Influência do fruto hospedeiro no controle de Ceratitis capitata por nematoides entomopatogênicos

Abstract

Ceratitis capitata (Diptera: Tephritidae) is a key pest in fruit production worldwide, being a polyphagous insect, causing damage to several orchards of economic interest. Currently, the use of chemical products to control the population of fruit flies is common, but the side effects are harmful to the environment and human health, in addition to selecting resistant populations. Biological control by entomopathogenic nematodes (EPN) is an important Integrated Pest Management (IPM) tactic for C. capitata, and studies show that the nutritional factor influences the development rate of fruit flies, which may interfere with the insect susceptibility and in EPN progeny. Thus, the objective of this work was to evaluate the efficiency of NEP from the genera Heterorhabditis and Steinernema on C. capitata larvae fed on different fruit-based diets. The bioassays were conducted at the Laboratory of Pathology and Microbial Control of Insects at the Federal University of Lavras – UFLA, under controlled conditions (25 ± 2°C, RH 70 ± 10%, 12h of photophase). Third-instar larvae that developed on an artificial diet were collected, applying 1 mL of suspension containing 100 infective juveniles (IJ)/insect from native and exotic EPN isolates, evaluating whether the diet formed a physical barrier and favored resistance to NEP. Another bioassay was carried out to identify the optimal dosage, susceptibility of C. capitata larvae to EPN, and, subsequently, inoculation of C. capitata eggs was performed on different fruit-based diets, including guava, apple, orange, mango and artificial diets. It was also analyzed the progeny and the effectiveness of IJ from larvae fed with different diets on Galleria mellonella (Lepidoptera: Pyralidade). C. capitata larvae were found to be susceptible to all EPN isolates, regardless of diet, and the mortality rate ranged from 38.3% (Heterorhabditis amazonenses RSC05) to 92.8% (Steinernema brazilense). For larvae without diet, mortality ranged from 53.3% (Heterorhabditis amazonenses RSC05) to 90.1%, with emphasis on S. feltiae. The JI of all isolates were recovered, both in the presence and absence of diet, and the mortality rate of larvae of C. capitata that received diet was lower than that of larvae without diet. Larvae mortality was proportional to the increase in IJ concentration, with LD50 16.41 IJ/Insect and 11.94 IJ/Insect, and LD90 of 108.01 IJ/Insect and 147.9 IJ/Insect for S. feltiae and S. brazilense respectively. The susceptibility of the larvae fed different diets showed a difference in the virulence of the EPN, and for S. feltiae, the treatment with the mango-based diet was lower (77.3%) and the artificial diet was higher (94.8%) in mortality. For S. brazilense the mortality rate ranged from 66.8% (mango-based diet) to 90.5% (orange-based diet). With this, it is concluded that there is a variation in the susceptibility of C. capitata larvae to EPN according to the food source, being necessary to carry out studies to verify the nutritional factors that interfere in the action of the entomopathogen.