Distribuição de ovos de Plutella xylostella (L.) (Lepidoptera: Plutellidae) e o parasitismo por Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae)

Abstract

-Oviposition site preference of Plutella xylostella (L.) and the parasitism by Trichogramma pretiosum Riley on cabbage plants at pre-and post-head formation were investigated in commercial cabbage fi eld. Groups of six plants were randomly caged. In each cage three pairs of 24h-old P. xylostella moths were released, followed by 1,200 T. pretiosum females released 12h later. After 48h from parasitoid release, plants were harvested and fully inspected with the oviposition mapped according to the leaf position and their parts (basal, median and border) and upper and bellow leaf surfaces. Moth oviposition and egg parasitism were equally distributed across the plant leaves at the pre-head formation stage. At this stage, the basal part and the upper leaf surface were the preferred places for oviposition and egg parasitism, respectively. Cabbage plants at the post-head formation stage exhibited greater oviposition and egg parasitism in the inner leaf attached to the head. At this stage, the leaf border and the upper leaf surface were the preferred places for oviposition and egg parasitism, respectively. The infestation of P. xylostella on cabbage can be determined by egg counting at the pre-and post-head formation stages at the basal part of the leaves or at the border of the leaf attached to the head, respectively. And, in both plant stages parasitized eggs by T. pretiosum are more likely to be found at the upper leaf surface.

Diamondback moth oviposition: effects of host plant and herbivory

“…In cabbage ( Brassica oleracea L. Capitata), canola ( Brassica napus L.), Brassica juncea (L.), Chinese cabbage ( Brassica rapa L. Pekinensis), and Brassica carinata L., P. xylostella preferentially selected lower regions of the plant stem over leaves for oviposition (Reddy et al., 2004; Sarfraz et al., 2005). Field studies show that egg distribution within plants can also change as the host plant ages; for example, in pre‐heading cabbage plants, P. xylostella eggs were distributed equally across all leaves (greatest numbers found on basal regions of the upper leaf surface within leaves), but in post‐heading plants more eggs were found on the borders of upper surfaces of inner leaves attached to the head (Zago et al., 2010). Although useful in describing the distribution of eggs in the field, such studies do not provide information on oviposition site preference per se as eggs will have been laid by multiple females (Thompson, 1988) and site selection is likely to be constrained and influenced by both abiotic (e.g., rainfall, wind) and biotic (e.g., ovipositing conspecifics, natural enemies, herbivory) factors.…”

Insecticidal and Acaricidal Activity of Essential Oils Rich in (E)-Nerolidol from Melaleuca leucadendra Occurring in the State of Pernambuco (Brazil) and Effects on Two Important Agricultural Pests

“…The method used to determine the ovicidal effects of the essential oils, compound and positive control on P. xylostella eggs was the same as that employed by Zago et al 23 Ten recently emerged mating pairs of P. xylostella were placed in screened recipients containing leaf discs (2.5 cm in diameter) of cabbage for oviposition. The leaf discs were in Petri dishes (10 cm in diameter) containing filter paper on sponge saturated with Milli-Q water to maintain the turgidity of the leaves.…”

Influence of cabbage resistance and colour upon the diamondback moth and its parasitoid Oomyzus sokolowskii

“…The DBM accomplishes the life cycle from eggs to adult emergence in about 2 weeks depending on temperature regime and food quality (Talekar & Shelton, ; Barros & Vendramim, ). Female moths are nocturnal with oviposition predominantly during the scotophase, laying about 200 eggs scattered over cabbage leaves and head (Zago et al., ). Newly hatched larvae bore into the leaf and feed on the mesophyll staying there for 2–3 days; older larvae eat the outer cell layer on the leaf underside producing small holes which break through the upper surface of the leaf.…”