Pitfall Traps: A Novel Method to Study Approaching Time of Ant Species

INTRODUCTION

Ants are vital components of the ecosystem not only because they constitute a great proportion of animal biomass but also because they are ecosystem engineers [1]. They are further significant in modifying the physical and chemical environment and can cause collision among plants, microorganisms, and other soil fauna [2]. Ants achieve a variety of roles, such as herbivores, predators, scavengers, seed dispersers, plant and arthropod mutualists, and soil engineers [3] and good indicators of the ecological condition [3, 4] for many reasons, such as they are diverse group, sensitive to environmental change, easily collected and assist in important ecological functions [5].

Ant fauna is social organisms which are having more sense to predict and approach prey items as well as pitfall traps. Usually, people scold the various ants for the sense of prediction of sugar or any other food items in our domicile. The sensation competence may be varied among the ant species. Pitfall trapping is the most common method for the collection of foraging arthropods, including ants, in areas of natural sciences [6]. It is less expensive and less laborious and is self-operating, sampling around the clock. It can better estimate the ant species richness and assemblage structure [7, 8], particularly in open habitats [9]. Pitfall traps are very efficient for the collection of ground-dwelling ants, particularly in low-leaf litter areas [10-12]. 

However, technical features of pitfalls should also be taken into account for maximizing capture competence, such as the diameter and depth of the collecting container, the liquid content [6, 13], the use of a cover (6) and bait [14], and trap design [6, 13]. Ant captures may be further biased depending on the ants' locomotion, activity, and avoidance of traps [15]. A bias in pitfall-trap catches due to their installation has also been reported [16], known as the digging-in effect [17].

Pitfall sampling is efficient for the estimation of the relative abundance of foraging ant species [18] as it captures both individuals and species in large numbers, hence making statistical analysis possible [19]. Few studies revealed various aspects of pitfall trap sampling for the collection of ant fauna. Pekar [20] has revealed the differential concentration of preservatives and detergents on the catching efficiency of active surface arthropods by pitfall traps. Cheli and Corley [13] tested four designs of traps, six types of preservatives, and different times of activation, as well as the number of traps for identifying the best pitfall, traps for surface or ground-dwelling arthropods.   Lasmar et al. [21] have evaluated the effect of pitfall trap installation on ant sampling. Taken together, understanding the foraging behaviors and food preferences of ants is crucial in pest management because it helps to locate nest sites, provide cues for effective bait preparation, and determine an ideal time to manage the ants [22, 23]. 

Species vastly differ in their Cuticular Hydrocarbon composition, but also within species, C.H.C. profiles vary among individuals of different sex, caste, fertility, age, health state, etc. This variation has been intensely studied, especially in eusocial insects like ants, where differences are likely to have a signaling function [24]. Previously did not study the above aspects and sensations of ants, and this is the first study that revealed the pitfall approaching the time of various ant fauna. So, the present investigation carried out an aspect of pitfall traps approaching or attraction time by the various ant species. It may give a good podium of ideas about the approaching time of specific species of ant fauna for future researchers.

MATERIALS AND METHODS

Study area

The study was Mannampandal Panchayat, Mayiladuthurai District, Tamil Nadu, India, and is located between 11" N latitude and 79' E longitude. The place is 28 km away from the Bengal Sea (Tranqubar) at an elevation of 19 m S.L. and 278km away from Chennai, the Capital of Tamil Nadu. It is also a part of the Cauvery delta region in the South–Eastern in alluvial plains. The entire belt is dominated by farming activity, and the site selected has vegetable crops and few common trees. The study was carried out from December 2018 to March 2019 on the basis of twice in a week.

Pitfall trap

The pitfall trap technique [13] suggested measuring the ant fauna over a study period in the study area by simple trap design (i e., without funnel and roof). A pitfall trap can be any small container placed in the ground with the top level with the surrounding surface and filled with a preservative and sugar solution. The pitfall traps liquid was prepared by using a mixture of 16 ml of 10% formaldehyde and 4 ml of 10% glucose solution.

A total of 20 pitfall traps were installed in an intervals of 5 meters and 10cm depth for each trap. Randomly selected traps were removed (5 numbers) for quantifying and qualifying the ant fauna from the field for intervals of 2, 4, and 6 hours. The remaining undisturbed traps were kept for 24 hours duration for the fulfillment of the study. The captured specimens in each trap were counted and then identified by an updated checklist of ants in India [25] and by the expert.

Statistical analysis

The collected data on every observation of each target species were entered and summarized in each observation-wise into an excel file. Hour-based (2hrs, 4hrs, 6hrs, and 24hrs) diversity indices and abundance were calculated by the statistical software of PAST 3.0. Species relative abundance, species assemblage were compared by Analysis of Variance (ANOVA) among the duration, as well as species by SPSS.

RESULTS AND DISCUSSION

A total of 16,334 individuals were identified, which is belonging to eight species and three sub-families, namely Formicidae, Myrmicinae and Dolichoderinae (Table 1) during the present study. Over time, there have been progressively a greater number of individuals. Moreover, species richness, dominance index, diversity index, Shannon H' index, and evenness do not show variation among the hours of pitfall trap sampling (Table 2). Species relative abundance of various time intervals, Camponotus chromaiodes (69%) were high abundance in two-hour duration followed by Camponotus floridanus (39%) and other species in two-hour duration. In a four-hour duration, the arboreal ant species of Oecophylla smaragdina were highly abundant species, and the rest of the species were observed to be less than 25 % of their total population during the study period. Monomorium minimum species occupied 50 % of the total ant occupancy during the six-hour interval. Likewise, Camponotus consobrinus and Camponotus compressus showed the highest abundance in the 24-hour duration of pitfall traps (Figure 1).

Table 1. Checklist of Ant fauna recorded during the study period (n-6)

Table 2. Diversity indices of Ant fauna against different hours of pitfall trap samplings (n=6)

The percentage of species assemblage significantly varied among the species at every time interval. In the two-hour interval, species assemblage was significantly varied among the species, in which Camponotus chromaiodes (27%) showed the highest percentage, followed by C. floridanus (15%), C. consobrinus (13%), Tapinoma sp. (12%), O. smaragdina (10.52%), S. geminate (9.48%), M. minimum (8.19%) and C. compressus (4.96%) (F=181; p<0.01).    O. smaragdina (28%) was the highest percentage in four-hour pitfall traps, followed by Tapinoma sp. (16%), M. minimum (15%), S. geminate (14%), C. floridanus (8%), C. compressus (8%), C. chromaiodes (7%) and C. consobrinus (5%) (F=158.8; p<0.01).  In six hours, the duration of pitfall traps showed the highest percentage in M. minimum (25%), trailed by Tapinoma sp. (17%), S. geminate (17%), C. floridanus (12%), C. consobrinus (8%), O. smaragdina (8%), C. compressus (7%) and C. chromaiodes (6%) (F=153.6; p<0.01).  In 24 hours, pitfall traps showed the highest proportion in C. compressus (33%), followed by C. consobrinus (24%), C. floridanus (13%), S. geminate (11%), O. smaragdina (7%), Tapinoma sp. (5%), C. chromaiodes (4%) and M. minimum (3%) (F=213.9; p<0.01) (Table 3).

Table 3. Percentage of species assemblage in different hours of pitfall traps (n=6).

The percentage of species assemblage was calculated on an hourly basis for the contribution of ants in pitfall traps. Every species considerably fluctuated throughout time, showing both positive and negative population trends. Six of the eight species show significantly differed over the different time periods. Camponotus compressus and Camponotus consobrinus have an increasing trend over time. On the other hand, Camponotus chromaiodes, Monomorium minimum, Oecophylla smaragdina, and Tapinoma sp. showed a declining pattern in relation to the time duration of the study period (Figure 2).