LIFE HISTORY AND FUNCTIONAL MORPHOLOGY OF THE ALIMENTARY

CANAL OF Selasia unicolor (COLEOPTERA: DRILIDAE)

BY

OKUMOH, OZOVEHE SAMUEL

MATRIC NUMBER: BIO/10/1907

A

DISSERTATION SUBMITTED TO

THE SCHOOL OF POSTGRADUATE STUDIES,

THE FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE, ONDO STATE,

NIGERIA.

IN PARTIAL FULFILLMENT OF THE REQIUREMENTS FOR THE AWARD OF THE

DEGREE OF MASTER OF TECHNOLOGY (M.TECH)

IN

ENVIRONMENTAL BIOLOGY AND PUBLIC HEALTH

FEBRUARY, 2021 ABSTRACT

Selasia unicolor is an important pest of snail feeding exclusively on the flesh of land snails, hence the name “Snail predator”. The adults exhibit sexual dimorphism, having small -like winged males and large apterous larviform females. The larval stage, which is the feeding stage, passes through six (6) larval instar stages before emerging as adults. The major difference across the instar stages is the size; each larval instar is different from the other in length. This study was carried out to determine the life history, the description and behaviour of S. unicolor as well as the anatomy and histology of the gut of S. unicolor larvae. Secondly, the optimal conditions for proteolytic enzymes in the gut of the snail predator were also determined using appropriate biochemical techniques. Larvae of S. unicolor were collected from the field and were reared and studied from egg to adult stage under natural conditions. Histological sections of the gut were performed while the activities of protease were determined in the gut homogenates. The first larval instar is the smallest with an average length of 4.3mm±0.011 while the largest is the sixth larval instar with average length of 40.7mm±0.046. The major distinguishing feature of the first instar is the presence of twelve (12) abdominal segment compared to the eleven (11) present in other larval instar stages. The first three larval instars spend an average of 23 days each in the shell while the last three stages spend 32 days each before emerging, with a total of 195 days (6 months) from eggs to adult. Larvae attack snails by first paralyzing them with certain chemicals released from the mouth, pushing them to safe area before entering into the shell head first through the aperture to feed on the snail’s flesh. The percentage attack and emergence increases with size of larva. The size of the adults that emerge is based on the size of the last (sixth) instar larvae; smaller larvae emerge into male and vice versa. After mating, females can lay between 250 to 950 eggs depending on size. Females shrink and die about an hour after laying eggs. Histological sectioning of the gut revealed that the digestive tract of the larvae is clearly divided into three regions; foregut, midgut and hindgut. The midgut is the longest and largest region for all instar stages while the hindgut is the shortest. Just like most protein feeding , the gut is short but about a few millimetres longer than the body length. The intestinal tract of S. unicolor comprised of buccal cavity, oesophagus, crop, midgut, ileum, rectum and anus. Histology of the ’s gut revealed the columnar epithelium of the midgut which is responsible for digestion of food and absorption of nutrients. The hindgut on the other hand is responsible for the reabsorption of water due to the presence of rectal pad. The proteolytic activity in the gut extract of S. unicolor larvae was at its optimum at 40oC, pH 7 and 2.0% substrate (casein) concentration incubated at 60 minutes.

CHAPTER ONE

INTRODUCTION

Drilid are unique sets of beetles with winged males and apteral larviform females (that is) the males are capable of flight while the significantly larger females are not (Trllova and Kundrata,

2015). Due to the morphological distinctiveness they had been long classified as a separate family of soft-bodied elateroids (Kundrata et al., 2014). The genus contains thirty five species and occurs chiefly within the West-Palaearctic region (Kundrata and Bocak, 2011). The primary

Selasia sp. delineate from the Palaearctic Region while Selasia bleusei, from Rhodes Island

(Greece) and S. atriventris, from northern Asian country (Wittmer, 1944) as cited by Kundrata and

Bocak (2011). Drilus beetles are commonest in lowland or lower mountain forest habitats in

Central Europe, and within the Mediterranean region in coastal marshes and high-altitude habitats

(Bocak et al., 2010). The Mediterranean, where all better-known genera are rumoured, is one in all the hotspots of (Bocak, 2007, Bocak et al., 2010). Two Drilus species occur within the

Netherlands: D. concolor (Ahrens) and D. flavescens (Geoffroy) (Baalbergen et al., 2016). Drilus concolor is known as the black snail eater and it occurs mainly within the centre of Netherlands.

Drilus flavescens is the common red snail eater and happens chiefly within the south of the province of Limburg (Baalbergen et al., 2016).

The drilid beetle had for long been better-known in African countries as snail eater, feeding on edible land snails (Omidiji and Amusan, n.d.). It’s the brute of the drilid beetle currently known as Selasia unicolor (Gruerin) (Omidiji and Amusan, n.d.) that feed solely on land snails throughout development. Selasia larvae are vital predators of the land snails, however

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