Open Access

Farmers' perception on the importance of variegated grasshopper (Zonocerus variegatus (L.)) in the agricultural production systems of the humid forest zone of Southern Cameroon

Journal of Ethnobiology and Ethnomedicine20062:17

DOI: 10.1186/1746-4269-2-17

Received: 02 January 2006

Accepted: 30 March 2006

Published: 30 March 2006

Abstract

Background

Zonocerus variegatus (Linnaeus, 1758) (Orthoptera: Pyrgomorphidae) is known as an agricultural pest in West and Central Africa. However, its importance in the agricultural production system in Cameroon has not been investigated. The study assesses farmers' perception on the importance of Z. variegatus in the agricultural production systems of the humid forest zone of Southern Cameroon.

Methods

Research was carried out in 5 villages of each of three Agro-Ecological, Cultural and Demographic Blocks (AECD-Blocks) of the Forest Margin Benchmark Area (FMBA). In each village, a semi-structured survey was used; male and female groups of farmers were interviewed separately.

Results

Z. variegatus is present throughout the humid forest zone of Southern Cameroon, where it is ranked as the third most economically important insect pest of agriculture. In the farmers' opinion, Z. variegatus is a polyphagous insect with little impact on young perennial crops. The length of the pre-farming fallow does not affect Z. variegatus pest pressure in the following crops. The increased impact of the grasshopper observed today in the fields, compared to what existed 10 years ago is as a result of deforestation and increase in surface of herbaceous fallow. The damage caused by Z. variegatus is higher in fields adjacent to C. odorata and herbaceous fallows than in those adjacent to forests and shrubby fallows. The fight against this grasshopper is often done through physical methods carried out by hand, for human consumption. The farmers highlight low usage of the chemical methods and a total absence of biological and ecological methods.

Conclusion

Farmers' perception have contributed to understanding the status of Z. variegatus in the humid forest zone of Southern Cameroon. The results are in general similar to those obtained in other countries.

Background

In general, from the human point of view, any insect that is not at the right place is a pest (Williams, cited by [1]). Pests are also harmful or awkward species, which need to be controlled for economic or social reasons (Clark, cited by [1]). Zonocerus variegatus is reported in the literature as a pest of many crops in West and Central Africa. The first reports on damages of this grasshopper on crops were in 1910 by Peacock and Lamborns in Southern Nigeria, Schoutedem and Mayne in Zaire and Small in Uganda (In [2]). Its geographical range and impact on the crops increase with time. In 1948, Z. variegatus accounted for 10% yield loss in the banana harvest in Guinea [2]. On garden eggs, it can cause 25 – 80% yield loss [2]. In Nigeria, it causes 50% loss in annual cassava yield [4]. Z. variegatus has been implicated in the transmission of okra mosaics viruses in Ivory Coast and cowpea mosaics viruses in Nigeria [3, 5]. It is thought to be responsible for the transmission of the bacterial burn of cassava in Nigeria [2, 3]. Due to the high damages it inflicts on crops, it is considered as an important agricultural pest in Nigeria [4, 68], Ivory Coast [6], Ghana [4], Congo Brazzaville [9], Southern Benin (Coffi, cited by [4]) and in the Sahel [10]. Z. variegatus is currently the most important of grasshopper pests for crops in the humid forests of low altitude and savannas of West and Central Africa [2, 4, 11, 12]. However, no scientific literature exists on the pest status of Z. variegatus in Cameroon. Apart from two works [13, 14] and one report [5], most other literature on the problems caused by Z. variegatus in Central and West Africa only have generalities on Cameroon [46, 9, 15, 16]. Determining the importance of an insect in any agro-ecosystems, contributes to the description of its status [17]. Such information is necessary for the formulation of a good pest management strategy.

This paper present the results of a group survey, administratered to the farmers of the humid forest zone of Southern Cameroon, to assess the importance of variegated grasshoppers Zonocerus variegatus in the agricultural production systems. The survey approach was justified by the concern of having a fast idea on the Z. variegatus status in the production systems in the southern Cameroon and the need of collaboration between farmers, scientists, and extension services in term of priorities definition about the crop protection strategies. Recent trends in agricultural research and development emphasize the need for farmer participation [18]. There has been increasing interest in the incorporation of farmer's knowledge into agricultural research and development programs [19]. The Participatory Action Research framework provides one useful approach towards achieving farmers' capacity building [18]. Farmers in general are good decision-markers (Goldman, cited by [20]) and their views have contributed to the understanding of various aspects of the bio-ecology of insects and the real situation of other pests. Taking their knowledge base and combining them with scientists'/extentionists' expertise can contribute to the improvement of local practices in pest management [18]. An ethnoentomological study, conducted in Tharu, a village in Nepal, offered a basis to improve pest management programs in terms of efficacy and acceptance [18]. In African farmer communities, insects are much more known as pest though others such as Apis mellifera (Hymenoptera: Apidae), Gryllotalpa africana (Orthoptera: Gryllotalpidae), Gryllus bimaculatus (Orthoptera: Gryllidae) have a great importance in the communities. In general, A. mellifera (bees) produce honey. In West Cameroon G. africana are heralding misfortune whereas the cries of G. bimaculatus at certain periods of the year, announce good news (Kwecheu Marie, Personal Communication). Farmers' knowledge of insects varies in quality and quantity depending on their interest in the subject, their environment, and the relevance of insects to their lives [18].

The objective of the present study was to determine farmers' perception on: (1) the incidence of Zonocerus variegatus in the humid forest zone of Southern Cameroon; (2) the factors responsible for variations of Z. variegatus incidence in the humid forest zone of Southern Cameroon; and (3) to assess how the farmers manage this grasshopper in their agro-ecosystems.

Materials and methods

Study site

The work was carried out in 15 villages of the humid forest zone of Southern Cameroon (3°27'-4°10'N and 11°32'-11°49'E) (Figure 1). These villages were selected among the 45 Forest Margin Benchmark Area (FMBA: 1.54 millions hectares) reference villages. Serving as a focal point for strategic diagnostic research in the sub-region, the benchmark approach was developed and implemented through the Eco-regional Program for the Humid and Sub-Humid Tropics of Sub-Saharan Africa (EPHTA). The 45 villages are situated along a gradient of natural resource utilization intensification, represented by 3 agro-ecological, cultural and demographic blocks (AECD-Blocks) namely Yaounde, Mbalmayo and Ebolowa (Figure 1). Five out of 15 villages of each block were selected for the study. These were Nkongmesse, Nkolmelok, Nkometou-II, Akak-II and Etoud for the Yaounde block; Awae, Evindissi, Ngat, Mvoutessi and Nkolmetet for the Mbalmayo block and Minsélé, Mekoe, Mengomo, Akok and Obang-II for the Ebolowa blocks. The 3 AECD-Blocks differ in several aspects. Yaounde has a high human density (14–88 habitant/km2); whereas low human population densities are observed in Ebolowa (2–15 habitant/km2) and intermediates (10–48 habitant/km2) in Mbalmayo [21]. On the agro-ecological level, forest degradation is more pronounced around Yaounde than in the Ebolowa, which still has some pockets of primary forest [21]. Mbalmayo constitutes an intermediate block. Farmers in these areas all practice slash and burn agriculture [22]. In the Yaounde block, the length of fallow is about three years shorter than that of Ebolowa (7.5 years) while that of Mbalmayo block is a transition (5.4 years). The main food crops are banana, plantain, cocoyam, cassava, yam and groundnut [22]. Cucurbits, okra, vegetables and spices are secondary crops [22] while cocoa and coffee are the main cash crops of this area. Their production is mainly in small-scale, through domestic or family exploitation. These areas have an equatorial climate type with two dry seasons and two rainy seasons. The average annual rainfall is 1510 mm, 1643 mm and 1820 mm in Yaounde, Mbalmayo and Ebolowa respectively. From an ethnological viewpoint, the "Etons", "Ewondoses" and the "Bulus" are the main ethnic groups in the Yaounde, Mbalmayo and Ebolowa blocks respectively. With regard to the diet, the Bulus consume more sauces made based on almond of the fruits of Irvingia gabonensis (named 'Ndo'o') while Etons and Ewondoses consumes more 'Okok' (pasta product made containing leaves of Gnetum africanum) and 'Kwem' (pasta product made containing leaves of Manihot esculenta) respectively (Lema Ngono, Personal Communication).
https://static-content.springer.com/image/art%3A10.1186%2F1746-4269-2-17/MediaObjects/13002_2006_Article_29_Fig1_HTML.jpg
Figure 1

The Forest Margin Benchmark Area (FMBA) of the humid forest zone of the Southern-Cameroon.

Survey

Information was obtained in each village between August and October 1998 using the rapid rural appraisal methods (RRAM) [2325]. There were 17 questions, divided in three parts; 5 relating to the annual crops and, 5 others relating to the young perennial crops and 7 general questions. The final questionnaire was prepared based on a preliminary one that was tested in Bikok and Abang, two other villages different from those used in our investigations. Based on the results of this pre-test, we decided to work with men and women farmers' groups separately in each village. We selected farmers growing annual or perennials crops. A total of 30 groups (389 farmers: 164 women and 225 men) were interviewed. Each group had 8 to 21 farmers aged 18 to 50 years. Participants were recruited in 3 strata based on the 3 blocks of the 'Benchmark' [23, 24]. Interviews of two hours per group were conducted at different hours of the same day for the two groups. Farmers were asked to rank the importance of Zonocerus variegatus among the other insect pest of the humid forest zone of the Southern Cameroon and rate the impact of Z. variegatus on crops in the humid forest zone of Southern Cameroon. Farmers were also asked to state factors, which influence the pest status of Z. variegatus, the methods used against the pest and to state what they need to suppress the pest population. In the questionnaire, we used opened-ended and close-ended questions.

Questions were asked in the local language and/or French. During the survey in each village, a sample of Zonocerus variegatus was shown to the farmers to enable them recognize the insect. For the various rankings, scores (described In [25]) were used while the farmers answered the other questions directly.

Statistical analysis

Data were analyzed by the Kruskal-Wallis test using the 'Nonparametric One Way' ('NPAR1WAY WILCOXON ') procedure of the software SAS ('Statistical Analysis Systems' version 8). All probabilities were appreciated at the 5% confidence level.

Results

Incidence of Zonocerus variegatusin the humid forest zone of Southern Cameroon

Zonocerus variegatus is present in all the surveyed villages. In all these villages, variegated grasshopper is well known to the farmers and they could describe the appearance of both nymphs and adults. All the farmers' group rate it as an insect pest. Z. variegatus is ranked the 3rd most important insect pest in the area and together with borers and scale insects cause about 54% of the insect pest problems on annual crops (Table 1). On young perennial crops, mirid, borers and caterpillars are the major constraints and they cause about 59% of insect pest problems while Z. variegatus is a minor pest (Table 1). However, for the females groups of Yaoundé (for the annual and perennial crops) and Mbalmayo (for the perennial crops only), these pests have equal importance (Table 1).
Table 1

Relative importance (%) of the main insect pests on annual and perennial crops in the humid forest zone of Southern – Cameroon.

All

Crops

AECD-Blocks

Termites

Borers

Caterpillars (Without Borers)

Aphids

Mirids

Scales Insects

Variegated grasshopper

Bugs (Without Mirids)

p-value

Annual crops

Yaounde

9

16

9

10

6

19

16

14

<0.001

 

Mbalmayo

2

21

10

9

7

22

16

13

<0.0001

 

Ebolowa

4

22

12

13

5

17

14

15

<0.0001

 

   p-value

<0.05

NS

NS

NS

NS

NS

NS

NS

 
 

   Mean

5

20

10

11

6

20

15

14

<0.0001

Young Perennial Crops

Yaoundé

14

14

12

11

21

18

7

5

<0.01

 

Mbalmayo

1

19

19

10

28

13

8

2

<0.0001

 

Ebolowa

3

22

14

14

28

5

11

4

<0.0001

 

   p-value

<0.001

NS

NS

NS

NS

<0.05

NS

NS

 
 

   Mean

6

18

15

11

25

12

9

4

<0.0001

Female

Annual crops

Yaounde

11

16

9

13

9

19

12

14

NS

 

Mbalmayo

3

21

10

12

9

22

12

13

0.0386

 

Ebolowa

5

22

11

14

3

17

14

16

0.0236

 

   p-value

NS

NS

NS

NS

NS

NS

NS

NS

 
 

   Mean

6

19

10

13

7

19

12

14

<0.0001

Young Perennial Crops

Yaoundé

14

15

7

14

18

23

3

11

NS

 

Mbalmayo

2

21

19

10

29

14

2

5

0.0005

 

Ebolowa

4

21

15

15

22

7

13

4

NS

 

   p-value

NS

NS

NS

NS

NS

NS

NS

NS

 
 

   Mean

7

19

14

13

23

15

6

6

<0.0001

Male

Annual crops

Yaounde

7

17

10

8

3

20

21

15

0.0072

 

Mbalmayo

2

21

10

7

6

23

20

13

0.0003

 

Ebolowa

3

23

13

12

7

17

14

14

0.0002

 

   p-value

NS

NS

NS

NS

NS

NS

NS

NS

 
 

   Mean

4

20

11

9

5

20

18

14

<0.0001

Young Perennial Crops

Yaoundé

14

13

16

8

24

13

11

3

0.0404

 

Mbalmayo

0

18

19

10

27

13

12

2

0.0007

 

Ebolowa

3

24

13

12

33

2

10

4

0.0006

 

   p-value

0.008

NS

NS

NS

NS

NS

NS

NS

 
 

   Mean

6

18

16

10

28

9

11

3

<0.0001

The values are averages of the scores for 10 groups (5 male and 5 female groups) of farmers interviewed per block; p-value is the significance levels of a non parametric test of Kruskal-Wallis; NS = no significant (p > 0.05). AECD-Blocks = Agro-Ecological, Cultural and Demographic Blocks.

Table 2

Food sources of Zonocerus variegatus among the annual and perennial crops in the humid forest of Southern Cameroon.

All

Crops

AECD-Blocks

General feeder (Polyphagous)

Oligophagous

Monophagous

No crop attacked

Absent in the village

Annual crops

Yaounde

60

40

0

0

0

 

Mbalmayo

70

30

0

0

0

 

Ebolowa

70

30

0

0

0

 

   Mean

67

33

0

0

0

Young Perennial Crop

Yaounde

20

20

10

50

0

 

Mbalmayo

20

20

10

50

0

 

Ebolowa

30

50

0

20

0

 

   Mean

23

30

7

40

0

Female

Annual crops

Yaounde

60

40

0

0

0

 

Mbalmayo

60

40

0

0

0

 

Ebolowa

60

40

0

0

0

 

   Mean

60

40

0

0

0

Young Perennial Crop

Yaounde

20

0

0

80

0

 

Mbalmayo

40

0

0

60

0

 

Ebolowa

40

40

0

20

0

 

   Mean

33

13

0

53

0

Male

Annual crops

Yaounde

60

40

0

0

0

 

Mbalmayo

80

20

0

0

0

 

Ebolowa

80

20

0

0

0

 

   Mean

73

27

0

0

0

Young Perennial Crop

Yaounde

20

40

20

20

0

 

Mbalmayo

0

40

20

40

0

 

Ebolowa

20

60

0

40

0

 

   Mean

13

47

13

33

0

The values are averages of the scores for 10 groups of farmers (5 male and 5 female groups) interviewed per block; AECD-Blocks = Agro-Ecological, Cultural and Demographic Blocks

Most farmers' groups (67%) reported that Zonocerus variegatus is a general feeder (polyphagous insect) (Table 2) that attacks all the annual crop species. These perceptions were higher at male (73% of groups) than female (60% of groups) (Table 2). Its food host range included cassava, groundnut and vegetables. None of the farmers' groups rated Z. variegatus as a monophagous pest on annual crops (Table 2). On young perennial crops, most groups (40%) perceived Z. variegatus as a non-harmful insect (Table 2). This perception was more pronounced in female groups (53%) than male groups (33%) (Table 2). Few farmers (23% of groups), especially the female (33% of groups) reported Z. variegatus as being olygophagous (Table 2) compared to only 13% of men groups. Their food range on perennial crops was more restricted to pear, cocoa, coffee, orange, oil palm and plum. Z. variegatus was rated by 7% (female only) of the groups as being monophagous (Table 2). In this monophagous behaviour, the grasshopper appeared to be a specialist feeder on pear or palm tree.

Factors responsible for variations in Zonocerus variegatusincidence in the humid forest zone of Southern Cameroon

Factors mentioned by the farmers

Compared to the scenario 10 years ago, most of farmers' groups (84%) surveyed in the humid forest zone reported that Zonocerus variegatus pressure in the fields has increased. These perceptions were higher in male (87% of groups) than in female groups (80% of groups). This increase of Z. variegatus incidence has been significant (73% of groups; 87% of male and 60% of female) mainly because of the increase in the surface of herbaceous fallow (73% of groups) and deforestation (60% of groups) (Table 3). Males (53% of groups) also give more importance to some factors such as high reproductive rate of Z. variegatus. Females perceived these factors as minors (Table 3). Most of other factors presented in table 3 were minors. Some factors like lack of human consumption, wide colonization of the fields by weeds, presence of cassava were only reported by males, while possible change in the Z. variegatus species has been proposed by females (Table 3).
Table 3

Reasons for the increase incidence of Zonocerus variegatus in crop fields in the humid forest zone of Southern Cameroon.

 

All

Female

Male

Reasons

Ydé

Mbyo

Ebwa

Means

Ydé

Mbyo

Ebwa

Means

Ydé

Mbyo

Ebwa

Means

Increased surfaces of herbaceous and C. odorata fallows

50

90

80

73

40

80

80

67

60

100

80

80

Deforestation

60

60

60

60

40

60

60

53

80

60

60

67

High reproductive rate of Z. variegatus

20

80

20

40

0

80

0

27

40

80

40

53

Lack, suppression or reduction of control measures against Z. variegatus

30

20

20

23

20

0

0

7

40

40

40

40

Increased food host range of Z. variegatus

40

20

10

23

60

20

0

27

20

20

20

20

Absence, suppression or reduction of human consumption of Z. variegatus

10

10

10

10

0

0

0

0

20

20

20

20

Wide colonization of the fields by weeds

10

0

10

7

0

0

0

0

20

0

20

13

Increase sun shine levels

10

20

10

13

0

20

20

13

20

20

0

7

Favorable climatic conditions

0

20

30

17

0

20

40

20

0

20

20

13

Change of the crop types

10

0

0

3

20

0

0

7

20

0

0

7

Reduction of spaces in sugar cane crop

10

0

10

7

20

0

0

7

0

0

20

7

Climatic changes

20

20

30

23

0

20

20

13

40

20

20

27

Presence of cassava

0

10

0

3

0

0

0

0

0

20

0

7

Possible change of the species of Z. variegatus

10

0

0

3

20

0

0

7

0

0

0

0

The values (% of answer) are averages for 10 groups of farmers (5 male and 5 female groups) interviewed per block. AECD-Blocks = Agro-Ecological, Cultural and Demographic Blocks. Ydé : Yaoundé, Mbyo: Mbalmayo, Ebwa: Ebolowa.

Factors presented to the farmers

- variations in Zonocerus variegatus incidence according to fields types
All field types were damaged by Zonocerus variegatus (Table 4) but, 51% of the damage was associated to food crop fields ('Affub bidi' and 'Affub owondo'). Z. variegatus pressure was low in dry season fields ('Esseps'); young perennial crops fields; garden crops and marsh' fields ('Assans'). The pressure of Z. variegatus in groundnut fields ('affub owondo') is higher in the Mbalmayo block. In Assans and 'Garden crops', this pressure is significantly higher in the Yaounde and Mbalmayo blocks (Table 4). However, for the female groups, these block effects appeared significant only in the garden crops (Table 4).
Table 4

Relative importance (%) of Zonocerus variegatus pressure in different fields types in the humid forest zone of Southern Cameroon.

All

AECD-Blocks

Affub owondo

Affub bidi

Assan

Essep

Garden crops

Young perennial crop

p-value

Yaounde

10

34

21

9

20

5

<0.0001

Mbalmayo

31

28

9

5

17

9

<0.0001

Ebolowa

19

28

20

12

7

14

<0.001

   p-value

<0.01

NS

<0.05

NS

<0.05

NS

 

   Means

20

30

17

9

15

9

<0.0001

Female

Yaounde

11

38

21

9

17

3

0.0121

Mbalmayo

29

21

12

8

25

5

0.0021

Ebolowa

20

28

22

9

5

16

0.0346

   p-value

NS

NS

NS

NS

0.0380

NS

 

   Means

20

29

18

9

16

8

0.0001

Male

Yaounde

10

31

21

9

22

7

0.0029

Mbalmayo

33

36

6

3

10

12

0.0010

Ebolowa

19

28

19

15

9

11

0.0175

   p-value

0.0209

NS

0.0220

NS

0.0422

NS

 

   Means

21

32

15

9

14

10

<0.0001

The values are averages of the scores for 10 groups of farmers (5 male and 5 female groups) interviewed per block. Affub owondo is Grandnut' field. Essep is dry season' fields. Assan is marsh' fields. p-value is the significance levels of a non parametric test of Kruskal-Wallis; NS = nonsignificant (p > 0.05). AECD-Blocks = Agro-Ecological, Cultural and Demographic Blocks.

- variations in Zonocerus variegatus incidence according to the age of the pre-farming fallow
The length of pre-farming fallow did not influence the extent of Zonocerus variegatus pressure in field crops (93% of groups) (Table 5). In the male and female groups, there were no significant differences in Z. variegatus pressure in the 3 types of fallow (Table 5). Similarly, the magnitude of the pressure did not differ significantly between blocks (Table 5).
Table 5

Influence of age of the pre-farming fallow on the pressure (%) of Zonocerus variegatusin crop fields established at the same site.

All

AECD-Blocks

Fallow of 1 -5 years

Fallow of 5 -10 years

Fallow > 10 years

p-value

Yaounde

39

31

30

NS

Mbalmayo

40

30

30

NS

Ebolowa

33

33

33

NS

   p-value

NS

NS

NS

 

   Means

37

32

31

NS

Female

Yaounde

33

33

33

NS

Mbalmayo

47

27

27

NS

Ebolowa

33

33

33

NS

   p-value

NS

NS

NS

 

   Means

38

31

31

NS

Male

Yaounde

44

29

27

NS

Mbalmayo

33

33

33

NS

Ebolowa

33

33

33

NS

   p-value

NS

NS

NS

 

   Means

37

32

31

NS

The values are averages of the scores for 10 groups of farmers (5 male and 5 female groups) interviewed per AECD-Blocks; p-value is the significance levels of a non parametric test of Kruskal-Wallis ; NS = nonsignificant (p > 0.05); AECD-Blocks = Agro-Ecological, Cultural and Demographic Blocks.

- variations in Zonocerus variegatus incidence according to the type of adjacent fallow
The magnitude of Zonocerus variegatus pressure varied with the type of adjacent fallow in field crops (93% of male and 87% of female). In the male and female groups, it is higher in fields adjacent to Chomolaena odorata fallow and herbaceous fallow than in forest or shrub fallows (Table 6).
Table 6

Influence of fallow types on Zonocerus variegatus pressure (%) in adjacent crop fields in the humid forest zones of Southern Cameroon

All

AECD-Blocks

C.odorata fallow

Herbaceous fallows

Shrubs fallow

Forest

p-value

Yaounde

52

35

10

5

<0.0001

Mbalmayo

44

40

11

7

<0.0001

Ebolowa

51

39

9

2

<0.0001

   p-value

NS

NS

NS

NS

 

   Means

49

38

10

4

<0.0001

Female

Yaounde

54

29

10

7

0.0052

Mbalmayo

45

40

10

5

0.0024

Ebolowa

50

43

7

0

0.0007

   p-value

NS

NS

NS

NS

 

   Means

50

37

9

40

<0.0001

Male

Yaounde

49

40

9

2

0.0007

Mbalmayo

42

39

11

8

0.0037

Ebolowa

51

34

11

4

0.0010

   p-value

NS

NS

NS

NS

 

   Means

47

38

10

5

<0.0001

The values are averages of the scores for 10 groups of farmers (5 male and 5 female groups) interviewed per AECD-Blocks; p-value is the significance levels of a non parametric test of Kruskal-Wallis NS = nonsignificant (p > 0.05); AECD-Blocks = Agro-Ecological, Cultural and Demographic Blocks.

- variations in Zonocerus variegatus incidence according to type of season
The pressure of Zonocerus variegatus on annual and perennial crops is higher in the short dry season and highest in the great dry season. Z. variegatus damage is very low in the fields during the rainy season. No significant difference was observed between the fields (Table 7). However, on the perennial crops, differences (non-significant) in Z. variegatus incidence variations (according the seasons) have been reported by females of Ebolowa and Mbalmayo blocks. (Table 7). According to farmers, there was a block effect in the dry season on young perennial crops with the Ebolowa block having the highest damage (Table 7). However, there was no block effect in gender perceptions in the annual and perennials crops (Table 7).
Table 7

Influence of season on the population pressure (%) of Zonocerus variegatus on annual and perennial crops in the humidforest zones of Southern Cameroon.

Crops

AECD-Blocks

Long dry season

Short rainy season

Short dry season

Long rainy season

p-value

Annual Crop

Yaoundé

72

4

16

9

<0.0001

 

Mbalmayo

70

7

11

13

<0.0001

 

Ebolowa

64

10

27

0

<0.0001

 

   p-value

NS

NS

NS

NS

 
 

   Means

69

7

18

7

<0.0001

Young Perennial Crops

Yaoundé

25

3

12

1

<0.05

 

Mbalmayo

36

5

10

10

<0.05

 

Ebolowa

63

9

29

0

<0.0001

 

   p-value

<0.05

NS

<0.05

NS

 
 

   Means

41

5

17

4

<0.0001

Female

Annual Crop

Yaoundé

76

1

13

10

0.0054

 

Mbalmayo

68

5

12

15

0.0071

 

Ebolowa

67

9

24

0

0.0015

 

   p-value

NS

NS

NS

NS

 
 

   Means

69

5

16

8

<0.0001

Young Perennial Crops

Yaoundé

15

0

5

0

NS

 

Mbalmayo

31

6

13

10

NS

 

Ebolowa

69

4

27

0

0.0017

 

   p-value

NS

NS

NS

NS

 
 

   Means

38

3

15

3

0.0014

Male

Annual Crop

Yaoundé

68

6

19

7

0.0061

 

Mbalmayo

72

9

9

10

0.0080

 

Ebolowa

61

10

29

0

0.0015

 

   p-value

NS

NS

NS

NS

 
 

   Means

67

8

19

6

<0.0001

Young Perennial Crops

Yaoundé

34

6

18

2

NS

 

Mbalmayo

40

3

7

9

NS

 

Ebolowa

57

13

30

0

0.0017

 

   p-value

NS

NS

NS

NS

 
 

   Means

44

7

18

4

0.0002

The values are averages of the scores for 10 groups of farmers (5 male and 5 female groups) interviewed per AECD-Blocks; p-value is the significance levels of a non parametric test of Kruskal-Wallis; NS = nonsignificant (p > 0.05); AECD-Blocks = Agro-Ecological, Cultural and Demographic Blocks.

Entomophagy

In the humid forest zone of southern Cameroon, only the adult stages of Zonocerus variegatus were an item of diet (63% of groups). This feeding behavior appeared more in Mbalmayo (90% of groups) and Yaoundé (70% of groups) blocks. Z. variegatus was eaten a little in Ebolowa block (30% of groups). Some people do not eat Z. variegatus because of its body odour (3% of groups) and the fact that, consumption would result in muscular and articular paralysis (6% of groups).

Protection of crops against Zonocerus variegatus

To protect crops against Zonocerus variegatus, farmers of the humid forest zone of Southern Cameroon use chemical and physical methods. No biological or ecological methods were used (Table 8). The physical fight is very much used (77% of groups) (Table 8). Through this method, grasshoppers are collected mostly for human consumption as mentioned by 63% of the groups (61% of female and 60% of male) (Table 8). Very few groups (13%) collect Z. variegatus for use as baits in fishing. Chemical control of Z. variegatus populations was poorly practiced (27% of farmers) (Table 8). The insecticides used are décis®, diméthoate®, orthene®, cipercal®, furadan® and methyl®. There were differences in the insecticide use in various fields. In Yaounde décis® and furadan® were not used while in the Mbalmayo block diméthoate®, orthene®, cipercal® and methyl® are not used. Insecticides are not used against Z. variegatus in Ebolowa. Rains are the only natural factors against Z. variegatus though its effect is only slightly perceived in the Yaounde and Mbalmayo blocks (Table 8). Some farmers groups (23%) do not have any means of fighting against Z. variegatus especially in the Ebolowa block (Table 8).
Table 8

Different methods used by farmers in the humid forest of Southern Cameroon of control Zonocerus variegatus.

All

AECD-Blocks

No method

Chemical method

Natural method (rain)

Physical method

Yaounde

10

50

40

90

Mbalmayo

0

30

30

100

Ebolowa

60

0

10

40

   Means

23

27

27

77

Female

Yaounde

20

40

20

80

Mbalmayo

0

20

20

100

Ebolowa

60

0

0

40

   Means

27

20

13

73

Male

Yaounde

0

60

60

100

Mbalmayo

0

40

40

100

Ebolowa

60

0

20

40

   Means

20

33

40

80

The values (%) are averages for 10 groups of farmers (5 male and 5 female groups) interviewed per AECD-blocks; AECD-Blocks = Agro-Ecological, Cultural and Demographic Blocks.

Discussion

The study shows that farmers regard Zonocerus variegatus as an important annual crop pest in the humid forest zone of Southern Cameroon. It is a minor pest of young perennial crops. Similar results have also been reported in many countries in Africa, notably Nigeria [4, 68], Ivory Coast [6], Ghana [4], Congo Brazzaville [9], Southern Benin (Coffi, cited by [4]) and the Sahel [10]. In most of these countries, Z. variegatus is known mainly as a food crop pest.

From the farmers' point of view, the definition of an insect pest has primarily economic implications, given that the insect causes significant damage to warrant the implementation of a control measure. This implies that having reliable information on crop damage at different pest densities is vital in understanding the interaction between pest and host plants. However, crop damage by Zonocerus variegatus is very difficult to evaluate, especially on food crops [2]. This underscores the importance of farmers' perceptions in understanding the pest status of a given insect [17]. Farmers' perceptions have contributed to the understanding of various aspects of the bio-ecology of insects [18]. These perceptions can be significantly different from scientific knowledge but have major implications for development [2730, 5, 31, 18].

The crops mentioned by the farmers in this study as food sources for Zonocerus variegatus have also been reported in previous studies [2, 38]. For the farmers of southern Cameroon, groundnut, cassava and vegetables are the most susceptible crops to Z. variegatus. The majority of the authors are unanimous on the high vulnerability of cassava [4, 6, 7] while the susceptibility level of vegetables and groundnut varies from one country to another. Cassava, groundnut and vegetables are the principal food crops of the humid forest zone of Southern Cameroon [22]. It thus gets clear a need for developing strategies of protection of these crops against Z. variegatus.

Many reports have also mentioned the growing importance of Zonocerus variegatus as a pest elsewhere as in the humid forest zone of Southern Cameroon. For example, before 1950, Z. variegatus was already known as a pest of primary or secondary importance in most countries of intertropical Africa [2, 5]. However, it was later reported as an important pest in the 1970s in Nigeria [6, 7, 12].

The farmers in this study recognize as Kumar [1] that several factors affect the pest behavior of Zonocerus variegatus. For example Z. variegatus avoids pure forest compared to deforested areas [6, 3, 32, 2, 4]. This preference of deforested areas had also been reported in earlier studies [6, 7, 2, 37]. Deforestation induces biotopes and conditions favorable for Z. variegatus such as increase in surfaces of herbaceous fallow. In addition, after deforestation, empty spaces are occupied by C. odorata, the main host plant of Z. variegatus. These may partly explain the high pressure of Z. variegatus observed by the farmers in the fields adjacent to C. odorata fallow [8] and herbaceous fallow compared to fields adjacent to forests. The increased damage observed in the dry season suggests that it is a seasonal pest as reported in other studies [3]. Probably, rains (natural mortality factor) induce morbid fungical infections in the natural populations of Z. variegatus among other mortality factors that would reduce the pest population.

The study showed that, Zonocerus variegatus is an item of diet. This agrees with the findings of Iduwu & Modder [8] and Page & Richards [38] in Nigeria. In Nigeria as in Cameroon, the insect is eaten after being fried [8, 38]. In fact, Z. variegatus is an important source of proteins [39].

In the present study, the main control method of Zonocerus variegatus in the humid forest of Southern Cameroon was through the physical removal of insects feeding on crops for human consumption. The consumption of Z. variegatus as control method has also been reported by Nigerian farmers [8]. However, physical control of Z. variegatus is generally difficult and not very effective. The high population of Z. variegatus in the humid forests of Southern Cameroon [33] indicates the lack of an adequate crop protection measure against the pest. Egg-pod exposure used by few Nigerian subsistence farmers is not known in southern Cameroon [4]. Southern Cameroon farmers seldom use chemical control, certainly because of the fall of the state aid, related to the economic crisis. This method, very much used by the farmers in Nigeria [8], was the main crop protection strategy in the tropical forest zones. Their utilization, in large areas has been one of the first important factors of reduction in crop loss due to pests [9]. However, because of their harmful effect on the environment, their utilization became weakly recommended [34, 35, 10, 1, 36]. The fact that biological control methods are not used here show that the 'green muscle' (biological acridicid) used successfully in the savannah zones may not have been introduced to farmers of Southern Cameroon. These farmers' perceptions showed a need to carry out an urgent control strategy in the agricultural production system against Zonocerus variegatus. However, the strategy needs to be directed a little more towards the integrated pest management as described by Modder [7]. An integration of the farmers is necessary [38].

This study also showed some perceptional gender differences in the humid forest zone of southern Cameroon. In Yaoundé (for the annual and perennial crops) and Mbalmayo (for the perennial crops only), females perceived the pest's incidence with an equal importance while males recognized Z. variegatus as one of the major and minor pests in the annual and perennial crops respectively. On young perennial crops, only the females rated Z. variegatus as monophagous. In these perennial crops, more female groups perceived Z. variegatus as non-harmful insect than male groups. The increase of Z. variegatus incidence in the fields has been more reported by men than women groups. For the female groups, block effect appeared significant only in the garden crops while in the male groups they also appeared in groundnut fields ('affub owondo') and Assan (Marsh field). More male groups observed that, the magnitude of Zonocerus variegatus pressure varied with the type of adjacent fallows in field crops. These perceptional gender differences have also been observed in Nepal [18]. In Nepal, with regard to the depredatory insects, men generally used more vague attributes like harmful or harmless, while women were more specific, often referring to the host plant [18]. The rate for instance, was referred to by women as a hole-making storage pest, while men did not refer to burrows at all [18]. This clearly reflected that in Nepal, women normally repair and clean the damage [18]. In fact, the perceptional gender differences have their origin in the division of labor [18]. In the humid forest zone of southern Cameroon, men and women spend most of their time in the field (agriculturals activities) but, women are also involved in tasks at household while other male tasks are community oriented.

Conclusion

Farmers' perceptions have contributed to the understanding of the pest status of Zonocerus variegatus in the humid forest zone of Southern Cameroon. Farmers rate Z. variegatus as an important polyphagous pest on food crops that warrants urgent management or control. The pest incidence has increased because of deforestation and increase of herbaceous fallows. It is therefore necessary to also consider this grasshopper among the major pests in the national strategies of plant protection. Integrated Pest Management (IPM) strategy is a comprehensive approach that combines all rational strategies to reduce pest densities to tolerable levels while maintaining a safe quality environment [7]. These farmers' perceptions are in general similar to the results of most experimental studies but may stimulate researchers to identify new research areas. Farmers' perception can differ profoundly from scientific knowledge, having significant implications for development [18]. Both farmers and scientific knowledge have strengths and weaknesses [18].

Declarations

Acknowledgements

The present study was supported by Grants from Weed and vegetation program (1228 budget) of International Institute of Tropical Agriculture-Humid Forest Ecoregional Center. We thank Dr Denis Sonwa (IITA-STCP-Cameroon), Dr Ousmane Coulibaly (IITA-Benin), Dr Chimère Diaw (CIFOR-Cameroon), Dr Nelson Ntonifor (University of Buea) and Dr Omer Njajou (University of California, San Francisco) for reading and commenting on the manuscript.

Authors’ Affiliations

(1)
International Institute of Tropical Agriculture, Humid Forest Eco-regional Centre
(2)
Zoology laboratory, Faculty of Science, University of Yaounde
(3)
International Institute of Tropical Agriculture, Biological Control Center for Africa

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This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://​creativecommons.​org/​licenses/​by/​2.​0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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