natural-products-in-plant-pest-management

178 M. Kostyukovsky and E. ShaayaTo obtain an insight into the nature of the activity of the oils, the activityof straight-chain fatty acids ranging from C5 to C18 at a concentration of4 g/kg was studied against C. maculatus (Table 8.2). The results showed thatC9–C11 acids were the most active in preventing oviposition at this concentration,with the C11 acid the most active: only 13, 13 and 0 eggs were foundon the treated seeds, respectively (Table 8.2).C12–C16 fatty acids were less effective and activity was remarkablydecreased for the lower C5–C7 and higher C17–C18 acids. At lower concentrationsof 1.6, 0.8 and 0.4 g/kg, the C11 acid was found to be the most active;fewer eggs were laid than with C9 or C10 and no eggs developed to adults.The data presented in Table 8.3 show clearly that C9–C11 acids are stronglyrepellent to C. maculatus, but they have no lethal effect on the adults.Field tests using crude palm kernel and rice bran oils showed that bothoils were effective in controlling C. maculatus infestation providing full protectionfor the first 4–5 months of storage at a rate of 1.5–3.0 g/kg seeds. Theypersisted in controlling insect infestation for up to 15 months. The numbers ofadult insects found in the treated seeds after 15 months of storage were onlyabout 10% of that in the control samples (results not shown).8.3 Studies with Essential Oils as Contact InsecticidesThe efficacy of a large number of essential oils has been evaluated for thecontrol of C. maculatus at a concentration of 400 ppm. The various oils testedwere found to have a toxic effect on the eggs laid and on the development ofthe eggs to adults (Table 8.4).Table 8.2. Biological activity of straight-chain fatty acids C5–C18 againstCallosobruchus maculatus.Fatty acidNumber of eggs laidAdult emergenceNumber %Pentanoic(C5) 185 110 59Hexanoic (C6) 130 92 71Heptanoic (C7) 112 66 59Octanoic (C8) 105 22 21Nanonoic (C9) 13 0 0Decanoic (C10) 13 0 0Undecanoic (C11) 0 0 0Dodecanoic (C12) 32 22 69Tridecanoic (C13) 32 20 62Tetradecanoic (C14) 62 45 73Pentadecanoic (C15) 72 56 77Hexadecanoic (C16) 65 37 57Heptadecanoic (C17) 120 88 73Octadecanoic (C18) 140 115 82Control 287 272 95Each fatty acid was used at a concentration of 4 g/kg chickpea. The data are the average of threeexperiments, each of which were in triplicate.