Examining the Predatory Relationship Between the Indigenous Firefly ( Aspisoma ignitum ) and the Invasive Giant African Snail ( Achatina fulica ) in Trinidad, West Indies

The current study investigates the predatory relationship between the firefly larvae ( Aspisoma ignitum ) and the giant African snail ( Achatina fulica ). The principal objective of this study was to examine the specific predator responsiveness of the firefly larvae against the giant African snails under experimental conditions. This was evaluated using two (2) treatments T1 and T2. T1 investigated giant African snail neonates of size 0.5 cm with a larva to snail ratio of 1:5. In T2, larvae to snail ratio of 3:1 was investigated using 2 cm giant African snail neonates. Control treatments were included in the experimental design with the absence of the larvae. Each treatment was replicated five (5) times. There were 100 % mortality effects for T1 and T2. Commonalities existed in both the spatial and the temporal characteristics to possibly consider the firefly larvae as an idealistic and highly compatible predator for the giant African snail neonates. Ecological engineering strategies to encourage the presence of the firefly will aid in suppressing the giant African snail population. The study concludes that the firefly larvae can be a possible predator for the control of the giant African snail once the firefly populations are encouraged in both crop and non-crop spaces.


Introduction
Invasive pests are a challenge to manage given the limited predators within the new habitat they now come to occupy.This may be attributed to predators being non-existent or that the newly introduced organism has not yet been desired by existing predators as a new food source.Invasive pests threaten local biodiversity by competing for food and shelter and have been known to adversely impact crop production spaces (Tu, 2009;Lurgi, Ritchie, & Fordham 2018;Naveena et al., 2020).It should be recognized that there is always a dimension of economic loss attributed to the presence of invasive organism introductions (Naveena et al., 2020;Kourantidou et al., 2021).According to Pysek and Ricardson (2010), "the ability of an alien species to overcome various barriers in the new environment is affected, positively or negatively, by the presence of other species, native or alien, already resident in the area".The consequent emergence of potential biological controls which emerge naturally overtime or are unnaturally introduced would be useful towards controlling the populations of introduced species.
The giant African snail (GAS) was discovered in Trinidad in 2008 and has now spread to almost all areas (5128 square kilometres) of the island.Given the destructive ecological characteristic of this pest, the Global Invasive Species Database has ranked it among the "100 Worst Alien Invasive Species" (Invasive Species Specialist Group, 2012).The GAS is a notorious generalist that consumes over 500 plant species and ranks consistently among the world's most invasive pests (Lowe, Browne, Boudjelas, & De Poorter, 2000;Simberloff, 2003).According to the International Union for Conservation of Nature (IUCN, 2010), this introduced snail is considered a threat to agriculture and the environment, whereas without natural enemies they consume the flora found crop and non-crop spaces.A study conducted by Prasad et al. (2004) indicated the specific behavioural attributes of this invasive snail enable this species to impede control strategies.As much as control strategies exist the most effective control for this invasive snail are still unknown (Andreazzi, 2017).This is possibly attributed to the swift population resurgence attributed to its high rates of proliferation.
Methaldehyde is a principal component in many products used to control snails and slugs (Castle et al., 2017;National Center for Biotechnology, 2022).However, as much as this can be useful, the resurgence of snails in areas where it is applied is highly possible much dependant on the formulation which is used.Although metaldehyde formulated molluscicides have proven to be somewhat useful the risk to the environment far prevails over its benefit.Metaldehyde is considered a pollutant which invites problems related to toxicity to the environment, humans and animals (Castle et al., 2017;Saad, Ismail, & Dahalan, 2017;Damalas & Eleftherohorinos, 2011).Given the report threats of this pesticide to the environment there is significance to finding alternative natural approaches which would prove useful in bringing some measure of control.The integration of agroecological principles into pest management is an emerging paradigm for sustainable crop protection practices (Reddy, 2017).This will reduce negative impacts to the environment specifically attributed to pesticide usage.
The identification and nurturing of potential biological organisms to support the population control of the giant African snail would support agroecological pest management strategies.Effective biological approaches to reduce and mitigate pests and pest effects through the use of natural enemies are considered to be environmentally safe (Sanda & Sunusi, 2016).The successful invasiveness of the giant African snail is attributed to the limited existence of identified biological control organisms naturally found in the ecosystem to promote their existence within infested spaces.In a study conducted by Fu and Meyer-Rochow (2013) examined the predator-prey relationship between the larvae of the firefly (Pyrocoelia pectoralis) and the land snail (Bradybaena ravida).The study concluded that firefly was an effective alternative method of control for the land snail.
The current study examines the predator-prey relationship between the indigenous firefly, Aspisoma ignitum and the invasive giant African snail, Achatina fulica in Trinidad.The rationale for the study came as a result of an unplanned in-field observation of a larva-type of organism feeding on neonates (snailets) of the giant African snail.Additionally, the need to discover predator-prey relationships for the control of the giant African snail will offer eco-smart pest control alternatives within the eco-system.The specific objectives for the study are: (1) To characterize the site selection of the organism found displaying targeted predatory behaviour against giant African snail neonates.
(2) To confirm the identity of the larva demonstrating the predatory behaviour.
(3) To examine the specific predator responsiveness of the firefly larva against the giant African snail.

Collection Site for the Observed Firefly Larvae Displaying Snail Predation Behaviour
Firefly larvae observed to be feeding on giant African snail neonates were collected from the ground within the proximity of bougainvillea plants located at the ECIAF Campus of the University of Trinidad and Tobago (UTT).Ciomperlik et al. (2013) described the giant African Snail neonate as measuring between 7-20 mm (shell length).The larvae were collected between the hours of 10 a.m. and 12 p.m. during the month of November, 2022.The larvae were most active during and after rainfall events.The authors spent a period of ten (10) days making in-depth direct field observations on the characteristics of the specific area.The identification and selected characteristics of the plants where the larvae were recorded.

The Identification of the Firefly Larvae and Emerged Adults
The confirmation of the identity of the firefly larvae took the sequential approach of collection, rearing in containment, identification of both the larva and the adult using Google Lens and the subsequent confirmation of the adults' presence at the collection site.The observation of the development of the larvae into the adult under the experimental conditions was crucial for confirmation of the insect.It was reported by Shapovalov et al. (2020), that Google Lens was a suitable means for the identification of insect pests.The confirmation of the adults at the collection site was done by a detailed inspection of the plants as well as by using the sweep net technique as indicated by Jaikla et al. (2020).In this regard, a total of ten (10) larvae were collected on the ground under several Bougainvillea spp.plants and divided into two (2) groups of five (5).The average length of the larvae was 1.3 cm.Additionally, a total of ten (10) giant African snail neonates of an average length of 0.5 cm were collected from an active breeding site.Each group of larvae were placed into a 155 cm 3 glass jar.Each jar contained a thin layer of damp soil and a total of five (5) giant African snail neonates.The jars were labelled J1 and J2.The snails were included as a source of food since it was observed that they were being fed upon by the larvae at the collection site.The experimental conditions for light, temperature and humidity was recorded using the LT300 Light Meter and the 3MTM EVM Series Environmental Monitor respectively.The glass jars were covered with a thin permeable cloth that would have provided sufficient ventilation but would have prevented the escape of both organisms.The larvae collected were of all different anatomical and physiological growth stages and as such the transition to the adult stage was expected to vary.

Estimation of Firefly Larvae Mobility (cm/s)
An estimation of mobility was undertaken to provide an indication of the movement ability of the firefly larvae.A total of ten (10) firefly larvae were randomly selected from the collection site.A 25 cm line was drawn on a sheet of white paper with a dimension 21.6 cm × 27.9 cm.The line drawn had 5 cm sub-divisions measuring 0 cm, 5 cm, 10 cm, 15 cm, 20 cm and 25 cm.Each larva was then placed one (1) at a time at the starting point 0 cm and the time was recorded for the larva to move from 0 cm to 25 cm.The time was also recorded at distances when the larva would have stopped and failed to complete the continuous movement from the 0 cm mark to the 25 cm mark.The larvae were given time to adjust to the experimental conditions before estimating its mobility.The speed (cm/s) was calculated for each larva to give an indication of the larva's mobility.

Predator Responsiveness of the Firefly Larva Against the Giant African Snail Neonates
The predatory responsiveness by the firefly larvae against the giant African snail neonates was investigated using two (2) ratios for larva and snail combinations, factoring the size of the neonates.In the first evaluation, treatment one (T1) neonates of size 0.5 cm was used in containment jars in a ratio of one (1) larva to five (5) neonates.In the second evaluation, treatment two (T2) a ratio of three (3) larvae to one (1) neonate was used.In the second evaluation, the snails were two (2) centimetres in shell length, hence the justification for increasing the number of larvae used.The snails and larvae were placed in a similar arrangement used for "J1" and "J2" in the identification stage of this study previously reported.However, the damp soil was excluded.
There were two (2) experimental controls used in this component of the study.In the first experimental control (C1) five ( 5) neonates measuring 0.5 cm were placed in a jar without any larvae.In the second experimental control (C2) a single snail measuring 2 cm was placed in jar without larvae.Each treatment including the control treatments were replicated five (5) times.Only larvae which displayed considerable mobility were selected.
The snails were sourced from an area which had an active breeding population.The experiment was conducted under laboratory conditions of 0.34 Lux, relative humidity 83.9% and with a temperature at 25 o C. The behaviour of the snails and larvae was monitored for the first hour and after twenty-four (24) hours.The mortality of the snails was determined for each treatment and replicates.Mortality of the 0.5 cm neonates were confirmed using visual inspection and by shining a light through the shell to observe its content.Shells which were empty was an indication of consumption.The mortality of the larger snails was confirmed by visual inspection and further confirmed using the probing procedures as outline by (Ciomperlik et al., 2013).The morality was expressed as a percentage.

Site Characteristics of the Larvae Predatory Behaviour
The larvae were found on the ground within a non-crop area comprised of eight (8) Bougainvillea glabra arranged in a linear landscape arrangement.The plants were located between a building on one side and an open savannah-type of field on the other side.The plants were regularly pruned and as such there were minimum floral bracts present on all plants.The area within the drip line of the canopy was bare soil.There were regular rainfall events in the area where these plants were located.The average humidity and temperature within the canopy of the plants were eighty-three (83%) percent and twenty-four (24) degrees centigrade respectively.Table 1 provides a detail description of the dimensions of the plants at the collection site. jas.ccsenet.

Predatory Responsiveness of the Firefly Larva
The predatory characteristics of the firefly larvae for both ratio combinations, T1 (1:5) and T2 (3:1), resulted in 100 % mortality against the giant African snail after twenty-four ( 24) hours (Table 3).Upon the introduction of the larvae with the snails in T1, the larvae were immediately attracted to the snails for all treatment replicates.The larvae and the snail were both present at the base of the jars in T1.In the experimental evaluation T2, the larvae were also attracted to the snails for all treatment replicates.There was marked contrast in the mobility of the snail in T2 when compared to treatment T1.The larger giant African snail neonates used in T2 given its size had greater mobility.In some instances, the snail ascended the jar to occupy a different location away from the larvae.Although, this was observed the snail was eventually compromised by the larvae at the base of the jar.It was observed within twenty-fours (24) hours that the mouth parts of the larvae in all replicated of T1 had burrowed into the exposed tissue of the snail.In a similar manner, the larvae mouth part was burrowed into the tissue of the larger snails in all replicates of T2.It was observed that when the mouth parts of the larvae made contact with the snails' tissue in both T1 and T2 that there was a prolong continuous feeding attachment for both treatments (Figure 2 and Figure 3).In T1, the contents within the shell of all the neonates in each replicate were consumed.In T2, given the size of the snails, the tissue was present but appeared to have a shrunken appearance.

Discuss
The Conservation biological control can be a useful approach to enhancing natural indigenous predators in fighting against invasive pest.Ecological engineering techniques as described by van Emden (2022) when applied to agroecosystems can be useful to improve the benefits of natural enemies within the environment.Ecological engineering will be useful in reducing the dependence on or elimination of pesticides.The main pesticide used for the control of the giant African snails around the world and in Trinidad and Tobago is metaldehyde.Metaldehyde is known to cause serious environmental problems and has also been banned in the United Kingdom (Castle et al., 2017).Hence, it would be valuable to encourage the presence of fireflies in snail infested crop and non-crop spaces as an agro-ecological crop protection strategy for giant African snail control.
Beetle banks are ecologically engineered spaces which comprises a variety of flora that is protected from pesticides and which encourages the proliferation of beneficial predatory insects.The concept of a beetle bank was described by (Marshall & Moonen, 1998).Although these spaces may also be attractive to the giant African snail, the predatory characteristics of the firefly larvae would become engaged.The study concludes that the firefly (Aspisoma ignitum) larvae can be a possible predator for the control of the giant African snail once their populations are encouraged in both crop and non-crop spaces.