Bioprospecção de insetos resistentes ao ecdisteróide 20-hidroxiecdisona.

Abstract

Pfaffia glomerata (Spreng) Pedersen is a species of the Amaranthaceae family found in South America, including Brazil. The ecdysteroid 20-hydroxyecdysone (20E) has been detected in its roots. Ecdysteroids (ECDs) are steroid hormones found in arthropods (zooecdysteroids, ZE), in some plant species (phytoecdysteroids, PE) and in some fungi (mycoecdysteroids, ME). In insects, ZE 20E is involved in several processes (embryogenesis, larval development, metamorphosis and molting) initiated or controlled by specific pulses of 20E. In plants, PE 20E acts as a protective agent against the attack of insects not adapted to 20E. With the objective to identify insects resistant to PE 20E, insects present in the Amazon rainforest that naturally feed on P. glomerata were collected, isolated and identified. Known as the leaf-rolling caterpillar, the species Omiodes indicata (Fabricius 1775) is a pest of legumes such as beans and soybeans, and was found feeding on the leaves of this species. To confirm its resistance to 20E, biological characterization of this insect fed only on P. glomerata plants was performed. The following traits were measured: size (length and width) and weight of the caterpillar, pupa and head capsule, number of instars, time spent in each instar of the caterpillar and pupa, wingspan of the adult insect, time of oviposition, number of eggs per female, digestibility and sexing. The analysis of the data obtained in this study allowed us to conclude that ECD 20E caused changes in the development of caterpillars of the species O. indicata, such as larger egg size, an increase in the number of instars with six stages, larger body size, presence of cephalic capsules and significant weight from the fifth instar when compared to caterpillars fed with soybean leaves, low mortality rate (only in the first, fifth and sixth instar). The species Omiodes indicata (Fabricius 1775) is resistant to 20E, thus presenting potential biotechnological applicability.