Population dynamics and diversity of Bactocera species and Dichasmimorpha longicaudata, its parasitoid in correlation with abiotic factors

Fruit flies are destructive pests and caused heavy losses in agricultural products by reducing crop production. The reported study was planned to evaluate the relationship between population dynamic of fruit flies and its parasitoid in guava orchards in relation to prevailing ecological condition. For this purpose, baited pheromone traps containing methyl eugenol with contact action Insecticides were installed in guava orchards in Faisalabad district during 2016-18. Trapped fruit flies were collected after every fortnightly interval and brought in the laboratory for identification of species. The infested guava fruits were also collected from fruit trees during the fruiting season and kept under laboratory conditions to identify and record parasitoids species as well as emerging Fruit flies. Results revealed that B. zonata, B. correcta and B. dorsata prevail around the year. However population of B. dorsata was more than B. zonata followed by B. correcta. Peak infestation of fruit fly was has been observed in October 2016-17 while in 2018 highest population was recorded in September. However, low population of fruit flies species had been recorded when temperature dropped < 05 oC. Emergence from infested fruit predicts that 60% emergence was solely by the population of B. dorsata followed by B. zonata and B. correcta throughout the year. The highest number of D. longicaudata was recorded in July and August and also directly influenced by pupae emergence from the larvae. Highest and lowest temperature exerted more effect on population fluctuation of pest as well as its parasitoid as compared to other factors.


Introduction
Guava (Psidium guajava) is most favorite and nutritional fruit in Asia as well as all over the world belongs to family Myrtaceae [1]. Fruit flies are most destructive pests of fruits, causing decrease in yield and deteriorating the market value. In 1907, it was first observed in Taiwan [2] but now it has been spread to Asia Pacific regions [3, 4]. It inserts the ovipositor in the fruits and lays egg inside, near fruit skin. Maggots develops inside the fruit. Latterly, maggots drill its way out after completing its period to pupate in soil and emerge as winged adult to continue the life cycle [5]. There is great taxonomic diversity in fruits fly withmore than 5000 species present all over the world [6] which not only infest the fruit but also affect the vegetables. Among all the fruit fly species Bactrocera zonata, B. correcta and B. dorsata are commonly found in guava orchards. Peak population of different species of fruits flies was recorded from April to august on guava and mango orchards [7] and caused 30 to 100% losses in these fruits. Fruit flies quarantine pest and caused hindrances in international trade [8].
Farmers use different techniques to control fruit fly attack. Chemicals used to control fruit fly are not encouraged due to residual effects [9]. Different environmental friendly techniques like Sterile Insect Technique (SIT) [10] pheromone traps [11] and sanitation (disposal of damage fruits) [12,13] are well adopted approaches for the management of fruit flies. The scientist observed population dynamics of this pest by using different traps like Mcphail traps and correlated it with environmental conations [14]. In recent decades, increasing interest in parasitoids into integrated pest management programs has been replaced by classical biological control. This is often likely to reflect not only an increased awareness of the non-target action of insecticides on beneficial insects and human beings but also significant advancements in rearing techniques and artificial diets for rearing hosts for augmentative biological control programs [15,16]Diachasmimorpha longicaudata Ashmead (Hymenoptera: Braconidae) is naturally available parasitioid in Pakistan and South East countries [17]. It parasitoid the larval and prepupal stages of fruit fly of genera Anastrepha, Ceratitis and Bactrocera. In Pakistan, Its parasitism rate exceeds 36% on B. Dorsalis and 44% in B. Zonata [18]. The objective of this studyis to evaluate the diversity and population dynamics of fruit fly species and it's parasitoid D. longicaudataco relation to environmental factors in Faisalabad during years 2016-18.

Materials and methods
Studies on population dynamics of fruit flies was conducted in different places of guava orchards in district Faisalabad during 2016-18. The fruit fly species mainly (B. zonata, B. correcta and B. dorsata) were recorded by installation traps in guava orchards. In the selected orchards, five fruit fly traps with methyl-eugnol and contact action insecticide (Malathion@1ml/trap) (as bait) was installed at 6 feet height from the ground and 12 m apart from each other. The baits in traps was replaced every 24 hours. The data regarding number of fruit flies were recorded fortnightly. Collected individuals were identified up to species level. The population fluctuation of three fruit fly species (B. zonata, B. correcta and B. dorsata) were kept in consideration in this study. Infested guava fruits were collected and kept in laboratory under favorable conditionsto identify the fruit fly species and their parasitoids. The obtaining pupae from larvae were kept in Petri dishes and emerging fruit fly specie and parasitoids from pupae were recorded and identified. The metrological data was also obtained from crop physiology section, Ayub Agriculture Research Institute Faisalabad.

Data analysis
The mean values of pest and parasitoid population along with standard error was calculated by using statistical software     (Table 3).

Table 1. Regression analysis (Hierarchical regression model) of population fluctuation of Bactrocera zonata with weather factor along with coefficient of determination for 2016-2018
Where, Y=Fruitfly (Bactrocerazonata) Population; X1= Fortnightly Maximum temperature; X2= Fortnightly Minimum temperature; X3= Average Fortnightlyrelative humidity; X4= Average Fortnightly rainfall (mm); * = Significant at P ≤ 0.05; **= HighlySignificant at P ≤ 0.01 Table 2 Highest population of B. dorsatawas observed during three years of study followed by B. zonata and B. correcta. The infested guava fruits were collected from the canopy of fruit trees and kept them under laboratory conditions to identify the fruit fly species and its parasitoid. The pupae of fruit fly emerged from larvae was recorded in April and attained its highest number in October while declined gradually in November and no pupae was observed in December, January and February. From emerging fruit fly, highest number of adults of the B. dorsata was recorded followed by adults of B. zonata and B. correcta. So it is concluded that Bactorcera dosrsata was found more prominent than other two species. The results are similar to the researchers who revealed the abundance of B. dorsalis and B. correcta in many important vegetable crops and different fruits [22,23,30]. The results showed that the population of fruit fly was higher in 2017 then from the previous year but similar population was recorded in 2018 and same pattern was also recorded for number of pupae. The highest parasitoid (D. longicaudata) were observed in July and August. The number of parasitoids directly influenced by the number of pupae emerged from the larvae. The parasitoid was positively affected by the temperature and relative humidity. The results are similar to scientist who indicated that the population of parasitoid and fruit fly population directly influence by relative humidity and temperature [35]. The correlation and regression among the fruit fly population, Parasitoids, Temperature, relative humidity, and rain fall were also worked out. The pest population of all three fruit fly population fluctuation of fruit fly species was significantly positive affected by maximum temperature and relative humidity but the pest population negatively inflicted by low temperature. The results indicated that fruits were more infested by fruit fly in July august and October during 2016-18. These months have high temperature and relative humidity as compared to other months. The researchers also concluded fluctuation in pest population due to maximum and minimum temperatures [3, 24,25].The scientist in Lucknow described the similar correlation between pest population and temperature in orchards [37] and the researcher in Karnataka indicated that the fruit fly positively influenced by wind speed in mango orchards [36]. Results indicated that relative humidity played negligible role in fluctuating the pest population. Similar the researcher also concluded that negative correlation of relative humidity with fruit fly population [25][26][27]. In the present study rain fall also slightly affected the pest population adversely. The scientist showed the significant positive correlation between fruitfly and maximum temperature while relatively negative relationship with rainfall and relative humidity [38]. Conclusion It is concluded that Bactrocera dorsata remained more abundant than B. zonata and B. correcta in guava orchard in Faisalabad district during 2016-2018. Pest population varied during whole year. Maximum pest was observed from 2 nd fortnight of April to October.
Among weather factors, temperature played key role in variation the pest population. The inferred results could predict the maximum infestation periods of fruit flies in guava orchards and help to adopt management practices accordingly.