natural-products-in-plant-pest-management

180 M. Kostyukovsky and E. ShaayaIn the case of seeds treated with Syrian marjoram, the number of eggslaid on the treated seeds was 83% of the control, but 0% of the eggs developedto adults. Other oils were found to cause a reduction in the number ofeggs laid on the treated seeds but were less effective on egg to adult development.In the case of clary sage oil, only 40 eggs were laid on the treated seeds(= 22% of control), but 55% of the eggs developed to adults. In contrast, theessential oil SEM76, obtained from Labiata plant species, was found effectiveon both the reduction of number of eggs laid (28% of control) and on thenumber of eggs that developed to adults (17% of control) (Table 8.4).8.4 Studies with Essential Oils as Fumigants AgainstStored-product InsectsIn order to isolate active essential oils we firstly screened a large number ofessential oils extracted from aromatic plants and isolated their main constituents,using space fumigation (Shaaya et al., 1991, 1993, 1994). The most activecompounds are summarized in Table 8.5.Among the tested compounds, the essential oil SEM76 and its main constituentwere found to be the most potent fumigants. To obtain the LC 90of allinsect species tested at adult stage, SEM76 oil was required at the concentrationof 0.6–1.2 μl/l air (Table 8.5). The main constituent of the oil, which accounts forapproximately 80% of the oil, was also found to have high activity, a little higherthan the oil, as expected (Table 8.5). Space fumigation studies with SEM76against various developmental stages of C. maculatus showed that eggs andyoung larvae before they penetrated into the seeds were the most susceptibleto the compound. A concentration of 0.5 μl/l air was enough to cause 100%mortality of the eggs and the first instar larvae. After the larvae penetratedinside the seeds, they became more tolerant (Table 8.6). Only pupae 1–2 daysbefore adult emergence again became sensitive to the compound (Table 8.6).Table 8.5. Fumigant toxicity of the most active monoterpenes tested on stored-productinsect pests in space fumigation tests.OryzaephilussurinamensisRhizoperthadominicaSitophilusoryzaeTriboliumcastaneumCompoundLC 50LC 90LC 50LC 90LC 50LC 90LC 50LC 901,8-Cineol 3.1 7.3 2.5 4.0 7.2 14.2 7.5 8.5Carvacrol – – >15.0 – >15 – >15.0 –Limonene >15.0 – 6.7 10.3 >15 – 7.6 8.6Linalool 3.0 6.0 6.0 8.5 10.1 19.8 >15 –Pulegone 1.7 2.8 2.8 4.5 0.7 1.4 2.5 3.2SEM-76 –