Castor Bean Cake: A Promising Alternative for Sustainable Spider Mite Management

Tetranychus urticae is an important phytophagous and cosmopolitan pest, affecting several cultures worldwide, such as papaya, strawberry, cotton, beans and soybeans. Chemical pesticides for mite control pollute the environment, poison humans and select resistant mite populations. Ricinus communis cake is a by-product of biodiesel production, containing compounds, such as ricinin and some fatty acids, described as toxic to arthropods. The objective of this work was to evaluate the castor bean cake acaricide potential on the spider mite, T. urticae. Ricinus communis dried seeds were pressed for oil extraction. Subsequently, the cake obtained after the oil extraction was ground in a knife mill to produce a fine powder. After, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 grams of castor bean cake powder were mixed into 100 mL of Tween 80 aqueous solution 0.05 % v v-1, stirred (30 minutes, at 25 °C) and left to rest (20 minutes) to decant the solid particles. Finally, the supernatant (castor cake extract) was separated from the solid part by simple filtration. For direct application, 6 mL of castor cake extract were sprayed onto 10 T. urticae females dispersed on a 4 cm diameter Canavalia ensiformis leaf. For indirect application, 10 T. urticae females were placed in discs leaf, previously immersed in castor bean extract. Ten replicates were used for each treatment, evaluating the mortality parameter as a time function (24, 48 and 72 hours) for both application forms. The obtained data were submitted to linear regression analysis. T. urticae mortality did not show a dose-dependent behavior as a function of the castor bean cake extract concentrations for both forms of application (direct and indirect). Castor bean cake extract at 2.5 % w v-1 caused the highest mortality T. urticae females treated directly or indirectly (95 or 88 %, respectively) than this extract in the other evaluated concentrations. The average mortality of T. urticae females treated directly or indirectly with this extract at the different concentrations evaluated were 88.4 and 77.7 %, respectively. The results showed that the castor bean cake extract, applied directly or indirectly in T. urticae, caused high mortality of females of this mite, being a promising alternative for the spider mite sustainable management.