Could sterile males be used to vector a microbiological control agent? The case of Rhynchophorus ferrugineus and Beauveria bassiana

Rhynchophorus ferrugineus (Coleoptera, Curculionidae) is the most threatening pest of palms worldwide. The potential of gamma-irradiated males to spread a pathogenic strain of the entomopathogenic fungus Beauveria bassiana (Ascomycota: Clavicipitaceae) to control this pest was studied. First, the effects of gamma irradiation (15 and 25 Gy) on the mating success and performance of adult males irradiated at age one day were studied in the laboratory. Although male longevity decreased after irradiation (118.6 vs. 244.7 days for irradiated and control males, respectively) and their testes suffered from the treatment, fecundity of mated females did not depend on the irradiation status of the male (86.8 +/- 5.5 eggs in 15 days). However, egg hatching was significantly lower in couples with irradiated males (31.4% vs. 86.5% for irradiated and control couples, respectively), and this value decreased after a second mating (6.1% vs. 85.9%). Therefore, irradiation did not affect male sexual competiveness but sperm quality. Second, a semi-field assay was carried out to evaluate infestation in young Phoenix canariensis caused by different combinations of couples with irradiated and/or B. bassiana-challenged males. The number of immature stages found in infested palms was significantly higher when females mated with untreated males and lower when mated with irradiated males (either B. bassiana-infected or not). Some females from the fungus-challenged treatments showed post-mortem hyphal growth, and this horizontal transmission proves that irradiated males could act as a vector for B. bassiana and should be considered as a new method to improve the biological control of R. ferrugineus

Evaluation of the pathogenicity of multiple isolates of Beauveria bassiana (Hypocreales: Clavicipitaceae) on Rhynchophorus ferrugineus (Coleoptera: Dryophthoridae) for the assessment of a solid formulation under simulated field conditions

A solid state formulation of Beauveria bassiana (Balsamo) Vuillemin has been developed for biological control of the Red Palm Weevil (RPW), Rhynchophorus ferrugineus (Olivier, 1790). Two kinds of bioassays (dry conidia and dipping) using 10 isolates from several coleopterans in Mediterranean environments, identified 2 RPW derived isolates (193 and 203) as most pathogenic to RPW larvae and adults (zero survival within first 4–5 d for dry conidia, and 14 and 23 d for dipping bioassays). Isolate 203 (5.1 × 108 ± 1.9 × 108 conidia g-1) was formulated with fragmented date seed into solid granules and tested in palms infested with RPW under semi-field conditions in Feb, Apr/May and Jun of both 2007 and 2008. Beauveria bassiana significantly reduced RPW adult survival with respect to controls in May 2007 and in the Apr/Jun 2008 experiments. Total RPW adult mortality was achieved within 30 days for all B. bassiana treatments, and was associated with increasing numbers of insects with signs of mycosis in 2008 experiments. Beauveria bassiana formulation reduced RPW multiplication in artificially infested palms compared to controls, and a positive correlation between numbers of larvae and time post-infestation was recorded. The suppression of RPW adult populations by B. bassiana persisted for at least 3 months under semi-field conditions. The Beauveria bassiana solid formulation, which induces great adult mortality and persistence in the field, could be applied as a preventive as well as a curative treatment for the integrated management of RPW.En el presente estudio, se describe un procedimiento para el desarrollo de una formulación en estado sólido basada en Beauveria bassiana (Balsamo) Vuillemin para el control biológico del picudo rojo, Rhynchophorus ferrugineus (Olivier, 1790). Al realizar dos tipos de bioensayos (conidios secos e inmersión directa) utilizando diez aislados de diversos coleópteros en ambientes Mediterráneos, se identificaron dos aislados derivados del picudo rojo (193 y 203) como los más patogénicos para los estadios larvarios y adultos del insecto (supervivencia nula en los primeros 4–5 días y 14 y 23 días para bioensayos con conidios secos e inmersión directa respectivamente). El aislado 203 de B. bassiana (5.1 × 108 ± 1.9 × 108 conidios g-1) se formuló en sólido utilizando dátiles fragmentados y se ensayó en palmeras infestadas con el picudo rojo bajo condiciones de semi-campo en los meses de Febrero, Abril/Mayo y Junio de 2007 y 2008. Beauveria bassiana redujo significativamente la supervivencia de los insectos adultos con respecto a los controles en los experimentos de Mayo de 2007 y Abril/Junio 2008. Se alcanzó la mortalidad completa de los adultos del picudo rojo en 30 días para todos los tratamientos con B. bassiana y lo que se correlacionó con el incremento del número de insectos con signos de micosis para los ensayos de 2008. El formulado de B. bassiana redujo la multiplicación del insecto en palmeras infestadas artificialmente con respecto a los controles, registrándose una correlación positiva entre el número de larvas y el tiempo de infestación posterior. La capacidad del formulado de B. bassiana para suprimir las poblaciones de insectos adultos tuvo una persistencia de al menos tres meses bajo condiciones de semicampo. El formulado sólido de B. bassiana, que ha generado una alta mortalidad en adultos así como una elevada persistencia, podría utilizarse tanto en tratamientos preventivos como curativos en el manejo integrado del picudo rojo.This research was financed with the INIA (TRT2006-0016-C07-02) and PETRI (PET2007-0469-01) project grants from the Spanish Ministry of Science and Education, and with a grant from Generalitat Valenciana to B. Güerri-Agulló (BFPI06/493). Jorge Ricaño was supported by a grant from the Mexico’s National Council of Science and Technology (CONACYT)

Research activities focused on management of red palm weevil at the UJI-IVIA Associated Unit (Region of Valencia, Spain)

During the past 5 years, the Associated Unit between Institut Valencia` d’Investigacions Agra`ries (IVIA) and Universitat Jaume I (UJI) has been working on the management of Rhynchophorus ferru- gineus. The host status of Washingtonia filifera, Chamaerops humilis and Phoenix theophrasti was established, and complete resistance via antibiosis was described for W. filifera. A thermal constant (egg to adult) of 989.3 degree-days has been established for R. ferrugineus when feeding in live P. canariensis. Based on this result, less than one annual generation is expected in areas with mean annual temperature below 15°C, and more than two if above 19°C. Assays on chemical control showed that a dose of 1.14 g aluminium phosphide m)3 for 3 days is enough to kill all stages of R. ferrugineus in infested palms. The efficacies of imidacloprid and a microencapsulated paint con- taining chlorpyrifos and pyriproxyfen were also studied. Imidacloprid had high efficacies when applied as a drench either as a preventive or a curative treatment, whereas the paint was effective as a preventive treatment only. Biological control by use of entomopathogenic nematodes and fungi has been explored. Steinernema carpocapsae resulted in high efficacies when applied in a chitosan formulation. Beauveria bassiana also gave very good results, and new assays are under way to improve its use