Antagonistic, additive and synergistic interactions in the lethality of rice husk ash based entomocides to Callosobruchus maculatus Fabricius (Coleoptera: Chrysomelidae: Bruchinae)

• J.E. Idoko

  Department of Crop, Soil & Pest Management, The Federal University of Technology, PMB 704, Akure, Nigeria.

  Author

• T.I. Ofuya

  Department of Crop, Soil & Pest Management, The Federal University of Technology, PMB 704, Akure, Nigeria.

  Author

• K.D. Ileke

  Department of Biology, The Federal University of Technology, PMB 704, Akure, Nigeria.

  Author

The study evaluated the lethality of powders of rice husk ash (RHA), Eugenia aromatica Baill.dry flower buds (EAP), Piper guineense Schum & Thonn. dry fruits (PGP), Zingiber officinale Roscoe shoot (ZOP), Ocimum gratissimum L. shoot (OGP) and Xylopia aethiopica (Dunal) A. Rich fruits (XAP) applied singly and in pairwise combinations (1:1 ratio), to the cowpea storage beetle, Callosobruchus maculatus Fabricius, under ambient laboratory conditions (28 ± 4C and 75 ± 10% relative humidity). The powders (singles and mixtures) were tested at the dosages of 0.0 (control), 0.2, 0.4, 0.6, 0.8, and 1.0 g/20 g of cowpea grain in plastic bottles with airtight lids against freshly emerged adult beetles. Adult mortality was observed 24, 48, and 72 hours post treatment. To determine antagonistic, additive and synergistic interactions, corrected mortality data was used to compute co-toxicity factors. The computation showed that most of the co-toxicity factors for the binary combinations of the rice husk based entomocides, irrespective of dosage and duration of treatment (61 out of 75) were < −20 indicating antagonistic interactions. A few of the computed co-toxicity factors, specifically lethality within 24 hours post treatment i.e. – 6.1 and – 18.7, for 0.4 and 0.6 dosages with RHA + PGP; – 19.8 for 0.2 dosage with RHA + OGP, and – 9.6 and – 11.8 for 0.6 and 0.8, dosages with RHA + XAP indicated additive interactions. Only the co-toxicity factor of + 23.1 and + 23.6 for 0.2 and 0.4 dosages respectively of RHA + ZOP and + 23.1 for 0.2 and 0.4 dosages of RHA + XAP within 24 hours of treatment, indicated synergistic interaction. In the treatments for 48 hours RHA + ZOP at 0.2 and 0.4 dosages with -18.1 and – 20.0 also indicated additive interaction. In the treatments for 72 hours RHA + PGP at 0.2 dosages with – 6.5, and RHA + ZOP with – 3.0 and – 17.1 respectively, for 0.2 and 0.4 dosages further indicated additive interaction.

1. J.E. Idoko, Department of Crop, Soil & Pest Management, The Federal University of Technology, PMB 704, Akure, Nigeria.

   Department of Crop, Soil & Pest Management, The Federal University of Technology, PMB 704, Akure, Nigeria.

2. T.I. Ofuya, Department of Crop, Soil & Pest Management, The Federal University of Technology, PMB 704, Akure, Nigeria.

   Department of Crop, Soil & Pest Management, The Federal University of Technology, PMB 704, Akure, Nigeria.

3. K.D. Ileke, Department of Biology, The Federal University of Technology, PMB 704, Akure, Nigeria.

   Department of Biology, The Federal University of Technology, PMB 704, Akure, Nigeria.

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