Abstract
Sucking pests are major threat to cotton field crop which cause unbearable losses to the crop yield. Aim of the current study was to record seasonal dynamics of major sucking insect pests including whitefly, jassid, thrips and their natural arthropod predators i.e. green lacewings and spiders in cotton field plots. The effects of surrounding field crops on pests' density and predatory efficiency of predators were also recorded. For sampling and survey of insects, the visual counting was found to be the most efficient method for recording the abundance of insects, trailed by net sweeping and tapping. Whitefly was the most dominant sucking pest found on the vegetative stage of cotton, followed by jassid and thrips. Fluctuated populations of predatory arthropods, spiders and green lacewings were also recorded during whole cropping season however, the densities of pests and predators varied with crop phenology. Spiders' population was encouraging at both vegetative and flowering stage and also the same trend of jassid and whitefly were observed at both stages of the crop. Surrounding habitats showed non-significant effect on population densities of insect pests and predators. For abiotic factors, the spiders showed strong positive correlation with humidity and temperature. However, green lacewing was only positively correlated with humidity. On the other hand, the populations of whitefly, jassid and thrips showed non-significant correlation with both temperature and humidity. Overall densities of sucking insect pests were found above economic threshold level. The plant age, crop stage and surrounding habitats effect on the population fluctuation of pests as well as the predators' abundance. The future studies are also warranted to investigate the altered habitats and multiple trap cropping to find out their impact on unattended insect predators and parasitoids in cotton crop.
Highlights
Cotton, Gossypium hirsutum L. (Malvales: Malvaceae) crop is attacked by a fairly high number of arthropod pests at its different phenological stages that cause significant loss to the farmers (Uthamasamy, 1994; Sahito et al, 2017). Yunus and Yousuf (1979) reported 93 insect species from cotton fields of Pakistan while Khan and Rao (1960) reported 235 insect species from Indian part of the sub-continent
The borers are considered as the main threat to the cotton crop but in the recent years due to the introduction of Bt cotton, this threat has been shifted to sucking insect pests, especially Jassid {Amrasca biguttula Ishida (Hemiptera: Cicadellidae)} and whitefly {Bemisia tabaci (Hemiptera: Aleyrodidae)} (Ellsworth et al, 2001; Dhawan et al, 2011)
A significant variation in population of pests and predators was found during all three crop stages (F = 51.09, P < 0.001 for whitefly, F = 52.15, P < 0.001 for Jassids, F = 38.58, P < 0.001 for thrips, F = 40.93, P < 0.001 for Green lacewing and F = 76.98, P < 0.001 for spiders (Figure 3)
Summary
Gossypium hirsutum L. (Malvales: Malvaceae) crop is attacked by a fairly high number of arthropod pests at its different phenological stages that cause significant loss to the farmers (Uthamasamy, 1994; Sahito et al, 2017). Yunus and Yousuf (1979) reported 93 insect species from cotton fields of Pakistan while Khan and Rao (1960) reported 235 insect species from Indian part of the sub-continent. Jassids are characterized as most critical of all sucking pests as they suck cell sap from the plant tissues and in return inject their poisonous saliva into the plant body during its feeding Their early attacks effects leaves and results in reduction in photosynthetic area of the plant (Sahito et al, 2017). Damage the cotton crop severely by sucking cell sap from the lower surface of leaves which reduces boll production by fifty percent (Ahmad et al, 2002) and it weaken the leaves and results in weakening of the whole plant (Umaharan et al, 1998). The population fluctuation of pests and their predators with reference to crop phenology is a facility to decide any management practice at any desired stage of the crop
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