Reproduction, Sex Ratio and Bacterial Communities of the Coffee Berry Borer Hypothenemus Hampei F. (Coleoptera: Curculionidae)
Mariño Cárdenas, Yobana Andrea
Bayman, Paul (Consejero)
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The coffee berry borer (CBB) Hypothenemus hampei is the world's most devastating coffee pest. Knowledge of the factors that affect its biology and ecology is an important tool to give effective management recommendations for this pest. Coffee plant management (e.g. sun vs. shade) can provide environments with contrasting abiotic conditions like temperature and relative humidity, which affect directly biotic factors such coffee quality and quantity, natural enemies and endosymbiotic bacteria. In this dissertation I combined field and laboratory experiments to determine the influence of abiotic factors as temperature and relative humidity and biotic factors such as infection with endosymbiotic bacteria (Wolbachia) on sex ratio, reproduction, population densities, diversity and composition of microbial communities of the CBB. Field experiments were conducted on three farms in the coffee-growing region of Adjuntas, Puerto Rico. In each farm two plots were chosen: sun coffee, in which plants are exposed to direct sunlight, and shade coffee, in which plants grow under the shade provided by up to nine tree species. I determined CBB infestation, population densities and sex ratio for the coffee-growing seasons of 2010 and 2011 (Chapter 1). In laboratory experiments I tested the effect of Wolbachia on population densities, sex ratio and population dynamics (Chapter 2), and I determined the effect of host stage of development, antibiotics and environmental temperature on bacterial communities of the CBB, with emphasis on Wolbachia (Chapter 3). Overall I found significant differences in temperature and relative humidity between sun and shade plots, and a significant effect of these abiotic factors on CBB infestation, which was higher in shade plots. The temperature appeared to be an important driver of CBB population densities and sex ratio: I found positive correlations between temperature and the number of pupae, females and males. Larger populations and more biased sex ratios (towards females) were observed in sun plots which were characterized by higher temperatures. In addition to the lower populations in shade plots, I observed that shade over coffee also enhanced the presence of natural enemies such as ants and the entomopathogenic fungus Beauveria bassiana. Moreover, we found that the treatment with antibiotic tetracycline at 0.1% (w/v) and the exposition to higher temperatures caused a significant reduction in Wolbachia in adult females fed with the antibiotic and those collected from infested fruits growing in coffee sun plots, in both cases the proportion was reduced to 0.04%. The treatment with antibiotic significantly affected the fecundity of CBB females, which produced fewer eggs and lower population densities; the sex ratio was less skewed towards the females in the offspring from females that were fed with tetracycline; also, populations from females treated with tetracycline had reduced population growth rate (λ) and longer generation time (T). These results suggest that Wolbachia have positive effects on CBB fecundity and may be necessary to assure its normal and successful reproduction. Finally, I found that diet influenced structure and diversity of the bacterial community of the CBB. Microbiota of individuals reared on artificial diet was significantly different from those collected in coffee fruits, and samples from the field were more diverse. Antibiotic treatment reduced the diversity in samples from adult females but not in eggs. Environmental conditions do not affect the overall diversity; however, communities from eggs and adult females collected in fruits from sun plots were significantly different from those collected in fruits from shade plots. Higher temperatures observed in sun plots apparently affected endosymbiotic bacteria like Wolbachia. In conclusion, reproduction and sex ratio of the CBB are affected by endosymbiotic bacteria and temperature. The combination of field and laboratory experiments showed a possible interaction between temperature and endosymbiotic bacteria, and higher temperatures reduced significantly the proportion of Wolbachia. The identification of the factors that contribute the reproductive success of the CBB and favor the presence of more females is necessary to develop more efficient management strategies for this important coffee pest.