Bioecology of Phonoctonus lutescens (Guérin Meneville and Percheron) Predator of Dysdercus voëlkeri (Schmidt, 1932), Feeding on Dysdercus voëlkeri in the Laboratory Conditions in Burkina Faso

The study was conducted at the agricultural experimental station of Farako-Bâ, specifically in the Cotton Program. Insects were collected in Farako-Bâ field and raised in the Cotton Program. Dysdercus voëlkeri Schmidt is one of cotton cultivation main pests in Burkina Faso. The control of this devastating cotton bug is based on chemical using. For researching alternative solutions, a part of the biological control method was investigated by using Phonoctonus lutescens which is D. vöelkeri natural enemy, in order to develop a biological control method. To understand the bioecology of P. lutescens, our study has been carried out on this insect under laboratory conditions when it was feed on its prey which is D. voëlkeri. The results have demonstrated that the pre-copulation period is 9.33 ± 2.14 days. The oviposition period is 6.97 ± 1.47 days, after which 366.73 ± 27.43 eggs on average are laid with 92.33% ± 4% hatchability. From hatching to adult stage, P. lutescens larvae development goes through five stages with variable durations according to the stage. The results showed that the development cycle lasted 57.23 ± 5.81 days at a temperature of 27.5˚C ± 2˚C and a relative humidity of 42% ± 3%. Survival rates ranged from 92% to 97.47%. Males and females lived respectively 87.5 ± 27.99 days and 107.97 ± 24.21 days. These results could permit a better use of P. lutescens through a mass rearing and an optimization of D. voëlkeri biological control.


Introduction
In Sahelian countries in general and in Burkina Faso in particular, cotton is one of the most cultivated plants. Burkina Faso is one of the main cotton producers in Africa. The contribution of Burkina Faso in world cotton production was 2.6 percent [1]. The cotton fields are under heavy parasites pressure with a very broad spectrum of pests with more than 70 arthropods species (Aphids, bugs and mites) diplopods and nematodes [2] [3]. Cotton cultivation is being adapted fruitfully and is likely to interest the protection of crop as a whole. This is probably due to the importance of crop losses caused by pest including Dysdercus voëlkeri at the end of cotton's cycle [4]. In general, the ability of insects to get around phytosanitary practices explains why scientifics are turning more and more towards the most ecological practices with the use of biological control agents. For example, [5] and [6], in a biological control approach, showed the potential of reduviidae and identified Rhynocorisalbopilosus and P. lutescens sp Guerin Percheron (Heteroptera) as predators of Dysdercus species. However, in Burkina Faso where cotton production is important, very little work exists on this insect which presence was previously announced by several authors. Apart from the summary description and systematic studied by [7] and the measurements made by [8], there are very few studies on the bioecology and its real potential for predation as a biological control agent. However, according to [9], knowledge of biology and predator voracity measurement is an important step in assessing the potential of a biological control. Thus, knowledge of the biological parameters of P. lutescens and ecological factors are essential for the elaboration of an integrated control program against D. voëlkeri in cotton growing in Burkina Faso. The final objective is to explain the biology mechanisms of P. lutescens in cotton farming areas.

Biological Material
The collection of derived insects was carried out from September 2016 to May 2017, in Farako-Bâ on Bobo-Banfora axis, about 10 km from Bobo-Dioulasso, located at 04˚20'W and 11˚06'E. Strains were manually picked up [10]. The collection was made with 25 cm × 25 cm × 25 cm plastic pots. Larval and adults' individuals of D. voëlkeri and P. lutescens were killed and placed in alcohol, then identified in CNRST (Centre National de la Recherche Scientifique et Technologique) laboratory by using [11] and [12] determination keys. Some works have been carried out on the subject, including those of [8], on the biology of certain Phonoctonus sp in West Africa, and another one on the description and distinction of the larvae and exuvia of Rhynocoris albopilosus done by [13] and the studies of [14] on the biology of the reduviidae in North America.

Phonoctonus lutescens Study Conditions
For this study, eggs and larvae were obtained from spawning pairs in cages kept in captivity. After hatching, the larvae are individualized and kept in captivity in  (30) females and Thirty (30) males were selected for the calculation of adults' longevity. Hundred (100) larvae were used for the survival rate. Hundred (100) larvae and Hundred (100) adults were killed and placed in 70% alcohol for morphometric measurements [15], which were performed using the digital caliper of maximum capacity 150 mm and the eye magnifier at 10 × 10 magnification.

P. lutescens Biological Parameters Study
The description of egg was based on its coloring and its size based on the study made on P. lutescens description [8]. Larvae and adults measurements were described based on the work on description and distinction of larvae and exuvia of Rhynocoris albopilosus done by [13]. The biological characteristics measured were: • The mean survival rate: The mean survival rate was calculated for each larval stage from: larvae variation rate [16]. (bi = incubation period, di = larval duration, dim = time from imago to adult and ki = adult number). • Sex ratio: In the adult stage, males and females were identified and counted and the sex ratios were obtained [16].
number of males Sex ratio number of females = • Pre-copulation: pre-copulation is the period that separates the imaginable moult from the first mating. The average period of pre-copulation is obtained according to the following calculation: average period of pre-copulation (days) [16].

P. lutescens Morphometric Parameters Study
The morphological characters measured were done by [8]:

P. lutescens Bioecological Parameters Study
The ecological parameters measured were essentially focused on temperature and relative humidity.

Statistical Analysis
For statistical analysis, the data collected was analyzed with the XL STAT software version 2007.7.02. The mean separation was performed by the Fisher test (LSD) at 5% probability level.

1) Eggs
The newly eggs of P. lutescens are light brown in color and dark 24 hours after laying They have a soft appearance and slightly glued to each over. The eggs are elongated but have a rounded posterior pole and an anterior pole truncated right and occupied by a hatching operculum. Eggs are more or less asymmetrical. Variance analysis reveals a highly significant difference between the length and width of eggs. The measures done on 100 eggs indicate 1.29 mm for width and 2.97 for length ( Table 1). Analysis of the incubation times showed that it was between 9 and 12 days and an average of 10

4) Measurement on Female and Male Bodies Parts of P. lutescens
The statistical analysis reveals three levels of significance for all parts of P. lutescens female and malebodies. Also, it reveals a highly significant difference (P = 0.0001) in measurements made on the body length, the abdomen and the three pairs articles of legs in female and male. There is also a significant difference (P = 0.004) in the length of rostrum and that of the average femur (P = 0.009). On the other hand, it does not reveal any significant difference between the articles for head, antenna and different parts of the tarsusdimension measurements, the femur length average (P = 0.355) ( Table 3).

5) Larval Survival
Rates and Sex Ratio of P. lutescens A significant difference was not noticed between larval survival stages ( Figure   2). But an increase on larval survival rate was observed from L1 to L4; a rate of

6) Mean Time of Pre-Copulation and Pre-Oviposition of Female
A significant difference was observed between mean period of pre-copulation time that was 9.33 ± 2.14 days after imaginal moult, and the average pre-oviposition time estimated at 6.97 ± 1.47 days (Table 5).

7) Adult's Longevity and Eggs Laid Per Female
For the follow up of eggs laid, females were observed from the first hatching to the last one. Mean number eggs laid have been estimated at 366.73 ± 27.43 with 38.1 ± 9.21 as mean frequency of eggs laid per female ( Table 6). Analysis of variance reveals that female life is significantly longer than that of male. Females and males lived respectively 107.97 ± 24.21 days and 87.5 ± 27.99 days ( Table 7).

Temperature
Relative humidity

Discussion
The observation on average incubation time during the experiment was 10.5 ± 1.41 days. This observations on incubation time differ from those of several authors Sahayaraj and Paulraj (2001) [17], Swadener and Yonke (1973) [18]. Vennison and Ambrose (1992) [19] observed for Rhynocorismarginatus with 6.81 ± 0.10 days. This difference could be explained by the fact that it is not the same species and fed on different diet. Although it is also known that the minimum period of life would accelerate the multiplication process of the predatory insect which average time are shorter. Eggs measurements gave 1.29 ± 0.14 mm for the width and 2.97 ± 0.25 mm for the length. These results are similar to those found by Stride (1956) [13] who worked on P. lutescens and R. albopilosus, concluded at the end of their study an appearance of a pair of wing draft at the level of mesonotum and metanotum at the end of the third instar. For the increase in size, an extension of the body of P. lutescens observed when passing from one stage to another. This increase in size could be related to a consumption of D.voëlkeri which increases with the age of the larvae to reach the fifth stage, the maximum of its consumption since the larvae of last stage need to accumulate reserves for the following stages moult and adult (stopping moult and reducing intake at the adult stage) Vargas (1970) [24], Quiroz (1976) [25] and Bogorni, (1999) [26].  [27] in P. bimaculatus in the laboratory on three diets obtained respectively with 1:0.71, 1:0.65 and 1:0.55. But it should also be pointed out that a difference seems to emerge from a sex relationship observed in laboratory reared reduviids such as Coranussiva and Brassivolahystrix and that it favors S. reclinatus Vennison and Ambrose (1992) [19]. The periods of pre-copulation and pre-oviposition obtained during rearing were respectively 9.33 ± 2.14 et 6.97 ± 1.47 days, and therefore shorter. These results are consistent with the results of Ambrose (1999) [28], who reported a pre-oviposition period of 6  Duviard (1977) [29], Babin (2009) [30]. In our study, the larvae were raised under optimal conditions, protected in particular from their natural enemies, and it is likely that the survival rates we obtained do not reflect the true survival capabilities of the larvae in the wild Cahan, P. (1961) [31]. Regarding the correlation between the development cycle and temperature, longer cycle of 61, 62, 63, 64, 65, 66 and 67 days are observed, under temperature varying between 25˚C and 26.5˚C. The study of the variation of the biological characters of an insect depends on temperature and humidity. The dependence may show that the variation of biological character is related to the evaporation phenomenon but that the importance of this depends to a large extent of temperature Brown et al. (2004) [32].
It has been observed that above 26.5˚C, the temperatures influence the dura-

Conclusion
The rearing presented in this study allowed us to maintain P. lutescens population for almost one year. The results suggest that changes in reproduction para-meters may account for a significant portion of the population dynamics of P. lutescens in the field. It isevident that in the wild, P. lutescens populations are influenced by a wide range of factors related to the cotton growing environment and to human intervention. These factors affect the ability to develop and propagate populations and consequently their density in fields. The knowledge obtained on P. lutescens biology opens up avenues for the development of agro-ecological management strategies of this predator. A new study is therefore needed to determine the role of P. lutescens survival in its natural habitat.