Influence of Cotton Plant Density on Insect Pest Phenology under Changing Climate Scenario

Abstract

Agriculture significantly contributes to Pakistan’s economy. Pakistan is the world’s fifth-largest producer of cotton, after China, United States, Brazil and India. Cotton consumption has risen in response to a significant increase in global population. However, Pakistan’s cotton production is declining due to changing environmental conditions, pest outbreaks, insecticide resistance and pest resurgence. To improve cotton cultivation and productivity, a study was conducted at Cotton Research Institute, Multan, to assess the response of different insect pests to varying planting densities. Data on the populations of whitefly, thrips, jassid, dusky cotton bugs, dusky cotton bugs and pink bollworm were recorded weekly across different plant spacings. Additionally, population of natural enemies and meteorological data were also recorded throughout the cotton growing season at these densities. Compact type cotton variety was sown using randomized complete block design (RCBD) with five treatments (T₁-T₅), each corresponding to different plant spacings of 6, 9, 12, 15 and 18 inches, respectively; each treatment was replicated three times. The results revealed that the population of whitefly, jassid, thrips, and dusky cotton bug differed significantly across the plant densities. The highest populations of these sucking insect pests (whitefly 5.87, jassid 2.34, thrips 1.98 and dusky cotton bug 3.86) were observed in T₁ (plant spacing = 6 inches), whereas the lowest populations (whitefly 4.02, jassid 0.11, thrips 1.14 and dusky cotton bug 2.90) were recorded in T₅ (plant spacing = 18 inches). Pink bollworm populations did not differ significantly among treatments. The population of ants, green lacewings, lady bird beetles, and spiders differed significantly among treatments, while population of these Geocoris and Orius bugs did not show significant difference at any plant density. In T₁, the populations these beneficial insects were highest, whereas they were lowest T5.  These results suggest that planting cotton at a 6-inche spacing could enhance production and minimize pest population through increased activity of natural enemies. This study may also be helpful in integrated pest management (IPM) for the control of pest population.