No abstract

In the present research, the toxicity, antifeedant activity and biological effects of ethanolic leaves extract of four medicinal plants named Eucalyptus rostrata, Dodonea viscosa, Rhyza stricta and Cymbopogon schoenanthus were evaluated on 2 nd , 3 rd and 4 th instar larvae of H. armigera under laboratory condition. The results showed that values of LC 50 in mg of different plant extracts in mg/100ml of the larval diet can be arranged in an ascending order as follows: Dodonea 7.23 > Cymbopogon 12.59 > Rhazya 14.52 > Eucalyptus 29.42 mg/100ml diet (the least LC 50 is more toxic than the higher one). All the tested extracts had antifeedant and starvation effects against the 2 nd , 3 rd , 4 th instar larvae. D. viscose extract possesses the least antifeedant effect even of their higher toxicity. There was clear relation between the percent of starvation and antifeedant of the 2 nd , 3 rd , and 4 th larval instar. All extracts were nearly the same in their effect on the biotic potential; of the insect, and possess latent effect when tested against 2 nd instar larvae, the value of LC 50 of the extract was added to the diet, extracts increased larval duration, deformation between pupae and adult stages, moths sterility, increased as decreasing in females egg production. Other effects were noticed, reduction in percentage of pupation and moths emergence. The plant extracts can be arranged ascending according to percentage of their sterility effects as follows: C. schoenanthus < E. rostrata < R. stricta < D. viscose. All extracts cause disruption on the biology and physiology of the insect, and all extract induced percentages of deformation between pupal and moth stages. The ethanolic extract of the plant leaves of the tested plans may be used for control H. armigera in combination with other methods in the integrated program in order to decrease the buildup of the resistance and protect the environment from chemical pollution.

The whitefly, Bemisia tabaci, is the main pest for many field and horticultural crops, causing main and significant problems. The efficiency of imidacloprid insecticide as seed treatment and foliar spray at three rates against the whitefly, B. tabaci, was evaluated in tomato plants under field conditions; in addition, insecticide residues were determined in tomato leaves and fruits. The obtained results revealed that the seedlings produced from treated seeds with imidacloprid were the most effective treatment in decreasing whitefly stages. Reduction percentages of whitefly stages in seedlings produced from treated seeds and sprayed with ½, ¾ and 1 field rates of imidacloprid were more than that produced from untreated seeds. Tomato fruit yield in seedlings produced from treated seeds and sprayed with one recommended rate of imidacloprid was more than that of untreated seeds. The residues of imidacloprid in leaves and fruits in seedlings produced from treated seeds and sprayed with field rate were more than that of untreated seeds; additionally, the residues were higher in leaves than in fruits. The residual level in fruits was less than the maximum residual level (MRL = 1 mg kg−1) of the Codex Alimentarius Commission. The half-life (t ½) was 6.99 and 6.48 days for leaves and fruits of seedlings produced from treated seeds and 5.59 and 4.59 days for untreated seeds. Residues in tomato fruits were less than the MRL, therefore, imidacloprid is considered an unconventional insecticide appropriate for B. tabaci control that could be safe for the environment.

Whitefly, Bemisia tabaci cause important losses for many crops especially tomato, therefore farmers often use many chemical insecticides which had dangerous side effects on human beings and environment, thus there are need to determine the residues of these chemicals in plant . The dissipation of thiamethoxam in tomato leaves and fruits followed the first order kinetics; Half-lives were 2.91 and 3.15 days for fruits and leaves, respectively. The residues of thiamethoxam were determined using a QuEChERS method with HPLC-DAD and it was 0.14 mg/ kg in fruits after 7 days of treatment and less than the maximum residue limit (MRL 0.2 mg/kg. The residue in leaves was more than in fruits. Seedlings produced from treated seeds were more resistant to different stages of the whitefly population and protect tomato plants from whitefly infestation for 6-10 weeks after transplanting. The three sprays of thiamethoxam increased the reduction percentage of B. tabaci stages and the highest increase was recorded after the third spray in egg, nymph, and adult stages. It could be recommend that Thiamethoxam is considered an unconventional insecticide appropriate for B. tabaci control and safe for humans and the environment.