Microbial Associations in the Coffee Berry Borer, Hypothenemus hampei (Ferrari) (Coleoptera: Curculionidae: Scolytinae)

Abstract

Coffee (Coffea arabica and C. canephora; Rubiaceae) is one of the most important agricultural commodities in tropical and subtropical regions in the world, generating industries that surpass an estimated US$170 billion annually. The coffee berry borer (CBB), Hypothenemus hampei, is the most devastating insect pest of coffee worldwide. The insect was first reported in 1901, and it has invaded most coffee-producing countries, causing severe economic losses surpassing more than US$500 million annually. The coffee berry borer was first reported on Kona, island of Hawaii in 2010, and by 2020, it had been reported on Oahu, Maui, Kauai, and Lanai, causing significant economic loss in the coffee industry in Hawaii. Determining how the coffee berry borer became a coffee pest has been an area of interest due to the fact that it is the only insect to consume the coffee seeds inside the berry. Survival on the seeds therefore implies a mechanism to degrade caffeine. Insects have evolved a diversity of strategies to overcome challenges imposed by plants. One of the strategies to mitigate these challenges is to establish mutualistic associations with symbiotic microorganisms that could enable insects to thrive and reproduce within the unfavorable environments. These microbial symbionts associated with insects play pivotal roles in host survival, reproduction, host metabolism, and affect hosts’ biology and phenotypes via a multitude of functions, providing vital nutrients such as essential amino acids, nitrogen, vitamins, and sterols, breaking down cellulose and lignin materials that are hard to digest, influencing host plant usage, and mediating interactions with natural enemies. Recent studies have provided strong evidence of coffee berry borer-bacterial associations and the mechanisms, revealing the coffee berry borer has a range of associations with its bacterial symbionts for the survival and possibly affected its evolution and adaptations. Vega et al. (2002), revealed coffee berry borer associations with the maternally inherited bacterium Wolbachia from many countries. Ceja-Navarro et al. (2015) demonstrated that the coffee berry borer relies on caffeine-degrading bacterial symbionts in the alimentary canal in order to live in caffeine-rich conditions that are unfavorable for other insects. The caffeine-degrading microbiome reported by Ceja-Navarro et al. (2015) consisted of 13 bacterial species, and only one of these bacteria, i.e., Pseudomonas fulva, had the caffeine demethylase ndmA gene (methylxanthine N-demethylase A). When the insect was fed an artificial diet containing antibiotics, they lost the ability to degrade caffeine, and their reproductive fitness was negatively affected (Ceja-Navarro et al. (2015). Additional investigations on the role of bacteria on the fitness of the coffee berry borer are needed in order to better understand the biology of the insect. The objectives of this study are to: (1) Determine the identity of bacterial species associated with the coffee berry borer in commercial coffee farms and wild coffee in Hawaii; (2) Explore the transmission mode of caffeine degrading bacteria by visualizing the bacteria within the insect eggs by fluorescent in situ hybridization (FISH) targeting the caffeine demethylation gene (ndmA); (3) Isolate and identify bacterial species associated with the eggs and determine if they are capable of breaking down caffeine; and (4) Conduct whole genome sequencing to identify them into species-level, and understand genome biology of bacterial species isolated from CBB eggs.