Impact of Four Plant Extracts on Bactrocera dorsalis a Pest on Fruits

Menthol extracts of four local plants (Ocimum tenuiflorum, Hibiscus, Mentha longifolia and Bougainvillea glabra) were analysed to check their toxicity on third instar larvae of B. dorsalis by estimating the larval mortality for four plant extracts and different times exposure (1-5 hr) and measured LT50 value for each plant extract. Larval mortality varies for extract of each studied plant as Ocimum tenuiflorum showed its highest value of 56.68% at 4.57hr, for hibiscus it was 72% at 3.5 hr., for Mentha longifolia it was 95.23% at 4 hr., while for Bougainvillea glabra it was 100% at 2 hr. exposure. The LT50 values for B. dorsalis varying from 1.011 for Bougainvillea glabra to 2.946 for Ocimum tenuiflorum whereas LT50 values were 1.402 and 1.123, forHibiscus and Mentha longifolia respectively. Present study results showed that Bougainvillea glabra was highly toxic whereas Ocimum tenuiflorum shows least toxicity.


INTRODUCTION
Synthetic pesticides have benefitted tremendously not only agriculture sector but also by its use in forestry and control of vector-borne diseases. The use of pesticides not only prevent crops from the damage from the pests by thereby improving productivity, also prevent reduction in

Original Research Article
crop yield, vector borne disease control such as malaria, quality of food etc. The estimated use of insecticide in India is 76% and globally is 44% [1]. For human health and environment, pesticides cause serious damages over time. Synthetic pesticides pose a potential risk to humans and other life forms and non-target organisms [2]. Through Fig. 1, we showed the bibliographic map analysis of the selected keyword, i.e., 'plant extracts and fruit flies' in the web of science database. A total of 191 studies reported in the previous 22 years, and all of them have been selected for bibliographic analysis. Among the total reported 1788 terms, the most relevant 102 terms have met the threshold with minimum occurrences of 5. Also, proximately 100% most relevant terms (i.e., 102) terms have been selected for analysis.
It has been found most of the studies are in relation to extract, petroleum ether, ethanol, ethyl, in laboratory on mango over time, lifespan, identification in either melon fly or peach fruit fly and Drosophila melanogaster. But a gap of studies has been observed for different compounds for investigations of insecticidal activity, resistance, mortality, fruit infestation in laboratory etc. (Fig. 2).
For pest control,the development of insecticides can be done from plants due to richness of bioactive compounds [3], [4]. Alkaloids, terpenoids, phenolics, and flavonoids are secondry compound of plants and can affect pest in various ways likewise act an attractant, repellent, antifeedants or effect life history of insect pest (increase or decrease development) [5], [6]. Plant extract and their bioactive compound have shown antifeadent, repellent, and ovicidal effect on pest [7]. Bactrocera dorsalis being an invasive pest has invaded in ~ 65 countries. 400 different species of genus Bactrocera are spread in Asia, China, Japan, Micronesia, Australia, and Hawaii, part of America, Oceania and continental Africa [8,9,10]. This fruit fly cause serious losses by direct feeding on guava and mango. It has emerged as a major threat to global agriculture and food security. According to distribution pattern [10], host range [11], rapid establishment of population [12,13] and economic loss, among 400 different Bactrocera species, B. dorsalis and B. cucurbitae are serious damaging pests. The losses incurred by B. dorsalis species are extremely large. In Japan, eradication from the Ryukyu Islands has cost more than 200 million euros [14]. Every year these species cause damage to various fruit and vegetables in India worth over 3000 million rupees, and in particular to major fruits, like mango, guava and citrus. Fruit flies caused direct loss of fruit production and indirectly losses of export market. Huge expenditure for maintaining fruit productivity and on eradication of this pest also causes great economic loss. These fruit flies cause direct loss in yield of crop as well as loss of export market. Costs of pest control and expenditures on fruit treatment maintenance also affect economy.In this paper we report toxic effect of four plant extract on the mortality and fecundity of Bactrocera dorsalis.

Plant Materials
Leaves of Ocimum tenuiflorum, Hibiscus, Mentha longifolia and Bougainvillea glabra plants were collected from Chandigarh University. Leaves of plants were cleaned with H 2 O and dried in shade and grind to powder with pestle morter. 10 gm powdered material of each plant soaked separately in the dark, in a solution of 10 ml water and 50 ml ethanol solvent. Solutions filtered after 24hr and kept in the refrigerator. Effect of plant extracts waschecked on the third larval stage of B. dorsalis to determine percentage mortality and effect on fecundity.

Mortality Test
Mortality rate of B. dorsalis third instar larvae tested with four plant extracts. With the help of a pipette 1 mL solution of each plant extract was mixed with inside a petri-plate (size = 6 cm). Twenty third instar larvae (1-2 days old) were put into each petri dish, and the same number was also confined to media treated with water and ethanol as an untreated check in replicates. The mortality of B.dorsalis was recorded at 1.0, 1.5,2.0, 2.5, 3.0, 3.5, 4.0, 4.5, and 5.0 hr after treatment. The mortality was checked and flies were considered dead when no leg or antennal movements were observed.

Statistical Analysis
The mortality (%) was corrected by Abbott's formula (Abbott 1925) and then subjected to probit analysis (Finny 1971) with time as the explanatory variable to derive the estimated hr for (LT 50 ) 50% mortality. We used VOSviewer for bibliographic analysis.

RESULTS AND DISCUSSION
In this paper we report the insecticidal activity of the four plant extracts used on B. dorsalis. Significant differences in larval mortality were shown for different plant extracts. Table 1  Mortality of B. dorslais was tested with four plant extract with different exposure times. Ocimum tenuiflorum attained its highest value of 56 .68% and at 4.57 hr able to prompt 50% mortality at 3.5 hr, whiles Hibiscus induced greater than 50% mortality after 1hr, and reached 72.88 % at 5 hr after treatment and Mentha longifolia cause more than 50% mortality after 1hr and 95.24 % at 5hr after treatment. Bougainvillea glabra bring out more than 50% mortality at 0.5 hr., and attained its maximum value of 100% at 2 hrs. These results are in accordance of Schleinet al. 2001 which show Bougainvillea glabra plant leaves have insecticidal activity in sand fly. Therefore, in this study we report the efficiency of the extracts of Bougainvillea glabra plant leaves on mortality of B. dorsalis. We found that the leaves of Bougainvillea glabra have the maximum toxic effect. It causes more than 50% mortality within half an hour and 100 % mortality within 2 hours. Results of this study clearly indicate that botanical extract have the potential to kill the pest. Various studies have examined the lethal concentration (LC) and lethal dose (LD) of these plant extracts for insect like rice weevil [15]; Spodoptera litura [16]; mosquito [17]; termites [18]; Callosobruchus maculatus [19] or other insects in mortality. But, there is paucity of data for mortality of B. dorsalis. B. dorsalis is a highly destructive pest and hence there is necessity to control this pest. LT 50 values for four plant extracts of B. dorsalis have been shown in Table  2

CONCLUSION
The results of the current study show that plants derivatives can be useful as pest control agents. The four plant extract used in this were moderately effective in reducing the number of B. dorsalis. Of the four test plant extract against larvae of B. dorsalis extract of Bougainvillea glabrawas found to be most effective followed by Mentha longifolia, Hibiscus and Ocimum tenuiflorum. Use of plant derivatives as an insecticide will prove beneficial for agricultural sector in poor countries as these plant derivatives are of low cost and eco-friendly.