Análise de imagens na avaliação do parasitismo de Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) em ovos de Anagasta kuehniella (Zeller) (Lepidoptera: Pyralidae)

Abstract

Egg parasitoids Trichogramma spp. (Hymenoptera: Trichogrammatidae) act to control several pest Lepidoptera and Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) is a more studied type and does not benefit the world due to breeding and aggressive pest control. However, for this parasitoid to be effective, it is necessary to establish a mass rearing, as well as evaluate parameters for quality control. The evaluation of parasitism is performed by counting dark eggs, which are parasitized eggs, using magnifying glasses and/or microscopes, not being feasible for large scale. The image analysis technique is used in several sectors of agriculture and shows itself as a potential to be used for the evaluation of the biological characteristic, percentage of parasitism. Therefore, the objective was to evaluate an image analysis technique to measure the parasitism of T. pretiosum in cards containing eggs of Anagasta kuehniella (Zeller) (Lepidoptera: Pyralidae), determining the most adequate Vegetation Index (IV) to quantify the parasitism and check whether the age of the eggs and the time of exposure to UV light affect the detection of parasitized eggs, non-parasitized eggs and dirt. Eggs of A. kuehniella from 1, 2, 3, 4 and 5 days were exposed to UV light for 30, 45, 60, 75 and 90 minutes. After each exposure period, the eggs were glued onto sheets of sky blue cardboard and inserted into glass tubes (8.5 x 2.5 cm) containing freshly emerged T. pretiosum. After 24 hours, as they were discarded and the tubes remained in an environment at 25 ± 3ºC, 70 ± 10% of U.R. and 12 h photophase. Seven days after the parasitism, they were adjusted as images of the cards for further evaluation. Parasitism and the most suitable IV to measure parasitism were taken. The experimental design was completely randomized, with 25 treatments composed of 20 repetitions, each repetition being a card. Data were prepared using analysis of variance. It was found that there was parasitism above 58.5% of T. pretiosum in A. kuehniella eggs regardless of the time of exposure to UV light and the age of the eggs. The percentage of parasitism was reduced with increasing time of exposure to UV light. It was also found that it is possible to measure the parasitism of T. pretiosum using image analysis, with the brightness index (BI) being the most suitable index.