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Tuesday, 22 September 2015

Contact and fumigant toxicity of five pesticidal plants against Callosobruchus maculatus (Coleoptera: Chrysomelidae) in stored cowpea (Vigna unguiculata)

International Journal of Tropical Insect Science


Research Papers


Prisila A. Mkendaa1, Philip C. Stevensona2a3, Patrick Ndakidemia4 c1, Dudley I. Farmana2 and Steven R. Belmaina2

a1 Department of Biological Sciences, Sokoine University of Agriculture, Morogoro, Tanzania
a2 Natural Resources Institute, University of Greenwich, Chatham Maritime, Kent ME4 4TB, United Kingdom
a3 Jodrell Laboratory, Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3AB, United Kingdom
a4 School of Life Sciences and Engineering, The Nelson Mandela African Institution of Science and Technology, Arusha, Tanzania
Abstract
Insecticidal activities of five pesticidal plant species, Tephrosia vogelii, Dysphania (Syn: Chenopodium) ambrosioides, Lippia javanica, Tithonia diversifolia and Vernonia amygdalina, which have been reported to control storage pests, were evaluated as leaf powders against Callosobruchus maculatus (Fabricius 1775) in stored cowpea. Their efficacy was compared with the commercial pesticide Actellic dust (pirimiphos-methyl) at the recommended concentration (50 g/90 kg), and with untreated cowpea seeds as a negative control. The plant powders were applied at concentrations of 0.01, 0.1, 1 and 3 g/10 g of cowpea seeds in 250 ml plastic containers (to measure contact toxicity), or 0.005, 0.05, 0.5 and 5 g tied in small muslin cloth bags and hung in 500 ml plastic bottles containing 10 g of cowpea seeds (to measure fumigant toxicity). Mortality of adults, oviposition deterrence, adult emergence, and percent seed damage were recorded. Complete protection of seeds and inhibition of adult emergence were achieved in Actellic dust-treated seeds; contact toxicity using leaf powders of T. vogelii at all concentrations, D. ambrosioides at concentrations of 0.1, 1 and 3 g and L. javanica at concentrations of 1 and 3 g; and fumigant toxicity using D. ambrosioides at concentrations of 0.5 and 5 g and L. javanica at a concentration of 5 g. Head space analysis of D. ambrosioides and L. javanica identified ascaridole and camphor, respectively, as components that could be responsible for the bioactivity of these plant species. These plants may, therefore, serve as effective but less harmful biopesticide alternatives to Actellic. Conversely, V. amygdalina and T. diversifolia were not effective, indicating that they should not be promoted for controlling bruchids in cowpea.
(Accepted May 26 2015)
Key Words:
  • Callosobruchus maculatus ;
  • cowpea;
  • contact and fumigant toxicity;
  • pesticidal plants;
  • post-harvest pest management;
  • stored product pests
Correspondence
c1 E-mail: patrick.ndakidemi@nm-aist.ac.tz
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