Predators that save Millions

The enemy: Hypothenemus hampeii

Biodiversity loss will likely have surprising and dramatic consequences for human wellbeing. Identifying species that benefit society represents a critical first step towards predicting the consequences of biodiversity loss. Though natural predators prevent billions of dollars in agricultural pest damage annually, characterizing which predators consume pests has proven challenging. Emerging molecular techniques may illuminate these interactions. 

No doubt, invasive species, pests, and disease vectors are a danger to humanity and cost us a lot of money. In that context it would be great if we could identify those species and populations that actually provide benefits to society by simply consuming harmful organisms. Identifying those service providers, however, is anything but straightforward. It is not like we are witnessing these particular predation events. For example, pest control is a critical service and insect predators likely saved farmers billions of dollars annually in avoided pest damage. But how can we identify predators that are so valuable to us. Visual identification of prey gut content used to be the number one methodological choice but it seldom delivers the necessary taxonomic resolution. In addition the necessary inspection labor is considerable and sampling techniques often result in high mortality rates among caught predators.

The use of molecular methods, such as DNA Barcoding, seems to be advisable. Firstly, molecular identification  would allow researchers to shift to feces or regurgitates from carnivores, insectivores, and herbivores of diverse taxa to infer their diet, making much less intrusive and less dangerous for the test subjects. We also know that molecular methods provide a much better resolution and higher accuracy than the morphological inspection of partially digested remains.

Researchers from Stanford University used molecular fecal analysis to identify bird predators of coffee’s most damaging insect pest— the coffee berry borer beetle (Hypothenemus hampeii). This pest has invaded almost every coffee-producing country in recent years. Earlier experiments have shown that birds consume the borer, but further insights have proven difficult because of the borer’s small size (~2 mm) which makes witnessing predation impossible.

The researchers collected samples at coffee plantations in southern Costa Rica and conducted feeding trials to determine the sensitivity of the method. They used borer-specific primers to target an 185 bp segment of the DNA Barcode region and came up with promising and interesting results:

While feeding trials confirmed the efficacy of our approach, detection rates were low. Low detection rates suggest that there are other species that consume the borer that we did not identify. Nevertheless, we identified six species that consume the borer. The species we did identify shared traits that may be characteristic of these other predators. These species had narrow diet breadths, thin bills, and short wings; traits shared with borer predators in other systems. Borer predators were not threatened; therefore, safeguarding pest control necessitates managing species beyond those at risk of regional extinction by maintaining populations in farmland habitats. Generally, our results demonstrate potential for pairing molecular methods with ecological analyses to yield novel insights into species interactions.