Toxicity and growth inhibitory activities of methanol extract and the b-carboline
alkaloids of Peganum harmala L. against two coleopteran stored-grain pests
Gomah Nenaah*
Department of Zoology, Faculty of Science, Kafrelsheikh University, 33516 Kafr El sheikh, Egypt
abstract
Methanol extract and the b-carboline alkaloids were extracted from the seeds of Peganum harmala
(Zygophyllaceae). Their toxicity, growth inhibitory and effects on the progeny production of Tribolium
castaneum and Rhyzopertha dominica was studied. To assess any additive effects among the extracted
b-carbolines, they were tested as binary mixtures (1:1) or as a crude alkaloid fraction. All extracts
exhibited a considerable adulticidal effect with increasing activities in response to increased exposure
period. Using the contact toxicity bioassay, the crude b-carboline fraction was the most effective (LC 50’s
were 20.1 and 36.7) mg/cm2, 48 h post-treatment against R. dominica and T. castaneum, respectively. LC50’s
of (harmaline þ harmine), (harmaline þ harmane), and methanol extract were (31.2, 39.4), (33.7, 47.2),
and (39.8, 65.2) mg/cm2, 24 h post-treatment against R. dominica and T. castaneum, respectively. At 48 h
post-treatment, LC50 of (harmaline þ harmine) reached 22.4 mg/cm2 against R. dominica. When mixed
with the insect’s diets, toxicity of all extracts were increased with the crude alkaloidal fraction the most
toxic (LC50’s were 7.8 and 14.7) mg/kg grains, 48 h post exposure against R. dominica and T. castaneum,
respectively. When the 2nd instar larvae were fed sub-lethal doses-treated grains, development and F1
progeny of both insects were significantly affected (P _ 0.001). At 3.5 mg/kg grains of the crude alkaloidal
extract, percentages of malformed larvae and pupae of T. castaneum were 19.7 and 33.4%, respectively. In
this case, a total life span of 81.3 days was recorded for the treated individuals compared to 44.2 for the
control. A reduction in the adult progeny of 56.9, 44.0 and 43.6% was obtained with 3.5 mg/kg of the
crude alkaloids, (harmaline þ harmine) and methanol extract, respectively. Meanwhile, the reduction in
adult progeny of R. dominica reached 79.2% with the same concentration of the crude alkaloid extract