August: Science & Medical Blog – Coconut Pest Threat

Oxbridge tutors have a reputation for sometimes being sticklers for tradition. Indeed, the ancient libraries and historical architecture can sometimes lure students into the illusion of studying in some sort of historical time warp! However, while both Oxford and Cambridge are hubs of cutting edge research, part of your natural sciences education will be to cultivate an appreciation for the development of traditional scientific practices and their history. Indeed in Cambridge, one of the courses offered as part of the tripos is the history and philosophy of science.

Interviewers at Oxbridge sometimes probe our understanding and appreciation of basic sciences, such as the classic interview question “Why should funding be provided to a project studying the mating habits of the Bolivian shrew rather than to oncology research?” As such, it is a strategic move to prepare for such questions by being able to discuss how basic and traditional science has been able to help solve modern problems.

As an example to discuss today, a case of mistaken identity has been solved by old-school taxonomy involving an insect pest threatening the coconut industry in the Philippines, the world’s second largest producer, scientists report July 23 in Agricultural and Forest Entomology.

To stop a pest requires knowing exactly what species one is up against and when the first of an estimated 1.2 million coconut palms started dying five years ago, Philippine authorities initially blamed an insect called Aspidiotus destructor, a pest that has caused prior coconut die-offs in Indonesia. However, careful taxonomy studies then discovered that a closely related bug, A. rigidus, was in fact responsible for the current blight.

Once A. rigidus had been correctly identified and determined as invasive to the Philippines, it was noted that it has few natural predators in their new ecosystem. Furthermore, it also lives 1.5 times as long as the wrongly accused A. destructor. However, in an example of biological pest control, transferring an A. rigidus predator – a type of ladybug — from its native habitat quelled an outbreak that hopped between Indonesian islands in 2005. In the study linked above, the authors believe this tactic could end the infestation in the Philippines.

This invasion occurred five years ago, when flat circular bugs called scale insects began sapping life from coconut trees in the Philippines. As many as 60 million of the insects can encrust the lower leaf surfaces of a single tree. Scale insects kill coconut palms by injecting a chemical that destroys the chlorophyll in their leaves, leaving the plant unable to absorb energy from sunlight The infestation rate was so fast that the local government was caught flat-footed, and poor farmers lacked the resources to cope and as a result fruit yields have plummeted. If the pest continues unabated, the Philippines could lose 60 percent of its coconut crop, denting its $1 billion in annual export earnings, according to Philippines government estimates. While A. destructor was initially suspected, it was an unlikely culprit; as the pest was so established in the Philippines, it seemed unlikely that a sudden flare up in their population would occur so spontaneously.

To identify the correct culprit (A. rigidus) researchers collected scale insects from across Southeast Asia, looking for subtle differences in shape, flexibility and other specific morphological details. As limited DNA information exists for the approximately 7,500 scale insect species, making genetic identification impractical, so researchers must rely on traditional taxonomy.

The specific morphological traits that revealed the pest’s true identity was a more rigid cuticle, as well as a crescent shape in the laid eggs, another characteristic of A. rigidus.