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1 June 2014 Biology of Bactrocera cucurbitae (Diptera: Tephritidae) on Cucumber
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Abstract

Present studies on biology of melon fruit fly, Bactrocera cucurbitae (Coquillett) revealed that the freshly laid eggs were glistening white, slightly curved, tapering at one end while rounded at the other end. The mean length and breadth of the egg were found to be 1.13 ± 0.14 mm and 0.28 ± 0.05 mm. The first and second instars measured 1.49 ± 0.28 and 6.40 ± 0.86 mm in length, respectively, and 0.31 ± 0.07 and 1.21 ± 0.09 mm in breadth, respectively. The third instar was very mobile and measured 9.62 ± 0.87 mm in length and 2.05 ± 0.32 mm in breadth. The puparium measured 5.72 ±0.13 mm in length and 2.46 ± 0.11 mm in breadth. The length and breadth of male was 8.74 ± 0.32 mm and 11.46 ± 1.16 mm, whereas, the female measured 9.94 ± 0.20 mm in length and 15.92 ± 0.74 mm in breadth. The duration of egg incubation, and the larval, prepupal and pupal periods were 16.8 ± 4.9 hours, and 4.5 ± 1.13, 0.8 ± 0.25 and 8.4 ± 0.51 days, respectively. Pre-oviposition and oviposition periods ranged from 10–15 and 12–28 days. Fecundity varied from 58–92 eggs, while egg viability was 86.1 ± 0.54. Sex ratio (male: female) was 1.10 ± 0.14. Longevity of adults was extended to 30–52 days for males and 30–60 days for females when fed either water, molasses and honey or water, molasses and proteinex. Lack of access to water led to sudden death of the flies.

The melon fruit fly, Bactrocera cucurbitae (Coquillett) (Diptera: Tephritidae) is widely distributed throughout the temperate, tropical and subtropical regions of the world (Fletcher 1987). It is the only tephritid species in India that is uniformly widespread, attacking a large array of cucurbit fruits. It has more than 81 host species, in which fruit losses can range from 30 to 100% (Dhillon et al. 2005). Cucumber (Cucumis sativus L.; Cucurbitales: Cucurbitaceae) is one of the most preferred hosts of melon fruit fly. The female fly punctures the soft and tender fruits with her ovipositor and lay eggs below the exocarp of the fruit. The maggots that hatch from the eggs bore into the fruit and feed on the placenta and other structures. The melon fruit fly is considered a federal quarantine pest in India and many other countries, due to its highly invasive nature as majority of them cause extensive damage to many fruits and vegetables especially cucurbitaceous vegetables. They have been reported as the major limiting factor in obtaining high yields and good quality fruits of cucurbits. Their attack on cucumber not only reduces the yield but also affects the quality of cucumber and as a result, the marketability of the crop is reduced and the vegetable growing enterprise is rendered unprofitable. In addition to direct losses, fruit fly infestation can result in serious losses in trade value and export opportunity due to strict quarantine regulations imposed by most importing countries. (Chen & Ye 2007).

The knowledge of biology and different life stages of insect pests is helpful in developing efficient management strategies that will prevent ill effects of insecticides. This study was undertaken to gain precise knowledge of the morphometrics of the various developmental stages, their duration, adult longevity, pre-oviposition and oviposition periods, fecundity and the effect of diet on adult longevity. This investigation was conducted under laboratory conditions.

Materials and Methods

The initial culture of B. cucurbitae was collected from infested cucumber fruits from the experimental area of the Central Institute of Temperate Horticulture, Srinagar, Jammu and Kashmir, India. The infested fruits were infested fruits were kept in 20 × 20 × 8 cm plastic trays on a 5 cm-thick layer of sieved moist sand to facilitate pupation. After every 3- 4 days, sand was sieved and newly formed pupae were collected. The pupae were kept in 10 cm-diam petri dishes (50 pupae/petri dish) lined with moist filter paper.

The newly emerged adult flies were collected and placed inside the rearing cages each 35 × 30 × 35 cm. Each rearing cage had wire mesh on 3 sides, glass on the top and a wooden door at one side. A round trap door was provided in the wooden door to facilitate collection of adult flies for experimental purpose and also to provide food and water. The male and female flies were identified according to Drew & Raghu (2002). On the bottom of each cage there was a 2 cm-thick layer of sieved sand with 5% moisture. A glucose solution (10% W/V) was provided inside the cage for adult feeding. This glucose solution was kept in a 50 mL beaker and a thumb sized water-soaked cotton swab was laid in such a way that half of it was immersed in glucose solution and remaining half stayed above rim of the beaker to keep the solution in reach of adult fruit flies. Slices of cucumber were kept inside each breeding cage for oviposition. These slices were replaced by fresh ones daily to avoid decay. The entire fruit culture was maintained at mean temperature of 23.97 ± 0.66 °C and 16.17 ± 0.81 °C with mean relative humidities of 66.39 ± 1.66 and 74.07 ± 1.63%, respectively. A binocular microscope was used to note the number of eggs present in each cucumber slice. This procedure was repeated until the death of the ovipositing females. The eggs collected were placed in 10 cm diam-petri dishes (50 eggs per petri dish) with moist filter paper at the bottom to prevent desiccation of eggs. After egg hatch, fresh cucumber slices were kept in each petri dish for feeding the young larvae. After 24 h cucumber slices were replaced by fresh ones until all the eggs had hatched. The cultures so established was used in biological studies.

Morphometric study of different life stages of B. cucurbitae was carried out by taking 10 replicates of each stage, viz., egg, freshly 1st instars, 2nd instars, 3rd instars (“fully grown larvae”), pupae and adults for linear measurements. In addition to the above parameters color, shape, size and periods of eggs, maggots, pupa and adults were also recorded. The study was conducted during Jul through Oct 2012.

Results and Discussion

Egg

The eggs of B. cucurbitae were glistening white, slightly curved, elongated and tapering at one end while rounded at the other end. The posterior extremity was broadly rounded while the anterior end appeared more pointed. The eggs are embedded vertically or slightly slanting and touching each other (Fig. 1). The eggs are laid singly or in clusters of 4 to 10. Morphometric observations revealed that the length of egg varied from 0.98 to 1.28 mm with a mean of 1.13 ± 0.14 mm, and the breadth varied from 0.21 to 0.34 mm with a mean of 0.28 ± 0.05 mm, respectively (Table 1).

Duration of development between laying and hatching, i.e., the incubation period was 12 to 24 h with a mean of 16.8 ± 6.19 h (Table 2). These results are in the close agreement with those of Waseem et al. (2012) who reported that incubation period on cucumber lasted from 24.4 to 38 h. Similarly, Khan et al. (1993) reported approximately the same incubation period as reported herein. Shivarkar & Dumbre (1985) found an incubation period of B. cucurbitae of 1.2