Background

Increasing population of the world worsens the serious problem of food security especially in developing countries (Belluco et al., 2013). However, even in the developed countries where food security is of less concern, health problems related to food is a grave factor and it entails food safety and environmental sustainability of food production. In this regard, new ways to increase yields while preserving quality of food is inevitable. Insects therefore are a possible solution based on their use as source of protein instead of red meat (Belluco et al., 2013). Insects as a source of food for human amongst communities in East African region, is gaining popularity (Christopher et al., 2017). Edible insects have been identified as key in complimenting efforts to feed the increasing global population (Kalemu et al., 2015). However, the abundance and quality of insect nutrient varies with habitat type, developmental stage, insect species and feed substrates (Rumpold and Schluter, 2013). In addition, insects play a vital role in pollinating flowering plants that forms the bulk of crops grown by farmers. It has been reported that about 80%~85% of wild flowering plants depends on insects for reproduction (James et al., 2015), hence insects are significant for survival of primary producers in terrestrial ecosystems.

Recently there has been concern about the declines of pollinating insect population as reported by Gretchen et al. (2012) and James et al. (2015), this is certain to have a diverse effect on ecosystem (Hallmann et al., 2017). Habitat modification itself has potential to significantly influence the distribution and abundance of most animals, this loss of native habitat for agricultural or urban use creates a lot of destruction to organisms (Raghu et al., 2000). Humans alter environment in several ways that this affect biodiversity, most striking are habitat destruction and alteration, changes to global and local climates, pollution and introduction of species to areas from which they were previously absent and in which they subsequently become invasive. All these processes have brought substantive changes to insect populations, either by causing local increases or declines in abundance. In some cases, these have led to extinction of all populations of some species (Chown and John, 2006). Habitat loss and fragmentation often creates a serious threat to biodiversity to an extent that species inhabiting small remnant habitat fragments, experience high extinction rates owing to lower population size and increasing isolation from other conspecific populations (Bommarco et al., 2010). Moreover, Phylum Arthropoda is the most diverse and dominant constituent of biodiversity in terrestrial ecosystems. It is the largest animal phylum, estimated as 85% of all known animals in the world (Ojija, 2016). It is reported that 1,170,000 species of Arthropod have been described and insect is the most diverse and abundant among the arthropod groups (Rahman et al., 2013; Balakrishnan et al., 2018). More importantly, most edible insects that had been described are member of class Insecta (Kalemu et al., 2015). They occur both in terrestrial and aquatic habitats and exhibit not only a rich variety of form, color, and shape, but also a range of ecological adaptations (Balakrishnan et al., 2014; Ojija, 2016).

1 Results

1.1 Dominant species of flying insects in different ecological habitats

Evaluation of dominant species in habitats (Table 1), revealed that mosquito (Order: Diptera) was the dominant insect species (31.1%) in Botanical garden habitat (BGH), and the least was Lake-fly (0.2%). In water shade habitat (WSH), mosquito was still dominant at 20.1% and praying mantis (Order: Mantodea) was the least group of insects collected (0.2%), while in open field habitat (OFH), Butterfly (Order: Lepidoptera) was dominant at 28.4% and mantis was least in this habitat (0.3%).

In both of the habitats, mosquitoes had the highest collection proportion (23.8%) followed by Butterfly (15.2%), Dragon fly (Order: Odonata) at 15%, Housefly (Order: Diptera) at 14.2%, Grasshopper (Order: Orthoptera) at 13.9%, moth (Order: Lepidoptera) at 8.8%, Beetle (Order: Coleopteran) at 6.7%, Lake-fly 1.6% and Mantis at 1.0%.

When the three habitats were compared (Table 2; Table 3), botanical garden habitat (BGH) had the highest mean abundance 136.25(41%), followed by water shed habitat (WSH) 119.25(35%), and open filed habitat (OFH) 81.42 (24%). However, the three habitats differ significantly in relation to species abundance (F= 21.888, df= 2, P= 0.000).

Amongst the nine (n= 9) collected insect species in three habitats, mosquitoes had the highest relative abundance (320.67 ± 102.14), then Butterfly (206.00 ± 26.69), Dragon fly (203.00 ± 31.07), Housefly (191.00 ± 80.00), Grasshopper (187.00 ± 39.61), moth (119.33 ± 21.16), Beetle (90.00 ± 11.67), Lake-fly (22.00 ± 10.01) and Mantis (19.67 ± 8.51) (Table 4). However, the nine species of insects collected three habitats differ significantly in relation to their relative abundance (F= 4.105, df= 8, P= 0.006).

1.2 Implication of insect collection time on distribution and abundance of insects

It showed that morning collections had high mean abundance 85.41(57%) compared to afternoon 64.52(43). However, the difference observed between morning and afternoon collections was not statistically significant (P= 0.209) (Table 5; Figure 1).

1.3 Identification of edible species of flying insects collected

Table 6 showed that Lake-fly 74.33 ± 6.76(27%) and grasshopper 73.67 ± 3.84 (26.7%) were the highest preferred edible insect species, followed by beetles 57.67 ± 4.70 (20,9%), Butterfly 32.33 ± 8.68(11.7%), Dragonfly 28.00±9.07 (10.2%), Moth 4.67 ± 1.76 (1.7%), mantis 2.33 ± 0.88(0.8%), while housefly 1.33 ± 1.33 (0.5%) and mosquitoes 1.33 ± 1.33 (0.5%) were the least identified possible edible insect species.

Figure 2 present the distribution of edible flying insect species as identified by student, teaching and non-teaching staff of Kisumu Polytechnic. However, there was no significant difference in the categories of respondent (F= 0.274, df= 2, P= 0.763).

2 Discussions

Our study hypothesized that a forested habitat is likely to positively influence the abundance of insects when compared to open land and water shed habitat. The study (Table 3) provide evidence that the botanical garden habitat (BGH) was highly inhabited (41%) by different flying insect species as compared to water shed habitat-WSH (35%) and open field habitat-OFH (24%).This finding is in agreement to a related study by Jennifer et al. (2000) in which they discovered that Diptera communities differs with respect to habitat type based on the dominant vegetation in the habitat. Juan et al. (2016) on his comparative study of different habitats also discovered that ground cover vegetation has the lowest attractiveness to flying predatory insects when compared to other habitats. This confirms our finding in which open field habitat (OFH) had the least insect abundance compared to BGH and WSH. The difference observed among the three habitats was significant (P= 0.000) as demonstrated by Ojija et al. (2016) in a study where they compared insect abundance in grassland and woodland habitats. With regard to species diversity (Table 1), Mosquito (Order: Diptera) was dominant in BGH (31.1%) while lake-fly was the least abundance (0.2%) specie of insect in this habitat. In WSH, 20.1% of insects collected were mosquitoes and Mantis was only 0.2%. Mantodea was the least order of insects sampled in water shed habitat. In OFH, the larger proportion of insect collected were Butterfly (28. 4%).

When assessing the abundance of flying insect species in both habitats combined (Table 2), we found mosquitoes to be the most abundant at 962(23.8%), Butterfly 618(15.2%), Dragonfly 609(15.0%), Housefly 573(14.2%), Grasshopper 561(13.9%), Moth 358(8.8%), Beetle 270(6.7%), Lake-fly 66(1. 6%) and Mantis 31(1. 0%). In Table 4, the mean abundance of mosquito was (320.67 ± 102.14), followed by Butterfly (206.00 ± 26.69), then Dragon fly (203.00 ± 31.07), Housefly (191.00 ± 80.00), Grasshopper (187.00 ± 39.61), moth (119.33 ± 21.16), Beetle (90.00 ± 11.67), Lake-fly (22.00 ± 10.01) and Mantis (19.67±8.51). However, the study revealed that the nine species of flying insects collected in the three habitats differ significantly with respect to their relative abundance (P= 0.006). The high number of mosquitos in western Kenya is a confirmation of a previous study conducted by Bryson et al. (2011). He discovered that mosquito productivity is greater even in small and unstable habitats. This is an alarm to the health department given that mosquito is a vector for malaria and other diseases. However, in terms of ecological balance, it is an indicator of ecological stability because it occupies a vital trophic level necessary for existence of other species.

Study on sampling time (morning and Afternoon) was based on the premise that morning and afternoon are hours when insects are most active in their habitats. Insect collection was done in the three habitats, both in the morning and afternoon hours. A total of four thousand and forty-eight (n = 4,048) insects were collected (Table 5). Out of this, morning collections constituted 57% and afternoon were 43%.This study revealed that insects can be sampled either in morning or afternoon hours because there is no significant different between them (P= 0.209). Figure 1 displays the distribution of different insect species as collected during morning and afternoon hours in the three habitats (BGH, WSH, and OFH).

In Kenya the history of consuming insect as food has been in existence among communities around Lake Victoria regions, as was explained by Kalemu et al. (2015). However, different ethnic communities have their own reservations on species of insects to be eaten and those that are forbidden. In our study three different categories of respondents (Figure 2) within Kisumu Polytechnic that comes from different ethnic communities gave their views on edible insect species. Most respondents identified Lake-flies 223(27%) and grasshopper 221(26.7%) as the most preferred edible insects amongst species collected (Table 6), moreover these traditional foods are consumed based on traditional norms and public health concerns (Kinyuru et al., 2012). Our finding concurs with the study conducted by Christopher et al. (2017), especially with reference to grasshopper as preferred edible insect. However, there was different among students, teaching and non-teaching staff with regard to choice of an edible insect (P= 0.763). This reveals a concept that, the decision on an edible insect is not a factor of profession. Most importantly, there is still need to explore the acceptability of others insect species as food by communities and their culturing conditions so as to increase the list of edible insects. Ayieko et al. (2010) raised a concern that the abundance of these edible insects is constantly affected by type of habitat and the climate change. It therefore a public interest to conserve environment in the interest of promoting natural existence of insects.

3 Materials and Methods

3.1 Study area

The study was conducted at the Kisumu National Polytechnic, Kisumu Campus (TKNP). Kisumu Polytechnic is in Kisumu town, near the shore of Lake Victoria in Western Kenya (0° 06’ 7.96” N, 34° 45’ 42.16” E; altitude 1,131 m (3,711 ft) above sea level, on the equator, leading to a hot and humid climate year-round. The area has two rainy seasons; the long rains, which extend from March to June, and the short rains which extend from November to December. Climatic conditions consist of temperature ranging from 20°C to 35°C and rainfall rangers from 258 mm to 816 mm per month.

3.2 Sweep net assemblage

A standard funnel-shaped white net, 45cm long was sewed using white thread onto a metallic circular frame of 37 cm in diameter. Metallic frame was then attached to a 71 cm long wooden handle of 12 cm in circumference.

3.3 Determination of dominant species of insect in different habitats

Three separate habitats were identified as open-field, botanical garden and water-shed habitats. They were approximately 100 m from each other. The habitats were not disturbed and/or altered for the period of the study. The Sweep net trap was standardized by taking 100 sweeps from each site at every collection time (Shweta and Rajmohana, 2015).

Collection was done twice a week and two times a day using sweep net at 0800 h (morning) and at 1400 h (Afternoon) by holding the net with handle and ring end nearest to the ground. The net was swung from side to side in a full 180-degree arc on short vegetation and in the air. Collected insects were anaesthetized by placing them in a labelled 250 mL beaker, covered with aluminum foil, containing 70% Chloroform, soaked in cotton wool. Insects were taken to the lab, identified, counted and recorded.

3.4 Implication of sampling time on distribution and abundance of insect species

Habitats were identified as indicated in 2.3.1 above, about 100 m apart. The habitats were secured from any human alteration for the study period. One hundred sweeps were a standard procedure (Shweta and Rajmohana, 2015).

Insects were collected 2-times a week but twice daily at 0800 h and 1400 h using sweep net, sweeping the net from side to side on vegetation and air. Collections were emptied in 250 mL beakers, secured with aluminum foil, containing 70% alcohol, soaked in cotton wool. Invertebrates were identified in the lab, counted and recorded.

3.5 Identification of edible species of flying insects

Three habitats were identified and labeled as open-field, botanical garden and water-shed, and were secured from any disturbance by fencing. Sweep net was standardized by making only 100 sweeps during collection as described by Shweta and Rajmohana (2015).

Invertebrates were collected on sites in the morning and afternoon hours (0800 h and 1400 h) using sweep nets, twice a week. Collected insects were emptied in a beaker (25 mL) containing cotton wool soaked in 70% chloroform. The beaker was closed with aluminum foil to prevent evaporation. The collected insects were taken to the laboratory, spread on a white sheet on the lab bench, identified, counted and recorded. Identified insects were pinned on the board to dry and photo taken. Photographed insects were printed and questionnaires developed for respondents to identify the edible and Non-edible insects. Three (n= 3) categories of respondents were involved in the study (students, teaching staff and Non-teaching staff). In each category, one hundred (n= 100) participants were randomly selected making a total sample size of three hundred (n= 300).

3.6 Statistical analysis

Data entry and validation was done using MS-excel 2010 version. Comparison of habitats types was done by Analysis of variance (ANOVA) at 5% significant level. The questionnaires were analyzed with weighted mean descriptive statistics using SPSS computer package version 20.0. Preferred sampling time (Morning or afternoon) was determined using independent sample t-test. All values were expressed as mean ± Standard error (SE).

Authors’ contributions

OBM designed the study, carried out the experiment, performed the statistical analysis, wrote and edited the manuscript. IAL, collected the data and edited the manuscript. CB collected the data and edited the manuscript. WFM participated in supervision, coordination and edited the manuscript. ACA participated in drafting and edited the manuscript. JMM participated in the design and supervision of the study. All authors read and approved the final manuscript.

Acknowledgements

We thank Kisumu Polytechnic staff; Lilian Akinyi and Willis Ochanda for chemical preparation and insect specimen storage. We also thank the Kisumu National Polytechnic management for providing the ground, laboratory space, chemicals and equipment for conducting research in collaboration with icipe-Thomas Odhiambo Campus.

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