ESTERASE ISOZYME VARIATION AND POLYTENE CHROMOSOME ANALYSIS IN THE MELON FLY, BACTROCERA CUCURBITAE {DIPTERA: TEPHRITIDAE)

Abstract

The melon fly Bactrocera cucurbitae (Coquillett) is well known as a destructive pest of fleshy fruits and vegetables in many parts of the world including Bangladesh. Esterase (EST) isozyme banding patterns were observed on 5% Polyacrylamide Gel Electrophoresis (PAGE) during the different life stages (i.e. egg, larva, pupa and adult) and also sweet gourd, which was used as larval food. Two bands, EST-1 and EST-2, showing seven allelomorphs were found. There were four electromorphs in EST-1 (Est-104*’, Est-10'"’8, Est-10X7 and List-11 00), had a high mobility and close to the anode and EST-2 had three allelomorphs (Est-2017, Est-20"7 and Est- 20'37), showed a low mobility and close to the cathode. The standard photographic maps of salivary glands polytene chromosomes were also observed in the different larval stages (lsl and 2"(l instar larvae) of B. cucurbitae. In second instar larvae, the whole polytene genome had been mapped by dividing it into 100 sections and the sub sections were lettered. The banding pattern was moderately developed here. The left end of the chromosome is characterized by dark bands in 4A. 6 and 14A. Sections 9 and 14B, each bears one pair faint bands. On the other hand, 15 comprises one pair moderately dark bands. The expanded regions in sections 3, 16 and 20 are not typical puff, rather section 16 bears a dotted band. The tip (section 1) has faintly stained two bands. Weak points are VIII found in 2 and 19. Deeply stained bands occur in sections 30, 31 and 41. Sections 33 and 40 are characterized by dotted bands; 39 and 42 comprise two moderately developed pulTregions. Breakage occurs at 26. Sections 52, 55- 57 are characterized by a series of dark bands. Sections 48 and 50 have similar single band. There is a poorly developed puff region in section 58. Lightly stained two pairs of bands present in section 68. Sections 72, 73, 74 and 79 possess single band. One pair lightly stained bands occurs at 77 and 78. There is a prominent puff in section 80 together with a dark band immediately proximal to it. Weak points arc found in 63, 76 and 81. Section 83 possesses three clear bands. A scries of lightly stained and deeply stained bands are found in the sections 87 and 95. Section 100 appears only as a well-developed puff in the total polytene chromosome complement. Three weak points are found in 91, 97 and 98. In the case of Ist instar larvae, salivary gland cells were at early stages of maturity. So the banding pattern of polytene genome was not developed at this stage. This observation showed that B. cucurbitae is an excellent genetical material for esterase isozyme and polytene chromosome analysis. The investigation has been proved to be very useful for obtaining more detailed genetic information on the natural populations of this pest