Ecology of Tree-Holes and Diversity of Insect Larvae in Tree-Hole Water in Mayiladuthurai Taluk

INTRODUCTION

Tree holes are especially appropriate habitats for comparative studies of population interactions [1]. Their range extends from the subarctic to the equator; they are ubiquitous in and harbor insects at all latitudes where hardwood trees occur, even in the Mojave Desert [2]. Over this range, these habitats exhibit tremendous variation in the surrounding climatic conditions, species composition, and community complexity. Tree holes or cavities filled with rainwater act as ephemeral pools called dendrothelms, and are used for breeding and hiding during daytime [1].  The ephemeral water bodies that are associated with living plants are inhabited by a high diversity of organisms, from bacteria to invertebrates and they occur worldwide [3]. A variety of macroinvertebrates use the tree holes as breeding sites and many species breed exclusively in this habitat [4].

Tree holes are formed by intrinsic growth patterns of the tree or extrinsic agencies such as wind breakage, forest fires, and cavity excavation by organisms such as woodpeckers or insects [5].  Using the direct method or stem flow method, rainwater fills the tree holes.Nutrients are transferred into the tree holes from foliage and bark through this process, and thus, the species of the tree and the dry atmospheric depositions on the bark are what the chemical content of the water depends on [6]. Rot-holes and pans occur with varying frequency, in water-filled tree holes. Water is in contact with the wood in rot-holes, in which holes are found in stems, branch breaks, and stumps. The hole is lined with bark in pans, which are made by stem and branch forks as well as between buttress roots. In a lot of tres, both types of water-filled tree holes can be found, but their frequencies have differences, between different species of the trees [7]. This habitat is the primary breeding site for many disease-causing vectors, especially mosquitoes and biting midges.Tree-hole contains water and organic detritus of leaf, wood, and animal origin. After a long literature review, the present investigation was designed and carried out the insect fauna in tree holes in various trees with associated physicochemical factors.

MATERIALS AND METHODS

The study was carried out in Sembarnarkoil (11º 06' N, latitude 79º 44' E longitude) region, Tharagambadi Taluk, Mayiladuthurai District, Tamil Nadu. The study area is a densely populated semi-urban, which predominantly has agricultural lands with paddy (Oryza sativa) as the major crop. Apart from the crops cultivated in this area, the tree covers are also highly distributed ie., Azadirachta indica, Moringa olifera, Samanea saman, Tamarindus indica, Tectona grandis, Pongamia glabra, Ficus religiosa, Madhuca longifolia, Mangifera indica, Polyalthia longifolia, etc.,According to the rainfall the study area are classified into four seasons viz., monsoon (October-December), post-monsoon (January-March), summer (April-June) and pre-monsoon (July-September). The present study was carried out between the seasons of monsoon to post-monsoon. Chosen various places to study tree hole properties and insect fauna distribution ie., Thiruchampalli, Kalagasthenathapuram, Vallum, and Parasalur.

Tree-holes were sampled from October 2019 to March 2020. Location of tree hole and type of tree hole were observed by direct vision. Tree hole length, width, depth, water level, and height from the ground-using scale in centimeter. Leaf litter will be preserved and its dry weight will be obtained after drying. Tree holes were studied by removing their contents by hand-collection up to hole depth (depending on hole morphology) [8]. Insect fauna was collected within a week after the rainfall and collected insects preserved in ethanol (70%), After bringing laboratory the insects were counted and identified with the help of Photomicroscopy (LABOMED STC- ML 100X10X) [8].

The following physicochemical parameters were assessed by using appropriate methodologies [9] such as temperature (probe thermometer), pH (Digital pH Meter), Nitrate, Ammonium, Alkalinity, Salinity, Total hardness, Nitrite, Iron, and Calcium.  The statistical analyses are diversity indices and ANOVA proved the significance of the study and it was done by using IBM SPSS version 25. 

RESULTS AND DISCUSSION

Totally 40 tree holes were surveyed which belong to eight species of trees. Namely, Azadirachta indica (6), Moringa olifera (9), Samanea saman (8), Tamarinudus indica (4), Tectona grandis (5), Pongamia glabra (4), Ficus religiosa (3)and Madhuca longifolia (1).  Among the eight species of trees, the Moringa olifera has the highest number of tree holes followed by Samanea saman and so on.  Manduca longifolia has the least number of tree holes. The tree height was measured and noted that the Tectona grandis was high (21m) and the least height was Ficus religiosa (7m). Two types of shapes were noted from the sampling trees ie., rod (48%) and pan (52%). Morphometric measurements of tree holes were assessed. The largest opening size, depth, height from the ground, water level, and litters of the tree holes were observed in Ficus religiosa and least observed in Samanea saman (Table 1).

Table 1. Morphometric measurements (Mean±SD) of trees holes surveyed during the study period (n=40)

The physicochemical factors of tree hole waters were analyzed.  The temperature was high in the Tectona grandis and least in Manduca longifolia.  The pH was high in Manduca longifolia and least recorded in Azadirachta indica. Ammonia level was high Pongamia glabra and least was in Ficus religiosa. Salinity was high in Azadirachta indica and least recorded in the Tectona grandis. As well as three species showed an absence of salinity (Ficus religiosa, Madhuca longifolia, and Tamarindus indica). Hardness and alkalinity were high in Samanea saman and the least was in Ficus religiosa. Few species of trees only have nitrate and iron.  Nitrite level was assessed and it’s showed absence in all the tree hole water. Calcium level was high in Azadirachta indica and lease was recorded in Madhuca longifolia (Table 2).

Table 2. Physico-chemical properties of tree hole water (Mean±SD) (n=40)

Six speciesof larvae were recorded from the tree hole water analysis belonging to five insects and one annelid.  Namely, Culex quinquefasciatus, Ades aegypti, Scirtidae sp, Chaboridae sp, Armadillidae sp, and Euborellia annulipes from the phylum of Arthropoda (Figure 1) and Naididae sp from the Annelida.  Among the six species of larvae, Culex quinquefasciatus has a large number of individuals followed by Ades aegypti and so on. The very least number of individuals was recorded in Euborellia annulipes. The diversity indices also calculated among the various tree species hole water, that shows species richness of fauna was high Azadirachta indica and Pongamia glabra and least in Madhuca longifolia.  The abundance and dominance index of fauna was high in Samanea saman followed by Tamarinudus India, Madhuca longifolia, Ficus religiosa, and so on. The Simpson diversity and Shannon H’ index were high in Azadirachta indica followed by Tectona grandis and so on (Table 3). The evenness index was high in Madhuca longifolia and the least was in Samanea saman (Table 3).

Table 3. Diversity indices of Insect fauna recorded from tree hole water (n=40)

AT- Azadirachta indica; FR- Ficus religiosa; ML- Madhuca longifolia; MO- Moringa olifera; PG- Pongamia glabra; SS- Samanea saman; TI- Tamarinudus indica; TG- Tectona grandis

Table 4. Analysis of Variance of variables studied during the study period in tree hole water (n=40)