The extensive surveys conducted with the help of methyl eugenol baited traps and fruit infestation to determine seasonal biology and marginal habitats of Bactrocera zonata (Saunders) revealed that this fruit fly was prevalent every year in the plains, semi-desert, sub-coastal and coastal areas of Pakistan. It was also recorded nom foot hills, Peshawar valley and the Western hills. It was not recorded nom the Northern hills. Based on the incidence and abundance of B. zonata, the abundant habitats were; Northern plains comprising of Lahore, Shaikhupur, Gujranwala, Faisalabad, Sargodha, Sahiwal, Pakpatan and Vehari; coastal and sub-coastal areas consisting of Hyderabad, Mirpurkhas, Karachi and Uthal and semi-desert areas i.e. Jacobabad, Larkana, Khairpur, and Multan. The foot hill areas such as Haripur, Sialkot, Hasan Abdal, Islamabad, Peshawar and Kohat are categorized as rare habitats. Certain areas of Northern hills such as Abbotabad and some of the semi-desert areas i.e. Bahawalpur, Rahim Yar Khan and Bahawalnagar are the rare habitats of H. zonata.
The life history traits of B. zonata reared on wheat shorts diet in the laboratory at 27+1°C and 65+5% R. H indicated that expected life of the male at eclosion was 56.2 days and the same for the female was 62.24 days. The gross and net fecundity was 402.40 and 297.22 eggs, respectively. Mean number of eggs laid per day per female was 9.26 and mean age fertility schedule was 32.52 days. The egg hatch parameters revealed that gross and net egg hatch was 73.0 and 77.8 percent, respectively. The computation of fertility parameters for females (n=25) living to the age of 65 days indicated that gross and net fertility was 293.82 and 229.7 eggs per female, respectively with a mean age hatch schedule of 31.57 days. However, the mean age of fertility schedule was 29.97 days. The mean number of fertile eggs/day per female was 7.16. The age specific survival (Lx) and mean weekly fecundity (Mx) varied significantly with the age of the females. The survival of the female flies declined drastically after 6 weeks of age. The first day of egg production was 13th day of female life. The egg production abruptly increased during third week of reproduction and reached to peak during sixth week of egg production. Thereafter, the eggs/female/week declined gradually and reached to minimum over a period of nine weeks. During the mean generation time of 26.4 days, the intrinsic rate of birth (b), death (d) and increase (r) was 0.23, 0.02 and 0.25, respectively. The finite rate of increase (I) revealed that fly population will multiply 1.35 times per day. The doubling time for the population of B. zonata on wheat shorts diet was 2.78 days.
Host specific demography on fourteen different hosts from eight different plant families indicated that B. zonata frequently oviposited in almost all the host fruits. However, rare oviposition was recorded in Citrus limon, C. sinensis and Carica papaya. The females did not oviposit in Musa acuminiata and Lycopersicon esculentum. The cohort parameters of development, survival, pupal size and fecundity as well as population parameters such as intrinsic rate of population increase (r) and mean generation time (t) indicated that no consistent quantitative relationship existed between r and pre-adult development and adult fecundity. However, few correlations existed amongst the cohort life history parameters themselves. The principal conclusion is that B. zonata is a successful generalist furgivore because of its developmental ability to offset the effect of host specific trait that tends to lower the r values with one that tends to raise the r-values. The net results are that this fruit fly can maintain relatively higher r-values.
The age specific variations in mean number of eggs/female and mean number of clutches/female revealed that mean age to first reproduction was 11.5 days and reproduction output reached to peak (9.85 eggs/female) when the fly age was five weeks. Thereafter, the oviposition capabilities declined towards the death of the cohorts. The clutch size was age dependent. The host colour and fly density effect on pre-oviposition was non-significant, however, the oviposition period was longer in the cages having 10 pairs of B zonata followed by 30 and 5 pairs. The number of eggs laid per female and average clutch size were higher in yellow coloured hosts followed by green and colourless hosts in all me fly densities indicating the preference of yellow colour for oviposition. The clutch size was significantly affected by host size and age of the female flies. The clutch size was maximum in a host size of 4 cm when the flies were 35 days old.
The comparative dernography of native and laboratory strains of B. zonata indicated that the duration of larval stage and pre-oviposition period differed significantly between laboratory reared and wild strains collected from different locations. The growth rates, growth times and reproductive parameters also varied significantly. The females reared under captivity on wheat shorts diet produced significantly the higher number of eggs than wild strains. The net reproductive rate varied significantly with the collection sites, however, laboratory reared B. zonata had the greatest reproductive potential. The intrinsic rate of increase was also higher for laboratory strain than wild ones. The reproduction concentration was recorded from day 15 to day 35 of the female age as the cumulative percent eggs and cumulative percent females were maximum during this age grourp. The reproductive heterogeneity was due to some individuals which were either late in maturity or died earlier and thus had less time for oviposition.
The development time and survivorship of the immature stages of B. zonata and longevity, pre-oviposition period and fecundity of adult flies at five temperatures between 15°C and 35°C indicated that the egg hatch significantly increased with temperature from 15°C (5I %) to 25°C (91.3%) and then decreased to zero at 35°C. The larvae failed to complete development at 15°e or 35°C. Larval and pupal survivals were the greatest at 25°C as were female fecundity (eggs laid) and fertility (10% egg hatch). The developmental times for all stages were inversely related to temperature. Egg development was the fastest at 25°C and 30°C, although larval, pupal and ovarian developments were the fastest at .30°C. The net and gross fecundity was significantly higher at 25°C than at 20 and 15°C. The net reproductive rate for females, intrinsic rate of increase (r), birth (b) and finite rate of increase was significantly higher at 25°C when compared with rest of the test temperatures. However, intrinsic rate of death (d) was less at 25°C than 20, 15 and 35°C. The doubling time indicated that the population of B. zonata will double after 2.77 days at 25°e when compared with 4.08 and 13.86 days doubling time at 20°C and 15°C, respectively.
The pupal size in the fly colony reared on whea shorts diet was variable and the percentage of the small sized puape (1.6 mm) was 9% whereas the percentage of the large sized pupae (2.4 mm) was significantly the highest (56%). However, pupae of 1.8, 2.0 and 2.2 mm size were 10, 11 and 16% of the total pupae produced respectively. Size specific gross fecundity of B. zonata was also variable and pupal size and egg production were significantly and positively correlated (r=O.879, p=O.05). The life expectancy of adults that emerged from the pupae of 2.4 mm was significantly the longest (52.8 days) when compared with rest of the pupal sizes. The gross and net fecundity were significantly .higher for the females that emerged from 2.4 mm pupae and the reproductive rate had positive significant correlation with pupal size. The intrinsic rate of increase (r) was identical (0.17) for females from 2.4 and 2.2 mm pupae and the r-values decreased with the reduction in pupal size. The finite rate of increase was almost identical for the pupae of all sizes and it ranged between 1.17 to 1.35 for 1.6 to 2.4 mm pupae. The mean generation time was the shortest (30.44 days) for the flies that emerged from 2.2 mm pupae and the flies from 2.0 and 2.4 mm pupae completed one generation in 34.29 and 33.16 days, respectively. The population of B. zonata emerging from 2.4 and 2.2 mm sized pupae will double after 4.08 days whereas doubling time increased as the pupal size decreased.
The demographic analysis of mass rearing of B zonata revealed that the adult survivorship decreased as the age of the flies increased, however it was almost constant when the fly age was between 10-20 days. The oviposition reached to its peak in 35 days old flies and thereafter reproduction declined drastically. Maximum fecundity and fertility was recorded when the flies were confined in male-female ratio of 40:60. The pupal recovery and pupal' weight was maximum when 5.0 ml eggs were seeded in one litre diet which then decreased as egg density per litre diet increased. The adult emergence was. also density dependent. The sex ratio in the mass reared flies was in favour of males i.e. 1.43:1 and 1.22:1 in first and second day pop outs, respectively but it skewed in favour of females in third and subsequent pop outs from the same batch of diet seeded with 0-18 hour old eggs. The adult emergence was 95.7% of which 90.5 percent flies were normal, however, the flier percentage was 87.8 which indicated that colonization was normal. In contrast, the flier percentage was 81.4 from the field collected flies. The deformed flies were comparatively less in mass reared flies as compared with field collected ones. These studies manifest that the adult flies should be discarded after 35 days, adults should be confined in 40:60 male-female ratios and 0.50 ml eggs/litre be seeded for a better harvest and healthier flies for competition with the native ones. It is advantageous to release flies from first two pop outs after sterlization to combat B. zonata through SIT as the sex ratio was in favour of males. The pupae from third and subsequent pop outs should be utilized for colony maintainance as these had higher number of females.