Plant Secondary Metabolites — A Necessary Resource for Both Man and Papilionid Butterflies Across West Bengal, India

: Chemical factors or plant secondary metabolites (PSM) contributes towards larval host plant choice among butterflies. Significantly, such PSM are the basis of ethnomedicinal plants as recognised by traditional healers since time immemorial. A total of 27 papilionid butterflies utilizing 26 species of medicinal plants as their ovipositing substrate were observed. Graphium cloanthus, G, sarpedon, G, eurypylus (PI values: 3.873) were polyphagous species. On the contrary, G. antiphates, G. nomius, Atrophaneura polyeuctes, A. aidenous, Troides helena , (PI: 1.000) were strictly monophagous. The medicinal utilization values (U v ) of such plant species was recognised. Aristolochia indica (U v =0.474) and Citrus medica (U v =0.44) appeared to be the most popular medicinal plant among the proponents of ethnomedicine.


Introduction:
Indigenous knowledge is known to generate an inexhaustible information database for its exponents. Such has been the contribution of medicinal plants towards the well being of its practitioners since centuries. The popularity associated with such plants have been mentioned even in Charaka Samhita, Susruta Samhita, Rig-Veda, Astanga Hridaya, Ramayana and Mahabharata [1,2]. WHO has reported the utilization of traditional medicines amongst 80% populace from developing nations [3]. Plant secondary metabolites (PSM) or more specifically alkaloids, terpenoids, flavonoids, glycosides, coumarins, saponins and tannins constitutes the basis of such formulations as used by folklore therapists. Their immense popularity thereby creates an urgent demand for the conservation and judicious utilization of these plant resources.
Interestingly, butterflies have developed an innate skill to recognise and utilize such plants as reliable ovipositing substrate. Several species have devised strategies to overcome the defensive substances (PSM) characteristics of plant taxa [4][5][6]. Although being totally dependant on floral resources as adult, the demand for tender foliage in their larval stage cannot be overlooked. Butterflies thus exhibit a "botanical instinct" in selecting the most perfect host plant suitable for egg deposition [7]. As larvae butterflies are known to exhibit host plant specificity by being monophagous, polyphagous or oligophagous. Significantly such chemical constituents (PSM) are critically important in establishing an intrinsic butterfly-host plant relationship.
Thus the present study would attempt to explain the significance of PSM in the life of butterflies as well as an essential element of ethnomedicine. The determination of medicinal utilization value (Uvs) for each studied plant species would also be helpful in deciphering their extent of therapeutic benefits. Additionally the degree of polyphagy would be investigated with an attempt to generate an idea of larval food plant specificity of butterflies.

Study Design
The entire study was conducted between June 2019 to May 2020 across tribal dominated districts of West Bengal (East and West Midnapore, Darjeeling, Jalpaiguri, Purulia and Bankura), India. The initial phase of study involved documentation of papilionid butterflies utilizing medicinal plants as their larval resource. Several instances of larvae feeding on plants belonging to one or more plant order or family or genera or species were observed for determining their monophagous / polyphagous nature.
Identification of butterfly larval host plants up to species was conducted from specially designed quadrats laid for such purpose. On field identification of plants was done based on earlier reports in most instances along with direct observation of larvae during such survey. Such observations were later confirmed from published literature [8][9][10]. Additionally plant species were also identified from previous publications [11][12][13][14][15][16][17].
In the final phase of investigation, detailed ethno-medicinal survey was undertaken to emphasise the therapeutic benefits of such plants. This involved an informal dialogue designed to gather information from knowledgeable and experienced populace including ojhas, kabiraaj and vaidyas. Such people were initially interviewed based on specially designed questions prepared for such purpose, followed by group discussion and informal meeting whenever required. Information thus obtained were documented in datasheet without any modification.

Data Analysis:
Polyphagy as evident among butterfly species was determined using polyphagy index (PI) where PI= (A×B) ½ ; where A= number of genera of host plants, and B=taxonomic diversity of the hosts (1=one plant species; 2=one plant genus; 3=one plant family; 4= one plant order; 5= two or more plant orders) [18].
Estimation of medicinal values (Uvs) of each species "s" was done based on the following: [19][20]. The formulae used was Uvs=Us/ns where Us in the number of medicinal uses of the species "s" as mentioned by informant and ns was the number of informants who provided the information.

Results:
A total of 27 papilionid species utilizing 26 species of medicinal botanicals as their larval food resource was identified across districts of West Bengal, India. Five plant families i.e. Rutaceae (38.46%), Lauraceae (19.23%), Magnoliaceae and Annonaceae (15.38%) and Aristolochiaceae (11.54%) were reported as larval food resource of butterflies (Table  1). Effective against cholera, fever, bowel problems, ulcers, leprosy, and skin diseases. Also being employed as an abortifacient and antineoplastic 0.47

Discussion:
Investigation on papilioninae has been conducted with the aim to explore the wide repertoire of medicinal botanicals satisfying their larval food resource requirements. Such strategies designed to effectively utilize these plants thereby enlightens the significance of these plants in life of butterflies. Additionally phytochemical and pharmacological properties of such plants have dominated most of the primary treatment imparted in healthcare system, Significantly, Rutaceae, Lauraceae, Annonaceae, Magnoliaceae and Aristolochiaceae known for their secondary metabolites constituents are beneficial not only for papilioninae but also for the folklore therapists.
Greater utilization values (Uv) of A. indica and C. medica in this study highlighted their probable benefits for the proponents of traditional medicine. Alkaloids, widely recognised for their immense therapeutic benefits viz. antitumor, anti-inflammatory, antimalarial and antiviral contribute towards several modern day drug formulation [52][53][54]. Equally beneficial and enormously popular, plant terpenoids are considered to be a proven remedy against fever, bronchitis, asthma, microbial, cancer, fungal and viral infection [55,37,56,22,29].
Episodes of G. cloanthus, G. sarpedon, G. eurupylus, G. doson and G agamemnon feeding from more than one plant family describing their polyphagous nature is probably aimed at utilizing a wide spectrum of secondary metabolites Papilio demoleus and P.polytes feeding on multiple species of rutaceous plants also denote their polyphagous nature Thus polyphagous species are known to employ a wide repertoire of phytochemicals probably as stimulus for oviposition. In contrast strict monophagy as evident among G.antiphates, G. nomius, A. polyeuctus, A. aidoneus, T. helenus signified their restricted feeding preference. Interestingly, such single family association among papilioninae viz.papilionii with Rutaceae and troidini with Aristolochiaceae are noteworthy [57][58].

Conclusion:
Ethnobotany serves as a tool for preparation of several novel herbal formulations by utilization of the indigenous knowledge of ethnic people. Custom associated with the use of wild population of medicinal plants has lead to the creation of enormous pressure leading to uncontrolled exploitation of forest resource for commercial purposes. Significantly such mismanagement of floral resources could negatively effect the larval population of butterflies dependant on those specific medicinal plants. Thereby proper conservation and management of medicinal plants becomes an important issue in the present scenario. Thus the present study could provide a platform for designing of futuristic policies regarding natural resource management keeping in mind the demand of traditional practitioners. Additionally such a system should also ensure the availability of larval food resource of butterflies in turn ensuring their survival.