Manejo de Plutella xylostella (Lepidoptera : Plutellidae) : parasitismo por Trichogramma pretiosum Riley (Hymenoptera : Trichogrammatidae) e susceptibilidade de populações a Bacillus thuringiensis Berliner

Abstract

The diamondback moth (DBM), Plutella xylostella (L.) is a key pest of cabbage in the Agreste area of Pernambuco state. Despite of being a key pest, the DBM is attacked by several natural enemies including the egg parasitoid, Trichogramma. In addition, formulated insecticides with different strains of Bacillus thuringiensis Berliner are widely used to control the larval stages. Thus, this research aimed to search for a local species or population of Trichogramma; to study its biological characteristics and parasitism on DBM eggs; to investigated the oviposition site preference of DBM and its parasitism by Trichogramma on cabbage plants at pre- and post-head formation in the field and; to investigate the susceptibility of 10 Brazilian populations of DBM relative to the commercial formulations of B. thuringiensis var. kurstaki (Dipel®WP) (Btk) and B. thuringiensis var. aizawai (Xentari®WG). Trichogramma survey was conducted in areas with organic-growing vegetables, Chã-Grande County, PE. The collected species wasTrichogramma pretiosum Riley. The biological characteristics and parasitism were similar for this population parasitizing DBM eggs and eggs of the laboratory standard host, Anagasta kuehniella (Zeller). In the field, the parasitism of DBM eggs by T. pretiosum was associated with the moth oviposition site preference and exhibited a positive relationship with egg availability; but, the eggparasitism rate was density independent across both plant ages. The oviposition of DBM on cabbage plants at pre-head formation and its parasitism was equally distributed across the plant leaves. At this plant age, the basal part of the leaf and the upper leaf surface were the preferred places for oviposition and parasitism. Plants at post-head formation stage had higher oviposition and parasitism on the central leaf wrapping the head and in the upper leaf surface. The susceptibility of DBM to the insecticides Btk and Bta resulted in significant levels of resistance. The resistance ratio was 180 and 999 times to the recommended rates of Bta and Btk, respectively. Furthermore, variation of larvae and adults regarding walking and oviposition behavior were observed among the populations using treated and untreated cabbage leaf discswith Bta and Btk.