPV and Btk are suitable for integration with releases of H. hebetor against H. armigera in chickpea fields, provided parasitoid releases are delayed until 2 days after pathogen application.

Management of Gram Caterpillar, Helicoverpa armigera (Hubner) with Bt Formulation in Chickpea under Organic Conditions

“…Similarly, the present investigations for higher yield in chickpea in the studies for management of gram caterpillar on chickpea crop are in agreement to those of Ahmed and Khalique (2012) and Taggar et al (2014) who also reported highest yield of pigeonpea in Bt treated plots over the untreated plots. The present work is in agreement with Allahyari et al (2020) who in their studies for management of H. armigera with Bt formulation also recorded higher yield in Bt treated plots (786.42 kg/ha) over the untreated plots (627.49 kg/ha).…”

Can the Combined Use of the Mirid Predator Nesidiocoris tenuis and a Braconid Larval Endoparasitoid Dolichogenidea gelechiidivoris Improve the Biological Control of Tuta absoluta?

“…Although some notable successes have been recorded [1,2], interactions between two or more natural enemies are not straightforward and the outcome may be counterproductive [3,4]. Interactions can be synergistic-the cumulative efficacy of both species being significantly higher than the efficacy of the two natural enemies when used separately [5]-or additive-when the combined use of both natural enemies is more effective and equal to the added efficacy by each species alone [6]. In other cases, interactions may be equivalent-when the combined impacts of both natural enemies are equal to the more effective of the two species [7].…”

Behavioral and Developmental Responses ofHabrobracon hebetor(Hymenoptera: Braconidae) to Larvae ofHelicoverpa armigera(Lepidoptera: Noctuidae) Inoculated With Various Concentrations ofBacillus thuringiensisvar.kurstaki(Bacillales: Bacillacae)

“…This eventuality might be delayed or precluded if releases of H. hebetor reduce the survival of resistant genotypes. Allahyari et al (2020b) found evidence of additivity between Btk and H. hebetor in controling H. armigera on chickpea in an earlier field study, which would support their effectiveness in joint application. Thus, even though Btk had some negative effects on H. hebetor under laboratory conditions, and the parasitoid failed to discriminate against hosts treated with low concentrations of Btk , we conclude that these two biocontrol agents are potentially compatible for combined application against H. armigera under field conditions.…”

“…The basal container was covered with a second container (15 cm diameter × 13 cm height) ventilated by means of a fine mesh glued to an aperture cut in the bottom (7 cm diameter). Both containers had sloping sides, so that a larva-proof seal was obtained when the larger container was placed upside down over the smaller one ( Allahyari et al 2020b ). The second-instar H. armigera larvae were then left to feed on the Btk -treated chickpea plants for 3 d under the same physical conditions as the insect colony.…”