Citation of this paper

Effect of rearing density on growth performance and survival rate of field cricket (Gryllus bimaculatus)

Vo Lam^1,2, Nguyen Thi Ut Em³ and Bui Phan Thu Hang^1,2

¹ Department of Animal Sciences and Veterinary Medicine, An Giang University
bpthang.agu@gmail.com
² Vietnam National University Ho Chi Minh City, Vietnam
³ An Giang Agricultural Extension Center

Abstract

This experiment was carried to examine the effect of rearing density on growth performance and survival rate of field cricket Gryllus bimaculatus in Mekong Delta of Vietnam. The nine thousand crickets at 7 days of age were arranged in a completely randomized design with 5 different densities (200, 250, 300, 350 and 400 individuals per cage) and 6 replications. Crickets were fed on concentrate diet with 22% crude protein content and fresh sweet cassava leaves ad libitum. The experiment lasted for 4 weeks.

The results showed that the nutrient intake was suppressed in increasing the number of crickets per cage. In the population density (200-300 crickets per cage), the daily weight gain as well as survival rate were high, as compared to in 350-400 crickets per cage. These results indicate that population density impacts nutrient intake, growth and survival rates of cricket Gryllus bimaculatus.

Key words: density, Gryllus bimaculatus, performance, survive

Introduction

Cricket Gryllus bimaculatus is one of the most abundant cricket species in subtropical and tropical countries. They often live solitary under stones or in burrows. They are widely distributed, easily collected and raised in the laboratory. They also have a simple life cycle and produce many eggs. Cricket is reared in captivity for used as a high source of proteins for human, quail, chicken, rabbit and many insectivores (Ibler et al 2009; Lam Viet Chieu 2020; Tran Minh Huy 2020; Bui Phan Thu Hang et al 2023). However, the effects of crowded conditions on the life span of Gryllus bimaculatus is not much available information. Allee (1934) determined that the effect of rearing density on the growth, development, and survival of many species of animals varies depending upon developmental stage and species. As the first reported in Chauvin (1958) house cricket (Acheta domestica) kept alone grew more slowly than those maintained in groups. The oocytes of female house crickets raised individually more slowly than did those of females raised in groups matured (McFarlane and Alli 1988; Gadot et al 1989, Clifford and Woodring 1990). Under crowded conditions, fecundity of cricket Acheta domestica was declined (Bradley 1976); insects were susceptible to insecticides (Zutshi et al 1980).

Therefore, the scope of the present experiment was to investigate the effect of population density on the growth performance and survival rate of cricket Gryllus bimaculatus.

Materials and methods

Location, animals and experimental design

The experiment was conducted in an HLF/Crickets farm, Long Xuyen city, An Giang province. The crickets Gryllus bimaculatus (n = 9,000; 1 week old) used in the present research were sourced from a rearing unit in An Giang University. Crickets were raised in plastic containers of 50 cm x 30 cm x 20 cm, given with cardboard egg cartons for hiding and moulting areas. They were randomly assigned to raising density levels: 200, 250, 300, 350, and 400 individuals per container, respectively. The experiment was a complete randomized design with 6 replications and lasted for 4 weeks.

Management and observation

Crickets were fed on concentrate diet with 22% crude protein content (Table 1) and fresh sweet cassava leaves. The feed and water were supplied ad libitum. The rearing procedures was almost the similar during the experiment. Feeds offered and refusals were recorded daily in the morning to identify the feed intake. Crickets in each container were weighed together at the beginning of the research by electric balance (SHINKO GS-3203A) with ± 0.001 g accuracy. Body weight gain was recorded every week. Dry matter conversion rate was calculated by dividing the total DM consumption by the total weight gain. The survival rate was also measured at the end of experiment.

Table 1. Ingredients and chemical composition of diet
Ingredients	Experimental ration (%)

Rice bran	25
Maize	35
Soybean meal	23
Fish meal	16
Premix mineral-vitamin	1
Chemical compositions, % of DM
Crude protein	22.0
Ether extract	9.4
Crude fiber	4.9

Chemical analysis

Feed offered and refused samples were analysed for DM, CP, CF and ash according to AOAC (2005).

Statistical analysis

The data from the experiment were subjected to analysis of variance using the General Linear Model (GLM) procedure of Minitab Software Release version 17 (2013). Sources of variation were population densities and error. Polynomial equations were fitted to the changes for consumed CP and OM, daily weight gain, and survival rate using the Excel option in Microsoft software.

Results and discussion

Feed intake, live weight gain and feed conversion

The cricket raised at an increase in number of individuals per replicate indicated in a decrease of OM and CP consumes (p<0.05) (Table 2). Figure 1 and 2 show that rearing density was highly correlated (p<0.05) with OM intake and CP intake. The DM conversion was no different in rearing densities (p>0.05) (Table 3).

Table 2. Feed intake of crickets at density levels, mg/cricket/day.
Items	200C	250C	300C	350C	400C	SEM	p

Dry matter
Homemade concentrate	42.97	42.18	41.85	40.06	40.95	1.00	0.31
Cassava leaves	6.63	6.97	6.14	6.29	5.66	0.33	0.10
Total	49.60	49.15	47.99	46.35	46.61	1.05	0.14
Crude protein	13.18^a	13.13^a	12.77^ab	11.94^bc	11.53^c	0.27	<0.01
Organic matter	44.48^a	42.86^ab	40.81^ab	39.82^b	40.63^ab	1.12	0.04
Crude fiber	3.21	3.20	3.20	3.28	3.22	0.92	0.96
^abc Means values within rows with different superscripts are different at P<0.05

The beginning of experiment, the body weight of crickets in different densities were similar (p>0.05). The results also show that the body weight and daily weight gain were already reduced in crowded conditions (350-400 crickets per cage) as compared to rearing densities from 200-300 crickets per cage (p<0.05) (Table 3, Figure 3). It was in good agreement with Iba et al (1995), who reported that the increasing in body weight was slow in the crowded crickets. There were trends for reducing survival as cricket density increased (p <0.05) (Table 3, Figure 4). The results of the present research were consistent with Agnew et al (2002), who stated that decreased larval densities of the mosquito (Aedes aegypti) leads to improved larval survival.

Table 3. Growth rate, FCR, and survival rate of crickets at density levels
Items	200C	250C	300C	350C	400C	SEM	p

Initial BW, mg/cricket	3.09	3.05	3.02	3.04	3.04	0.02	0.11
Final BW, mg/cricket	1026^ab	1055^a	1031^ab	978^b	984^b	14.9	<0.01
Weight gain, mg/cricket /day	36.51^ab	37.56^a	36.72^ab	34.80^b	35.05^b	0.53	<0.01
DM feed conversion	1.35	1.31	1.31	1.33	1.33	0.02	0.39
Survival rate, %	75.25^a	72.20^ab	72.83^ab	70.24^ab	68.04^b	1.59	0.04
^ab Means values within rows with different superscripts are different at P<0.05


Figure 1. Curvilinear trend in crude protein intake (mg/head/day) of cricket at density levels	Figure 2. Curvilinear trend in OM intake (mg/head/day) of cricket at density levels

Figure 3. Curvilinear trend in mean weight gain (mg/head/day) of cricket at density levels	Figure 4. Curvilinear trend in survival rate (%) of cricket at density levels

Conclusions

Rearing density is an important factor in nutrient intake, growth performance and survival rate of cricket.
Lower rearing density result in a higher weight gain and survival rate.
In the present research, rearing density from 200 to 300 crickets per cage, has a high growth and survival rates, can be practical application.

Acknowledgements

The authors are grateful acknowledge for the infrastructure support for this research from an HLF/crickets farm in Long Xuyen city, An Giang province. We also acknowledge group of DH20CN students for help with cricket care.

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