EFFECTIVENESS OF LEMON AND SPEARMINT OIL EXTRACTS ON THE SPINY BOLLWORM, EARIAS INSULANA (BOISD.)

Abstract

laboratory experiments were conducted at Plant Protection Research Institute (Sharkia branch), Bollworms Research Department to evaluate the toxicity of two medicinal plant extracts i.e. lemon, Citrus limon (L.) and spearmint, Mentha spicata (Briq.) oils against the spiny bollworm, Earias insulana (Boisd.). The LC50, LC90 for both extracts after 24 hours were determined. Moreover, the effects of lemon and spearmint oils on some biological and physiological aspects of the SBW were studied. The obtained results showed that C. Limon and M. spicata oils had toxic effect against newly hatched larvae of E. insulana. The LC50, LC90 values were 0.033, 0.2418 for C. limon, and 0.0007, 0.1597 ppm for the M. spicata, respectively. For lemon, the mortality percentage recorded 78.67, 71.33, 65.33 and 24.00 % for 1st instar larvae at concentration 0.150, 0.0750, 0.0375 and 0.0156 ppm. While mortality percentage for spearmint extract was 80.00, 77.42, 75.94 and 62.59 % at concentration of 0.0325, 0.0162, 0.0081 and 0.0040 ppm, respectively. Also, the spearmint oil was more toxic than Lemon oil. Otherwise, treatment with both oils caused pronounced short larval duration, pupal period, adult longevity, oviposition periods; larval and pupal weight, pupation and sex ratio percentages. Both oils significantly reduced adults fecundity and eggs hatchability percentage compared to control. On the other hand, adult moths fed on C. Limon and Mentha spicata oils decreased oviposition periods compared to untreated adults. Additionally, it exhibited a reduction in the numbers of laid eggs, while, in the case of M. spicata the higher concentrations caused infertility for female moths compared to control. The results of the physiologic analysis showed a significant decrease in some biological characteristics of the spiny bollworm, especially the weight of the larvae and pupae, the number of eggs and the hatching rate. The results showed the changes in the activity of carbohydrate enzymes in the spiny bollworm larvae treated with C. limon and M. spicata was a significant increase in amylase and trehalase, aspirate aminotransferase (AST) enzymes and total soluble protein contents in the spiny bollworm larvae treated with C. limon and M. spicata compared to control. While, the invertase, alanine aminotransferase (ALT) and acetylcholinestriase (AChE) enzyme fluctuated from negative to positive activity up to the oil concentration compared to control. In conclusion, the lemon and spearmint oils could be tested in semi-field and field experiments to clarify its role in reduction infestation of SBW in cotton fields especially at the low infestation in the begging of the cotton season and then incorporated into integrated control programs as one of the vital factors for control the spiny bollworm. L