In spite of the tireless efforts of the Department of Agriculture (DOA) personnel, public awareness on the threatening pest species, Papaya Mealybug (PM), remained at a low level until some political parties used ‘Piti Makuna’ in the Western Provincial Council election speeches.

The Papaya Mealybug is an alien invasive insect species, scientifically known as Paracoccus marginatus. This type of an alien pest can accompany any live material like fruits, flowers, seeds, floriculture/foliage plant parts that the public usually bring in their luggage from foreign countries. Therefore, anyone could have inadvertently brought it to Sri Lanka. This is another very good example for the need to respect the quarantine regulations of the country which are blatantly violated by some due to ignorance, carelessness or power.

This Polyphagous (which feeds on many plant species) pest was first detected in mid 2008 and it has already spread throughout Colombo and Gampaha districts and now threatening its spread throughout the country. It has already killed many Papaya plants and capable of surviving on and damaging more than 80 different plant species. Due to the nature of the pest and the variety of host plants it attacks, insecticidal control is not practicable.

Therefore, to control this pest the DOA has decided to introduce a tiny (less than 0.5 mm in length) parasitic insect that has already proved to be successful in controlling PM elsewhere in the world. Recently I told one of my friends that the DOA has taken necessary action for managing this pest by way of introducing a natural enemy. His response was that the public is aware of the proposed biocontrol attempt but doubtful of the appropriateness of introducing another alien insect to control the pest. What my friend told me was exemplified by the huge title in one of the daily newspapers which read; ‘Many problems due to importing American insects to control Mealybug’. The newspaper article stated that a minister has raised the issue of effects on non- target organisms due to introduction of alien parasitoids. This doubtfulness, I consider as a very positive indicator of the increased environmental concern and awareness of our society.

The objective of this article is to discuss the proposed PM management procedure by the DOA and the public concern mentioned above.

Deliberate introduction of natural enemies into a new country to control an exotic pest (insect, disease or weed) is known as Classical Biological Control. Historically, people have realized when an organism invades a new country with suitable habitats, the invading organisms thrive very well mainly due to lack of its natural enemies. This understanding led to exploring the pest’s ‘original habitat for its’ natural enemies and introducing the natural enemies to newly invaded areas by the pest. Termed Classical Biological Control this practice is considered an economical, ecologically and socially sound pest control strategy in contrast to use of pesticides.

Papaya Mealybug is an exotic insect known to be native to Central America (Mexico), which has no natural enemies in Sri Lanka. Since its introduction to the country in 2008, no local predator or parasitoid has managed to keep the Papaya Mealybug population under control, irrespective of many known local parasitoids and predators of 37 native Mealybug species already being present in Sri Lanka. This and the impracticability of using insecticides for control make PM a typical candidate for a classical biological control attempt.

Surveys of scientific literature show that the PM has spread from Mexico, where it is not a pest due to the presence of natural enemies, to the Caribbean region in 1994, Florida in 1998 and to the Pacific Islands in 2000. More recently, it has established itself in Malaysia, Indonesia, Thailand, and India. The Mealy bug has become a very serious pest of Papaya in Florida, the Caribbean, and Pacific regions. Entomologists have surveyed Mexico and found three parasitoids from the original habitats of the Mealybug. These parasitoids have multiplied and been introduced into Florida, the Caribbean and Pacific regions to control the Papaya Mealybugs. One year after introduction, the pest population has decreased by 97-99% making those classical biological control programmes an astounding success. All three insects, Anagyrus loecki, Pseudleptomastix maxicana and Acerophagus papayae, belonging to the family Encyrtidae (Hymanoptera), are tiny parasitoids (less than 0.5 mm length) of Mealybugs. Detailed studies of the impact of these parasitoids on PM have shown that most of the control has been done by Acerophagus papayae after introduction. Acerophagus papayae is known to be a specific parasritoid, i.e. feeds only on Papaya Mealybug, while Anagyrus loecki feeds on more than one Mealybug species. Based on this knowledge, the DOA scientists have decided to import and release Acerophagus papayae to control Papaya Mealybug. The parasitoids will be imported from Puerto Rico, where PM parasitoids are being cultured by Puerto Rico Department of Agriculture in collaboration with Animal and Plant Health Inspection Service (APHIS) of the United States Department of Agriculture (USDA). Release of the parasitoids and monitoring of its establishment will be carried out in selected areas where the pest has already spread.

The decision to import and release Acerophagus papayae gives rise to two major questions. Will this parasitoid be able to control the pest? Will there be any impact of the parasitoid on non- target organisms? Although a definite answer cannot be given to any of the questions, available scientific evidence and our experience suggest that release of A. papayae will bring down the Papaya Mealybug population to a negligible/manageable level and there will be no impact on non- target organisms. One might wonder what will happen to the parasitoid after it controls the PM. Two things can happen. Either parasitoid will co- exist with PM in a low population equilibrium or the parasitoid will become extinct if it manges to eradiate the PM.

This is not the first time Sri Lanka has faced such threatening exotic pests. In 1970 the coconut leaf miner (Promecotheca cumingi) devastated our coconut cultivation and we imported a parasitod (Dimmokia javanica) which completely eradicated the exotic pest. In 1998 beet leaf minor (Liriomyza huidobrensis) threatened the vegetable cultivation in the hill country. The DOA imported a parasitoid (Diglyphus isaea) which is still keeping the pest under control. In 1990 Guava white fly (Aleurodicus dispurses) killed many guava trees and infected almost every home garden tree. This pest population was brought down to a negligible level by a parasitoid, Encarsia transvena.

The above mentioned are not the only biocontrol programmes that DOA has implemented. In addition to classical biocontrol programmes many neoclassical (non classical) biocontrol programmes have been implemented in Sri Lanka. No adverse impacts on non- target organisms have so far been recorded from any of these biocontrol agent introductions (both alien insects and pathogens). However, it should be mentioned that no research has been conducted to find out any such impacts either, mainly due to lack of support for basic research.

Popular press stories of horrors due to Biological Control attempts, such as ‘cane toad introduction in Australia’ have made some people doubt the value of classical biological control as an acceptable pest control method. It is true that there is some scientific evidence on the harmful impacts of introduced natural enemies on non target organisms. These few cases need to be individually analyzed to understand what has gone wrong. Most of such introductions with unwanted results were done in the past using general predators before biological control advanced into a modern scientific discipline.

Predators (e.g. lady bird beetles) are usually generalists. That means they feed on more than one species. Since the capability is already there in predators to eat many species, it is easy for them to shift their host and attack non- target species when introduced to a new area. But the relationship of parasitoids with their hosts is very specific. Most parasitoids have co- evolved for millions of years to acquire the capability of developing within the body of their hosts while the host itself continues to grow and moult (Koinobionts). Such relationships are highly specific and host shifts can expect to be evolutionary events not ecological events. The proposed parasitoid for release, Acerophagus papayae, is a Koinobiont and, therefore, no impact is expected on any non- target species.

Today there are international standard guidelines and protocols to follow when introducing natural enemies to new areas. Under the International Plant Protection Convention there are guidelines for safe importation and release of biological control agents (ISPM No. 3 of 2005). The DOA will adhere to these guidelines. Accordingly, the first imported consignment of parasitoids will be kept under quarantine and host specificity tests and pest risk analyses will be carried out before field release of the imported parasitoids.