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Mango Pulp Weevil Sternochetus frigidus: An invasive species with economic significance in the Philippines

| July 22, 2015

Mango is the third most important fruit crop in the Philippines, based on export volume and value. It is ranked next to banana and pineapple (DA, 2015). The locally grown mango varieties have established a large domestic and international market, in both fresh and processed forms. In 2011, the Philippines recorded a total production area of 187k hectares for this crop, which yielded a production of 788k metric tonnes of fresh mango. The same year the country exported 21,081 metric tonnes of fresh mango worth $16 million USD. Exports from the country generally takes place to destinations such as Hong Kong, Japan, South Korea, Singapore and USA. For dried fruit, top export markets include USA, Japan, Hongkong, Canada and China (DA, 2015). Among a dozen provinces, the province of Palwan is a major producer of mango in the Philippines. However production has shown a decline over the years linked to the mango quarantine action that was implemented when the pest Sternochetus frigidus (Fabricius) or Mango pulp weevil (MPW) was detected in the province (Fig.1).

Mango pulp weevil, Sternochetus frigidus (Fabricius, 1787): The adult weevil is a dark brown weevil with paler patches. This small stout weevil has a small head and the body covered with papillate scales. T. Fenner & L de Jesus (NAQS, Mareeba). Source Pest and Diseases Image Library, Bugwood.org.

Fig. 1 – Mango pulp weevil, Sternochetus frigidus (Fabricius, 1787): The adult weevil is a dark brown weevil with paler patches. This small stout weevil has a small head and the body covered with papillate scales. T. Fenner & L de Jesus (NAQS, Mareeba). Source Pest and Diseases Image Library, Bugwood.org.

The pest feeds on the flesh of the mango fruit and destroys both value and marketability of the product (Fig 2).

Damaged fruit with weevil

Fig. 2 Damaged fruit with weevil

History of occurrence in Philippines

The pest is believed to have originated from Malaysia, and was first noticed in the southern part of the Philippines and later in the island of Palwan (McKinley, 2012). The weevil is known to exist in parts of Northeast India, Bangladesh, Myanmar, Thailand, Malaysia, Singapore, Indonesia, Pakistan and Papua New Guinea and is catagorised as an invasive species.

MPW started infesting mango plantions in the southern most part of Palawan in 1987 (Basio, 1994). In 1995, infestation of occurred sporadically in Puerto Princesa City and in the central part of Palawan. In Brooke’s Point in central Palawan, infestation was recorded as high as 43% (Catindig and Kong, 2005). Later the pest distributed itself through out the island, but is known mostly in the south and central part of the island.

Infested area under quarantine

Quarantine restrictions were implemented soon after the detection of the pulp weevil and mango movement from the Palwan district is restricted. Source http://bit.ly/1Rvlcsm

Quarantine restrictions were implemented soon after the detection of the pulp weevil and mango movement from the Palwan district is restricted. Source http://bit.ly/1Rvlcsm

Quarantine restrictions were implemented soon after the detection of the pulp weevil and mango movement from the island was restricted. To protect the nation’s mango industry, the Palawan Island group was placed under quarantine through the Bureau of Plant Industry (BPI) special quarantine administrative order No. 20 Series of 1987 (PCCARD). Its continued presence in Palawan has caused farmer’s profits to decline over the years. A study reveals that from 1990 to 2009, Palawan’s farmers have lost an estimated 120.82 million USD. Consequent to this, the retail economy of the entire island of Palawan also suffered (Macinley, 2012).

Behavior of the weevil

During the fruiting season, the adults feed on the developing fruits by making very small punctures on the peel. However, the larvae are the most destructive because they feed and develop on the pulp. The weevils feed exclusively on mango regardless of the variety (De Jesus, et al., 2005). The infestation caused by the pest is difficult to detect since the damage they cause cannot be seen from the outside. By the time the fruits are harvested, the tiny entry holes created by the young larvae, is not detectable anymore. In the absence of mango fruits, the adult weevil have been found feeding onmango flowers or panicles during full bloom stage with peak activity observed at 0600-1000h (De Jesus, et al., 2005).

Weevil biology

The adult of the pulp weevil is a small hard-bodied insect. It is black withbrown patches on the elytra and legs. The female adult lays single eggs on young mango fruit. Eggs are opaque and turn light yellow. The female later covers the eggs with black sticky exudate, which later turns into brown, dry and hardened egg plug. This egg plug serves as protection by holding the eggs in place. Eggs are 0.4 mm long and 0.5 mm wide and hatch in 9.3 d. Eventually the neonate larvae enter the young mango fruits by boring through the soft skin, preferring the area closer to the seed causing the darkening of the affected tissues (Catindig and Kong, 2005).

The mango pulp weevil undergoes five larval instars over approximately 20 days. Older larvae create feeding canals or tunnels as they move from one area to another in order to feed. Development from larva to prepupa to pupa to adult takes place inside the fruit. The pupa is exarate and active. Total development of S. frigidus from egg to adult stage is 32 days. The adult remains inside the fruit for another 37 days. 70% of the adults exit the fruit by boring a hole directly underneath the pupal chamber (Catindig and Kong, 2005).

Weevil management

A long term solution to the problem of MPW infestation in the province of Palawan has yet to be found. Short term measures, covering chemical and cultural practices, provide limited control and current approaches are inadequate to eradicate the pest at source.
Since discovery of the pest, some progress has been made to understand the bioecology of the pest weevil, including information on floral volatile atrractants, oviposition stimulants and options for insect trapping.

Present controls involve restrictions on movement of plant material (to limit spread) and field management of affected sites. Transport of plant materials and all parts, including fruits from known infested areas such as Palawan, is prohibited. A post-harvest pest control approach, implemented recently, is the use of irradiation as part of quarantine treatment. This approach appears to be more economical compared to other post-harvest pest control treatments, such as the application of heat and fumigation.

To iradicate the pest, a wholestic study of the pest, including biology and distribution, needs to be conducted. Further studies on techniques for detecting the pulp weevil through the use of synthetic sex pheromones would be needed to improve exporting opportunities for local growers.

References

Basio, R. G.; Johnson, P. J.; Pua, D. R.; Bergonia, H. T.; Diloy, C. C.; Villegas, E. L (1994) Mango pulp weevil (Sternochetus frigidus (Fabr.)) (Curculionidae, Coleoptera) found in Palawan. Philippine Entomologist, 1994, 9, 3, pp 350-351

Catindig, Josie Lynn A. and Heong Leon Kong (2005) http://www.niaes.affrc.go.jp/ techdoc/apasd/Sternochetus%20frigidus%20-B.html, accessed March 2015.

De Jesus LRA, Calumpang SMF, Medina JR, Ohsawa K (2005) Feeding behaviour of the mango pulp weevil Sternochetus frigidus (Fabr.) at different phenological stages of mango Mangifera indica L.Philippines Agricultural Scientist 86, 282-289.

Departhment of Agriculture (DA) http://hvcc.da.gov.ph/mango.htm,

McKinley,Justin D., Adam H. Sparks, Valerien O. Pede, Bart Duff (2012). An Economic Assessment of the Impact of Mango Pulp Weevil on the Agricultural Sector of Palawan, Philippines. Philippine Agriculture Scientist. Vol 95, No 3.

Published in International Pest Control – May/June 2015.

Author: Partho Dhang*

*Partho Dhang, 2410 Belarmino Street, Bangkal, Makati City 1233, Philippines, partho@urbanentomology.com

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Category: Agriculture

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