Prospect of Managing Invasive Plants by Native Insect Herbivores: A Case Study of Kashmir Himalaya

Biological invasions are considered a massive threat to native biodiversity engulng both terrestrial and aquatic ecosystems worldwide while having cascading ecological and economic effects on the invaded regions. Kashmir Himalaya, an important constituent of the biodiversity hotspot, is heavily invaded by invasive alien plants. An inventory of species diversity of invasive plants and native insect herbivores was carried out in different terrestrial habitats of Kashmir Himalaya in the years 2018-19 and 2019-20. The results showed maximum value (3.39) of Shannon’s diversity index at district Kupwara with minimum value (2.967) at district Srinagar. Margalef Index attained maximum value (5.966) at district Bandipora and a minimum value (4.724) at district Srinagar. Our data revealed maximum value of evenness (0.732) in district Baramulla with minimum value (0.650) at district Pulwama. Similarly, district Baramulla of North Kashmir showed highest Simpson value (0.957) while district Srinagar with minimum value (0.934). Plantago major belonging to the family Plantaginaceae was found to be the most dominant invasive plant species followed by Taraxacum ocinale of family Asteraceae. Altica himensis was the most abundant native insect herbivore feeding on almost all invasive plant species with maximum damage on Rumex hastatus of Polygonaceae family. A total of 42 invasive plant species were recorded during the entire study period, of which 12 are worst invaders namely Plantago major, Taraxacum ocinale, Trifolium rapens, Trifolium pratense, Plantago lanceolata, Cyanodon dactylon, Anthemis cotula, Clinopodium umbrosum, Ranunculus arvensis, Veronica persica, Dactylis glomerata and Vulpia myuros. A total of 14 native insect herbivores species were identied on these invasive alien plants, of which the prospect of 06 insect herbivore species as potential biocontrol agents is promising. Among the collected insect herbivores, a few namely Chrysolina herbacea, Melanoplus differentialis, Pieris brassicae and Altica himensis are being reared on native and invasive plant species under laboratory conditions. Preliminary results of these native insect herbivors as potential biocontrol agents against invasive alien plants are encouraging. These novel, non-coevolved insect herbivores can not only be exploited to control the spread of invasive plants but could also thwart huge economic losses associated with the management of invasive plants worldwide. index, Simpson index, and Evenness for drawing logical conclusions. feeding Rumex like forests, grasslands, horticultural plants biological control be the competent method, where natural enemies are an important role to keep them in check in their early stages. The present study highlighted the diversity of native insect herbivore species feeding on different invasive plant species in Kashmir Himalaya with an overall 49 observatory sites selected which accounted for invasion process due to open landscape areas. Field visits were made to the selected sites in order to collect invasive plant species and native insect herbivores. A total 14 native insect pest species were collected that were feeding and causing damage to different


Introduction
Invasive species are newly introduced organisms that alter negatively the invaded habitats and bioregions. Due to globalization, the number of plant and animal species, translocated by humans and other animals, either deliberately or accidently, has drastically increased. [1][2][3][4][5] Biological invasions by aliens have been widely recognized as the second greatest threat to the global biodiversity, ecosystem structure and function. 1,3 Biological invasions have been shown to cause considerable changes in native species extinction likelihood, genetic composition of native populations, behaviour patterns, species richness and abundance, phylogenetic and taxonomic diversity, trophic networks, ecosystem productivity, nutrient cycling, hydrology, habitat structure, and various components of disturbance regimes. 6,7,8 In economic terms, the annual losses caused by Invasive Alien Species (IAS) in Australia, Brazil, India, South Africa, the United Kingdom and the United States have been calculated in the range of USD 300 billion per year. 9,10 In Europe alone, the economic costs of biological invasions are estimated to be at least EUR 12 billion per year. 11 An important role in understanding the invasiveness of introduced alien species is often attributed to their release from natural enemies. 12 Alien species, which generally leave their specialized enemies behind, often encounter less herbivory than native species and thus may ourish in the new environment 13 , this is known as the enemy release hypothesis 12,14,15 . Classical biological control provides an opportunity to partially reconstruct the natural enemy complex of an invading non-indigenous insect pest or weed 16 (Mills, 1994), and its application has been highly recommended to control established non-indigenous invasive insect pest or weed populations 17 (Wittenberg and Cock, 2001). Despite many proven bene ts 18 (Greathead, 1995), classical biological control has recently come under scrutiny because introduced natural enemies may adversely affect native species, including rare and endangered species 19,20,21,22,23,24,25 .
India has been one of the early adopters of Classical Biological Control (CBC) of insect pests and weeds alike. The rst exceptional success in CBC of a weed was achieved with an incorrect introduction of mealybug, Dactylopius ceylonicus (Green) from Brazil in 1795, that was introduced in place of Dactylopius coccus Costa, which dramatically brought down the population of the prickly pear cactus, Opuntia vulgaris Miller, within 5 to 6 years in central and north India 26 . The opuntia experience resulted in a series of introductions of phytophagous insects such as Ophiomyia lantanae (Froggatt) (ex-Mexico, via Hawaii in 1921) against lantana weed (Lantana camara L.) Procecidochares utilis Stone (ex-Mexico, via New Zealand in 1963) against crofton weed, Ageratina adenophora (Sprengel) and Pareuchaetes pseudoinsulata Rego Barros (ex-Trinidad in 1973) against Siam weed (Chromolaena odorata) 27 . In the post-independence era, CBC became more systematic and scienti c with speci c programmes managed by the erstwhile Indian Station of the The CBC nds an important place in the Perspective Plan ('Vision 2025') document of PDBC, Bangalore that aims at introducing the alien natural enemies of the alien organisms (which have become pests in the absence of natural checks in the new environment) in order to re-establish the balance between the pests and natural enemies. Although the results are checked and cross checked to avoid the damage to other species, many in the conservation biology community view this pest management technology as a high-risk enterprise because of the possibility of collateral damage to non-target species 23,25 . Moreover, little attention has been given to potential con icts between insect biological control and weed biological control using invertebrate agents. Potential negative impacts of weed in question and candidate entomophagous biological control agents on weed biological control agents have been rarely considered before initiating a biological control programme and not even de ned as a potential con ict of interest amongst practitioners and researchers of weed biological control. This is surprising as predation and parasitism were suspected as important factors in limiting the success of biological weed control agents 28, 29 .
India with about 10 per cent of the world fauna of insects is one of the 12 megadiversity nations in the world in terms of insect diversity. Our insect biodiversity is unique as evidenced by the high level of endemism. At the generic level, endemism is as high as 75% in Hymenoptera and 45% in Coleoptera and at the species level, it is 68% in Hymenoptera and 46% in Hemiptera 30 . As a novel resource the invasive plants can affect the performance of native insect herbivores and their natural enemies such as parasitoids and predators, and this can lead to host shifts of these herbivores and natural enemies 31 . Thus, on one hand the resident insect herbivores can provide the rst line of defense against the invasive species, on the other hand the invasive plants can in uence the spatial and temporal dynamics of native insect (meta) populations and communities, ultimately leading to changes at the landscape level; however, the impact of invasive plants on the population dynamics of resident insect species has been rarely examined. Thus, the need of the hour is to identify the local native insect herbivores which can be augmented to act as a rst line of defense against alien invasive plant species, and alternatively evaluate the impact of these alien invasive species on identi ed native potential biocontrol agents. Kashmir Himalaya is a part of the Himalayan biodiversity hotspot that is heavily invaded by alien plant species. Despite harmful impacts of these invasive species on native biodiversity, economic and ecological systems of the region, a holistic eld-based intensive sampling study for management of invasive species is lacking, which merits urgent research attention, because the resultant research knowledge base will guide better management. An assessment of the invasive plant species and native insect herbivore diversity of the North, Central and South Kashmir regions of Kashmir Himalaya was carried out during the years 2018-19 and 2019-20. The current study provides an inventory of the diversity of invasive plant species as well as native insect herbivores feeding on them and their relative abundance with special reference to species richness and evenness in forty-ve sites of nine districts of Kashmir Himalaya.

a) Field Surveys and Sampling
Surveys were conducted in different terrestrial habitats like forests, grasslands, horticultural and agricultural elds of Kashmir valley during years 2018-19 and 2019-20. Insect herbivores were collected from native and invasive plant species. The sampling was done from leaves, in orescence, seeds and stem of native and invasive plants by collecting infested plant parts. The study sites comprised of invasion prone landscapes is shown in Table 1. Specimens collected during the whole study do not include any threatened species and hence it does not affect the survival of any threatened or vulnerable species as listed in IUCN Red list of threatened species. Further, the permission for sampling of plant and insect herbivores was granted by DST-SERB, Government of India, New Delhi vide le no. EMR/2017/000215, dated 28th September, 2018 for a period of three years from 11th October 2018 to 10th October 2021.  32 . Each invasive plant species is provided with its scienti c name, family and voucher specimen number with voucher numbers ranging from 3755-KASH to 3796-KASH (Table 2) while the plant specimens were deposited in internationally recognized Kashmir University Herbarium (KASH). All legal procedures and regulations were adopted during the whole study as per recommendations of IUCN. Anantnag (17), district Pulwama, (15) and district Srinagar (12) (Fig. 1A) while maximum native insect herbivore species feeding on these invasive plant species were also reported from district Kupwara (15) and district Baramulla (15), followed by district Bandipora (14), district Budgam (12), district Kulgam (11), district Pulwama (10), district Ganderbal (10), district Anantnag (10), and district Srinagar (08) (Fig. 1G). In district Kupwara, 05 sites visited, and data collected suggested Plantago major (92) as the most abundant invasive plant species, followed by Trifolium rapens (91), Taraxacum o cinale (78), and Plantago lanceolata (55) while the most abundant herbivores found were Altica himensis (170) followed by Chrysolina herbaceae (112), Agrotis nigrisigna (103) and Nezara viridula (102). In district Baramulla, 05 sites were visited which revealed Ranunculus arvensis (70) as strong invasive species followed by Dactylis glomerata (61), Plantago major (60) and Clinopodium umbrosum (59). The dominant native insect herbivore in district Baramulla was Altica himensis (144) followed by Agrotis nigrisigna (98) and Chrysolina herbacea (87). In case of district Bandipora of the Northern region, 06 sites were selected for the data collection, where Plantago major (88) was the most abundant invasive plant species followed by Cyanodon dactylon (45) Plantago lanceolata (40) and Taraxacum o cinale (39) while potential insect herbivores were Altica himensis (120) and Plagiodera sp., (97).
From Southern region, a total of 03 districts were selected namely Anantnag, Kulgam and Pulwama with 05, 05 and 06 study sites, respectively (Table 1). In Anantnag district, the data from the select 05 sites revealed that Plantago major (59) is the most abundant invasive plant species followed by Taraxacum o cinale (56), Trifolium pratense (48) and Trifolium rapens (48), while potential insect herbivores reported were Nezara viridula (83) followed by Altica himensis (67), Agrotis nigrisigna (64), Chrysolina herbacea (59) and Formica spp. (34). In district Kulgam, a total of 24 invasive plant species were reported from all 05 select sites and the native herbivore species feeding on them were 12 species. Out of all 24 plant species, Taraxacum o cinale (60) was the most abundant insect species followed by Trifolium pratense (56), Trifolium rapens (52), Anthemis cotula (40) and Plantago major (40). From all 12 native insect herbivores species feeding on these invasive plant species, 02 insect species Chrysolina herbacea (78) and Altica himensis (73) were found to be potential herbivores attacking primarily Plantago major (40) Tables 3 and 4. On comparing the data of invasive plant species in various districts of Southern, Central and Northern regions of Kashmir Himalaya, the total number of invasive plant species was highest in district Kupwara (1017) followed by Baramulla (891) and Bandipora (718) (Fig. 1B). Total number of individuals of native insect herbivores feeding on invasive plants was highest in number in district Kupwara (770) followed by district Baramulla (616) and district Bandipora (615) of Kashmir Himalaya as shown in Table 4 and Fig. 1H. Simpson's diversity index was highest at district Kupwara (0.955), while least at district Srinagar (0.893) which signi ed that Kupwara had high dominance of invasive plant species (Fig. 1C). Similarly, Simpson ' s index for native insect herbivores was highest at district Bandipora (0.885) and Kupwara (0.879) followed by Baramulla (0.868) and Kulgam (0.859) while it was minimum at Srinagar (0.803) (Fig. 1I). Shannon-Weiner index (H) was highest in the district Kupwara indicating that these districts have maximum diversity of invasive plant species (Fig. 1D). On the other when the same index was applied to native insect herbivores feeding on these invasive plants, data depicted the highest value of H was at districts Bandipora (2.395) and Kupwara (2.358) and least at district Srinagar (1.764), revealing that the Bandipora and Kupwara districts have high diversity of native insects while district Srinagar had least diversity (Fig. 1J). Species evenness for invasive plant species depicted the highest value of 0.880 at district Pulwama and lowest of 0.709 at district Kupwara which illustrated that invasive plant species were more evenly distributed at district Pulwama (Fig. 1E) while in case of native insect herbivores, maximum value of 0.737 was observed at Anantnag and minimum 0.603 at district Baramulla ( Fig. 1K). Margalef s diversity index (MI) had its peak value at district Kupwara (5.776) and lower most at district Srinagar (1.882) which in other words means that Kupwara shows maximum distribution pattern and richness of invasive plant species while it was minimum in district Srinagar (Fig. 1F). Following results were obtained on applying same index on native insect herbivores feeding on these invasive plants with a peak value of 2.335 at district Baramulla and only 1.334 at district Srinagar (Fig. 1L).
The Relative Abundance of all the invasive plant species and insect herbivore species at nine locations was also worked out by dividing the number of individuals of a species to the total number of individuals of all species and expressed as percentage (Figs. 2 and 3). Perusal of data revealed that Plantago major (9.372%) was the most dominant invasive plant species and highly ourished in Northern regions than Central and Southern regions. It was followed by Taraxacum o cinale (8.557%), Trifolium rapens (8.185%), Trifolium pratense (7.104%) and Plantago lanceolata (6.821%). On the other hand, Altica himensis were the most dominant native insect herbivores feeding on these invasive plants with a total percentage of 17.640% followed by Chrysolina herbacea (16.809%), Nezara viridula (15.456%) Agrotis nigrisigna (14.221%) and Plagiodera spp. (9.425%).

Discussion
Diversity enables us to understand the relationship between the habitat and ecosystem 33  more crucial for the Indian economy and is at a higher risk 39, . Keeping these above facts under consideration, a promising management strategy should be available to reduce their indiscriminate spreading and loss to our native diversity. One of the promising management strategies is biological control, where native natural insect species feed on these invasive plant species are seen and is being considered as a safe and cost effective, alternative strategy against many alien plant species. The introduction of coevolved natural enemies from an alien species home range (classical biological control) has been one of the key methods for suppressing invasive species 40,41,42 . However, host speci city tests of natural enemies are required worldwide before release; as insects introduced for biocontrol of invasive plants may negatively affect native plants due to potential host shifts and/or host range expansion 23,43,44,42 . These deliberate introductions of alien insects may subsequently lead to direct or indirect cascading effects on native food webs and ecosystems 45,46  The analysis of manipulative eld studies revealed that native herbivores suppressed alien plants, whereas alien herbivores facilitated both the abundance and species richness of alien plants 53 . Both outcomes suggest that plants are especially susceptible to novel, generalist herbivores that they have not been selected to resist. Thus, native herbivores provide biotic resistance to plant invasions, but the widespread replacement of native with alien herbivores (in biocontrol programmes) eliminates this ecosystem service, facilitates plant invasions, and triggers an invasional ''meltdown'' 54 . Therefore, the need of the hour is to exploit the potential of native herbivores, which are evolutionarily novel enemies that alien invaders may not be adapted to deter, in order to limit the establishment or spread the invasive alien species. Alternatively, as a novel resource the invasive plants can affect the performance of native insect herbivores and their natural enemies such as parasitoids and predators, and this can lead to host shifts of these herbivores and natural enemies 31 . Thus, on one hand the resident insect herbivores can provide the rst line of defense against the invasive species, on the other hand the invasive plants can in uence the spatial and temporal dynamics of native insect (meta) populations and communities, ultimately leading to changes at the landscape level. Preliminary results of these native insect herbivores as potential biocontrol agents against invasive alien plants are encouraging notwithstanding, more eld studies are underway to gather comprehensive information of invasive plants species and native insect herbivores. Here in Kashmir Himalayan, no any invasive species were deliberately introduced for any speci c purpose. The reason behind there invasion may be due to global trade, tourism and hitchhike mechanisms. In addition to the alien invasive from across political borders, invasion of pests can also occur from one geographic location to another within the same country.

Conclusion
Globalization has increased import and export of almost all products including agricultural and horticultural products and has increased the movement of propagating material and seeds that has elevated the risk of invasive species entering India 55 . Once these invasive plants became established in new natural or semi natural ecosystems, these threaten the native biodiversity and may lead to huge economic losses. These invasive species are considered as a major driver of biodiversity loss worldwide due to their fast growth, early maturity, ability to go without food and water for a longer time, e cient means of spread and high reproduction. Native insect pests have caused signi cant damage to almost all visited elds like forests, grasslands, horticultural and agricultural elds of Kashmir Himalaya during years 2018-19 and 2019-20. In order to overcome from these ourished invasive plants biological control seems to be the competent method, where natural enemies are playing an important role to keep them in check in their early stages. The present study highlighted the diversity of native insect herbivore species feeding on different invasive plant species in Kashmir Himalaya with an overall 49 observatory sites selected which accounted for invasion process due to open landscape areas. Field visits were made to the selected sites in order to collect invasive plant species and native insect herbivores. A total 14 native insect pest species were collected that were feeding and causing damage to different parts of invasive plants particularly to foliage. Preliminary results of these native insect herbivores as potential biocontrol agents against invasive alien plants are encouraging. These novel, non-coevolved insect herbivores can not only be exploited to control the spread of invasive plants but could also thwart huge economic losses have associated with the management of invasive   Field observations of native insect herbivores feeding on invasive plant species in various selected sites. A. Altica himensis feeding on Urtica dioica; B. Larvae of Aglais cashmeriensis feeding on Urtica dioica; C. Damage on Rumex hastatus by Altica himensis; D.Spittle bug on Cannabis sativa; E. Altica himensis feeding on Rumex hastatus; F. Chrysolina herbaceae on Mentha longifolia; G. manual insect collection; H. Chrysolina herbacia feeding on Mentha longifolia; I. Altica himensis feeding on Rumex hastatus; J .Infestation in Vitis ora by Altica himensis; K. Euphorbia owers with visiting pollinators; L.Mating process of Chrysolina herbacia on Mentha longifolia.