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Photo 1. Crickets at 1 week of age |
Photo 2. The cages housing the crickets |
| Livestock Research for Rural Development 36 (4) 2024 | LRRD Search | LRRD Misssion | Guide for preparation of papers | LRRD Newsletter | Citation of this paper |
This study aimed to determine the appropriate age of two-spotted crickets (Gryllus bimaculatus) for harvest to get optimum growth and survival rate, and low feed conversion ratio. The seven thousand and two hundred crickets at 7 days of age were arranged in a completely randomized design to harvest at 4 stages of age (4, 5, 6 and 7 weeks of age) and 6 replications. Crickets were fed on a concentrate with 22% crude protein content and fresh cassava leaves ad libitum. The experiment lasted for 6 weeks.
The results show that daily weight gain of crickets when harvested at 5 weeks of age (35.8 mg/head/day) was higher than the other treatments (P<0.01). Total biomass production of crickets harvested at 5 weeks (229 g) was not a significantly different to that at week 6 (232 g) and 7 (217 g). However, the feed conversion ratio of crickets harvested at 5 weeks of age (1.55) was lower than that of crickets harvest at 6 weeks (1.79) and 7 weeks of age (2.57) (P <0.01). Survival rate of crickets harvested at 5 weeks (76%) was significantly higher than compared with crickets harvest at 6 weeks (71.72%) and 7 weeks of age (68.83%) (P<0.01). Therefore, the results confirmed that the optimum time to harvest Gryllus bimaculatus crickets was 5 weeks of age.
Key words: two-spotted crickets, harvesting ages, feed conversion ratio, survival rate
The rapid increase in the world's population has escalated the demand for food security while the exploitation of available resources for food production will quickly reach its limits (FAO 2017), according to FAO global population is expected to reach 9.7 billion by 2050. Alternative food sources for humans and feed for animals are emergently being explored to overcome the planet's finite resources with a sense of sustainable production for food security (FAO 2022). Historically, collecting and eating insects (entomophagy) has a long tradition in Southeast Asian countries with relatively widespread use in the region (Mitchaothai et al 2022). However, cricket farming has only emerged over the last decade as a new venture of livestock production, mainly for domestic consumption.
In practice, smallholder farmers in the South of Vietnam have gained more interest in the mass rearing of two-spotted cricket (Gryllus bimaculatus) for food due to a more acceptable taste (e.g., big in size, meaty, fatty and fragrant). While Mitchaothai et al. (2022) and Ngonga et al (2020) confirmed it is in short production cycle among edible cricket production and abundant returns. In addition, crickets (Gryllus bimaculatus) are interesting as food because they are rich in protein (58-78%) and trace minerals (FAO 2013; Adul Razak et al 2012; Finke et al 2002). Previous studies in the area were focused on the utilization of available feed sources for feeding G. bimaculatusand rearing densityat farm conditions (Vo Lam et al 2023; Bui Phan Thu Hang 2022; Vo Lam et al 2022; Bui Phan Thu Hang et al 2020). However, there is not much available information about the appropriate harvest periods to get the optimum growth of G. bimaculatus crickets in captivity in Vietnam.
This research was designed to evaluate the growth performance at different ages of development stage. The hypothesis was that the optimum weight gain of crickets would be around the growth phase due to the accumulation of nutrients of feed.
This study was carried out in HLF/Crickets farm, Long Xuyen city, An Giang province, Vietnam. The crickets Gryllus bimaculatus used in the present research were sourced from a rearing unit in An Giang University. The crickets (n = 7 200 pinheads; 7 days old (Photo 1)) raised in plastic containers of 57 cm x 38 cm x 21 cm, given with cardboard egg cartons for hiding and moulting areas. They were randomly assigned to 24 plastic containers and harvested at 4 (before the last moulting), 5 (adult), 6 (bearing eggs) and 7 (laying eggs) weeks of age, respectively. These harvest milestones were selected based on physiological characteristics of G. bimaculatus posed in practice, these are the growth stage of development and the optimum stage of biomass accumulation.
The experiment was a complete randomized design with 4 treatments and 6 replications and lasted for 6 weeks.
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Photo 1. Crickets at 1 week of age |
Photo 2. The cages housing the crickets |
Crickets were fed on a concentrate with 22% crude protein content (Table 1) and fresh sweet cassava leaves. The feed and water were supplied ad libitum . The rearing procedure was similar during the experiment. Feeds offered and refusal 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. The relative and absolute growth, feed conversion ratio, biomass production and survival rate were also calculated at the end of the experiment.
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Table 1. Ingredients and chemical composition of diet (% as DM) |
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Ingredients |
Experimental ration (%) |
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Rice bran |
34 |
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Maize |
35 |
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Soybean meal |
18 |
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Fish meal |
12 |
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Premix mineral-vitamin |
1 |
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Chemical compositions, % of DM |
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Crude protein |
22.0 |
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Ether extract |
7.0 |
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Crude fiber |
4.9 |
The ingredients, cassava leaves, feeds offered and refused were analysed for DM, CP, CF and EE according to AOAC (2005).
The experimental data were subjected to analysis of variance using the General Linear Model (GLM) procedure of Minitab Software Release version 17 (2013). Sources of variation were treatments and error. The fitting polynomial functions (Microsoft Excel Version 10) to the data was used to determine the response curves, relating outputs (weight gain and feed conversion) with inputs (harvested crickets of age).
Dry matter, CP, OM and EE intake were significantly improved with the increasing the age of crickets harvested (Table 2, Figure 1), the highest at 7 weeks of age, and the lowest in crickets harvested at 4 weeks of age. The results of the present research agreed with Mitchaothai (2020), who reported feed intake of crickets increased after 42 days of age.
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Table 2. Feed intake during the experiment, mg/head/day |
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Item |
4WO |
5WO |
6WO |
7WO |
SEM |
p |
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Dry matter |
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Concentrate |
28.0 c |
47.3 b |
46.3 b |
54.7 a |
0.79 |
<0.01 |
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Cassava leaves |
4.33 c |
8.58 ab |
7.99 b |
9.76 a |
0.32 |
<0.01 |
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Total dry matter |
32.3 c |
55.8 b |
54.3 b |
64.5 a |
0.75 |
<0.01 |
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Crude protein |
7.62 c |
13.2 b |
12.8 b |
15.3 a |
0.17 |
<0.01 |
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Organic matter |
30.1 c |
52.0 b |
50.6 b |
60.2 a |
0.69 |
<0.01 |
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Ether extract |
2.13 c |
3.64 b |
3.56 b |
4.22 a |
0.05 |
<0.01 |
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Crude fiber |
1.91 c |
3.39 b |
3.25 b |
3.80 a |
0.06 |
<0.01 |
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4WO, 5WO, 6WO and 7WO: denoted the crickets were harvested at 4, 5, 6 and 7 weeks of age.
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Relative and absolute growth of experimental crickets were presented in Table 3. The relative growth of crickets is the highest at 1 - 2 weeks of age (160%), then quickly decreased (p<0.01). The absolute growth of crickets were low at the 1 to 2 weeks of age (4.95 mg/head/day) and increases very rapidly (around 13 times) in crickets at the 3 - 4 weeks of age. Absolute growth also gradually decreased with the increasing age of the cricket.
The relative and absolute growth of experimental crickets at the stage of 6 - 7 weeks had negative values. Currently, no reports have been found to explain this fact. However, this phenomenon can be explained by the fact that after the last molting, crickets spend almost all stored energy on the reproductive process and then end their life cycle after a short stage of the collective reproductive.
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Table 3. Relative growth rate and absolute growth rate of experimental crickets |
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Age |
Relative |
Absolute growth rate, |
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7-14 days |
160 a |
4.95 e |
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14-21 days |
141 b |
27.1 c |
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21-28 days |
99.0 c |
64.0 a |
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28-35 days |
39.1 d |
47.1 b |
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35-42 days |
7.32 e |
11.1 d |
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42-49 days |
-4.42 f |
-6.79 f |
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p |
<0.01 |
<0.01 |
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abcdef Means within columns with different superscripts are different at p<0.05 |
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The daily weigh gain of crickets harvested at 5 weeks of age was the highest (35.8 mg/head/day) compared to crickets harvested at 4 (31.7 mg/head/day), 6 (30.6 mg/head/day) and at 7 weeks of age (24.9 mg/head/day) (Table 4, Figure 2). This result is similar previous researches by Vo Lam et al (2022); Bui Phan Thu Hang et al (2020) conducted on two-spotted crickets when feeding crickets with a concentrate with 22% CP and Ngonga et al. (2020) raised with commercial feed improvised cage systems. Feed conversion increased up to in crickets harvested at 7 weeks age (Figure 3).
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Table 4. Daily weight gain and feed conversion ratio of experimental crickets |
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Items |
4WO |
5WO |
6WO |
7WO |
SEM |
p |
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Initial BW (mg/con) |
4.15 |
4.27 |
4.35 |
4.29 |
0.08 |
0.45 |
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Final BW (mg/con) |
670 c |
1006 b |
1076 a |
1053 ab |
14.2 |
<0.01 |
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ADG (mg/head/day) |
31.7 b |
35.8 a |
30.6 b |
24.9 c |
0.39 |
<0.01 |
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Relative growth rate (%) |
197.5 b |
198.3 a |
198.4 a |
198.4 a |
0.04 |
<0.01 |
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FCR (mgDM/mgADG) |
1.02 d |
1.55 c |
1.79 b |
2.57 a |
0.04 |
<0.01 |
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4WO, 5WO, 6WO and 7WO: crickets harvested at 4, 5, 6
and 7 weeks of age.
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Figure 1. Effect of harvesting ages on DM intake of crickets |
Figure 2. Effect of harvesting ages on growth of crickets |
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Figure 3. Effect of harvesting ages on feed conversion ratio of crickets |
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Table 5. Maturation, biomass production and survival rate of experimental crickets |
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Items |
Treatments |
SEM |
p |
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4WO |
5WO |
6WO |
7WO |
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Maturation rate (%) |
0.00 d |
75.3 c |
98.4 b |
100 a |
0.32 |
<0.01 |
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Total biomass (g) |
173 c |
229 ab |
232 a |
217 b |
3.25 |
<0.01 |
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Survival rate (%) |
85.9 a |
76.0 b |
71.7 c |
68.8 d |
0.50 |
<0.01 |
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4WO, 5WO, 6WO and 7WO: denoted the crickets were
harvested at 4, 5, 6 and 7 weeks of age.
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Photo 3. Crickets at 4 weeks of age |
Photo 4. Crickets at 5 weeks of age |
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Photo 5. Crickets at 6 weeks of age |
Photo 6. Crickets at 7 weeks of age |
Feed intake and feed conversion ratio of experimental crickets gradually increased with age, but the average daily weight gain of crickets tended to decrease with age and was the highest in crickets harvested at 5 weeks of age. In addition, the survival rate also decreases with the age of crickets. The results of this study show that G. bimaculatus crickets harvested at 5 weeks of age give good results in terms of ADG, FCR, biomass yield and survival rate.
The authors are grateful for the financial for this research from Vietnam National University Ho Chi Minh City (VNU-HCM) under grand number C 2023-16-05/HÐ-KHCN.
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Bui Phan Thu Hang, Nguyen Van Cop, Dao Thi My Tien and Vo Lam 2022 Effect of fresh foliage leaves on biomass growth of crickets fed rice bran as the basal diet. Livestock Research for Rural Development. Volume 34, Article #36. Retrieved May 14, 2024, from http://www.lrrd.org/lrrd34/5/3436bpth.html
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Food Agricultural Organization 2022 Looking at Edible Insects from a Food Safety Perspective: Challenges and Opportunities for the Sector. Available online: https://www.fao.org/policy-support/tools-and-publications/resourcesdetails/en/c/1394684/ .
Mitchaothai J, Grabowski N T, Lertpatarakomol R, Trairatapiwan T, Chhay T, Keo S and Lukkananukool A 2022 Production performance and nutrient conversion efficiency of field cricket (Gryllus bimaculatus) in mass-rearing conditions. ANimal 12. https://doi.org/10.3390/ani12172263
Ngonga C A, Gor C O, Okuto E A and Ayieko M A 2020 Growth performance of Acheta domesticus and Gryllus bimaculatus production reared under improvised cage system for increased returns and food security. Journal of Insects as Food and Feed 7 (3). https://doi.org/10.3920/JIFF2020.0082
Vo Lam, Nguyen Thi Bich Hanh and Bui Phan Thu Hang 2022 Effect of replacing dietary protein with cassava leaf meal on performance and nutritional composition of two-spotted crickets (Gryllus bimaculatus). Livestock Research for Rural Development. Volume 34, Article #48. Retrieved May 14, 2024, from http://www.lrrd.org/lrrd34/6/3448vo.html
Vo Lam, Nguyen Thi Ut Em and Bui Phan Thu Hang 2023 Effect of rearing density on growth performance and survival rate of field cricket (Gryllus bimaculatus). Livestock Research for Rural Development. Volume 35, Article #39. Retrieved May 14, 2024, from http://www.lrrd.org/lrrd35/5/3539bpth.html