DISCUSSION. incidence of sucking pests such as whiteflies, leaf hoppers, aphids and thrips in cotton

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1 DISCUSSION Sucking pests Whiteflies Jambhunkar et al. (1998) found that intercropping cotton with legumes reduced incidence of B.tabaci. Balasubramanyam et al. (1998) also reported low incidence of sucking pests such as whiteflies, leaf hoppers, aphids and thrips in cotton intercropped with cluster beans or green gram. The results of two years study revealed that whitefly populations were always high in cotton monocrop compared to cotton intercropping systems. Particularly cotton intercropped with soybean consistently showed lesser incidence of whiteflies which corroborates with the findings of Sheshadri and Natarajan (1998). Among the intercrop combination cotton with black gram attracted more whiteflies compared to red gram or green gram intercropping. Hirano et al. (1995) pointed out the population dynamics of whiteflies B.tabaci was influenced by temporal variations in quantity and quality of host plants in the area. Intercropping systems in cotton which broughts such variations resulted in differential levels of infestation. Balasubramanian et al. (1998) also found the among six intercrops green gram was more effective in suppressing early season sucking pests than black gram. Venkatesan et al. (1987) also reported whitefly incidence was higher in cotton intercropped with black gram than in green gram. The population behaviour of whitefly showed higher numbers of peeks in monocrop than in intercropped with cotton. It was interesting to note that in cotton with soybean intercrop the population of whiteflies remained stable. Activity of whiteflies was high during high temperature and humidity and declined during winter as 118

2 reported by Horowitz (1986). Though unlike aphids for instance, whitefly infestation can lost throughout the whole cropping season. Thrips Thrips appeared early in the season and continued till the break of winter in the first of week of November. Thrips were significantly less in cotton + soybean compared to cotton + green gram, red gram or black gram. Balasubramanian et al. (1998) also reported lesser incidence of thrips in cotton + green gram. In soybean intercropping there was an abrupt crash of thrips population compared to continued infestation in other intercrop situations. Thrips (Megalothrips sp.) attack is more on green gram and attracted higher incidence of natural enemies of thrips (predatory thrips, lady birds etc) which migrated to main crop of cotton and resulted reduction of thrips in cotton. Sreekanth et al. (2002) also reported that thrips cause at least 40% yield loss in green gram. It was observed that thrips were unusually high in cotton intercropped with red gram. Intercropping red gram with cotton was found to be unfavourable (AICIP 2007) though many workers reported that with short duration pegionpea as intercrop, thrips damage was much reduced in cotton. Den Belder et al. (2000) reported increased damage by western flower thrips in chrysanthemum intercropped with subterranean clover. Increasing thrips population in cotton + red gram with intercropping may be congenial micro climate offered by long duration pigeonpea utilized in the experiment. High humidity positively correlated with increased incidence of thrips in cotton Khan et al. (2000). Though natural enemy complex was found to be higher in cotton + red gram, it was not exercising any influence on the thrips population in cotton. The predators found on red gram were 119

3 found to be more aphidophagous insects where as in soybean intercropping thrips population remained very low all through the cropping season as observed by Venugopala Rao et al. (1995). Jassids Jassids are early season sucking pests. The incidence was observed late August and terminated in first week of November in 2004 and two weeks later in Jassids were found at least 16 50% higher in sole crop of cotton than various intercropping situations. Cotton + soybean intercropping consistently showed significant lower infestation levels compared to other intercrop combinations. There was not much variations in population rise in different intercropping situation as observed for thrips and whiteflies. The findings were in conjunction the results obtained by Venkatesan et al. (1987) where in significantly less population of the leaf hopper was observed in cotton + green gram and cotton + black gram. Balasubramanian et al. (1998) also observed similar effect in cotton + cluster bean. Swaminathan et al. (2002) also postulated crop diversity approach to manage cotton leaf hopper. Aswathanarayana Reddy et al. (2006) also obtained similar results with intercropping of irrigated chillies with onion, marry gold, maize and beans. Hormachan et al. (2009) in Thailand used okra, sunflower, castor as trap crops to decrease leaf hopper populations in cotton. They used non-host plants as intercrops and host plants as trap crops for leaf hopper. In our study all the intercrops were non-host plants (Sharma and Singh 2002) because of non-host plants of the leaf hopper intercropped with cotton the reduction over monocrop was greater. In yet another experimentation of intercropping affects on sucking pests population. Tingey and Lamont 120

4 (1998) showed that Empoasca fabae and Aphis fabae were significantly less in field beans intercropped with winter wheat compared to sole crop of bean. Aphis gossypii In 2004 a initial colonization of aphid population was noticed in August. Reduction in percent infested plants of cotton in different intercropping situations was 19 66% over monocrop. During September October the reductions were much lesser over previous observations which shows adaptability of aphid population to intercropped habitat except in cotton + green gram where in reduction increased to 20%. In 2005 no such non preference to green gram intercropping was observed. The initial colonization appeared in August and terminated in October and again reappeared in December first week. It was also observed by Rathod and Bapodra (2004) that A.gossypii populations initialize infestation of young cotton plants in India during July and activity peaks reach at last week of November and continue till December. Cotton + soybean consistently showed lower percentage of plants infested by the aphid. However, cotton + black gram the infestation continued at a level equal to monocrop situation. Viera et al. (1983) also reported that when cotton was intercropped with maize or cowpea (Vigna unguiaculata) the infestation of A. gossypii was 14 times less than in monoculture. Chamune et al. (2007) also observed the same effect in cotton intercropped with pigeonpea and crotalaria area orchroluca, further they observed the population of natural enemies were abundant. Jackson (2005) in his experiments in organic farming in cotton in Kutch, Gujarat (India) observed that cotton aphids appear early in August on young cotton plants and reduce to insignificant levels and when aboitic / biotic conditions favour, they buildup to damaging levels by last week of November or early December, which was also 121

5 observed in our experiment. Mohapatra (2008) also made similar observation in Orissa (India) with major sucking pests of cotton namely leaf hoppers, aphids and whiteflies with three peeks in August September, October and November last week respectively. Flint and Roberts (1998) in their review of cotton cultivation of moderate and small scale growers in California (USA) concluded that intercropping cotton with alfalfa and oats as companion plants reduced pest infestations. Girma et al. (2004) in Kenya (Africa) reported such reduction aphid, R.maidis infestation in maize associated with certain insectary plants as hedgerows. Balasubramanian et al. (1998) in a similar study of intercropping effects in cotton on sucking pest incidence showed that cotton + cowpea and cotton + green gram had significantly reduced incidence of aphids, thrips, leaf hoppers and whiteflies than in monocrop. Rathod and Bapodra (2004) in Rajasthan (India) monitored aphid infestation on cotton which showed initiation of infestation from July onwards in remain highly active from October to December which corroborates our findings. Parajulee and Slosser (1999) in their study on utilization of relay strip crops viz., canola, Vicia villosa and wheat observed effects of strip cropping on aphid incidence was significant in cotton. Weekly buildup of aphid, Lipaphis erysimi in mustard was significantly reduce by intercrops like garlic or onion (Sarker et al. 2007). It is also important that adequate host population has to be present for aphid predator activity particularly the lady beetles, Phoofolo et al. (2010) observed when relay intercrops in sorghum, like winter wheat, alfalfa and cotton were unable to attract and retain high population of lady beetles while in main crop sorghum with higher infestation of aphids resulted in more retenction of lady beetles. In our study the higher levels of 122

6 coccinellid activity in monocrop of cotton compared to intercrop cotton at certain times may be attributed to continuation of aphid infestation while it was terminated in intercropped situations. Lepidopterous pests H. armigera H.armigera populations initiated in October in both the years and continued till January last week. Significant population reduction with respect H. armigera throughout the two years study, while increased levels of infestation at par with monocrop of cotton were noticed in case of cotton + red gram consistently. The rate of increase of infestation levels in intercropped cotton was noticed during January due to harvesting of the intercrops except in case of red gram. Though there was consistency in population reduction from initiation to termination in cotton + soybean, the other intercrop situations also were more or less at par with soybean. During pod formation stage of green gram infestation of H. armigera also increased which might have contributed higher levels of infestation in cotton + green gram. Green gram pods were particularly more attractive to H.armigera than soybean or black gram. Observations of reduction in H.armigera with maize and cowpea as intercrops in cotton was reported by Amoako et al. (1993). Hedge (2003) observed that intercropping sorghum with cotton due to predatory activity of lacewings was kept at below ET levels. Pesticide post (2009) also reported that in central and southern India intercropping in cotton with black gram, green gram and cowpea diverted population of both sucking pests and American cotton bollworm H. armigera from cotton and enhanced parasitism and predation by natural enemies. The increased infestations in 123

7 cotton + red gram intercropping were also observed by Ravi et al. (2005) in cotton ecosystem associated with pigeonpea (red gram) and chickpea which harboured significantly greater egg and larval population of H. armigera than cotton. The H.armigera population reduction with soybean or groundnut as intercrops in cotton was reported by Venugopala Rao et al. (1995). Wu and Guo (2005) opined that large number of small scale, family owned farms in China which practiced mixed plantings of Bt cotton with corn, soybean and groundnut contributed to slower buildup of resistance to Bt toxin in H. armigera though the Bt cotton was introduced over several years. Though cotton + red gram traditional intercropping or mixed cropping practice, it was reported by All India Cotton Implement Project (AICIP) experiments that red gram contributed to higher incidence of H. armigera in cotton and also repels natural parasitization by Trichogramma and thus unsuitable choice as intercrop in cotton in modern cotton cultivation. Surulivelu (2009) reported that intercropping cotton with black gram and chillies will reduce the intensity of bollworm infestation in cotton. Yelshetty et.al (2009) in a validation of integrated pest management modules for management of pod borers H.armigera in pigeonpea based intercropping found that intercropping with soybean reduced incidence of H. armigera compared with intercropping with cotton, groundnut and green gram. Spodoptera litura The larval population of Spodoptera litura ranged from larva per plant in and larva per plant in The infestations appeared from October onwards in both the years. Cotton + soybean and cotton + red gram contained lesser infestation than cotton intercropped with black gram or green gram. The 124

8 populations remained more or less constant without much fluctuations. Red gram is a non-host plant for Spodoptera litura and that might be the reason for lower incidence of S.litura in cotton + red gram where as similar effects in cotton + soybean may be attributed to abundance of natural enemies of S.litura in cotton + soybean. Particularly higher incidence of S.litura in cotton + black gram is due to the preferential oviposition on black gram, however all the intercrops situations of cotton in both the years generally showed lesser incidence of S.litura than monocrop. Regarding lepidopterous pests, researchers Asman et al. (2001) observed diamond back moth, Plutella xylostella can be reduced by intercropping in cabbage. Similarlly, Alteri et al. (1978) recorded 14% reduction of armyworm Spodoptera frugiperda in maize by poly cultures, which also collaborates our observations with H.armigera and S.litura infestation reductions in cotton intercropping over sole crop of cotton. Insect infestation in intercrops The insect pest infestation in intercrops when grown separately was on par with the monocrop of cotton on the natural enemies populations among the intercrops were not significantly differing. However the population levels were as good as those observed when the intercrops were grown in companion with cotton. Natural enemies Cheilomenes sexmaculata Coccinellid predators C. sexmaculata populations were monitored at all their life stages namely egg, larva, pupa and adult. Activity of predator coincided with the appearance of aphids which started colonization on young cotton plants in August. 125

9 Fortnightly observations were made from August January. Significantly highest egg populations ranging from 14-50% was recorded in cotton + red gram and cotton + soybean. Cotton + green gram attracted greater oviposition by the predator than cotton + black gram. However towards the end of the season in January due to the senescent period of intercrops more oviposition was noticed in sole crop of cotton. The migratory nature of lady beetles was shown by Lin et al. (2003) in China when cotton intercropped with alfalfa which attracted greater number of lady beetles, lacewings and spiders and when alfalfa was cut to force migration of natural enemies on to cotton. Egg laying by Coccinella septumpunctata and Menochilus sexmaculata was reported to be 4 5 weeks before infestation of Lipaphis erisimi in mustard (Rana, 2006). Aphid infestation during 2004 in cotton + green gram was noticed only for a fortnight (August 4 th week to September 1 st week), in other intercrop situations aphid infestation continued till last week of September. Egg populations of C.sexmaculata also reached high levels during September and continued till December second week. Adult activity, oviposition and aphid infestation showed positive trends with each other and exhibited favourable response to increasing aphid infestation. Wells et. al (2001) also reported similarly that densities of Coccinellids in cotton closely tracked the aphid population. It was also established by Evan and Dixon (1986) in a laboratory study that cues for oviposition of lady beetles were aphid odours and aphid honey dew. Larval and pupal population of C.sexmaculata was also found to be higher in cotton + soybean and cotton + red gram systems, however all the intercropped situations were better than monocrop as regards to presence of higher number of larvae and pupae of C. sexmaculata. 126

10 Chrysopa Sp. The egg larval and adult population of Chrysopa species were significantly high in cotton intercropped with soybean or red gram. However at certain times larval populations were equally high in cotton monocrop which may be due to migration of larvae. Cotton plants it self is highly attractive to Chrysopa Sp. due to the host plant released synomones like caryophyllene and aphid honey dew containing indole acitic acid. Hedge et.al (2003) found similar response of Chrysoperla carnea due to intercropping grain sorghum in cotton. Hanumantharaya et al. (2008) also found that intercrop of lucrene in 1:1 ratio increased the effectiveness of C. carnea. The observations of Lin et al. (2003) also corroborate our findings that intercropping cotton with legumes increase the abundance of the lacewing. Kranthi and Russel (2009) in their review of changing trends in cotton pest management mention about the lady beetles and lacewings as important predators in cotton intercropped with different pulse crops. Spiders In cotton eco system 21 species of spiders grouped under 16 genera belonging to 8 families were reported and the predatory potential of the spider Paradosa viridianum was maximum on sucking pests in cotton (Rajeswaran et al. 2005). Spiders are generalist predators and essential in community balance of the cotton insect eco system. In all cotton intercropping systems spiders were more abundant than in cotton raised as monocrop. They were significantly high in cotton intercropped with soybean followed by red gram, compared to other intercrops. Balasubramanian et al. (1998) observed higher incidence of spiders in cluster bean intercropped in cotton. In maize cultivation Brust et. al. (1986) reported higher population of spiders and carabids in 127

11 intercropped situations than monocultures. Mensah (1999) quantified that 2.1, 2.5 and 1.2 times abundance of predatory beetles, bugs, lacewings and spiders per meter row in intercropped cotton compared to monocultures. The species composition of spiders was rich in contrast with monocrop. Geocorids Cotton intercropped with either soybean or red gram contained highest number of geocorid bug activity. Cotton in other intercrops was also better than monocrop in retaining the presence of geocorid bugs in both the years. In western Kenya Van den Berg and Cock (1995) reported that anthocorids and geocorids are important mortality factors of H.armigera in cotton. It was also shown by Johnson et al. (2006) that the mere presence of the predator, Geocoris lubra on a plant can have a strong influence on the movement and behaviour of H. armigera. Predators do more than just reduce numbers of herbivours, they influence, feeding, displacement and subsequently the distribution of the pest in the plant canopy. Soil dwelling insects Carabids Ground dwelling carabids (Coleoptera : carabidae) are important in regulating the soil inhabiting life stages of foliar insects of cotton. Diverse habitats and diversity of cropping system are proposed as promoters of ground beetle diversity in intensely managed agricultural crops like cotton, maize and wheat (Liu et al. 2010). Carabids were found to be highest in cotton + red gram intercropping systems followed by other cropping modules in both the years of study significantly contained higher populations than those found in monocrop. 128

12 Millipedes Millipedes are the macro arthopods important in primary recycling of plant litter in the form of dead leaves, twigs, flowers and flower buds etc. millipedes were found to be active during the months of September November in cotton cropping systems. In both the years of study they were found to be high in cotton + red gram and cotton + soybean. The other two cropping systems were at par with monocrop. Brevault et al. (2009) in their project report similarly mentioned leguminous soil cover harboured more individuals of particularly earth worms (Lambricidae), millipedes (Julidae), centipedes (Scolopendridae) and spiders (Arachinidae) and detrivorous millipedes are mostly numerous in soil cover mulches that provide habitat. Collembola Collembolans are the meso arthropod fauna essential in as secondary trophic level of the detrivourous soil recycling community. They are also designated as indicators of soil health and eco system sustainability and are known as springtails. In this study of cotton intercropping system cotton + red gram significantly had the highest density of collembolans and other cropping modules were at many instances at par with the monocrop. Crop residues and minimum tillage operations encourage these delicate members of the soil biota. Poveda et al. (2008) in their review of research papers on crop diversification in monocultures reported that out of 62 detailed reviews of original studies of last 10 years showed that diversification practices (a) enhance natural enemies in 52% (b) reduce pest pressure in 53% (c) increased yield only 32% of the cases. 129

13 Parasitization by Trichogramma sp Trichogramma species are ubiquitous egg parasites of many lepidopteran insects besides parasitizing eggs of spiders and members of other insect orders. T.chilonis in cotton eco system is used as an inundative release biocontrol agent. Cotton + soybean intercropping system exhibited highest degree of parasitization by T.chilonis in the two years observation. In a study of intercropping systems in cotton Hegde et. al (2003) recorded similar observations in cotton intercropped with sorghum. As was the experiment of Scholz and Parker (2004) with the same intercropping system. Andow and Risch (1987) also establish the fact that poly cultures of maize / bean / squash and maize / clover improved parasitism rates of T.minutum by 1.9 times over monocultures of cotton. In our study that cotton + pigeonpea system recorded the lowest parasitization rates by T.chilonis which was reported by many workers that the cotton + pigeonpea eco system surely inhibited the efficiency of the parasitoid. Larval parasitization of H. armigera Larval parasitization of H. armigera was significantly improved with different intercropping systems over monocrop. Consistently high levels of parasitization was observed with cotton + soybean intercropping. Parasitization by Encarsia sp. Encarsia sp. the aphilinid parasitoids are of world wide distribution parasitizing many species of whitefly pupae and are mass multiplied for inundative releases. The obseravations on encarsia parasitization of whitefly pupae revealed that cotton + soybean with highest rates of 4-5% parasitization was better than other cropping modules. Deguine (2007) in their review of sustainable pest management for cotton 130

14 production reported the use of wheat as intercropped with cotton in China which increased the abundance of natural enemies of sucking pests including encarsia sp. these reports collaborate our observations that significant increase in parasitization in cotton was the result of intercropping. Parasitization by Aphilinus sp Aphid parasitoids like Aphilinus and Aphidius in conjunction with the community of aphidophagous predators limit aphid populations below ETLs. The intercropping system practices in this study namely cotton + soybean and cotton + red gram improved the parasitization of aphids in cotton by Aphilinus over the monocrop. Particularly cotton + soybean exhibited 3-4 times improvement in parasitization over monocrop. Intercropping systems in cotton were reported to the encouraging for the activity of aphid parasitoids (Deguine et al. 2008), which are inconjunction with our findings. 131