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Insect Sci. Applic. Vol. 21, No. 3 pp. 257-265

FARMERS' OPINIONS AND INFLUENCE OF CULTURAL PRACTICES ON SOIL PEST DAMAGE TO GROUNDNUT IN WEST AFRICA

V. C. UMEH1, F. WALIYAR1, S. TRAORé2, I. M. CHAIBOU3, B. OMAR4 AND J. DETOGNON5

1International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), B.P. 320, Bamako, Mali; 2Institut d'Etudes et de Recherches Agricoles ( INERA), 01 B.P. 910, Bobo-Dioulasso, Burkina-Faso; 3Institut National de Recherches Agricoles du Niger (INRAN ), B.P. 240, Maradi, Niger; 4Kano State Agricultural Development Authority (KNARDA), P.M.B. 3130, Kano, Nigeria; 5Institut National de Recherches Agricoles du Benin (INRAB) BP 884 Cotonou, Benin

Accepted 21 November 2001

Code Number: ti01031

Abstract-Farmers in the groundnut belts of Mali, Burkina Faso, Niger, Nigeria and Benin in West Africa were interviewed for their ability to identify economically importanct soil pests infesting their groundnut (Arachis hypogaea L.) crops, and to obtain information on farm histories and cultural practices which may influence soil pest infestation and spread in a field. Termites, whitegrubs and millipedes were recognised by the farmers as being the most important soil pests, with termites being the most damaging group. A negative correlation (P < 0.05) was found between the number of years a farm was cultivated and the frequency of termite occurrence in it. Information on cultural practices obtained from interviews and field visits indicated that practices such as late harvesting and the leaving behind of residues of previous sorghum, millet and maize crops increased termite infestation. The cutting down and burning of the vegetation in a farm before planting significantly (P < 0.05) reduced the percentage of plants attacked by termites. The cultivation of short-duration (< 100 days) varieties to escape drought at the end of the cropping season did not significantly reduce termite damage, due to late harvest. Other farmers' practices which are likely to have contributed to soil pest damage are also discussed.

Key Words: cultural practices, groundnut, Arachis hypogaea, intercropping, millipede, termites, whitegrub

Résumé- Les fermiers de la zone de culture de l'arachide, du Mali, du Burkina-Faso, du Niger, du Nigeria et du Bénin ont été interrogés afin d'estimer leur capacité de reconnaissance des ravageurs du sol d'importance économique, infestant leurs cultures d'arachide (Arachis hypogaea L.). Cette enquête a également permis d'obtenir des informations sur l'histoire et les pratiques culturales pouvant influencer l'infestation et la propagation des ravageurs du sol dans un champ. Les ravageurs du sol les plus importants reconnus par les fermiers sont les termites, les vers blancs et les mille-pattes, les termites étant responsables des dégâts les plus importants. Une corrélation significativement négative (P < 0.05) a été trouvée entre le nombre d'années de culture du champ et la fréquence des termites dans ce dernier. Les informations obtenues sur les pratiques culturales à partir des questionnaires et des visites au champ indiquent qu'une récolte tardive et la présence dans le champ de résidus des cultures antérieures de sorgho, de mil et de maïs augmentent l'infestation par les termites. Le défrichage et le brûlage de la végétation avant les semis réduisent significativement (P < 0.05) le pourcentage de plantes attaquées par les termites. La culture de variétés à cycles courts (< 100 jours), permettant d'éviter la sécheresse en fin de cycle cultural, n'a pas réduit significativement les dégâts provoqués par les termites car la récolte a été trop tardive. Les autres pratiques culturales qui contribuent vraisemblablement aux dégâts des ravageurs du sol sont également discutées.

Mots Clés: pratiques culturales, arachide, Arachis hypogaea, culture associée, lille-pattes, termite, ver blanc

INTRODUCTION

Groundnuts (Arachis hypogaea L.) are widelygrown in the semi-arid tropics of WestAfrica both for local consumption as a source of protein and as a cash crop. However, groundnut production in the region has declined greatly over the past two decades, due in part to biotic and abiotic stresses, including drought, pests and diseases (Yayock et al., 1976; Lynch et al., 1986) and inappropriate cultural farm practices. Numerous insect pest species have been associated with groundnut damage to varying degrees of economic importance.

Termites (Isoptera: Termitidae) and whitegrubs (Coleoptera: Scarabaeidae) attack both the root system and the pods of groundnut. In extreme infestations they attack the whole plant. Millipede (Myriapoda: Odontopygidae) damage is limited to pods and is usually prevalent on germinating seeds or soft pods (Masses, 1981; IRHO, 1982).

Microtermes and Odontotermes (Isoptera: Termitidae) are the major termite genera known to cause groundnut damage, reducing yields and quality (Johnson and Gumel, 1981; Johnson et al., 1981; Lynch et al.,1986). Termites are widely distributed in West Africa, where they also damage cereals crops (IITA, 1971; Wood et al., 1980). Johnson et al. (1981) reported yield losses of up to 40% in Nigeria. Termite damage gives access to fungal infections, including Aspergillus spp. associated with aflatoxin contamination (Johnson and Gumel, 1981; Waliyar et al., 1994; Wightman and Wightman, 1994). Mercer (1978) also reported invasion by rot-causing fungi on pods damaged by whitegrubs in Malawi.

Reports by extension and research workers with the national agricultural research system (NARS), and complaints by groundnut farmers in West Africa have continued to suggest the increasing economic importance of termites, whitegrubs, and millipedes in groundnut production, and the need to provide interventions focusing on these three groups of soil pests.

In order to gain a better understanding of the factors which influence soil pest infestation and spread, it is necessary to obtain information from farmers and through field visits. The present article reports on a study aimed at investigating the relationship between cultural practices and soil pest infestation, with a view to developing appropriate management practices. The study involved interviews and visits to the farms of 100 groundnut farmers in Mali, Burkina Faso, Niger and Nigeria in the 1996 cropping season, as well as in Benin in 1997. Visits were also made to 5 additional groundnut farms in the early stages of the crop in Fada N'Gourma, Burkina Faso. Although the owners of the latter farms were not interviewed nor the farms visited at harvest, samples were taken during the early stage of groundnut growth.

MATERIALS AND METHODS

One hundred groundnut farmers were interviewed from late July to the end of August 1996 along the groundnut belts of Mali, Burkina Faso, Niger and Nigeria. In Benin, the farmers were interviewed in October 1997. All the sites are located between latitudes 8 o and 13 o30' N (Fig. 1) and receive 600-1200 mm rainfall annually. The interviews, which were conducted with questionnaires, dealt with farm histories, cropping systems, cultural practices, soil pest problems and control measures as summarised below:

  • the period over which land was cultivated
  • type of bush fallow system
  • farmers' rating of importance of soil pests of groundnut
  • use of chemical fertilisers
  • use of manure
  • methods of land clearing and their contribution to soil pest occurrence
  • periods in the cropping season during which soil pest damage was observed
  • duration of cultivated groundnuts
  • harvest period in relation to groundnut duration
  • farmers' soil pest control methods.

Farms belonging to the interviewed farmers were sampled at 25-45 days after planting (dap) and at harvest to identify soil pest species associated with groundnut damage, and the factors related to farmers' responses that may contribute to the spread of soil pests. In Benin, fields were visited only at harvest, while in the locality of Fada N'Gourma (Burkina Faso) the farms were visited only at the early stage of the crop but no interviews were conducted.

During field visits, sole or intercropped groundnut plants were sampled along transect lines (two diagonals of each farm). Based on farm size, 40 or 60 plants were sampled from farms < 2500 m2 and >2500 m2 respectively. Damaged groundnut plants were uprooted and the soil pests observed on them were identified. The percentage of plants attacked by the various soil pests were recorded per farm. Data from localities belonging to the same agroecological zones or having only slight variations in their annual rainfall were grouped together.

Statistical analysis
Regression analyses were computed for the relationship between soil pest frequency of occurrence in infested farms and the period of time such farms were cultivated. Some variables from farmers' responses and field observations were expressed as percentages. All parameters where farmers responded 'yes' or 'no' were represented as 1 or 0 respectively and treated as dummy variables.

The dependence of termite occurrences on these parameters was analysed using Chi-square analysis where necessary. The differences between the long and short cycle varieties, in terms of the percentage of plants damaged at maturity by the various soil pests, were assessed by t-test analyses. All statistical tests were computed using SAS program (SAS Inc. USA, 1985).

RESULTS

Soil pests and crops present in farmers' fields
Farmers recognised three major groups of soil pests-termites, whitegrubs and millipedes-in their fields. Field visits indicated that Microtermes and Odontotermes were the predominant genera. The important species of whitegrubs and millipedes identified included Schyzonycha africana Lap. and Peridontopyge spp. respectively.

Groundnuts were planted alone or intercropped with cereals (sorghum, millet or maize) and other legumes depending on the market or domestic requirements of the localities. The surface area cultivated to groundnut per farmer ranged between 0.05 and 3.5 ha, with 80 % of the farms covering 0.2 -1 ha. In Mali, Burkina Faso, Niger, Nigeria and Benin, the percentages of farms monocropped to groundnut were 70, 73, 51, 20 and 75 % respectively. The percentages of farms with the predominant cropping systems in the various localities are shown in Table 1. With the exception of Nigeria and Benin, the combinations included groundnut/millet; and to a lesser extent groundnut/sorghum (Table 1). In Kita area (Mali), groundnut was predominantly intercropped with Bambara nut (Vigna subteranea L.). Intercrop combinations in Nigeria were groundnut/sorghum and groundnut/sorghum/millet. Cowpea was sometimes included in the latter combinations. In Benin, the predominant combination was groundnut/cowpea and to a lesser extent groundnut/cassava and groundnut/maize. Many intercropping arrangements/patterns were observed during the survey, ranging from row intercropping (with varying number of rows of each component crop) to mixed intercropping (with irregular arrangements). Groundnut spacing between and within rows also varied considerably from one locality to another according to the cropping pattern and ranged from 35-100 cm and 15-50 cm respectively. Inter-row spaces also tended to be larger when groundnut was planted on ridges, as was observed in parts of Nigeria. Among the identified soil pests, only termites attacked both groundnut and intercropped cereals in infested farms. Termite presence in farms was found to be partly favoured by the presence of cereals (sorghum, maize, millet) (χ2 = 65.0; P < 0.01; df = 48).

Table 1. Cropping patterns, farmers' rating of groundnut soil pests and percentage of damaged plants in
Mali, Burkina Faso, Niger, Nigeria and Benin as determined by field visits
Country/
Localities
(No. of farms)
Predominant cropping
system (%)+
Major Crop combinations++
Minor
Farmers' rating of soil pests+++
Mean % of attacked plants
25-45 dap Maturity
T Wg Mi T Wg Mi
Mali










Sikasso (10) Kita/Kayes(10)
M (70) M (60)
Gr/Mt Gr/Bn
So
-
T >Wg > Mi
T > Wg, Mi
10.0
3.1
0.56.8
0.0
4.2
12.0
39.4
2.0
0.0
13.0
0.0
Burkina Faso










Bobo-Dioulasso/ Niangoloko (10) Saria (5)
Fada N'Gourma (5)
I (60)

M (80) M (100)

Gr/Mt

-
-

So
Ma
Mt
-
T > Mi > Wg

T > Mi > Wg
-

1.3

0.0
2.9

1.2

0.0
1.5

2.5

0.0
1.2

12.0

1.5
-

0.0

12.0
-

0.6

0.0
-

Niger










Bengou (5)
Maradi (10)
M 100)
I 98)
- Gr/Mt
-
So
Wg, T > Mi
T > Wg > Mi
0.0
2.7
0.0
1.0
9.3
1.5
11.0
14.0
11.0
0.5
1.5
0.4
Nigeria










Kano/Dambatta (10)

Zaria/Kaduna (10)

I (100)

I (60)

Gr/So; Gr/So/Mt Gr/So;
Gr/So/Mt

Co

Ma

Mi > T > Wg


Mi , T > Wg

6.0


1.9

0.0


1.4

2.6


3.7

20.3


6.4

0.6


1.3

0.4


9.0

Benin










Kandi (10)
Ndali (10)
Save (10)
M (100) M (67) M (57)
-
Gr/Co
Gr/Ca
-
Ma
So
T > Wg, Mi
T > Wg, Mi
T > Wg, Mi
-
-
-
-
-
-
-
-
-
17.5
12.2
6.2
0.0
0.0
1.3
1.0
0.0
2.0
dap, days after planting. + M = monocropping; I = intercropping. ++ Gr, groundnut; Mt, millet; So, sorghum; Bn, bambara nut; Ma, maize;
Co, cowpea; Ca, cassava.
+++T = termite; Wg = whitegrub; Mi = millipede

Farmers' rating of soil pests
Seventy-five percent of the interviewed farmers in Mali, Burkina Faso, Niger and Benin rated termites as the most damaging soil pest of groundnut, followed by 15 % collectively for whitegrubs and millipedes. The remaining 20 % could not rate any of the soil pests according to their level of importance (data not shown). The majority of groundnut farmers in Nigeria (60%) rated millipedes and termites as being the most damaging groundnut soil pests; only 5% thought that whitegrubs were most important (data not shown). Results from sampling plants for soil pest damage during the surveys supported the farmers' views except in the Kano/Dambatta area of Nigeria, where termite damage was most prevalent (Table 1). Some farmers did not give answers on the relative importance of soil pests in their farms during the survey. In such situations, the farmers reported having observed stand losses without knowing the cause.

Our observations across the sub-region during field visits corresponded with farmers' responses on period of soil pest damage during the cropping season (fields in Benin were visited only at harvest and therefore were not included in the latter study). Generally, the farmers indicated the periods of highest soil pest (termites, whitegrub and millipede) attack to be the early stage (30 %), late stage (30 %) and early and late stages (33 %). However, they could only discern correctly termite damage. Forty-six percent of the farmers observed that termite damage was most important both at the early and mature stages of the crop. Only 19 % of the farmers maintained that termites caused significant damage at the early stage of the crop, while 17.6 % observed damage at plant maturity (data not shown). These responses often corresponded with the periods of attack of termites observed in the given localities. No conclusive responses were obtained specifically on the periods of attack of millipedes and whitegrubs; indeed, in some localities none of the farmers could reliably indicate the period of pest infestation.

Effect of groundnut variety and time of harvest
In the surveyed areas, both long-duration (> 110 days) and intermediate- to short- (< 100 days)-duration varieties of groundnut were planted (Table 2). Local names given to the varieties were not consistent across localities. T-test analysis (t = 0.305; P > 0.05; n = 18) showed that there was no significant difference (P > 0.05) between the percentages of termite-attacked plants in the three varieties, as observed in data collected from Sikasso (Mali); Saria (Burkina Faso); Bengou and Maradi (Niger); and Kandi (Benin), where all these varieties were cultivated (Table 3). In all sampled localities in Nigeria, as well as in Kita, Mali, and Bobo-Dioulasso/Niangoloko in Burkina Faso, long-duration varieties were mostly common.

Table 3. Percentages of groundnut plants of various durations attacked by soil pests in farms at
Sikasso (Mali), Saria (Burkina Faso), Bengou and Maradi (Niger) and Kandi (Benin) localities+
% of plants/farm attacked
Sampled
>100 days duration varieties
< 100 days duration variety
farms
Millipedes
Termites
Whitegrubs
Millipedes
Termites
W hitegrubs
1

25
5
25
32
10
5
2

13
10
10
30
10
10
3

75
10
5
25
30
7.5
4

5
7.5
5
35
10
5
5

33
7.5
5
28
8
10
6

25
4.5
31.2
7.5
3.6
10
7

5
17.5
10
10
15
22.5
8

28
-
2.5
10
-
6.5
9

30
-
5
33
-
21
10

30
-
12
-
-
-
11

20
-
21
-
-
-
12

17
-
0
-
-
-
13

28
-
17
-
-
-
14

33
-
10
-
-
-
15

5
-
15
-
-
-
+Data compiled from farms only in localities where both long and short duration varieties were cultivated.

Termite damage was most pronounced at plant maturity (which coincides with the onset of the dry season) at these localities. In localities where both short- and long-duration varieties were cultivated, whitegrub and millipede infestations were mainly observed at the early stage of groundnut, irrespective of whether a short- or long-duration variety was cultivated. There was no significant (P > 0.05) difference between the percentages of plants attacked by whitegrubs (t = 0.97; P > 0.05; n = 7) or millipedes (t = 0.027; P >0.05; n = 9) in the < 100 days or ≥ 100 days varieties (Table 3). Due to the relatively late period of harvesting (end of October) in the groundnut-producing areas of northern Benin, millipede and whitegrub damage was not observed. Generally, groundnut was harvested late by the farmers.
Based on interview responses 20, 55, and 25 % of the farmers claim to harvest early, at the right time, or late respectively (data not shown). However, based on the time of planting, none of the farmers harvested early; indeed 80 % of the farmers harvested late (with a time lag of 10-24 days).

Farmers' cultural practices in relation to soil pest spread
Generally, farmers' cultural practices were similar within a particular locality, but varied across localities. In all the surveyed farms where the crops preceding groundnut were cereals (sorghum, millet and maize), farmers did not burn, destroy or remove the stem and stubble of the harvested cereals. Termites were observed on these residues.

The period over which a farm was cultivated varied considerably across the groundnut belt, ranging from 4-70 years (Table 2). Half of the farms had been cultivated for less than 15 years (data not shown), while less than 35% were cultivated for < 10 years. In infested farms, regression analysis of the period over which a land was cultivated (X) against the frequency of termite occurrence (Y) in soil samples indicated a slight decrease in occurrence with increase in the number of years of cultivation (r2 = 0.17; Y = 2.674 ± 0.42 - 0.120 ± 0.05X; n=24; P < 0.05)]. No such relationship was observed in the case of whitegrubs or millipedes.

Table 2. Responses by groundnut farmers on their cultural practices in Mali, Burkina Faso, Niger, Nigeria and Benin
Country/ DGV
Localities
(No. of farms)
DGV
LFC <10yrs UCM UIF MLP UI PSPD
Predominant Minor
Mali









Sikasso (10) Kita/Kayes (10)
90 (100)
120 (50)
-
90 (50)
>10-25
<10- 25
0
20
0
40
20
0
P (100)
SB(100)
5
25
MG(20);M(70)E (60); EM(40)
Burkina-Faso









Bobo Dioulasso
/Niangoloko(10)
Saria (5)
120 (60) 90 (100)
90 (40)
5-55

< 25

30

80

20

0

8

0

P (100)

S (100)

6.2

12.6

EM (60); M (30)
M (60); MG(20);
EM (20)
Fada N'Gourma
(5)
90 (100)
-
-
-
-
-
-
-
-
Niger









Bengou (5)

Maradi (10)

90 (100)

90 (80)

-

120 (20)

5-30

30- 60

40

0

0

30

10

10

P (20);
S (20);SB (60)
SB (100)
0

40

E (40); EM (60)
M (40);
EM (60)
Nigeria









Kano /
Dambatta (10)
Zaria/
Kaduna (10)
100-120
(90)
90 (60)
90 (10)

100-120

(40)
20-70

5-20

0

20

33

0

9

100

SB (100)

SB (100)

0

5

E (70); EM (30)

M (10); E (50);

Benin

EM (40)







Kandi (10)

Ndali (10)

90 (60)

120(80)

120 (40)

90 (20)

5-20

5-50

60

50

0

0

0

0

SB (70);
B (30)
SB (100)
21

0

M (50); MG(10); EM (40)
E (20);
MG (10)
M (40);
EM (20)
Save (10)
90 (70)
120 (30)
4- 20
60%
0
0
SB (30);
0
M (100)
B (70)
DGV = duration of groundnut variety in days (% of farms); LFC = length of farm cultivation (in years) ; <10 = % of farms cultivated for < 10 years; UCM =use of compost manure (% farms); UIF = use of inorganic fertiliser (%); MLP = method of land preparation (% farms): P = ploughing weeds under the soil, S = slashing only, SB = slashing and burning, B = burning only; UI, use of insecticide (%); PSPD =period of soil pest damage (% farms): E = early period, MG = mid-growth, M = maturity period, EM = early and maturity periods.


The bush fallow system (whereby a piece of land previously cultivated is left uncultivated for a number of years to regenerate lost nutrients) was widely practised by farmers in the Kita area of Mali. In other surveyed localities, less than 10% of the farmers practice this system. These farmers stated that the practice did not affect the abundance and spread of soil pests. No relationship was established between farmers' responses and our field observations, due to the low number of farmers that practised the system.

In whitegrub-infested areas, farmers who use compost manure for soil fertilisation complained of an increase in whitegrub infestation whenever an excessive quantity of manure was applied. The percentage of interviewed farmers who used compost manure was too low (24 %) for any meaningful relationship to be established. However in parts of Kita area in Mali where compost manure was widely utilised, more whitegrub-infested farms were observed. The use of inorganic fertiliser by farmers in the surveyed areas was generally low (29 %) due to its unavailability or high cost. In Benin, groundnut was not fertilised, but may benefit from fertiliser applied to the previous cotton crop in a rotation. Farmers in these localities were not aware of any effect of inorganic fertiliser on soil pest damage.

The methods of land preparation in the surveyed areas were slashing, slashing and burning, burning only, or by ploughing weeds with tractors or animal traction to decay in situ under the soil (Table 2). Most farmers (63 % ) clear their farms by slashing and burning the vegetation, 21 % plough their fields, and 6 % slash the vegetation and leave it on the soil surface (data not shown). Some farmers in Benin (10 %) clear their farms by directly burning any vegetation therein. Fifty-five percent of the farmers who burn the vegetation after slashing or without cutting claimed to have fewer soil pest problems. T-test analysis of percentage of plants attacked in farms where any form of burning was practised and those of other methods of land clearing showed that significantly lower (t = 3.1; P < 0.003; n = 40) termite damage occurred where burning was practised (mean damage = 8.6 ± 2.3 %) compared to others (mean damage = 21.7 ± 3.4 %). Such a relationship was not observed with the other soil pests.

In Mali, Burkina Faso and Niger the percentages of interviewed groundnut farmers who use insecticides were 30, 18.7 and 40 % respectively, while only 5 % of the farmers used insecticides in Nigeria. However, damage studies showed that more than 60 % of the farms that were treated recorded more than 20 % crop damage due to soil pests, thus it would appear that the wrong pesticides or dosages may have been used.

DISCUSSION

The termite genera Microtermes and Odontotermes that were found to be infesting groundnut and mature sorghum in our study have been associated with damage to groundnut in many parts of Africa (Appert, 1966; Feakin, 1973; Johnson et al., 1981), and cereals in sub-Saharan Africa (IITA, 1971; Anon, 1987). Designing strategies for termite control in groundnut intercropped with cereals such as sorghum should therefore take into account the presence of these cereal hosts.

During the survey, farmers associated whitegrubs (Schyzonycha spp.) and millipedes (Peridontopye spp.) with groundnut, but not cereal damage. Whitegrubs and millipedes have also been identified as important groundnut pests in other producing countries in Africa (Wightman and Wightman, 1994; Mercer, 1978). In West Africa, however, earlier reports did not consider whitegrubs to be important soil pests of groundnuts. Intercropping did not appear to reduce the damage (Hasse and Litsinger, 1981) due to the insect pests identified in the surveys. This may be due to their subterranean nature.

The duration of cultivated groundnut varieties did not significantly affect the percentage of damaged plants. With the relatively high mean annual rainfall (1100 mm) obtained in certain areas where short-duration varieties were grown, we expected these varieties to escape the onset of the dry season when termite damage is most severe. However, our observations showed that due to late harvest, termite damage was not avoided. With low soil moisture associated with the dry season, termites tend to concentrate on available groundnut plants for food and moisture. It has been reported that termite damage increases with delay in harvest (McDonald and Harkness, 1968). Prompt harvesting could therefore play a role in reducing damage.

Generally, at crop maturity less damage by whitegrubs and millipedes was observed, due to low soil moisture levels at the onset of the dry season. However, early harvest is still important in minimising disease infection and its spread, especially in already damaged pods.

Farmers recognised the identified soil pests as being economically important in various periods of the cropping season. However, it appeared that farmers did not know of the effect of cereal residues on termite damage in succeeding groundnut crops. It has been reported that some termites are pests of cereals in West Africa (IITA, 1971; Wood et al., 1980). Farmers usually do not burn or destroy stubble and stems of cereals in infested farms after harvest, thereby creating a conducive environment for termite spread. The destruction of stalks has been reported to effectively control stemborers in cereals (Sagnia, 1983; Ajayi, 1990). However, until quantifiable proof of its economic benefits is available, the destruction of stalks may prove difficult for West African farmers to adopt, since they use these for many domestic purposes, including fence making.

Farmers could also be encouraged to stack cereal stalks under tree shades away from areas cultivated with groundnut, but also far from buildings, to avoid the transfer of infestation to the buildings from the stalks.

The continuous cultivation of land associated with intensive agriculture reduces termite populations to some extent. This was also supported by our regression analysis involving the length period of cultivation and the frequency of termite occurrence, although the model showed only little variation. Continuous tilling of the soil exposes a certain proportion of termites to desiccation and predators. However, such a practice can only reduce but not eliminate Microtermes species populations, due to their deep subterranean habitats (Collins, 1984).

Some whitegrub species are known to feed on organic matter before feeding on plant roots. It was not clear in the present study whether the identified species fed on organic matter. Similar to farmers' observations of whitegrub damage related to manure applications, in Nigeria the use of compost manure has also been observed to increase whitegrub infestation (O. Ajayi, pers. commun.). When applied on preceding cereal crops such as sorghum and maize, infestation was minimised. More studies are needed on the effect of fertiliser applications or bush fallow system on soil pest infestations.

The major termite species, such as Microtermes and Odontotermes species, are plant litter feeders. Therefore clearing and burning of plant litter may help to minimise the incipient termite population that might re-infest new crops. Farmers reported reduced soil pest damage following the burning of vegetation during land preparation. T-test analysis of the percentage of termite-attacked plants in farms subjected to burning during farm preparation, and those not burned, supported the farmers' observations. It should be noted that this practice cannot completely eliminate Microtermes spp. which can descend to deeper soil and re-emerge later. If burning is desired, cutting and heaping of the vegetation before burning is advisable. Burning is unlikely to affect whitegrubs and millipedes, which infest the crops after planting.

Conventional pest control methods, such as the use of chemical pesticides, are rarely used by groundnut farmers in West Africa because of their high cost. In cases where pesticides were purchased, they were often used as broad spectrum pesticides even when they were not appropriate for the target pests. Some farmers also used pesticides meant for foliar insects or diseases on soil pests or applied sublethal doses of the insecticides. Such practices often result in control failures. From the present studies which showed that 60 % of farms where chemical pesticides were applied still recorded high termite damage, it would appear that the wrong pesticides or dosages might have been used by farmers.

The survey showed that farmers in West Africa recognised termites, whitegrubs and millipedes as major pests of groundnuts. Some of their cultural practices, such as leaving cut vegetation in fields during land preparation, likely contributed to increased termite damage. Leaving residues of previous cereal crops and late harvesting led to increased termite damage. Late harvesting may also have contributed to damage on short-duration (<100 days) varieties, which otherwise would have escaped the high termite damage that usually occurs at the end of the cropping season. These practices did not seem to affect groundnut damage by whitegrubs and millipedes.

Further investigations are needed to highlight farmers practices and other factors which may increase soil pest problems, with a view to developing an effective integrated management system for their control.

Acknowledgement-We thank Drs A. Ratnadass, O. Ajayi, and O. Youm for their useful suggestions; and the NARS of various surveyed countries for facilitating our easy interaction with the farmers. We are also grateful to anonymous reviewers at Insect Science and Its Application for their constructive criticisms. Manuscript submitted as a journal article JA No. 2102 by ICRISAT.

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Copyright 2001 The International Centre of Insect Physiology and Ecology

 


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