Mortality of Conotrachelus humeropictus in response to combined application of the nematode Steinernema brazilense and the fungus Beauveria bassiana

Lucas Detogni Simi,José Nilton Medeiros Costa,Roselaine Nunes Da Silva Bueno,Antonio Batista Filho,Leandro Ezequiel Oliveira,Fabio Silber Schmidt,Olzeno Trevisan,Luís Garrigós Leite

doi:10.1590/1808-1657000092016

Abstract

ABSTRACT: The fruit borer Conotrachelus humeropictus is one of the most important pests of the cupuaçu crop, and can promote yield losses of around 50%. The present study involved the selection of Beauveria bassiana isolates on Conotrachelus psidii larvae, which was used as test insect due to its taxonomic closeness to C. humeropictus. In order to assess their interaction using combined application, we studied the ability of the nematode to carry conidia of B. bassiana and Metarhizium anisopliae to soil layers. This study also aimed to establish a biological control method for cupuaçu borer with the use of the fungus B. bassiana at 10 kg/ha and the entomopathogenic nematode Steinernema brazilense at 1, 3, 9, and 27 IJ/cm2, applied as single and combined treatments. In the selection of B. bassiana strains for C. psidii, the IBCB 276 and IBCB 165 isolates were the most promising ones, causing 86 and 84% mortality, respectively. The IBCB 276 strain was applied in the field to control C. humeropictus. In the study of carriage of conidia in soil, the nematode S. brazilense was found to be capable of carrying conidia of B. bassiana to deep 7 to 10 cm soil layers. This was not observed with M. anisopliae, found only in the topsoil. In field trials against C. humeropictus larvae, B. bassiana promoted 15.6% mortality. The nematode promoted 60.0% mortality at the highest concentration used, and their combined use with B. bassiana (10 kg/ha) increased mortality to 65.6%, with an additive interaction observed between the two entomopathogens.

Highlights

Larvae of the insect Conotrachelus humeropictus (Fiedler, 1940) (Coleoptera: Dryophthoridae) attack cocoa and cupuaçu fruits, causing damage that depreciates the product and can result in production losses of up to 50% (LAKER; TREVISAN, 1992)
The nematodes Steinernema and Heterorhabditis (Rhabditida: Steinernematidae; Heterorhabditidae) act against a great diversity of species of insects, mainly those that inhabit the soil. They differ from other entomopathogens by establishing a mutual association with bacteria of the genus Xenorhabdus spp. and Photorhabdus spp. These nematodes undergo an immature stage of free life known as the infective juvenile (IJ) stage, during which they live in the soil and are able to enter the host through natural openings, and in the case of the Heterorhabditidae, through the cuticle
The guava weevil was used in this test because it was easy to obtain in the regions near Campinas, São Paulo, and in the guavas of Valinhos, São Paulo, and because of the difficulty of obtaining C. humeropictus, which is found only in the Amazon region

Summary

INTRODUCTION

Larvae of the insect Conotrachelus humeropictus (Fiedler, 1940) (Coleoptera: Dryophthoridae) attack cocoa and cupuaçu fruits, causing damage that depreciates the product and can result in production losses of up to 50% (LAKER; TREVISAN, 1992). They differ from other entomopathogens by establishing a mutual association with bacteria of the genus Xenorhabdus spp. and Photorhabdus spp These nematodes undergo an immature stage of free life known as the infective juvenile (IJ) stage, during which they live in the soil and are able to enter the host through natural openings (mouth, anus, and spiracles), and in the case of the Heterorhabditidae, through the cuticle. The combination of nematodes and Paenibacillus popilliae (Dutky, 1940) or Bacillus thuringiensis (Berliner, 1911) strain Buibui, resulted in a significant increase in mortality of Cyclocephala hirta larvae (Coleoptera: Scarabaeidae) when compared to each agent tested in isolation (THURSTON et al, 1994; KOPPENHÖFER; KAYA, 1997) This was observed when the fungus Metarhizium anisopliae (Metschnikoff, 1879) Sorokin, 1883 was evaluated in combination with the nematode H. bacteriophora against the grass pest Hoplia philanthus (Füessly, 1775) (Coleoptera: Scarabaeidae), promoting control of up to 95% under field conditions (ANSARI et al, 2006). The objective of this study was to evaluate the virulence of different isolates of the fungus Beauveria bassiana (Balsamo) Vuillemin, 1912 on guava weevil larvae, Conotrachelus psidii (Marshall, 1922) (Coleoptera: Dryophthoridae), and the effect of combined S. brazilense with the fungi B. bassiana and M. anisopliae, in the carriage of conidia in the soil and on the mortality of C. humeropictus larvae

MATERIAL AND METHODS

RESULTS AND DISCUSSION

CONCLUSIONS