Seletividade de inseticidas a Tetrastichus howardi (Olliff, 1893) (Hymenoptera: Eulophidae) e seu desenvolvimento em pupa de Chrysodeixis includens (Walker, [1858]) (Lepidoptera: Noctuidae)

Abstract

The use of the parasitoid Tetrastichus howardi (Olliff, 1893) (Hymenoptera: Eulophidae) in biological control programs is of great notoriety, and has been gaining prominence through the control of lepidopteran-pests of important agricultural and forestry crops. However, further studies should be prioritized with this important control agent in order to fully explore its performance in new hosts. Thus, we evaluated the age of the host pupae, density of parasitoids exposed to parasitism and selectivity of insecticides on the parasitism and development of the parasitoid T. howardi in pupae of the host Chrysodeixis includens (Walker, [1858]) (Lepidoptera: Noctuidae) under conditions of laboratory and semifield (simulated). For that, the experiments were carried out in the premises of the Laboratory of Biological Control of Insects (LECOBIOL) belonging to the Federal University of Grande Dourados (UFGD) in Dourados, Mato Grosso do Sul, Brazil. In the first experiment, pupae of C. includens aged 24, 48, 72, 96, 120, 144 or 168 hours were exposed to parasitism by a female of T. howardi aged 24 hours in glass tubes (150 mm length x 20 mm wide) and after 24 hours, the females of T. howardi were removed from the tubes and the pupae evaluated until the emergence of the parasitoids. In the second experiment, pupae of C. includens up to 48 hours of age were exposed to parasitism by females of T. howardi at density of 1:1, 5:1, 10:1, 15:1, 20:1 and 25 :1 (parasitoid females: pupa), in a 24 hours period of exposure. In the third experiment, 24 hours old females of T. howardi were submitted to a mortality test exposed to different insecticides for 24 to 168 hours using the ASPECLE system (Assessment of Pesticides Selectivity in Extended Laboratory Conditions). In the fourth and last experiment, tests of parasitism and development of T. howardi in pupae of C. includens were performed, where the parasitoid and pupae were exposed to insecticide residues for 24 hours using the ASPECLE system. To carry out the tests with insecticides, the methodological guidelines recommended by the IOBC/WPRS International Organization for Biological and Integrated Control of Integrated Control of Noxiouns Animals and Plants were used. All experiments were carried out in an acclimatized room with a temperature of 25 ± 2 ºC, relative humidity of 70 ± 20 % and a photoperiod of 14 hours. In the first experiment, it was concluded that the highest rates of parasitism and development of T. howardi were obtained in pupae of C. includens with 24 to 96 hours, being this age group favorable for the creation of this parasitoid in laboratory conditions. This is the first record of T. howardi reproducing in pupae of C. includens under laboratory conditions. In the second experiment, a female of T. howardi is able to parasitize and develop into a pupa of C. includens, which is important information for further studies to be carried out with this parasitoid under field conditions. In general, five to ten females of T. howardi is the ideal density for its creation in pupae of C. includens. The conclusion of the third experiment was that the insecticides acephate and methomyl + novaluron are harmful to adult females of the parasitoid T. howardi, attributing to these insecticides as non-selective, in simulated semifield conditions. The insecticides mineral oil, Bacillus thuringiensis, B. thuringiensis + mineral oil (0.2%), flubendiamide, novalurom, teflubenzuron, teflubenzuron + mineral oil (0.5%), superdose teflubenzuron, superdose teflubenzuron + mineral oil (0.5 %), are innocuous and therefore selective for adult females of the parasitoid T. howardi. It is concluded that in the fourth experiment, the insecticides acephate and methomyl + novaluron interfered negatively in the biological characteristics of adult females of T. howardi, when exposed to parasitism in pupae of C. includens, being attributed to these insecticides as non selective to the parasitoid in semifield conditions. The insecticides mineral oil, B. thuringiensis, B. thuringiensis + mineral oil (0.2 %), flubendiamide, novalurom, teflubenzuron, teflubenzuron + mineral oil (0.5 %), superdose teflubenzuron, superdose teflubenzuron + mineral oil (0.5%). 5 %) did not affect the biological characteristics of adult females of T. howardi when exposed to parasitism in pupae of C. includens, which were considered selective for the parasitoid under semifield conditions. The results obtained in this work foster knowledge about the development and reproduction of T. howardi, presenting unprecedented results regarding the parasitism of C. includens pupae by T. howardi females at different ages (hours) and density, confirming the plasticity and the ability of T. howardi females to parasitize C. includens. As well as the selectivity of insecticides on this parasitoid, which allowed the determination of the innocuousness of these pesticides under expanded laboratory conditions.