Dermestes maculatus Degeer infestation impact on market loss of dried fish in Kwara State, Nigeria

Dried fish vendors located at three markets in Kwara State, Nigeria were surveyed and Dermestes maculatus Degeer-infested specimens of dried Chrysichthys nigrodigitatus, Heterobranchus bidorsalis and Oreochromis niloticus were analyzed in the laboratory. The dried fish species were exposed to D. maculatus larvae and adults for 35 days at ambient laboratory conditions that coincided with their developmental cycle after which the level of damages were recorded. The vendor survey showed that the Ipata market had the most dried fish vendors within the age of 20-30 years (46.66%) and that 60% of the fish vendors had, atmost, 20 years of experience. The weight loss in dried fish due to D. maculatus infestations (larval, adult) was H. bidorsalis (22.66 ± 1.20g, 29.00± 3.05g), O. niloticus (14.33± 2.96g, 20.00 ± 0.58g), and C. nigrodigitatus (14.00 ± 1.53g, 15.00± 1.15g) in decreasing order. This suggests that the development of cost-effective methods for pest control in dried fish would greatly reduce market loss of product for dried fish vendors from D. maculatus and other pestiferous species, making the dried fish business more profitable in Nigeria. © 2018 Published by Elsevier B.V. on behalf of Shanghai Ocean University. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).


Introduction
Nigerians consume fish, one of the main animal protein sources, in large quantities. There is little or no religious bias, which gives it an advantage over other animal protein sources, like pork (Eyo, 2001;Ligia, 2002). Despite the large volume of both fresh and marine water that serves as fish habitat in Nigeria, only about 50% of the fish demand is currently met by local supply. The most common method of preserving this fish for optimum supply to smoke it. Smoked or dried fish form a traditional part of the diet for a large protein of the world population. (Ayuba & Omeji, 2006;Okonta & Ekelemu, 2005). Fish, in addition to its nutritional value, is a major source of employment and trad for millions of people living close to water via harvesting, handling, processing and distribution (Bene & Heck, 2005;Al-Jufaili & Opara, 2006;Mufutau, 2012).
Only a small percentage of the fish were sold fresh, which is why preservation methods such as freezing, smoking, drying and heat treatment were applied to extend the shelf-life of the product (Ikenweiwe, Bolaji, & Bolaji, 2010;Babarinde, Adebayo et al., 2016). Preservation was carried out locally as described by Davies, Davies, Inko-Tariah, and Bekibele (2008), who processed fishery products that were stored using traditional storage technologies. The methods of preservation differs between countries and within the same country depending on the species of fish the type of product desired (Ogbonnaya & Ibrahim, 2009). Despite the efforts made to preserve catches, pest infestation were common in most developing countries, including Nigeria. This implies that, the efficiency of any preservation method is very important for insuring the quality, yield and highest possible profits to be achieved in the fishing industry.
Common pests that have been commonly found on dried fish in Nigeria are beetles (Coleoptera), flies (Diptera) and mites (Acarina) (FAO, 1989) and genera like Calliphora, Chrysomia, Lucillia and Musca (Diptera), Dermestes and Necrobia (Coleoptera) have been oberved as pests in dried fish (Mufutau, 2012;Babarinde et al., 2012, Babarinde, Adebayo et al., 2016, Babarinde, Sunnie-Ododo et al., 2016Osuji, 1985. Beetles of the family Dermestidae invade fish from the earliest stages of drying and breed in the dried product (Abolagba, Akise, & Orukpe, 2015) and are also associated with spread of anthrax and contaminants of insect origin in the foodstuffs of some countries, resulting in market value reduction for fish vendors (Osuji, 1985).
Pest infestation, a lack of adequate handling, processing techniques and good storage facilities contribute significantly to the low fish availability that rural dwellers have, living far away from fish sources that account for three quarters of the population in developing countries, like Nigeria (Ayuba & Omeji, 2006;Osuji, 1973).
The growth and development of dried fish pests are promoted by poor traditional processing methods, storage and packaging. The local dried fish vendors sprinkle water on dried fish to promotes D. maculatus growth and provides a suitable breeding ground for several other species of flies and beetles. There are limited studies that focus on the activities of fish vendors, fish sources, processing, level of insect infestation and damage done to many species of dried fishes, especially for Kwara State, north-central Nigeria. This study assess the socio-economic characteristics and activity of dried fish vendors and compares the level of infestation of D. maculatus on different fish species.

Market survey and sample collection
Three markets, noted for their sale of dried fish in Kwara State were surveyed. Questionnaires and interviews were administered to obtain demographic information of the dry fish vendors and their fish processing methods. 50g of fresh, pest infested and dried samples of catfish and tilapia were obtained randomly from the markets in Ipata (Ilorin East LGA), Idi-ape (Ilorin West LGA) and Gbugbu (Edu LGA) Kwara State, north-central Nigeria. Each sample was cut into pieces and insect pest were extracted using a scalpel. Several males and females of D. maculatus were obtained for laboratory exposure of the three dried fish species samples.

Entomological experimental setup
Three fish species Chrysichthys nigrodigitatus (Silver catfish), Heterobranchus bidorsalis (African catfish) and Oreochromis niloticus (Tilapia) were obtained, weighed, oven dried at 60 C and then allowed to cool at room temperature. 50g of each dried fish sample was weighed and placed in experimental jars with 10 pairs of newly emerged male and female adult D. maculatus. In-star larva species were separately introduced and covered with muslin cloth held tightly with a rubber band to allow aeration but prevent the escape of insects. Uninfested fish samples of each species (50g) served as control for the experiment. Jars were examined twice daily between 10:00 and 11:00am, and temperature and relative humidity readings were recorded for 35 days corresponding with the life cycle duration of D. maculatus.
The pre-infestation weight of fish, post-infestation weight of fish, weight of frass, pre-infestation weight of D. maculatus and post-infestation weight of D. maculatus were recorded.

Results
The analysis of survey data from the markets (Idi-ape, Ipata and Gbugbu) showed that Ipata market had the highest fish vendors within the age range of 20e30 years (46.66%), with only 1 above 50 years of age. 60% of the total fish vendors in Gbugbu market had 20 years' experience, with only 1 vendor having 15 years' experience. A majority (90%) of the fish supply at Gbugbu market was supplied from Kwara State, while only 10% were obtained from Niger state. Likewise, 46.66% of the dried fish vendors at Idi-ape market had at least a primary education while 33.34% had no formal education (Tables 1 and 2).
The result of infestation level from the three different markets revealed that there was high infestation level in O. niloticus,