Pathogenicity of Beauveria Bassiana (Deuteromycotina: Hyphomycetes) Against the White Grub Laniifera Cyclades (Lepidoptera: Pyralidae) Under Field and Greenhouse Conditions (Report‪)‬

Translation by the authors. The prickly pear cactus or nopal Opuntia spp. is one of the most important plants of Mexico, especially in semi-arid and arid regions where few crops can be cultivated. The main production of the cactus is for fruits and vegetables for human consumption, forage for livestock, and for industrial products such as cosmetics and dyes (Vigueras & Portillo 2001). The white grub Laniifera cyclades Druce of nopal is one of the pests limiting the production of Opuntia spp. (Badii & Flores 2001). The adults deposit eggs in groups of 30 to 50 on the cladodes, and the gregarious larvae perforate the cladodes devouring the inner part and gradually penetrating the tissue forming large galleries until reaching the central axis of the plant, where inside they pass through larval stages and pupate. During their movement through the inner part of the nopal, the larvae make orifices to the exterior in order to expel their excrements, forming on the ground what growers call "little mountains of rice." These wastes serve as signs for detecting the presence of the pest, which enables destroying larvae mechanically, but often a major part of the plant must be destroyed. Strategies for control of L. cyclades recommended by governmental institutions consist in application of chemical insecticides through the orifices made by the larvae (Saenz 1998), thereby contaminating the whole plant and its fruits. Thus, an alternative biological control would be of great utility. Microbial pathogens offer possibilities as biopesticides, but little is known about the microbial enemies of L. cyclades. Beauveria bassiana Vuillemin is the entomopathogenic fungus most widely distributed in the world, and it infects insects in tropical, temperate, humid, and desert areas (Zimmermann 2007). Various products based on B. bassiana are commercially available for controlling insect pests of agricultural importance, such as the coffee berry borer Hypothenemus hampei Ferrari and various species of Curculionidae (Adane et al. 1996; de la Rosa et al. 1997). Lepidoptera are also important hosts of this fungus, including several species of agricultural importance (Abdel-Razek et al. 2006). One factor that affects the efficacy of B. bassiana is sunlight; persistence and infectivity are reduced within a few minutes after exposure to sunlight (Fargues et al. 1996). Reduced environmental humidity also affects the efficacy and survival of the fungus because the most effective germination of the spores on the insect cuticle requires a relative humidity (RH) range of 92 to 100%, but there are reports of B. bassiana infection at 60-70% RH (Zimmermann 2007). The relative humidity of the semi-arid region in the municipality of Noria de Angeles, Zacatecas is on average 49%, but the use of infested cadavers might afford protection to B. bassiana. Koppenhofer et al. (1997) and Shapiro-Ilan et al. (2001) reported that entomopathogenic nematodes could survive under dry conditions for long periods of time if they remained inside cadavers of host insects. Larvae of the wax moth Galleria mellonella L. have been used as cadavers infested with the entomopathogenic nematode Heterorhabditis bacteriophora Poinar for controlling the sweetpotato weevil Cylas formicarius (Fabricius) (Jansson & Lecrone 1994). Cadavers of G. mellonella infested with B. bassiana and placed in the holes of nopal plants infested with L. cyclades could prevent exposure to sunlight and protect the fungus from the low RH outside the plant. The aim of this investigation was to evaluate the pathogenicity of the strains BbZ3 and BbZ4 of Beauveria bassiana to L. cyclades after introducing infested cadavers of G. mellonella into the excretion orifices in the nopal stem pads, under greenhouse and field conditions.