Behavioral response of cotton (Gossypium hirsutum) against the infestation of different sucking insect pests in Southern Punjab, Pakistan

The present study was accomplished with aim to identify changes in cotton sucking pest population during different seasons in Southern Punjab, Pakistan. The study spanned three years (2014-2016) beginning from cotton sowing to harvesting season each year. Three species of sucking pests were under observation namely Jassid (Amrasca biguttula), dusky bug (Oxycarenus laetus), and thrips (Thrips tabaci). Their common predators were also noted like Geocoris, Chrysoperla and Argiope. Population of adults and counts of eggs of pests and predators were recorded. Cotton behaves variably against these pest populations during the study. Significant infestation was observed on Non Bt as compared to Bt variety. One-way analysis of variance was performed to analyze the data. The adults of Amrasca biguttula, Oxycarenus laetus and Thrips tabaci varied across the years, variety and seasons. Among the predators Geocoris and Argiope population varied due to these factors throughout the study period except Chrysoperla. No significant difference was observed in the total number of eggs of different sucking pests yearly, on varieties and different months at experimental site.


Introduction
Agriculture is the lifeline of Pakistan's economy accounting for 19.5 percent of the gross domestic product, employing 42.3 percent of the labour force and providing raw material for several value-added sectors. It thus plays a central role in national development, food security and poverty reduction. The rapid growth of Pakistan's urban areas indicates that demand for highvalue perishable products such as fruits, vegetables, dairy, and meat is rising. China Pakistan Economic corridor will help to improve the supply chain and agribusiness benefits by tapping value-added product innovation. Cotton is one of the most important commercial crops in the world. Among the cotton growing countries, India has the largest area of 9.0 million hectare grown under diverse agro ecological areas listed 1326 species of insects and mites recorded on cotton. In Pakistan 159 species of mites and bugs were reported. The great majority of these are of little or no economic importance so far as cotton is concerned, and some, although collected on cotton have not been observed to feed on it. Many are sporadic casual or accidental visitors to the crop. Fortunately, only a relatively small number of insects are of major economic important, but individually or by their combined effect they can cause significant yield loss. Among the phytophagous cotton pests, 24 have attained the pest status and the important can be classified as sap feeding insects, leaf feeding insects and mites. Thrips are generally one of the main early season cotton pests [15]. They initially damage the cotyledons and then several other parts and the types of damage vary according to the parts of the plant attacked. Most damage occurs during early vegetative stage of the crop, when nutritional quality of tissues is ideal for these insects. Both adult and nymphs usually remain on the under surface of leaves, lacerate the tissues and suck the cell sap. The affected leaves become thickened, blistered and bronzed due to continuous feeding. Feeding on developing bolls, makes them turn brown due to development of necrotic patches [13]. Thickening of boll rind can also be noticed when bolls are attacked, boll opening is affected [13].Thrips populations are checked by certain predatory thrips. The predators on thrips include Anthocoridae, Lygaidae and mites [14]. But their role is very limited. The cotton whitefly, an occasional pest of cotton in India has emerged as a major pest of cotton. Severe outbreak was first observed in Guntur region of Andhra Pradesh during 1984-85seasonss and now continuous to be in all the cotton growing regions of India [7] and Pakistan. In addition to direct pest it also acts as a vector of cotton leaf curl virus in north zone. The nymphs and adults remain in colonies on the under surface of leaves and suck the plant sap. Due to continuous feeding chlorotic spots develop on the leaves which later coalesce and the leaves become reddish, brittle and finally drop prematurely. This results in reduced nutrition to the plant leading to stunting, shedding of fruiting bodies and reduction in boll size. The bolls are also forced to burst prematurely loading to poor quality lint. The 'honeydew' excreted by whitefly drops on the upper surface of lower leaves and bolls which favor the development of black sooty mold on the leaves, which in turn reduces photosynthesis and physiology of leaves. Heavy fungal growth on honeydew leads to premature leaf drop [5]. Honeydew on open bolls causes stickiness of cotton which interferes with picking, ginning and spinning thus the lint value is reduced. In addition to Bemisia tabaci the spiraling whitefly, Aleurodichus disperses also attack cotton and cause similar damage as cotton whitefly. A. dispersus is more common in summer cotton rather than winter cotton [6]. Dusky cotton bugs (Oxycarenus laetus) also called as cotton stainers occur on cotton during peak boll formation stages of cotton. They are generally gregarious, bright red colored. They are not serious pests but at time cause considerable damage to developing seeds impairing seed viability as well as staining the kapas [18].Knowing, the importance of the sucking insect pests attacked on the cotton, the present research was designed to find the behavioral response of the cotton against these pests.

Materials and Methods Study site and plan of study
The study was planned to record number of adults and their eggs regarding three sucking pests of cotton jassid (Amrasca biguttula), dusky cotton bugs (Oxycarenus laetus) and thrips (Thrips tabaci) along with their predating insects Geocoris, Chrysoperla and Argiope from the cotton growing areas in Multan region, beginning from sowing to harvesting season on fortnightly basis during 2014-2016. Cotton varieties (IUB-33, Lalazar, Sitara, MNH988, and NIAB Non Bt) were grown in ten different randomly selected plots in the experimental area. Local agronomic practices were adopted. Seeds were purchased from local market at the rate of Rs.300/kg for Bt and Rs 250/Kg for non-Bt varieties. Before sowing, the seeds were treated with 95% conc. H 2 SO 4 to remove the fuzz on cotton seeds. Raised beds were prepared at the distance of 2.5ft from each other. Two to three seeds were placed on these raised beds at the distance of 25cm from each other. Irrigation was supplied time to time when needed, urea and diamonium phosphate (DAP) were used as fertilizers. No pesticides were used.

Recording of the data
Counting number of adults and eggs of three types of cotton sucking pests was started when plumule of plant erupted the soil and leaves began to appear. Ten plots were randomly selected where cotton was grown.
Signboards were placed and plants in each field were tagged at suitable places inside the fields for enumeration purpose.

Statistical analysis of the data
The data of insect and egg counts were edited and fed into MS Excel sheet to check any error and omissions. Further the data were analyzed by one way analysis of variance (ANOVA) and means were tested for significant differences using Statistix (Version 8.1) software at 5% level of significance.

Results
The analysis of variance presented as under explained the effect of year, cotton variety and season (month) on sucking pests and their predators. The average number of Jassid (Amrasca biguttula), dusky bugs (Oxycarenus laetus) varied due to year, variety and month significantly. Among predators average number of Geocoris and Argiope was also affected significantly by variety, month and year. However, average number of Chrysoperla was not influenced by these factors significantly. Average number of eggs of the sucking pests of cotton was also influenced by year, variety and month factors significantly as shown in (Table 1).     Table  4).Comparison of means showed that highest average number of dusky bugs (Oxycarenus laetus) was found in 2015, followed by 2014 and 2016, respectively ( Table 4). Variation of average number of dusky bugs (Oxycarenus laetus) presented that lowest and highest average population of dusky bugs (Oxycarenus laetus) was found during April and September (Table 4) Table 5).The lowest number of Argiope was recorded during April of every year. The highest population was found in September 2014, August 2015 and July 2016. Overall order from highest to lowest count was: 2016<2015<2014 with minor change in size ( Table 5).The average population count of Geocoris was lowest and highest in months of April and July during 2014, April and August to September 2015 and April and September during 2016, respectively. There were minor differences among yearly population size, yet 2015 had the highest and 2014 the lowest population count of this insect ( Table 5).