Efficiency of protective barrier approach for controlling movement of large instar larvea of the cotton leafworm, Spodoptera littoralis, boisd

A protective barrier approach was suggested as to avoid the movement of large instar larvae of the cotton leafworm from one crop to another specially at harvesting time. Chemicals of different groups were used for this study: inorganic salts group (calcium sulfate gypsum and sodium chloride) alkaline group (calcium hydroxide slaked lime and sodium hydroxide), acidic group (sulfuric acid), oils (tar oil), sulfur (agriculture sulfur) and conventional insecticide (malathion 1% DP). Sodium chloride, sodium hydroxide ,sulfuric acid and tar oil were prepared as dust powder contained 7.5 % a.i. diluted with talc powder, while the other powders were used as it is without dilution. The protective barrier was made by spreading of each material powder in a circle shape on plastic sheet. Then, ten larvae of each instar larvae fourth, fifth and sixth were transferred to the central zone of the barrier. Fresh castor bean leaves were put out the barrier as attractive and feeding material to larvae. Number of escaped larvae, dead and alive larvae inside or outside the barrier after 24hrs exposure were counted. To study the latent effect on the alive larvae, of each treatment, they were collected and fed with fresh castor leave bean until to pupation stage, percent of larval mortality , pupation and moth emergency were calculated The efficiency of barrier for protecting crops against larval attacks was determined by calculating the consumed food by the rest alive larvae during 48hrs exposure for each treatment compared with untreated To clarify the residual activity of the tested barriers, the same procedure was carried out after 3 and 7 days of barrier spreading. Results obtained indicated that malathion 1% DP achieved the highest activity since all passed and unpassed larvae through the barrier were killed and did not cause any damage, Moreover, malathion showed the same effect up to 3 and 7 days of spreading the chemical barrier. The other tested materials had a weak effect on passing and killing larvae within 24 hrs. exposure but their latent effects on larval mortalities, pupation and moth emergency percent were increased. They showed moderate effects on larval feeding, specially with the locally formulated material. Finally, it could be recommended the application of malathion 1% Dp as a protective barrier for controlling movement of large instar larvae of the cotton leafworm. The other materials prepared as dust powder could be applied with higher active ingredient contents ( 7.5%).