Research Article |
Corresponding author: Charly Oumarou Ngoute ( coumaroungoute@yahoo.fr ) Academic editor: Ludivina Barrientos-Lozano
© 2019 Alfiery Laurel Djomnang Nkwala, Franklin Simo Talla, Charly Oumarou Ngoute, Sévilor Kekeunou, Alain Christel Wandji, Marcelle Mbajoun Nzike, Alain Simeu Noutchom, Mpoame Mbida.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Nkwala ALD, Talla FS, Ngoute CO, Kekeunou S, Wandji AC, Nzike MM, Noutchom AS, Mbida M (2019) Morphology, development, and reproduction of Eyprepocnemis plorans ibandana (Orthoptera: Acrididae) in South Cameroon rainforests. Journal of Orthoptera Research 28(2): 145-154. https://doi.org/10.3897/jor.28.33370
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Eyprepocnemis plorans ibandana is a very common grasshopper species in open environments and agricultural systems of tropical Africa. It is a pest that significantly benefits from forest degradation in southern Cameroon, hence the need to study the bioecology of this subspecies. We studied the reproduction as well as the morphological characteristics and development times of the post-embryonic instars of E. p. ibandana. Sixty-one adult pairs were obtained from sixth instar nymphs caught in grassy vegetation in the Nkolbisson area (Yaoundé) and bred in the laboratory. After hatching, the first instar nymphs were individually placed in cages and fed every two days using fresh leaves of Manihot esculenta. The postembryonic development of E. p. ibandana took six instars in the male and six to seven instars in the female. Mean nymphal development took 79.16 ± 0.51 days in males, 89.93 ± 0.58 days in 6 instar females and 94.96 ± 1.22 days in 7 instar females. The survival rate of the first instar was low (53%). However, from the second instar on the survival rate was very high (> 87%). Sexual dimorphism is distinct in adults, fifth and sixth nymphal instars. Adults of E. p. ibandana took on average 32.57 ± 3.88 days to start mating, and mating lasted 2.12 h on average (1–3 h). Oviposition took place on average 52.03 ± 5 days after first mating; each female deposited one to eleven oothecae with an average of 34.93 ± 2.37 eggs per ootheca. Our study provides important information for the control of this subspecies in southern Cameroon.
Cameroon, ecology, grasshopper pests, nymphal development
Knowledge of an organism’s life cycle is a prerequisite for any management, control, or conservation action (see
Eyprepocnemis plorans — also called Clover or Berseem grasshopper — is widely distributed in Africa, southern Europe, and southwestern Asia, and consists of four geographic subspecies (
In the Sahelian zone, this species is found throughout the year as both nymphs and adults (
Study area.—The individuals raised in the laboratory were caught between August 2014 and March 2017 at Nkolbisson, Yaoundé. Yaoundé is located in a semi-deciduous forest area, but the natural vegetation is highly degraded because of anthropic activity. The region is characterized by alternating hills and swamps (
Sampling.—Adults of E. p. ibandana (n = 61 adult pairs) used in this study were obtained from sixth instar nymphs collected on grass vegetation at Nkolbisson using a sweep net. Nymphs were transported to the laboratory in cylindrical polypropylene plastic boxes (type 1 cages: 9 cm high and 13 cm in diameter) closed with a wire mesh lid. In the laboratory, these nymphs were reared individually in the same type 1 cages on a shelf.
Meteorological data collection in the laboratory.—Temperature and relative humidity (RH) in the laboratory were recorded daily during the experiment (morning, afternoon, and evening) with a Gottingen Thermohygrograph. The temperature and RH during the breeding period are provided in Fig.
Reproduction.—After the final molt of the specimens collected in the field, the adults were paired in 15 wire cages (type 2 cages: 11 cm high and 10 cm in diameter) closed by a mesh cover. Each cage was one third filled with heat-sterilized wet sand, serving as an oviposition medium. Observations were conducted every two days to record pre-mating, mating, oviposition, and hatching dates.
Post-embryonic development.—First instar nymphs obtained from each adult pair were counted and placed individually in type 1 cages, then kept on shelves for development monitoring. A dry stem of Chromolaena odorata (14 cm long) was placed in each cage to support molting of the nymphs. Each cage was labeled with hatching date, number, stage, and sex. Each nymph was fed every two days with a cassava leaf (Manihot esculenta). The presence of exuviae was recorded daily and the state (dead or alive) of the nymphs was noted. The cages were also cleaned and the leaves used as food were renewed.
Morphology and morphometrics.—The morphology and morphometry of E. p. ibandana were recorded from freshly dead individuals during rearing. The morphological characteristics were observed using a Heerbrugg binocular lens. For each developmental instar, measurements were made and, for paired structures, the right structure was measured and their shape and color were described. The following parameters were measured as described by
Drawings were made with the same magnifying glass in a light chamber and at 25–50X magnification.
Data analysis.—Data were analyzed using Excel (version 2016) and PAST (version 2.5) softwares. Excel was used to draw the different curves; PAST was used to calculate averages of development times and morphometric parameters. The averages were compared with the Kruskal-Wallis and Mann Whitney tests at the 5% significance level.
Number of instars and duration of postembryonic development.—In the laboratory, nymphal development of E. p. ibandana went through six instars in males and six (75% of females) to seven (25% of females) instars in females (Table
Nymphal survival rate.—We obtained 2,603 hatchlings, 793 (30.46%) of which reached the adult stage. The transition from the first instar (L1) to the second (L2) was marked by a very high mortality rate (47%), but from the L2 instar on the survival rate was high, with values between 87% and 92% (Fig.
Eyprepocnemis plorans ibandana, male and female nymphal instars average development time (mean ± standard error in days), under laboratory conditions. Number of specimens: 388 males, 325 six instar females, 143 seven instar females.
Sexes | Instars | Kruskal Wallis Test | Total duration | |||||||
---|---|---|---|---|---|---|---|---|---|---|
L1 Nymph | L2 Nymph | L3 Nymph | L4 Nymph | L5 Nymph | L6 Nymph | L7 Nymph | H Value | P Value | ||
Males | ||||||||||
Duration | 12.22±0.13aA | 11.32±0.17bAB | 11.53±0.17bAB | 12.64±0.19aA | 13.5±0.20cA | 18±0.28dA | – | 517 | <0.0001 | 79.16±0.51A |
Range | (4–28) | (4–24) | (2–33) | (6–38) | (6–46) | (6–38) | (54–124) | |||
Females of six instars | ||||||||||
Duration | 12.78±0.17aB | 11.70±0.19bA | 12.10±0.22bA | 13.72±0.25cB | 14.92±0.31dB | 24.72±0.48eB | – | 249.4 | <0.0001 | 89.93±0.58B |
Range | (6–26) | (4–28) | (4–27) | (4–33) | (2–48) | (9–51) | (67–131) | |||
Females of seven instars | ||||||||||
Duration | 12±0.27aAB | 10.81±0.24bB | 11.19±0.30bB | 12.74±0.40aA | 13±0.34aC | 14.27±0.42cC | 20.52±0.63d | 260.9 | <0.0001 | 94.96±1.22C |
Range | (6–26) | (2–21) | (2–27) | (4–33) | (5–32) | (4–37) | (5–56) | (67–161) |
Reproduction: courtship, mating, and oviposition.—Courtship began 32.47 ± 3.88 days (8 to 59 days) after the final molt, by contact of the palps and antennae between both sexes. The male clung to her pronotum; when the latter was not receptive, the male remained on her back (this could last more than 2 hours). In some cases, the female used her hind legs to prevent the male from clinging to her. When the female was receptive, the male clung to her pronotum with his prothoracic and mesothoracic legs, the metathoracic legs being free and folded. In this position, the male bent his abdomen about 180° to the left or right below that of the female in order to bring the two genital regions into contact. He then introduced his phallus between the genital valves of the female to the vaginal opening. The coupling (n = 61) lasted for 2.12 h on average (between 1 and 3 hours) if uninterrupted.
After pairing, the first ootheca was deposited 9 to 70 days later (average 52.03 ± 5 days). Females laid between 1 to 11 egg pods (average 3 ± 1.4) and the number of eggs per ootheca ranged from 14 to 50 (34.93 ± 2.37 on average). On average, the females took 52.02 ± 5.1 days for laying of the first pod, 73.23 ± 6.84 days for the second pod, and 101.3 ± 10.31 days for the third pod.
Morphology of the different developmental stages.—
Egg: The eggs of E. p. ibandana are 3 to 5.5 mm long (average 4.37 ± 0.44 mm) and 1 to 1.5 mm in diameter (average 1.00 ± 0.05 mm). The eggs have a yellowish color, an elongated shape, are slightly curved and with rounded ends.
Adults: The general body color is of a variable brown, sometimes light beige, or brown-gray. The eyes are streaked with a small black band highlighting the sub-ocular suture. The pronotal disc is flat, with weakly pronounced lateral carina that are blurred in the metazona; the posterior border is slightly angular. The pronotal disc has two light bands running along the lateral carina and surrounding a dark brown zone; the dark zone narrows towards the anterior and posterior margins; the prosternal process is cylindrical. The elytra and wings are fully developed, slightly shorter, reaching or extending beyond the posterior apex of the abdomen and bearing a beige longitudinal stripe in the median field. The lower outer half of the posterior femora is usually yellow or light beige, lighter than the upper half. The basal half of the posterior tibiae is blue, the apical half reddish with whitish spines and black apices. The posterior tarsi are red.
Males are 21 to 27 mm long (average 24.33 ± 1.60 mm). The head is between 5 and 7 mm (average 6.30 ± 0.67 mm) long; the eyes bear six longitudinal eye stripes; the antenna carries 24 articles, measures 9.90 to 10 mm (average 9.99 ± 0.03 mm) and reaches dorsally almost the posterior margin of the pronotum. The thorax measures 6 to 9 mm (average 7.72 ± 0.98 mm); the pronotal disc measures between 4 and 5 mm (average 4.81 ± 0.37 mm). The abdomen is 11 to 14 mm long (average 12.74 ± 0.84 mm); the sub-genital plate is conical with acute apex (Figs
Females that passed through six nymphal instars have a body of 29.80 to 41.70 mm (average 35.86 ± 2.94 mm) long. The head measures 7.10 to 10 mm (average 8.45 ± 0.65 mm); the antenna carries 24 to 25 articles, measures between 9.30 and 12 mm (average 10.74 ± 0.73 mm), and reaches dorsally almost the posterior margin of the pronotum. The eyes bear six clearly visible longitudinal eye stripes. The thorax measures between 9 and 12 mm (average 10.44 ± 0.77 mm). The pronotal disc is between 5.50 and 7 mm (average 6.35 ± 0.49 mm) long. The abdomen measures between 17 and 27.50 mm (average 21.79 ± 2.7 mm). The genital valves are very robust and slightly curved towards the rear. The posterior margin of sternite 8 is undulating without a median process (Figs
Females that passed through seven nymphal instars are not significantly different in size than females that have passed through six instars (Table
Common characteristics of the nymphal instars.—The body is usually dark brown in color with spots and light beige bands. The head is weakly conical, dark brown in color with a beige band behind each compound eye, extending onto the anterior border of the pronotum. The fastigium is trapezoid in shape with a slight mid and concave longitudinal depression; it is brown, with a midlength pale beige band extending over the pronotum to the posterior end of the abdomen. The face is light beige with brown spots; the frontal ridge is concave with two more or less parallel longitudinal carinae reaching the base of the mouthparts. The pronotum is cylindrical in shape, weakly roof-like, bearing three brown sutures dotted with beige spots forming the median carina. The mesosternal space is open, much wider than long, with rounded lobes. The elytra are absent. The abdomen has ten segments visible dorsally and nine visible ventrally. The cerci are conical with an acute apex slightly exceeding the epiproct. The epiproct is triangular, bifurcated and with a rounded apex dorsally beyond the paraprocts (Figs
Eyprepocnemis plorans ibandana, male and female measurements of morphological characters.
Instars | Sex/type | Lt | Lcc | lcc | Lth | Labd | Lpr | La | Na |
---|---|---|---|---|---|---|---|---|---|
L1 | Male | 5.01±0.63 (3.20–6.00) (32) A | 2.01±0.14 (1.30–2.20) (32) A | 1.26±0.12 (1.00–1.50) (32) A | 1.83±0.26 (1.20–2.50) (32) A | 2.12±0.29 (1.40–2.60) (32) A | 0.98±0.06 (0.80–1.10) (32) A | 1.70±0.23 (1.10–2.10) (32) A | 11±00 (11–11) (32) A |
Female | 5.19±0.78 (3.80–6.90) (30) A | 2.10±0.17 (2.00–2.90) (30) A | 1.29±0.16 (1.00–1.50 (30) A | 1.73±0.34 (1.00–2.10) (30) A | 2.49±0.60 (1.70–3.90) (30) A | 0.98±0.04 (0.90–1.00) (30) A | 1.77±0.16 (1.40–2.10) (30) AB | 10.63±0.49 (10–11) (30) A | |
L2 | Male | 7.35±0.83 (5.90–8.80) (30) B | 2.31±0.18 (2.10–2.90) (30) AB | 1.83±0.13 (1.50–2.00) (30) B | 2.29±0.28 (1.90–3.00) (30) B | 3.96±0.56 (2.50–5.00) (30) B | 1.29±0.12 (1.10–1.70) (30) B | 2.16±0.13 (1.90–2.50) (30) B | 15±00 (15–15) (30) B |
Female | 7.76±0.73 (6.50–9.30) (30) B | 2.48±0.28 (1.30–2.80) (30) B | 1.94±0.08 (1.80–2.00) (30) B | 2.45±0.25 (2.00–3.00) (30) B | 4.05±0.47 (3.00–5.00) (30) B | 1.39±0.12 (1.20–1.60) (30) B | 2.28±0.18 (2.00–2.60) (30) B | 15±00 (15–15) (30) B | |
L3 | Male | 10.58±0.76 (9.00–12.00) (30) C | 3.18±0.15 (2.90–3.50) (30) C | 2.17±0.09 (2.00–2.30) (30) BC | 3.29±0.26 (2.80–4.00) (30) C | 5.76±0.52 (5.00–7.00) (30) C | 1.94±0.08 (1.80–2.00) (30) C | 3.07±0.09 (2.90–3.30) (30) C | 16.87±0.34 (16–17) (30) C |
Female | 10.46±0.72 (9.00–11.50) (28) C | 3.21±0.16 (3.00–3.50) (28) C | 2.19±0.07 (2.10–2.30) (28) C | 3.34±0.28 (2.80–3.80) (28) C | 5.69±0.52 (4.60–6.40) (28) C | 1.97±0.05 (1.80–2.00) (28) C | 3.05±0.12 (2.80–3.30) (28) C | 16.71±0.46 (16–17) (28) C | |
L4 | Male | 11.71±1.76 (10.1–14.00) (30) C | 3.77±0.29 (3.30–4.60) (30) D | 2.79±0.34 (2.40–3.90) (30) D | 3.60±0.39 (3.00–4.50) (30) C | 6.30±0.88 (5.20–8.00) (30) C | 2.35±0.24 (2.00–3.10) (30) D | 3.78±0.30 (3.20–4.50) (30) D | 19.06±0.36 (18–20) (30) D |
Female | 12.10±1.38 (9.40–15.00) (31) C | 3.85±0.37 (3.00–4.90) (31) D | 2.75±0.28 (2.00–3.20) (31) D | 3.73±0.46 (2.80–4.70) (31) CD | 6.47±0.74 (5.00–8.10) (31) C | 2.41±0.34 (1.90–3.00) (31) D | 3.84±0.47 (2.90–5.00) (31) D | 19.03±0.18 (19–20) (30) D | |
L5 | Male | 14.40±1.56 (12.1–18.00) (33) D | 4.40±0.27 (4.00–5.00) (33) E | 3.09±0.11 (3.00–3.30) (33) E | 4.09±0.41 (3.50–5.00) (33) DE | 8.04±1.34 (6.10–11.00) (33) D | 3.16±0.09 (3.00–3.30) (33) E | 4.91±0.27 (4.20–5.30) (33) E | 21.09±0.68 (20–22) (33) E |
Female 6 | 17.3±0.95 (16.00–18.3) (23) E | 5.50±0.41 (4.90–6.00) (23) F | 3.87±0.21 (3.50–4.00) (23) F | 4.93±0.26 (4.30–5.10) (23) F | 9.81±0.60 (9.20–10.60) (23) E | 4.04±0.16 (3.70–4.20) (23) F | 6.09±0.65 (5.00–7.40) (23) F | 21.00±00 (21–21) (23) E | |
Female 7 | 16.05±1.65 (14.5–18.00) (20) E | 4.58±0.45 (4.10–5.10) (20) E | 3.30±0.26 (3.00–3.60) (20) E | 4.26±0.84 (3.30–5.10) (20) E | 9.44±1.07 (8.40–10.70) (20) E | 3.12±0.15 (3.00–3.30) (20) E | 4.64±0.30 (4.30–5.00) (20) E | 21.00±00 (21–21) (20) E | |
L6 | Male | 17.20±1.36 (15.0–19.2) (36) E | 5.01±0.16 (4.80–5.50) (36) G | 3.62±0.28 (3.20–4.00) (36) G | 5.27±0.39 (4.80–6.00) (36) F | 9.44±1.19 (7.50–11.00) (36) E | 3.96±0.23 (3.50–4.30) (36) F | 6.23±0.42 (5.50–7.00) (36) F | 23.00±00 (23–23) (36) F |
Female 6 | 25.17±2.00 (21.0–27.0) (30) F | 7.18±0.53 (6.50–8.00) (30) H | 5.04±0.46 (4.20–5.50) (30) H | 7.09±0.57 (6.00–7.70) (30) G | 13.88±1.94 (11.0–16.0) (30) F | 5.74±0.40 (5.10–6.10) (30) G | 8.76±0.95 (7.30–10.00) (30) GH | 23.00±00 (23–23) (30) F | |
Female 7 | 25.80±0.54 (25.2–26.7) (32) F | 6.93±0.26 (6.50–7.30) (32) H | 5.52±0.52 (5.00–6.10) (32) I | 7.10±0.25 (6.70–7.50) (32) G | 15.15±0.39 (14.8–16.00) (32) G | 5.98±0.16 (5.70–6.20) (32) H | 8.44±0.88 (7.00–10.00) (32) G | 23.00±00 (23–23) (32) F | |
L7 | Female 7 | 25.61±2.13 (21.0–27.0) (38) F | 6.93±0.23 (6.50–7.20) (38) H | 4.94±0.31 (4.30–5.30) (38) H | 7.15±0.49 (6.10–7.50) (38) G | 15.31±1.52 (12.0–16.3) (38) G | 5.97±0.22 (5.50–6.20) (38) GH | 9.02±0.88 (7.30–10.00) (38) H | 24.00±00 (24–24) (38) G |
Adult | Male | 24.33±1.60 (21.0–27.0) (25) F | 6.30±0.67 (5.00–7.00) (25) I | 3.99±0.33 (3.90–4.00) (25) F | 7.72±0.98 (6.00–9.00) (25) H | 12.74±0.84 (11.0–14.0) (25) F | 4.81±0.37 (4.00–5.00) (25) I | 9.99±0.03 (9.90–10.00) (25) I | 24.00±00 (24–24) (25) G |
Female 6 | 35.86±2.94 (29.8–41.7) (36) G | 8.45±0.65 (7.10–10.0) (36) J | 5.42±0.36 (5.00–6.00) (36) I | 10.44±0.77 (9.00–12.00) (36) I | 21.79±2.79 (17.0–27.5) (36) H | 6.35±0.49 (5.5–7.0) (36) J | 10.74±0.73 (9.30–12.00) (36) J | 24.05±0.23 (24–25) (36) G | |
Female 7 | 35.78±4.40 (30.0–44.0) (26) G | 8.36±0.42 (8.0–9.20) (26) J | 5.43±0.37 (5.00–6.00) (26) I | 10.69±1.01 (9.00–13.00) (26) B | 23.17±3.94 (17.0–29.00) (26) I | 6.36±0.47 (5.7–7.0) (26) J | 10.52±0.63 (9.0–11.0) (26) J | 24.23±0.43 (24–25) (26) G |
Eyprepocnemis plorans ibandana, male and female measurements of morphological characters.
Instars | Sex/type | Lel | Lail | Lcu1 | Lcu2 | Lcu3 | Lti1 | Lti2 | Lti3 | Nse |
---|---|---|---|---|---|---|---|---|---|---|
L1 | Male | – | – | 0.98±0.04 (0.9–1.00) (32) A | 1.06±0.06 (0.90–1.10) (32) A | 3.05±0.09 (2.70–3.20) (32) A | 0.99±0.03 (0.90–1.00) (32) A | 1.09±0.17 (1.00–2.00) (32) A | 2.96±0.13 (2.40–3.10) (32) A | 1.00±0.00 (1.00–1.00) (32) A |
Female | – | – | 0.99±0.04 (0.90–1.10) (30) A | 1.08±0.06 (0.90–1.20) (30) A | 3.07±0.11 (2.90–3.30) (30) A | 0.98±0.04 (0.90–1.00) (30) A | 1.06±0.06 (0.90–1.20) (30) A | 2.94±0.10 (2.70–3.00) (30) A | 1.00±0.00 (1.00–1.00) (30) A | |
L2 | Male | – | – | 1.12±0.06 (1.00–1.30) (30) A | 1.26±0.09 (1.10–1.50) (30) AB | 4.04±0.18 (3.60–4.30) (30) B | 1.13±0.06 (1.00–1.30) (30) AB | 1.30±0.10 (1.10–1.50) (30) B | 3.75±0.19 (3.10–3.90) (30) B | 2.00±0.00 (2.00–2.00) (30) B |
Female | – | – | 1.17±0.09 (1.00–1.40) (30) A | 1.36±0.16 (1.10–1.70) (30) B | 4.31±0.25 (3.60–4.80) (30) B | 1.15±0.08 (1.00–1.30) (30) B | 1.35±0.12 (1.20–1.60) (30) B | 3.92±0.22 (3.40–4.30) (30) B | 2.00±0.00 (2.00–2.00) (30) B | |
L3 | Male | – | – | 1.69±0.08 (1.60–1.90) (30) B | 1.85±0.16 (1.20–2.00) (30) C | 5.64±0.32 (5.10–6.10) (30) C | 1.63±0.14 (1.40–1.90) (30) C | 1.85±0.13 (1.50–2.00) (30) C | 4.70±0.30 (4.10–5.80) (30) C | 3.00±0.00 (3.00–3.00) (30) C |
Female | – | – | 1.70±0.11 (1.50–2.00) (28) B | 1.91±0.09 (1.70–2.00) (28) C | 5.71±0.22 (5.40–6.20) (28) C | 1.61±0.11 (1.40–1.90) (28) C | 1.90±0.10 (1.70–2.00) (28) C | 4.77±0.17 (4.30–5.20) (28) C | 3.00±0.00 (3.00–3.00) (28) C | |
L4 | Male | – | – | 2.02±0.15 (1.80–2.50) (30) C | 2.17±0.26 (1.90–3.00) (30) CD | 7.24±0.66 (6.20–9.00) (30) E | 2.01±0.21 (1.80–2.50) (30) D | 2.27±0.24 (2.00–2.90) (30) D | 5.87±0.44 (5.10–7.10) (30) D | 4.00±0.00 (4.00–4.00) (30) D |
Female | – | – | 2.04±0.19 (1.70–2.70) (31) C | 2.16±0.28 (1.60–3.10) (31) D | 7.33±0.86 (5.40–9.20) (31) E | 1.96±0.18 (1.60–2.30) (31) D | 2.35±0.29 (2.00–3.00) (31) D | 6.07±0.57 (4.70–7.50) (31) D | 4.00±0.00 (4.00–4.00) (31) D | |
L5 | Male | 2.11±0.13 (1.90–2.30) (33) A | 2.32±0.22 (2.10–2.70) (33) A | 2.52±0.36 (1.90–3.00) (33) D | 2.85±0.18 (2.50–3.00) (33) E | 9.31±0.75 (8.30–11.10) (33) F | 2.49±0.24 (2.20–2.90) (33) E | 3.13±0.29 (3.00–4.00) (33) E | 7.49±0.40 (6.70–8.00) (33) E | 5.00±0.00 (5.00–5.00) (33) E |
Female 6 | 2.82±0.27 (2.30–3.00) (23) A | 3.04±0.22 (2.50–3.20) (23) A | 3.08±0.17 (2.80–3.30) (23) E | 3.51±0.32 (3.00–3.90) (23) F | 12.14±0.77 (10.90–12.9) (23) G | 3.03±0.23 (2.70–3.50) (23) F | 3.97±0.23 (3.40–4.20) (23) F | 9.58±0.58 (8.80–10.10) (23) F | 5.00±0.00 (5.00–5.00) (23) E | |
Female 7 | 1.25±0.19 (1.20–1.30) (20) A | 1.19±0.10 (1.10–1.30) (20) B | 2.61±0.26 (2.20–2.90) (20) D | 2.86±0.24 (2.60–3.10) (20) E | 9.50±0.64 (8.50–10.20) (20) F | 2.51±0.24 (2.00–2.70) (20) E | 3.05±0.27 (2.50–3.30) (20) E | 7.61±0.58 (7.00–8.30) (20) E | 5.00±0.00 (5.00–5.00) (20) E | |
L6 | Male | 5.55±0.68 (4.00–7.00) (36) B | 4.90±0.48 (4.10–6.00) (36) C | 3.13±0.19 (3.00–3.70) (36) E | 3.67±0.31 (3.10–4.00) (36) F | 11.58±0.76 (10.3–13.1) (36) G | 3.10±0.24 (2.90–4.00) (36) F | 3.88±0.20 (3.50–4.20) (36) F | 8.93±0.59 (8.00–10.00) (36) G | 6.00±0.00 (6.00–6.00) (36) F |
Female 6 | 8.01±1.64 (5.20–9.50) (30) C | 9.44±1.07 (8.40–10.70) (30) D | 4.23±0.60 (3.20–4.80) (30) F | 4.69±0.46 (4.00–5.10) (30) G | 16.63±0.99 (15.0–18.0) (30) H | 4.12±0.10 (4.00–4.10) (30) GH | 5.15±0.08 (5.00–5.20) (30) GH | 13.14±0.88 (11.5–14.00) (30) H | 6.00±0.00 (6.00–6.00) (30) F | |
Female 7 | 8.10±0.18 (7.90–8.40) (32) C | 7.09±0.58 (6.10–8.00) (32) D | 4.57±0.14 (4.30–4.70) (32) F | 5.16±0.19 (5.00–5.50) (32) H | 16.87±0.90 (15.2–18.00) (32) H | 4.18±0.14 (4.00–4.40) (32) G | 5.23±0.20 (5.00–5.50) (32) G | 13.19±0.81 (12.0–14.0) (32) I | 6.00±0.00 (6.00–6.00) (32) F | |
L7 | Female 7 | 8.10±0.77 (7.00–10.80) (38) C | 7.15±0.51 (6.20–8.00) (38) D | 4.44±0.34 (4.00–5.00) (38) F | 4.90±0.40 (4.00–5.20) (38) GH | 16.83±1.06 (15.0–18.0) (38) H | 4.12±0.08 (4.00–4.20) (38) GH | 5.15±0.11 (5.00–5.30) (38) GH | 12.36±0.45 (11.6–13.20) (38) J | 7.00±0.00 (7.00–7.00) (38) G |
Adult | Male | 20.22±1.57 (17.0–23.0) (25) D | 18.29±1.62 (15.3–21.0) (25) E | 4.92±0.39 (4.00–5.70) (25) G | 5.59±0.39 (5.00–6.00) (25) I | 14.66±0.91 (13.0–16.0) (25) I | 3.98±0.28 (3.00–4.90) (25) H | 4.98±0.22 (4.50–5.90) (25) H | 12.31±0.61 (11.0–13.0) (25) J | 6.00±0.00 (6.00–6.00) (25) F |
Female 6 | 28.35±2.05 (23.5–32.00) (36) E | 26.07±2.23 (21.5–30.0) (36) F | 5.45±0.41 (5.00–6.00) (36) H | 6.34±0.44 (5.50–7.00) (36) I | 20.83±0.39 (17.0–26.5) (36) J | 5.01±0.18 (4.60–5.50) (36) I | 6.75±0.45 (6.00–7.30) (36) I | 16.39±0.89 (15.0–18.1) (36) K | 6.00±0.00 (6.00–6.00) (36) F | |
Female 7 | 28.06±2.63 (24.0–32.0) (26) E | 25.61±2.74 (21.5–30.0) (26) F | 5.48±0.37 (5.00–6.00) (26) H | 6.36±0.44 (6.00–7.10) (26) | 20.88±1.82 (17.0–23.2) (26) J | 5.23±0.33 (4.90–6.00) (26) J | 6.56±0.33 (4.90–6.00) (26) I | 16.75±1.11 (14.9–18.6) (26) K | 7.00±7.00 (7.00–7.00) (36) S |
Identification key for post-embryonic instars.—Refer to the key of
Sexual dimorphism.—We observed a clear sexual dimorphism from 5th nymphal instar to adults. At these instars, the length of body, head, thorax, abdomen, pronotum, antennae, elytra, wings, femora, and metathoracic tibiae are larger in females than in males.
Growth rate.—The growth rate was similar for both sexes from the first nymphal instar to the fourth. Starting from 5th instar, the growth of males became slower than that of the two types of females (six and seven instar females). At the sixth nymphal instar, six instars females increased faster in size than seven instar females, but as the latter passed through an additional instar, there was no significant difference between the sizes of the two types of adult females (Fig.
Postembryonic development of E. p. ibandana.—Our study showed that the number of instars varies between the two sexes in E. p. ibandana: six in the male and six or seven in the female, confirming the results obtained by
The tropical grasshopper Cornops aquaticum may have five to seven nymphal instars depending on the host plant, humidity, and its distribution range from Mexico to Argentina (
From our results, the nymphal development of E. p. ibandana was longer than in
Nymphal survival rate.—The survival rate of the first nymphal instar was quite low in our study compared to the later instars. This lower survival of first instars in the laboratory and in nature is common in other grasshoppers and locusts, e.g., desert locust, Australian plague locust (
Reproduction of E. p. ibandana.—The mating of E. p. ibandana is similar to that observed in most other short-horned grasshoppers (
We found that a female of E. p. ibandana lays between one and eleven oothecae during her adult life-span. The number of eggs per egg pod ranged from 14 to 50. In the laboratory, S. gregaria females produce a mean of 22 pods, each containing 47.6 eggs (
Sexual dimorphism in E. p. ibandana.—Sexual dimorphism is marked in adults, as well as in 5th and 6th nymphal instar of E. p. ibandana. These results corroborate those of
Two major hypotheses have been proposed to explain the ultimate causes of dimensional dimorphism: the intersexual competition hypothesis and the differential equilibrium hypothesis (
Under laboratory conditions, nymphal development of E. p. ibandana fed on cassava went through six instars in males and six (75%) or seven (25%) instars in females. The average development time in days was 79.16 in males and 89.93 to 94.96 in females. Fifth and sixth nymphal instars showed slightly longer development times. The survival rate of the first nymphal instar was low in our study compared to the later instars. Data on instar recognition and development times are useful for treatment programs by providing information on what stage the grasshoppers are at and how much time is left for treatment before the more damaging adult stage. It also gives an idea of how quickly treatments need to be performed to reduce nymphal populations in the field and reduce damage.
The Theodore J. Cohn Research Grant 2016 of the Orthopterists’ Society funded this work. We also thank members of the Plant Protection Service, Cameroon (2PC) who helped in data collection in the laboratory.