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Mango pulp weevil: A 'he' or a 'she'?
by Likha C. Cuevas |
April-June
2004
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 It's such a disappointment when you open a luscious and perfect-looking mango and find a wormy thing burrowed inside It ruins your appetite.
That 'wormy thing' inside the mango fruit is the mango pulp weevil or Sternochetus frigidus (Fabr.) to the scientific world. This pest is found only in Palawan here in the country but it also poses problems in India, Bangladesh, Burma, Thailand, Malaysia, Singapore, and Indonesia.
Aside from making the prospective consumer lose his appetite, the mango pulp weevil (MPW) destroys the fruit, rendering it inedible. The immature weevil eats the fruit's pulp where it also develops and grows into an adult.
However, according to Louella Rowena A. de Jesus (Department of Agriculture Regional Field Unit 4), Jose R. Medina (University of the Philippine Los Baños or UPLB), and Satoshi Nojima and Kanju Ohsawa (Tokyo University), the chemical basis for the weevil's preference for mango over other crops remains a mystery. Before these scientists venture into this issue and on the weevil's behavior, they have to know the sex of the weevils and look for the best method in telling them apart.
So, first thing's first.
The mango pulp weevil threat
What's the big deal with these weevils? Before that can be answered, we first have to look at the context of how important mango is to the country.
The Philippines is the 6th largest producer of mangoes and has 9% share in the world market valued at $34 million in 2000. According to reports, the Philippines is expecting to capture about $70-million for the export of fresh mangoes in the US market which is currently dominated by Mexico.
Dr. Hernani Golez, National Mango Research Development, and Extension (RDE) Network team leader, took 14 years to persuade the U.S. to certify that mangoes from Guimaras in Visayas is free from mango-pulp weevil and to permit mangoes from Guimaras to enter the U.S.
“But Mr. Golez's efforts to meet U.S. standards have been drawn out,” Margot Cohen of the Truth About Trade and Technology wrote. “The first big hurdle came in 1987, when a survey of 33 mango-producing provinces discovered evidence of mango-pulp weevils in Palawan. Mr. Golez agreed to U.S. demands for quarantine while seeking alternate sources of mangoes. Guimaras, surrounded by water, was a natural place to start. It took until 1993 for the U.S. to declare Guimaras mangoes weevil-free after a series of fruit samples turned up negative.”
The threat of this pest is so alarming that the Bureau of Plant Industry has a program specifically for the weevil, “Delimiting and Monitoring Survey of Mango Pulp Weevil”. This program launched specifically for Palawan aims to confine the mango pulp weevil in its present location to ensure protection of MPW-free areas in Palawan. The Department of Agriculture Regional Field Unit 4 (DA-RFU4), the Palawan Local Government (through the Office of the City Agriculturist), and the BPI- Plant Quarantine Section are also conducting various researches on the weevil in support of the control program to strengthen domestic quarantine for MPW.
Sex discrimination
It's now imperative to solve this mystery why these pests love mangoes --- and knowing the sex may lead us to the answer.
As of now, the only method of telling whether the weevil is a male or a female is by dissecting dead weevils since the sex can't be determined through ocular inspection. “No morphological differences are known,” the team said. Usually for coleopterans (or insects like the mango pulp weevil), you can tell the difference between the male and female through their antennae, upper body, and the sternum. But the MPW's case is different. Color can't even be a reliable indicator (like that in other animals) since it changes as the weevils age.
But now, these scientists have found an accurate way of telling a live weevil if it's a he or a she.
The mango pulp weevil has tergites, which are the top or back part of the segments in the weevil's body. When you clip the elytra (pair of anterior wings) of the weevil, you will see that the end part (or the terminal tergite) of the male is truncated while the female's end is tapered. Another identification mark is the number of male tergite. The male has seven but the terminal tergite is divided in to two so it has an 8th tergite whereas the female has the usual seven.
The scientists have said that this is the first time that this method of differentiating a live male and female mango pulp weevil was documented. This study may provide the springboard for other mango pulp weevil researches.
References:
1) De Jesus, Louella, Rowena A., Nojima, Satoshi, Medina, Jose R.., and Ohsawa, Kanju. Method in sex discrimination in the mango pulp weevil Sternocheus frigidus (Fabr.) (Coleoptera: Curculionidae). Appl. Entomol. Zool. 37 (2): 251-255 (2002)
2) Asia Pulse. Philippine president seeks u.s. funds for irradiation facility for mangoes. Http://www.organicconsumers.org/irrad/PhilipMangoes.cfm
3) Cohen, Margot. Truth about Trade and Technology. Http://www.truthabouttrade.org/article.asp?id=1942
4) Lacson, Larry. Detection, Monitoring and Management of Invasive Plant Pests in the Philippines. http:// www.baphiq.gov.tw
5) Palawan Sun Online. MPW Task Force holds Info-caravan on Mango pulp-weevil. http://palsun.fateback.com/826/story8.htm 
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