Habitats of antlions larvae (Neuroptera: Myrmeleontidae) in the Sudano-Guinean and Sudano-Sahelian zones of Cameroon

Antlions (Insecta: Neuroptera) are flying insect associated with sunny weather at adult stage. During larval stage, xerophilous insects they are familiar to arid soils with critical temperature, hygrometry and luminosity. These 3 climatic parameters are used to discriminate among larval habitats of antlions in the Soudano Guinean and Soudano Sahelian Savannah of Cameroon. Investigations made during 3 years from 2015 to 2018, consisted in survey of larvae’s funnels. At the level of each active pit-traps, the 3 parameters were recorded during the whole dry season. Analysis of data computerised pointed out that larvae of Cueta bourborni Navas 1935, and those of Cueta sp, are frequent within sites that are warm (40.57±0.64°C to 52.14±4.08°C); dry (10.91±0.8216.81±2.74%rh) and lighted (94380.2 ±16109.4 lux) habitats. On the other hand, larvae of Myrmeleon quinquemaculatus Hagen 1853 are associated with sites that are: humid (75.46±4.50% RH), cloudy (448.232±300. 491 lux) with tendency to moist (22.11±0.88°C to 28.10 ±2.14°C). Presence of C. bourbonni sometimes in the moisty Soudano Guinean zone could only indicate episode of warming. DOI: https://dx.doi.org/10.4314/jasem.v24i4.18 Copyright: Copyright © 2020 Bakodi et al. This is an open access article distributed under the Creative Commons Attribution License (CCL), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Dates: Received: 11 February 2020; Revised: 14 March 2020; Accepted: 22 March 2020

Habitat selection is the process by which organisms distinguish and choose among several sites of different qualities, the one that is ideal for their survival because it provides them with the highest fitness gain (Clobert et al., 2012). At the population level, this habitat choice significantly affects the way individuals are distributed among habitats, which in turn influences population dynamics (Bowler and Benton, 2005). To assess habitat quality, animals take into account various biotic and abiotic factors, particularly resource availability and habitat structure (Dubois et al., 2009). Antlions larvae prefer a specific micro-habitat on fine sand or soft soil (Scharf et al., 2011). They are sessile and their mobility being mostly reduced to walking backwards over very short distances to hide (Ngamo et al., 2010;Ngamo et al., 2014). Larvae are inferred from the site chosen by the female at the time of oviposition (Ngamo et al., 2016). Site selection is thus dictated by habitat characteristics such as shade (Scharf et al., 2008a), photoperiod (Scharf et al., 2008b), substrate moisture (Morrison, 2004), temperature (Bakoidi et al., 2018), disturbance (Barkae et al., 2010), substrate particle size, substrate depth and hardness (Klokocovnik et al., 2012), substrate density , prey availability and abundance . Larval habitats in forested areas, except in Mediterranean regions are distinguished by two major characteristics: open (unprotected from rain, direct sunlight or any illumination) (Barkae et al., 2012), and protected or covered (protected from rain, disturbance, direct sunlight or any illumination) (Abraham, 2006;Scharf et al., 2008b;Adar et al., 2016;Klokocovnik et al., 2016). However, whether or not they are open to sun and rain is not sufficient to discriminate between the different habitats of these insects as they are very sensitive to ecological disturbance. Climatic factors may further specify the characteristics of habitats that best favour the development of antlion larvae to the point that they are bio-indicators. The objective of this work is to provide more specifications in the characterization of antlions larval habitats using abiotic characteristics (temperature, relative humidity, light) that have an impact on their survival. Current events in recent years cite global warming as a threat to the survival of humanity. Research on life forms or behaviours resilient to these harsh conditions is interesting in this context. The aim is to discover forms of life that are resistant to extreme conditions for mankind.

MATERIALS AND METHODS
Presentation of the study area: The sampling site extends from the Adamawa highlands to the Chad lake. It includes the moist savannahs of the Adamawa Region, the Benoue lowlands and the Logone Plains and Mandaras highlands in sahelo Sahelian zone with extreme drought, 2 agro-ecological zones are concerned.
The Guinean High Savannah zone, which covers most of the Adamawa Plateau, is characterized by a humid climate with an average of 1000 mm of rainfall per year. The wet season extends from April to October with maximum rainfall between August-September (Djoufack- Manetsa et al., 2011). The dry season lasts between four and five months, with an average annual temperature of 28°C and a temperature difference of 6°C (Tchotsoua and Gonne, 2010). In this zone, antlions larval collection and recordings of climatic parameters were carried out in Ngaoundéré and its surroundings. The Sudano-Sahelian zone with a semi-arid climate covering the Far North and North Regions. It is characterized by a long dry season (9 months) and a short rainy season (3 months). It receives an average rainfall of between 400 and 1,200 mm/year and has a great diversity of soils. The highest temperatures are observed in the dry season (over 40°C in March and April) (Fotsing, 2009). The relative humidity of the air is between 30 and 35% and the further north one goes the harsher the climate becomes. The following localities: Garoua, Kaélé, Yagoua and Pouss were chosen for the collection of antlions larvae and the recording of climatic parameters at the level of active pits.
Habitat characterisation and antlions larval population dynamics: Observations of antlions pits were made on the University of Ngaoundéré Campus site in the Sudano-Guinean zone on a weekly basis for two years, 2016 and 2017 in order to note the appearance of the first pits at early dry season and disappearance of the last ones at the return of the rains of each year and to establish the dynamics of the larval pits. Thus, once a week the presence of pits was noted and the numbers of pits recorded whether under trees, near buildings or in open areas over an area of 25m². During the period of high density, under trees (March: temperature 35°C RH 27% and April: temperature 34°C; RH 36%) and closer to buildings or under wet covered habitat (every month), pits were counted on four 25m² grids for each sampling site.
On the different sites in the Sahelian and Guinean zones, at the level of each active pit within the chosen 25cm² area, the ground climatic parameters were recorded during the months of high abundance. For the whole zone, continuous measurements of climatic data were made using a HOBO onset H8 data logger from 2015 to 2018.
Climatic parameters recorded at the level of the ground at each sampling were analysed by one-way ANOVA test. In the post test a Duncan procedure was proceeding to access the less significant difference among means observed.

Rearing of collected larvae in laboratory:
The antlions larvae extracted from the active pits brought back to the laboratory are raised in plastic cups filled to a third with sea sand sieved to 500 microns placed in rearing cages provide with temperature control monitor. Rearing was made in cages monitored at 22°C, 27°C, 40°C. All observed larvae were fed ad libitum on third instar larvae of Tribolium castaneum Herbst 1797 (Coleoptera: Tenebrionidae). Growing of larvae was followed till it turns into a cocoon. The cocoon is observed separately till adult emerges.

Pits traps Fluctuation and Characterisation of Antlions Larval Habitats: (a). Seasonal Fluctuation in pits of Antlions Larvae:
The variation in the number of pits in different habitats in the Study Area during the two years of observations shows that the number of pits within a single habitat varies from month to month ( Figure 2 and Scharf et al., (2009)  (b) Influence of hygrometry on the occurrence of pit building antlion larvae: Hygrometry is an important climatic factor in characterising the habitat of antlions larvae. Larval activity, as a function of hygrometry varies from one agro-ecological zone to another and also from one habitat to another (Figure 3a and b). In the Sudano-Guinean zone, larvae in covered and cool environments are active from 85% RH and can withstand dry conditions up to 25% RH (Figure 3a).
.   (Figure 3b). Peaks in their activity are observed at 14%, 22% and 11% RH values at which more than 70% of larval activity has been observed.
The activity curve of the species in the covered environment shows that larval activity can range from 20% to 35% RH and are very active from 30% RH and moderately active at 22% and 33% RH.
(c) Influence of the temperature on the occurrence of pit building antlion larvae: Recording of ground temperature at active pits in the Sudano-Guinean zone shows that larvae are active from 18°C to 42°C, while in the Sudano-Sahelian zone activity ranges from 31°C to 51°C (Figure 4).   (Figure 4b).  activities of antlion larvae. Figure 5 presents the activity of antlion larvae as a function of light intensity and shows that activities are observed from 15x1000 lux up to 106.592x1000 lux. In the Sudano-Guinean zone, larval activity shows two peaks of abundance: a peak at 35x1000 lux corresponding to the lowest values and a peak of 65 to 75x1000 lux corresponding to the highest values. Larvae in covered habitats have two peaks of activity at 35x1000 lux, which is the highest, and a second peak of activity at 65x1000 lux; species in open habitats have a single peak at 75x1000 lux (Figure5a). In the Sudano-Sahelian zone, larval activities show two peaks of abundance: a peak at 36.930x1000 lux corresponding to the lowest values and the peak from 83.645 to 106.592x1000 lux corresponding to the highest values (Figure 5b). Larvae from open habitats have two peaks of activity at 106.592x1000 lux which is the highest and a second one at 83.645x1000 lux; species from covered habitats, on the other hand, have a single peak at 36.930x1000lux

(e)Characterization of habitats and diversity of antlions larvae:
The recordings and analysis of climatic parameters such as relative humidity (Table  1) at the pits of antlions allow us to distinguish between two types of habitat: open and covered environments. Within the covered habitats, temperature and luminosity recordings made it possible to separate these environments into wet and dry habitats. The analysis of variance shows that the difference is significant for each parameter recorded (Temperature: F=273.82*** and ndl=4:28; for Relative humidity: F=80.35*** and ndl=4: 282; for light intensity: F=282.81*** and ndl=4: 282). Duncan's test separates them into 4 classes for temperature, 3 classes for relative humidity and 4 classes for light intensity. Variations in the density of antlion larvae are directly related to fluctuations in climatic parameters such as temperature, luminosity and relative humidity. However, it is clear that antlions in a humid environment prefer temperatures above 18°C and a mean sunshine below 45000Lux and a relative humidity above 45%. As far as the larvae of the fresh canopy living under the trees are concerned, they prefer temperatures between 30°C and 42°C and a relative humidity lower than 45% and higher than 25% with a light intensity higher than 45000Lux. For the larvae of the open environment their activities are best carried out at temperatures above 42°C, a relative humidity below 25°C and a light intensity above 65000Lux. Therefore, higher or lower values of climatic parameters such as temperature, relative humidity and light intensity inhibit the activities of antlion larvae in their natural environment. These results are coherent with the work of Maogé et al., (2014) who showed that the hottest periods of the year correspond to the high density of pits of antlion larvae in the northern regions of Cameroon. The recorded climatic parameters and the distribution of larvae in the different sites show that not all antlions live in habitats with the same characteristics. The major characteristics: open (unprotected from rain, direct sunlight, etc.) (Barkae et al., 2012), covered (protected from rain, disturbance, direct sunlight, etc.) (Abraham, 2006;Adar et al., 2016;Klokocovnik et al., 2016) give a first idea of the larval habitats taking into account the relative humidity factor and sun exposure. This is not sufficient to qualify a species, because the position of a species in a habitat depends on the area and the seasons of the same area, this is the case with M.