In each year untreated check plots, on which only water ..... Eveleens, K.G. (1983) Cotton-insect control in the Sudan Gezira: analysis of a crisis. ... Naranjo, S.E., Flint, HM. and Henneberry, T.J. (1996) Binomial sampling plans for estimating ...
ENTOMOLOGY
M. Naveed et al. (2008) Phytoparasitica 36(4):377-387
Effect of Foliar Applications of Some Insecticides on Bemisia tabaci, Predators and Parasitoids: Implications in Its Management in Pakistan
M. Naveed,*, 1 A. Salam, 2 M.A. Saleem a and Ali H. Sayyed 4 Three experiments were carried out during three consecutive years to evaluate 19 insecticides and 12 tank mixtures of different groups of insecticides against the whitefly Bemisia tabaci and its predators and parasitoids under field conditions in cotton. In the first experiment, the whitefly population was lower in treatments with thiacloprid and higher in those with black warrant (a.i. alcohol) and cypennethrin; the number of predators was higher with Agri-50 and spinosad and lowest with cypermethrin, whereas percent parasitism was higher with thiacloprid and lower with methamidophos. In the second experiment, the whitefly population was lower in treatments with buprofezin, pyriproxyfen and diafenthiuron and higher in those with endosulfan, imidacloprid and thiamethoxam; the number of predators was higher with pyriproxyfen and lower with thiamethoxam, whereas percent parasitism was higher with pyriproxyfen and lower with thiamethoxam. In the third experiment, the whitefly population was lower in a treatment mixture with buprofezin + fenpropathrin and higher in that with thiamethoxam + chlorpyrifos; the number of predators was higher with buprofezin + fenpropathrin and lower with deltamethrin + triazophos and deltamethrin + chlorpyrifos, whereas percent parasitism was higher with the mixture of pyriproxyfen + chlorpyrifos and lower in imidacloprid + chlorpyrifos, betacyfluthrin + triazophos, and deltamethrin + triazophos. Effective use of these insecticides to manage whitefly infestations and to save predators and parasitoids is discussed. KEY WORDS: Gossypium sp.; insect growth regulators; insecticides with novel modes of action; nicotinoids; organophosphates; synthetic pyrethroids; whitefly. INTRODUCTION The whitefly Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) is a key pest of cotton, vegetables and legumes in several countries of the world including Pakistan and threatens cotton production at the farm level. Predators and parasitoids play an important role in regulating whitefly populations (13). However, their potential remains largely untapped in multiple cropping systems (10), and the most significant problem is the disruption of natural enemy populations by the indiscriminate use of insecticides with broad-spectrum toxicity to both pests and their natural enemies (7). This problem is most serious in the cotton ecosystem, as more than 80% of pesticides applications are on cotton, mainly to control B. tabaci and Helicoverpa armigera in Pakistan. Received Nov. 19, 2007; accepted May 4, 2008; http:www.phytoparasitica.orgposting August 7, 2008. 1Central Cotton Research Institute, Multan, Pakistan. *Correspondingauthor [e-mail: naveed_ento@yahoo,com]. z Institute of Pure and Applied Biology, Bahauddin Zakariya University, Multan, Pakistan. 3University Co[[ege of Agriculture, Bahauddin Zakariya University, Multan, Pakistan. 4University of Sussex, Brighton, UK.
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Whiteflies and other sucking pests were mostly controlled by organophosphate (OP) insecticides during the 1970s and then also by pyrethroids during the 1980s. As the use of insecticides intensified, whiteflies developed a high level of resistance to OPs and pyrethroids in Pakistan in the early 1990s (2,6). When the control of whiteflies and other pests became difficult with single compounds, insecticide mixtures became popular, starting in the mid-1980s. Because of their dissimilar modes of action, OPs and pyrethroids were often pre- and tank-mixed to enhance the control spectrum as well as putatively to counteract resistance. Mixtures of pyrethroids plus OPs were successful in controlling B. tabaci in Pakistan during the 1980s until the development of multiple resistances to both pyrethroids and OPs during the 1990s (2). In the mid 1990s, the more selective insecticides with novel modes of action, such as imidacloprid, diafenthiuron, acetamiprid, thiamethoxam, buprofezin and pyriproxyfen, were introduced into Pakistan for whitefly management. These compounds are known to be highly effective in suppressing whitefly populations (9,22) and are generally considered to be relatively benign to natural enemies (16). Although lethal and sublethal effects of some of these insecticides on whitefly, its predators and parasitoids have been studied in various laboratories, little attention has been paid to the selectivity of these compounds under field conditions (19,26). Because of multiple pests on cotton in Pakistan, insecticides are likely to remain a major component of integrated pest management and therefore the overall effects of both broad-spectrum and selective materials need to be studied in the field. Field trials were laid out to determine the impact of some organophosphates, synthetic pyrethroids, and insecticides having novel modes of action when used alone or in tank mixtures on the abundance and activity of B. tabaci, its predators and parasitoids. The main objectives were to conserve natural enemies and to formulate new strategies for integrated management of whitefly under field conditions in Pakistan. MATERIALS AND METHODS Experiments were conducted over 3 years at the Agricultural Experimental Farm of the Central Cotton Research Institute, Multan, Pakistan. In the first year, the experiment was conducted on (i) organophosphates (methamidophos, triazophos), and treatments consisted of: (ii) synthetic pyrethroids (cypermethrin, deltamethrin, fenpropathrin, bifenthrin, esfenvalerate, lambda-cyhalothrin), and (iii) 'new chemistry' insecticides (spinosad, Agri50, black warrant [a.i. alcohol; W.S. Homeopathic Pharmacy and Research Centre, Lahore, Pakistan], and thiacloprid). In the second year the treatments consisted of (i) organochlorine (endosulfan), (ii) insect growth regulators (IGRs) (buprofezin, pyriproxyfen), (iii) thiourea (diafenthiuron), and (iv) neonicotinoids (acetamiprid, imidacloprid, thiamethoxam). In the third year the experiment was undertaken with 11 tank mixtures: (i) IGRs plus chlorpyrifos (buprofezin + chlorpyrifos and pyriproxyfen + chlorpyrifos); (ii) thiourea plus chlorpyrifos (diafenthiuron + chlorpyrifos); (iii) neonicotinoid plus chlorpyrifos (acetamiprid + chlorpyrifos, imidacloprid + chlorpyrifos and thiamethoxam + chlorpyrifos); (iv) synthetic pyrethroid plus organophosphates (deltamethrin + chlorpyrifos, deltamethrin + triazophos and betacyfluthrin + triazophos); (v) neonicotinoid plus abamectin (imidacloprid + abamectin); and (vi) neonicotinoid plus synthetic pyrethroid (acetamiprid + betacyfluthrin), all under field conditions. Cotton variety 'CIM-473' was planted in all 3 years during the first week of June in 378
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76-cm-wide beds. Each treatment was replicated four times on plots of 40 x 18.2 m using a randomized complete block design. The standard cultural practices recommended by the Agriculture Department, Government of Pakistan, were followed. The experimental field was kept unsprayed initially, and sucking pests and their natural enemies were allowed to develop. Whitefly adults and nymphs were recorded throughout the season, and spray was initiated when both nymphal and adult populations of whitefly reached the economic threshold level of five nymphs per maximal leaf (39). A knapsack hand sprayer was used with a spray volume of 250 l ha- 1. In each year untreated check plots, on which only water was sprayed, were kept for comparison. Both nymph and adult populations of whitefly were recorded using the leaf turn method described by Naranjo et al. (31). Fifteen randomly selected leaves from the 5th to 8 th main stem down from the terminal one were taken one week after each spray. Commonly found predators such as Chrysopa spp., Geocoris spp., Coccinellid spp., Orius spp. and spiders were counted in whole plant counts, where all plants in a 1.33-m strip were examined visually and the number of predators was recorded. Parasitism was estimated from 1020 leaf samples per plot having the highest numbers of 3rd instar whitefly nymphs from the treated as well as the untreated plots one week after each spray. These leaves were brought to the laboratory. Afterwards, a 20 cm 2 piece of leaf with the maximum number of 3~d instar nymphs was excised with a leaf cutter and placed in a sealed glass petri dish. At least ten leaf samples per plot were held in the laboratory at 2 8 i 2 ~ and 65• r.h. The number of whitefly and parasitoid adults that emerged was recorded. Percent parasitism was defined as: percent parasitism = number of emerged parasitoids / (number of emerged parasitoids + number of whitefly) * 100 (34). Each year two spray applications were applied and the mean number (• S.E.) of whitefly nymphs, adults, and nymphs + adults per leaf, 72 h and 1 week after spray, and the mean percent (+ S.E.) of parasitism per 200 cm 2 leaf area, and the mean number (• S.E.) of predators per stick sample, one week after spray, are presented in this manuscript.
Identification of parasitoids Three species of aphelinid parasites, Encarsialutea(Masi), Encarsia sophia and Eretmocerus mundus Mercet were identified from cotton samples by Prof. Jian Huang (Director, College of Plant Protection, Fujian Agriculture and Forestry University, Fuzhou, Fujian, People's Republic of China). Data analysis Whitefly and predator data collected in the field and percent parasitism recorded in the laboratory were analyzed using the MSTATC program (29) for randomized complete block design and means were compared by Fisher's Significant Difference (FSD) test. RESULTS
Effect of organophosphates, synthetic pyrethroids, and 'new chemistry' insecticides The lowest populations of B. tabaci nymphs per leaf were recorded in thiacloprid and adults in methamidophos, 72 h after spray, whereas one week after spray the populations of nymphs and adults were less in thiacloprid, and during the same period nymphs were higher in black warrant and adults in methamidophos (Table 1). Numbers of predators per 1.33m-row-length were significantly higher (F=14.59; df=12, 36; P
