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Some Aspects of Food Habits and Gonadal Devolopment of Sternochetus FRIgidus (col: Curculiondae) in Off Season

M. A. Bashar
Department of Zoology, University of Dhaka, Dhaka-1000, Bangladesh.

M. Anwar Hossain
Department of Zoology, Dohar-Nababganj College, Nababganj, Dhaka-1320, Bangladesh.

Masuder Rahman
Department of Zoology, University of Dhaka, Dhaka-1000, Bangladesh.

Abstract/ Executive Summary:

The common mango weevil, Sternochetus frigidus, is an important pest of green mango along the eastern belt of Bangladesh.This is a monovoltine insect and host specific on the mango tree, Mangifera indica. It is strictly monophagous and survives only on mango. During the off season (May-September, 1998-1999) they were supplied with tender stem and young leaves of mango plants in the laboratory condition (28 ± 5ºC). The weevils consumed the supplied food and the quantity of the food consumed increased gradually. Several mango weevils from the experimental stock were examined by dissecting them during May-September. The study showed that the females with developing eggs in their ovaries consumed much of the supplied food.

Keywords: Sternochetus frigidus, Mango, Monovoltine, Gonadal development.

Location: The eastern belt of Bangladesh

Start Date:

End Date:

Program Area: Pest Management

Commodity: Mango

Objectives:

To examine the effects of young leaves/tender stem of the host plant (M.indica) on their gonad development after supplying the food to the hibernating adults.

Methodology:

To study the activities and gonadal development of the adults under laboratory condition (28 ± 5ºC) during the non-flowering stage of the host plant (M. indica), the weevils were reared in a wooden cage (L 25 cm × B 16.5 cm × H 19.5 cm) ensuring enough ventilation as in nature. The adults were collected by dissecting matured mangoes and they were released in the wooden cages. As the infestation of mango by the pest weevil is not apparent from outside, the traditional mango trees were assumed to be infested in the earlier years. About 40 S. frigidus adults were released in the cage on the 1st June 1999. The weevils were active while released as evidenced from their crawling and short flight activities. From the date of maintenance of the colony in a captivity, the examination of fat bodies in the body cavity, the size of ovaries and the gut contents were recorded regularly in about every 20 days of intervals. The laboratory colony of S. frigidus was supplied with 9, 14, 10 and 5 newly grown mango leaves in June, July, August and September, respectively. The weight of the supplied leaves was measured with a digital electric balance and the quantity of food consumed by an individual adult per day was calculated. On the 4th and 24th June, 16th July, 2nd and 26th August and 15th September '99 the experimental weevils were dissected under a binocular microscope to observe the gut contents, gonad development and fat bodies in the body cavity. The quantity of gut contents was assessed visually and the weevils were categorized on the basis of available gut contents as (i) Plenty (+++) - when the alimentary canal was found with full of food- residue; (ii) abundant (++) - when the food residue was less than full in the alimentary canal; (iii) a few (+) - when the small quantity of residue was found in stomach or just at the end of the alimentary canal and (iv) Nil (-)- when the trace of food residue was found in the alimentary canal. The ovarian development of the female insects was examined and also categorized visually as: i) Primary state (-), when no oocyte development was initiated. ii) Secondary state (+), when yolk deposition in oocyte started, ovarioles slightly enlarged but no countable eggs. iii) Tertiary state (++), when small countable round eggs in vitellogenesis; final state (+++), when full sized eggs apparent along with developing eggs in vitellogenesis. The analysis was made to assess the gradual development of eggs in S. frigidus females and their relation with the appearance of reproductive stage in the mango tree in nature.

Source of Information: Bangladesh J. Zool. 34(2): 213-220, 2006

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

In the present investigation, at the end of the insect's inactivity period the eggs were found in vitellogenesis, but egg-lying behavior was not apparent. This type of eggs development in vetellogenisis was seen under laboratory condition when these weevils were fed with mango young vegetative parts. In the case of S. frigidus, further experiments on the naturally occurring individuals of S. frigidus are to be conducted for confirming that in absence of due time appearance of mango bloom and feeding on young mango parts, the females do not go for egg-maturation. It is reported that the increases of activities in mango weevil synchronize with mango flowering and fruit-set (Johnson 1989). Hansen et al. (1989) described that time-lag between the oviposition period of the mango weevil and the fruitification of common mangoes carries a significant role in the intensity of attack by the mango weevils. It is obvious that the appearance of mango-flowering and arrival of weevil adults on the host population should be coincided. The authors emphasize that the intake of pea pollens can cause the termination of reproductive diapause in the pea weevil. If the pea pollens are not fed, the termination of reproductive diapause does not occur in the weevil. The association of mango reproductive stage was found essential for egg maturation in S. frigidus in the present investigation, but the situation is not the same as in the case of the pea weevil reported by the authors.

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