Biological invasions by exotic species are of major concern to the native ecosystems, biodiversity, and livelihood security. These frequent invasions are causing nearly 25% of economic loss globally. Being an agrarian economy, India constantly realizes the havoc of invasive pests, particularly insect menace. So far, more than 110 exotic insect species have been reported from India (Mandal 2011). Among these insects, exotic whitefly, Aleurodicus rugioperculatus Martin (Hemiptera: Aleyrodidae), commonly known as the rugose spiraling whitefly (RSW), is one of the worst species causing frequent losses in agriculture, horticulture, and forestry (Naveena et al. 2020). Although the species origin occurred from Belize, South America (Martin 2004), it was first reported on coconut plantations of the Pollachi area of Tamilnadu, India in 2016 (Sundararaj and Selvaraj 2017). Further, it spread to many parts of the country, wrecking direct and indirect damages (Sumalatha et al. 2020). The polyphagous species has a shorter life cycle of 37-48 days (Pradhan et al. 2020), exhibiting phenotypic plasticity and high competitiveness with other native species. Data on Climate Match Index (CMI, 0.62-0.73) predicted through CLIMEX based modeling by Chakravarthy et al. (2017) revealed that the eastern region of India, Odisha, Andhra Pradesh, West Bengal, in particular, is the potential area for the incursion of the RSW. In general, the degree of climate similarity is considered the factor governing the spread and establishment of the pest, i.e., a higher CMI value coupled with the higher chance of settlement of RSW in that particular locality. This pest wreaks severe havoc and worries over 5000 coconut farmers in Cuttack, Odisha, in 2020. (https://www.newindianexpress.com/states/odisha/2020/nov/09/whitefly-pesttakes-a-toll-on-coconut-trees-in-odisha-2221319.html). Later, it affected the Acacia auriculiformis plantation in India drastically (Sundararaj et al. 2021). Although in global scenario, many continents were reported the invasion and diverse host menace of RSW, reports on the occurrence of RSW on various host ranges in east coastal region of India are unavailable. Therefore, the present studies aimed to document and assess the expansion of host range, nature, and intensity of damage caused with the economic impacts of this cryptic invasive species in coastal tract of India particularly Odisha. This study could provide awareness to various stakeholders and help to develop a sustainable management strategy for the upcoming time.
A continuous and systematic roving survey was conducted during January-May 2021 in Bhubaneswar (20°24’05.13’’ N and 85°78’17.62’’ E at 62.37 meter above mean sea level) and its surrounding areas. Fruit orchards, coconut plantations, vegetable cultivated areas, ornamental and avenue areas, and wild germplasm resources were focused for the survey. The infested host plants were collected along with whitefly adults and preserved with 70% ethanol. The host plants were identified by observing visual images contained during the study with the help of the taxonomists. The nature and extent of damage were examined critically on each host plant species. The intensity of damage was assessed on randomly selected five leaves (leaflets) per plant. An assessment of their population level (intensity) was carried out following the scale described by Sundararaj (2021). (i.e., Low: less than ten live egg spirals or adults/leaflet; moderate: 11-20 live egg spirals or adults/leaflet; severe-more than 20 live egg spirals or adults/leaflet). In addition, the dissimilarity index was estimated using XLSTAT statistical software (XLSTAT Premium 2020.2.1, Adinsoft, NY)
The RSW was identified based on the descriptions given by Martin (2004) and Stocks and Hodges (2012). It could be easily identified under field conditions by its larger size (compared to commonly found species in the real world), the spiral pattern of occurrence, and sluggish nature. In general, RSW mostly noticed on the abaxial surface of the leaf with white flocculent matter dispersed in a spiraling pattern. Close observation under microscope 10X (Olympus CX21i, India) depicted brown patches on the forewings. A pair of sword-like pincer structures was noticed at the tip of the abdomen in male species. The investigation revealed the whole body of the adult was white and appeared like a tiny moth. The study also explored that nymphs were oval with waxy material all over the body, whereas the pseudopuparium is considered the final nymphal stage. The RSW was found to feed twenty-seven plant species, including economically important cultivated plants and palms in the covered study area. Its infestation was found on Mangifera indica L., Anacardiun occidentale L., Annona squamosa L., Psidium guajava L., Syzygium aqueum Alston, Syzygium jambos L. Alston, Syzygium cumini L. Skeels, Averroha carambola L., Cocos nucifera L., Areca catechu L., Roystonea regia, Acacia auriculiformis, Solanum torvum Swartz, Amaranthus tricolor, Polyalthia longifolia , Zea mays L., Trichosanthes dioica Roxb., Musa sp., Aegle marmelos L.Correa, Ficus religiosa, Hylocereus undatus, Ficus benghalensis, Carica papaya L., Zizyphus mauritiana Lam., Artocarpus heterophyllus Lam., Codiaeum variegatum L., and Manilkara hexandra (Roxb) Dubard (Fig 1). The natural infestations on various host plants are in accordance with the earlier reports (Stocks and Hodges 2012; Selvaraj et al. 2016; 2017; Anonymous 2017). The present study explored the expansion of its host plant (Table 1). Our study found two new host crops i.e. Amaranthus tricolor L. and Solanum torvum Swartz invaded by RSW, that reported firstly to the scientific society. The present findings agree with the observations of Sundararaj et al. 2021. Hierarchical clustering was performed based on RSW incidence on different host plants. The 27 host plants were grouped into two clusters (20 host plants in cluster I and 7 host plants in cluster II). In cluster II, four host plants i.e. coconut, banana, guava, and jamun showed severe levels, and three host plants i.e. areca nut, custard apple, and royal palm exhibited moderate to severe levels of infestation (Fig 2). The present study revealed the variation in infestation level on twenty-seven host plants. Further its incidence on multi-flora is surmised due to favorable weather factors and availability of host plants.
Both nymphs and adults were usually found crowded on the abaxial surface of leaflets causing direct damage by driving phloem sap. Indirectly, larger excrement of honeydew facilitates the growth of black fungus, Capnodium sp. (sooty mold), which affects normal photosynthesis and disrupts leaf configuration. Further, it caused leaf drooping and wilting. Moreover, in jamun and wax apple (Fig 1b), leaf litter was also covered with a heavy infestation of the sooty mold with white mealy matters along with RSW infestation. The infestation was also not exempted from reproductive parts i.e., mango, guava, wild brinjal, etc (Fig. g-i). The initial feeding and colonization of RSW were observed on amaranthus, wild brinjal, ashoka, custard apple, ber, and other ornamental plants. Still it found that the insect failed to feed continuously and establish successfully in those plants. As RSW is a highly polyphagous pest on more than a hundred hosts (Stocks and Hodges 2012), frequent monitoring is essentially required from further havoc.
RSW poses a serious challenge to the agricultural sector and economy as the biologist and public witnessing and recognizing the damage caused. Despite the severe ecological damage and economic loss caused by the RSW, the factors contributing to its success remain elusive. Further, the ongoing dispersal and establishment of RSW are some of the most remarkable biological outcomes of climatic variability (Gao and Reitz 2017). In addition to that, the prediction report revealed an increase in the number of invasive species like RSW increase number for India (Bellard et al. 2013) and particularly eastern Part of the country, including Odisha (Chakravarthy et al. 2017) and across the world indeed. Interestingly the current study reveals that although the climate of east coast of India is favorable for many major and minor fruit crops, the host preference of RSW towards coconut, banana, jamun, and guava is more (Fig 2). Our study claims that its establishment on these hosts plants and spreading in this region is highly conducive.
Prevention, early detection, and eradication are the key to mitigating RSW as an invasive pest (Wittenberg and Cock 2001). Under severe infestation, it was recommended to apply neem oil at 1% concentration as foliar spray and starch solution at 2% was also suggested to manage sooty mold on the leaf surface. So, far no chemical pesticides have been recommended against RSW as none of the insecticides have been label claimed, specifically for this. Further, it is advised to install yellow sticky traps for effective trapping of the adult flies. As natural enemies are imperative for any invasive pest, effort is put forth upon various conservation and augmentation strategies and advocated to farmers through awareness programs.
The invasive RSW is indeed an alarming threat and is now well established on twenty-seven species of host plants in east coast region of India. Although intensity level varies from low to severe in the focused area, regular monitoring is necessary to check its further spread and timely management. A holistic approach is the need to adopt rapid response strategies against its invasion, which could be possible by educating farmers and creating awareness among various stakeholders and field entomologists.