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 35. It is thought to be responsible for the transmission of the bacterial burn of cassava in Nigeria 23. Due to the high damages it inflicts on crops, it is considered as an important agricultural pest in Nigeria 4678, 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 241112. However, no scientific literature exists on the pest status of Z. variegatus in Cameroon. Apart from two works 1314 and one report 5, most other literature on the problems caused by Z. variegatus in Central and West Africa only have generalities on Cameroon 45691516. 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).
<p>Figure 1</p>
The Forest Margin Benchmark Area (FMBA) of the humid forest zone of the Southern-Cameroon
The Forest Margin Benchmark Area (FMBA) of the humid forest zone of the Southern-Cameroon.
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Survey
Information was obtained in each village between August and October 1998 using the rapid rural appraisal methods (RRAM) 232425. 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' 2324. 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 variegatus in 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).
<p>Table 1</p>
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.
<p>Table 2</p>
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 variegatus incidence 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).
<p>Table 3</p>
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).
<p>Table 4</p>
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).
<p>Table 5</p>
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