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R. PRASANNA LAKSHMI, K. MANJULA* AND T. MURALIKRISHNA
Department of Entomology, S.V. Agricultural College, Tirupati-517 502, Andhra Pradesh, India
A field trial in RBD was conducted at S.V. Agricultural College, Tirupati to study the Positive influence of intercrops on coccinellid and spider fauna in groundnut during kharif 2011. The systems studied were groundnut + red gram, groundnut + castor (at 7 : 1 ratio), groundnut + cowpea, groundnut + field bean (at 6:1 ratio) and sole groundnut. Coccinellids and spiders were predominant during crop growth period. Various species of coccinellid predators were considered as a group, and their presence was recorded in all the cropping systems. All the spiders, irrespective of the family to which they belonged, were recorded together as one unit. Among the coccinellids, Chelomenes sexmaculata was the predominant predator which accounted for 70 per cent of the population. Spiders belonging to Lycosidae family were predominant. Population of coccinellids and spiders were increased up to 60 – 70 DAS and declined later. This may be due to availability of sufficient prey like aphids, jassids etc during vegetative stage of the crop. Change in microclimate due to shredded/shrinked foliage at later stages of the crop also may not favor the natural enemy fauna. The data showed that coccinellid population was comparatively high in groundnut + cowpea system (2.44 per plant). Aphids that prefer cowpea might have attracted the grubs and adults of coccinellids towards the crop, as coccinellids are the major predators of aphids. In the remaining intercrop systems also, significantly higher lady bird beetle population was observed. Spider population was comparatively higher in groundnut + field bean system (1.66 per plant) followed by groundnut + cowpea system (1.32 per plant). Other systems had 0.8-1.3 spiders per plant.
Coccinellids, Groundnut, Intercrop, Spiders, Sole crop.
Groundnut, (Arachis hypogaea L.) is one of the major oilseeds cum valuable cash crops for millions of small scale farmers in the semi-arid tropics. It is the world’s 4th most important source of edible oil and 3rd most important source of vegetable proteins. India has prime position in average area (4.93 million ha) and production (7.17 million tones) of groundnut. However, the productivity is low (1144 kg ha-1) compared to that of USA (3000 kg ha-1) and China (2600 kg ha-1). Andhra Pradesh holds a key position with an area of 16.22 lakh ha and with production of 14.57 million tones and productivity of 898 kg ha-1 (Annual report, 2011 ANGRAU).
The insect pests of groundnut inflicts serious losses both directly as defoliators, sap suckers, root feeders etc and indirectly as vectors to dreaded viral diseases of the crop. More than 350 spp of insects damage the crop in different parts of world (Stalker and Campbell 1983).
Chemical control is being recommended with success but the awareness of deleterious effects of chemicals led
to the thinking about alternatives to chemicals. Cultural operations in agriculture have well established history for their role in insect pest management. Of these, inter/mixed cropping systems have been considered as an important components and constitutes the most practical oriented approach. Intercropping can affect the microclimate of the agro ecosystem and ultimately produce an unfavorable environment for pests. Thomas (1991) reported that natural enemies of insect pests tend to be more abundant in intercrops than in monocrops, as they find better conditions, such as better spatial and temporal distribution of nectar, pollen and prey sources and more congenial micro habits for their special requirements thereby enhancing the biological control of crop pests. The present studies were carried out to find out the influence of some intercrops on the occurrence of natural enemies of insect pests of groundnut.
A field experiment was conducted during kharif, 2011 with the groundnut variety Narayani at Wetland Farm, S.V. Agricultural College, Tirupati. The experiment was laid
out in a Randomized Block Design (RBD) with five treatments and replicated four times in a plot size of 10 × 5 m. The crops viz., redgram (LRG-41), castor (local variety), cowpea (TPTC-8) and field bean (TFB-5) were used for intercropping with groundnut.
The treatments consisted of growing one row of red gram after every seven rows of groundnut (1:7), one row of castor after every seven rows of groundnut (1:7), one row of cowpea after every six rows of groundnut (1:6), one row of field bean after every six rows of groundnut (1:6) and a sole crop of groundnut. Sowing was done during first fortnight of July (6th July), 2011. All agronomic practices from sowing to harvesting were followed. The trial received no plant protection measures.
Various species of coccinellid predators were considered as a group, and their presence was recorded in all the cropping systems. All the spiders, irrespective of the family to which they belonged, were recorded together as one unit. The final pooled mean data was analyzed and presented.
The data was subjected to analysis of variance outlined by Panse and Sukhatma (1978) and statistical significance was tested by CD value.
Observations on coccinellid and spider population
During the study period several coccinellids were observed viz., Cheilomenes sexmaculata, Coccinella transversalis, Coccinella septumpunctata, Scymnus spp etc. Among the coccinellids, Chelomenes sexmaculata was the predominant predator which accounted for 70 per cent of the population. Several spp of spiders were recorded in different cropping systems. Spiders belonging to Lycosidae family were predominant. The data on coccinellid and spider population is presented below.
At 20 DAS
High population of coccinellids of 0.79 per plant was observed in groundnut + cowpea intercropping system. Remaining systems recorded nearly 0.44 to 0.64 coccinellids per plant (Table 1).
Groundnut + field bean system recorded 0.75 spiders per plant where as other systems recorded 0.4 to 0.69 spiders per plant (Table 2).
At 30 to 40 DAS
Groundnut + cowpea and Groundnut + redgram systems recorded higher number of coccinellids (0.75 to
1.72 per plant) which were significantly different from remaining systems. Groundnut + field bean, groundnut + castor systems and sole groundnut recorded 0.50 to 1.12 coccinellids per plant (Table 1).
Spider population was also slightly increased in different treatments (Table 2).
At 50 DAS
The population of coccinellids was slightly increased in all the systems when compared to 40 DAS. Groundnut + cowpea system recorded high population i.e. 1.99 per plant followed by groundnut + redgram and groundnut + castor systems with 1.44 and 1.35 coccinellids have recorded respectively. Sole groundnut and groundnut + field bean only 0.94 to 1.27 coccinellids per plant (Table 1).
Comparatively high spider population was noticed in Groundnut + field bean system (2.15 per plant). In other systems, 1.05 to 1.88 spiders per plant were present (Table.2).
At 60 DAS
High population of coccinellids was noticed in groundnut + cowpea system i.e. 3.13 per plant and it is significantly different from other systems. Groundnut + redgram and groundnut +field bean consisted of 2.4 coccinellids per plant. Comparatively less population of 2.0 per plant was there in sole groundnut and groundnut + castor systems (Table 1).
Groundnut + field bean system recorded high population of spiders 3.18 per plant and it was significantly different from other systems. Groundnut + redgram and groundnut + cowpea systems recorded 2.1-2.3 spiders per plant. Sole groundnut and groundnut + castor systems recorded 1.2-1.5 spiders per plant (Table 2).
At 70 to 80DAS
At 70 DAS, the coccinellid population was increased. Groundnut + cowpea harboured highest population i.e. upto 5.60 per plant followed by groundnut + redgram system (4.75 per plant). Groundnut + field bean, sole groundnut and groundnut + castor recorded 3.4 -3.8 coccinellids per plant. At 80DAS, groundnut + cowpea system had 3.29 coccinellids per plant where as remaining systems recorded nearly 1.7 to 2.20 per plant (Table 1).
Spider population was slightly decreased at 70 and 80 DAS when compared to 60 DAS. Among all the intercropping systems groundnut + fieldbean system recorded comparatively high spider population i.e. 2.0 per plant (Table 2).
At 90 DAS
The coccinellid population was decreased at 90 DAS when compared to 80 DAS. All the intercropping systems recorded nearly 0.8 to 1.72 coccinellids per plant (Table 1). Spider population at 90 DAS was ranged from 0.4 to 1.0 per plant (Table 2).
The above data shows that, the population of coccinellids and spiders increased continuously from 20DAS up to 70 DAS and declined later. This may be due to availability of sufficient prey like aphids, jassids etc during vegetative stage of the crop. As the prey population decreased, predator population also declined due to lack of sufficient food. Change in microclimate due to shredded/shrinked foliage at later stages of the crop also may not favor the natural enemy fauna. Duffield (1993) noticed peak population of cocinellids on sorghum during early September.
The data in the above table shows that coccinellid population was comparatively high in groundnut + cowpea system (2.44 per plant). Aphids that prefer cowpea might have attracted the grubs and adults of coccinellids towards the crop, as coccinellids are the major predators of aphids.
In the remaining intercrop systems also, significantly higher lady bird beetle population was observed. Baskaran et al. (1993) reported that growing.
Intercrops such as cowpea and pearl millet reduce pest damage and favours natural enemies on groundnut.Kennedy et al (1994) noticed that intercropping groundnut with pearl millet favours the predators and parasites of groundnut insect pests. Duffield and Reddy (1997).
Reported increased activity of coccinellids and spiders in leguminous intercrops. Surulivelu (2004) reported that Cowpea is a short–duration pulse crop which attracts aphids, thus increasing occurrence of coccinellids and multiplication of coccinellids and other predators in groundnut. (Srinivas rao 2007) stated that Coccinellids were significantly more abundant in pigeonpea with sorghum or greengram or groundnut systems.
Spiders were comparatively high in groundnut + field bean system (1.66 per plant) followed by groundnut +cowpea system (1.32 per plant). Other systems recorded 0.8-1.3 spiders per plant. The aggregation of predatory spiders at higher levels might be due to availability of sufficient food, shelter and congenial microclimate in the groundnut + field bean cropped area.
Singh et al. (1991) studied influence of intercropping on natural enemy complex in groundnut and reported that the population of spiders was higher in intercropping system than that of the sole crop. Wu (1991) reported that intercropping maize in cotton fields increased the population of Araneae, Coccinellidae and Chrysopidae significantly compared with control fields. Mahabaleshwar et al. (2003) noticed that average population of C. carnea and spiders were significantly high on cotton intercropped with lucerne, cowpea, and groundnut.
Gavarra and Raros (1975) found more predatory spiders and predatory coccinellids in groundnut and maize intercropping system than in sole crop of groundnut.
Gyawali (1988) studied the effect of companion crops on the incidence of predatory spiders in rice and soybean fields in Nepal. The population densities of the predatory spiders were higher in the maize + soybean intercrop compared to the rice + soybean intercrop and soybean alone.
