Semioquímicos envolvidos nas interações tritróficas entre a palma forrageira, a chochonilha de escama Diaspis echinocacti (BOUCHÉ, 1833) (HEMIPTERA - DIASPIDIDAE) e dois de seus predadores, Zagreus bimaculosus (MULSANT, 1850) (COLEOPTERA: COCCINELLIDAE) e Chilocorus nigrita (FABRICIUS, 1798) (COLEOPTERA: COCCINELLIDAE)

Abstract

The palm is an important crop, primarily for its forage potential, being an alternative to feeding livestock is scarce native grasslands, especially during periods of prolonged drought. One of the main problems in the cultivation of cactus pear is the infestation of pests such as mealybug in scale, Diaspis echinocacti, when uncontrolled can cause severe yield losses, reaching 100%. The Integrated Management is an alternative to control this pest and maintenance of production out of economic damage. Therefore, this study aimed to evaluate the interaction between the spineless cactus, cochineal scale and two of its natural enemies, Zagreus bimaculosus and Chilocorus nigrita. Volatile organic compounds (VOCs) released by ten varieties of cactus, healthy and infested by D. echinocacti, as well as the volatiles released by the two natural enemies studied were collected by aeration and extracted with n-hexane HPLC. The extracts were subjected to behavioral bioassays in olfatometre Y to identify their attractive activity for natural enemies, Z. bimaculosus and C. nigrita, and then subjected to chemical analysis by gas chromatography coupled to mass spectrometry (GC-MS) for identification of VOCs. Electrophysiologic testing with gas chromatography coupled to electroantennograph (GC-EAG) of the extracts that showed activity in behavioral bioassays were conducted. The results showed that the species of ladybugs are attracted by the extracts studied, mostly after the process of infestation with D. echinocacti, and that the profiles of the emission of VOCs of ten varieties studied differed. Among the VOCs identified in extracts of Z. bimaculosus and C. nigrita, are the 1-ethyl-hexanol, 3,7-dimethyloctanol, 1-heptacosanol, 1-decanol, 2-propyl-1-heptanol and farnesol, which were identified as components of the aggregation pheromone of beetles and beetle cuticular constituents. It also observe that new compounds were found in the extracts of ten varieties of cactus infested with cochineal scale of D. echinocacti, among these compounds are the n-octanal, geranyl linalool, linalool, n-nonanal, n-decanal and squalene, which are associated with plant defense, including the attraction of natural enemies. These results demonstrate the importance of VOCs produced by plants for their defense, after a process of herbivory, including with regard to the attraction of natural enemies. VOCs released by two species of ladybugs can be studied components of the aggregation pheromone, since attractiveness was demonstrated in behavioral bioassays.