Insect Pests of Fruits, Plantation, Medicinal & Aromatic Crops

2. 2. Habitat diversification

• Habitat diversification makes the agricultural environment unfavourable for growth, multiplication and establishment of insect pest populations.
  
• The following are some approaches by which the pest population can be brought down.
2. 2. 1. Intercropping system

• Intercropping system has been found favourable in reducing the population and damage caused by many insect pests due to one or more of the following reasons.
• Pest outbreak less in mixed stands due to crop diversity than in sole stands
• Availability of alternate prey
• Decreased colonization and reproduction in pests
• Chemical repellency, masking, feeding inhibition by odours from non-host plants.
• Act as physical barrier to plants.
• The following table gives a few examples of intercropping system where reduction in damage level was noticed
Table 1. Effect of intercropping system on pest levels

Sl. No.	Crop		Pest reduced
	Sole crop	Intercrop
1.	Cauliflower	onion	Diamond back moth
2.	Cauliflower	Mustard	Diamond back moth
3.	Onion	Agathi	Thrips
4.	Banana	Marigold	Nematodes
5.	Brinjal	Solanum nigrum	Whiteflies


• Interplanting maize in cotton fields increased the population of Araneae, coccinellidae and Chrysopidae by 62.8-115.7% compared with control fields. Maize also acted as a trap crop for H. armigera reducing the second generation eggs and damage to bhendi. Hence it is highly important that appropriate intercropping systems have to be evolved where reduction in pest level occurs.
2. 2. 2. Trap cropping

• Crops that are grown to attract insects or other organisms like nematodes to protect target crops from pest attack. This is achieved by
• Either preventing the pests from reaching the crop or
• Concentrating them in a certain part of the field where they can be economically destroyed
Table 2. List of successful examples of trap crop

Sl. No.	Main Crop	Trap crop	Pest
1.	cauliflower	Mustard	Diamond back moth
2.	Tomato	African marigold	Helicoverpa
3.	Bhendi	Castor	Spodoptera


• Growing mustard as trap crop 2 rows per 25 cabbage rows for the management of diamond back moth. First mustard crop is sown 15 days prior to cabbage planting or 20 days old mustard seedlings are planted. Growing castor along the border of cotton field and irrigation channels act as indicator or trap crop for Spodoptera litura. Planting 40 day old African tall marigold and 25 day old tomato seedlings (1:16 rows) simultaneously reduces Helicoverpa damage.
• Growing trap crops like marigold which attract pests like American bollworm to lay eggs, barrier crops like maize/jowar to prevent migration of sucking pests like aphids and guard crops like castor which attracts Spodoptera litura in cotton fields was reported by Murthy and Venkateshwarulu (1998).
2. 2. 3. Fertilizer management

• Plant growth is dependent on the nutritional status of the soil which in turn has indirect effect on pests. High levels of N fertilizer always favour insects and makes plants more susceptible to insect infestation (Rathore and Lal, 1994). On the other hand lower potassium supply favours the development of insects, while optimum and high K has depressant effects (Dale, 1988).
  
• The following table (Table 3) shows the role of nutrient management on pest levels.
Table 3. Effects of host plant nutrition on insect pests



Sl. No.	Host plant	Insect	Response
1.	Rice	Thrips, GLH, Whorl maggot, Leaf folder	High K application reduces pest incidence
2.		Leaf folder, gall midge, BPH, Yellow stem borer, WBPH	High N levels increases pest population and damage
3.	Wheat	Cutworm (Mythimna separata)	Increased N increases incidence
4.	Sorghum	Shootfly	High P reduced incidence
5.	Cotton	Pink boll worm, leafhopper	High N increased incidence
6.	Chickpea	Helicoverpa armigera	N increased infestation while P and K reduced

2. 2. 4. Planting dates and crop duration

• Planting dates should be so adjusted that the susceptible stage of crop synchronizes with the most inactive period or lowest pest population. The plantings should be also based on information on pest monitoring, as the data varies with location. Crop maturity also plays an important role in pest avoidance. The following table (table 4) shows the importance of planting dates on pest population and damage
Table 4. Role of planting dates on pest population and damage

Sl. No.	Host plant	Insect	Response	Reference
1.	Rice	Leaf folder	Early palnted rice (upto 3rd week of June) suppressed population	Dhaliwal et al. (1988)
2.		BPH	Planting in end of July in Kharif and Early in Rabi escapes attack in AP	Krishnaiah et al. (1986)
3.		Gallmidge	Lowest incidence iof planted in Aug or Oct	Uthamasamy and Karuppuchamy (1986)
4.	Sorghum	Shootfly	Advancing sowing date (Sept - Oct) decreased incidence	Kotikal and Panchbavi (1991)
5.	Cotton	Leafhopper	Higher incidence in late sown crop	Dhawan et al. (1990)
6.	Chickpea	H. armigera	For every 10 day delay in sowing 4.02% increase in pod damage	Devendra Prasad et al. (1989)
7.	Tomato	Whitefly (B.tabaci)	Incidence less if planted within Jul- Nov	Saikia abd Muniappa (1989)
8.	Chillies	Thrips	Late planted crop severely affected by thrips and leaf curl virus	Bagle (1992)

2. 2. 5. Planting density

• Plant nutrient status, interplant spacing, canopy structure, etc., affect insect behaviour in searching food, shelter and oviposition site. It also affects natural enemy population. The effect of plant density on pest population is shown in Table 5.
Table 5. Effect of plant density on pest population


Sl. No.	Crop	Spacing/ density	Insect	Response	Reference
1.	Rice	Dense planting	Leaf folder, BPH	High incidence	Kushwaha and Sharma (1981) Kalode and Krishnaiah (1991)
2.	Chickpea	Dense plant population	H.armigera	High incidence	Yadav (1987)
3.		Less dense population	Aphis craccivora	High incidence	Lal et al (1989)
4.	Sugarcane	Dense seed rate	Topshoot borer	Low incidence	Singla and Duhra, 1990
			Early shoot borer	High incidence


2.2.6. Destruction of alternate host plants

• Many insects use a wide range of cultivated plants especially weeds as alternate hosts for off season carry-over of population. Matteson et al. (1984) reported that weeds around the crop can alter the proportion of harmful and beneficial insects that are present and increase or decrease crop damage.
Table 6. Alternate hosts to be removed to reduce damage by pests

Sl. No.	Crop	Pest	Alternate host to be removed	Reference
1.	Groundnut	Thrips (Caliothrips indicus)	Achyranthus aspera	Mohan Daniel et al. (1984)
2.	Rice	Gallmidge	Wild rice (O.nivara)	Kalode and Krishnaiah (1991)
3.		GLH	Leersia hexandra
			Echinochloa colonum
			E.crusgalli
			C.dactylon
4.		WBPH	Chleres barbata
5.	Sorghum	Earhead midge	Grassy weeds	Prem Kishore (1987)


• Destruction of off types and volunteer plants, thinning and topping, pruning and defoliation and summer ploughing are other cultural methods which can reduce pest load in field.
2. 2. 7. Water management

• Availability of water in requisite amount at the appropriate time is crucial for proper growth of crop. Hence, water affects the associated insects by many ways such as nutritional quality and quantity, partitioning of nutrients between vegetative growth and reproduction etc.
  
• The following table shows the effect of irrigation on pest population / damage.
Table 7. Effect of irrigation on pest population / damage.


Sl.No	Crop	Insect	Response	Reference
1.	Rice	Mealy bug	Continuous ponding of 5cm water reduced incidence	Gopalan et al. (1987)
2.	Rice	Caseworm and BPH	Draining of water to field capacity reduces incidence	Thomas (1986)
3.	Fruit tree nursery	Termite	Copious irrigation reduces incidence	Butani (1987)
4.	Groundnut	Aphids	Copious irrigation increased incidence	Rao et al. (1991)


2. 2. 8. Crop rotation

• Sustainable systems of agricultural production are seen in areas where proper mixtures of crops and varieties are adopted in a given agro-ecosystem. Monocultures and overlapping crop seasons are more prone to severe outbreak of pests and diseases. For example growing rice after groundnut in garden land in puddled condition eliminates white grub.
2. 2. 9. Organic manure

• Application of press mud in groundnut @ 12.5 t/ha had a better influence on leaf miner with lower leaflet damage at 38.84 per cent and 2.48 larval numbers per plant during summer 1991. It was 34.93 per cent and 2.72 numbers during kharif, 1991 (Sathiyanandam and Janarthanan, 1995). Rajasekar et al. (1995) reported that farm yard manure, Azospirillum and Phosphobacteria has no significant influence on the control of leaf hopper and fruit borer in bhendi. The incidence of paddy plant and leafhopper was low in Azospirillum combined with farmyard manure (Athisamy and Venugopal 1995). Application of organic manure lowered the rice gall midge incidence (5.28%) (Mohankumar et al., 1995).