Cotton Whitefly Research Articles

Cotton whitefly (Bemisia tabaci) resistance to organophosphate and pyrethroid insecticides in Pakistan.

Resistance to three organophosphate and four pyrethroid insecticides was monitored from 1992 to 2000 in field populations of adult whiteflies, Bemisia tabaci, from Pakistan using a leaf-dip method. There was generally a very high resistance to dimethoate and deltamethrin, and a moderate resistance to monocrotophos during 1992 to 1996. From 1997 to 2000, resistance to these insecticides dropped to low levels because of less reliance on them for whitefly control, and introduction of new chemistries with novel modes of action that had no cross-resistance to conventional insecticides. Concurrently, whitefly resistance to acephate, fenpropathrin, lambda-cyhalothrin and bifenthrin mostly remained low. An insecticide resistance management strategy is recommended that particularly emphasizes the rotation of still-effective insecticides from different chemical classes along with the use of novel chemicals and other tactics of integrated pest management.

Determination of Effective and Economic Dose of Two Carbamate Insecticides Against Cotton Whitefly Bemisia tabaci (Genn.) on Niab Karisham Cotton at Faisalabad (Pakistan)

Determination of Effective and Economic Dose of Two Carbamate Insecticides Against Cotton Whitefly Bemisia tabaci (Genn.) on Niab Karisham Cotton at Faisalabad (Pakistan)

Controlled release of aldicarb from carboxymethyl cellulose microspheres:in vitro and field applications

Aldicarb is a carbamate pesticide that is widely used throughout the world in the protection of crops (eg cotton, nuts, potatoes, onion, tobacco, sugar beet and sugar cane). In Turkey, especially in the Çukurova region, it is used for the control of the cotton white fly (Bemisia tabaci) which attacks cotton plants cultivated in this region. Aldicarb contamination in surface and ground water is a serious problem in several countries, partly due to its high water solubility. It is also highly toxic to mammals. In order to overcome these problems, microspheres of aldicarb were prepared using carboxymethyl cellulose (CMC) as the biodegradable support material cross-linked with aluminium chloride. A strong hysteresis behaviour was observed upon drying and reswelling. Encapsulation efficiency was in the range 12–23% and aldicarb contents of 5.7–10.3 mg per 100 mg of microspheres was achieved. In vitro release was distinctly Fickian, and Higuchi constants were very close to 0.5. Release in pots revealed that only one sample had a release capability for more than four weeks. In the cotton plot much longer durations of release (more than seven weeks) were observed while a commercial granular formulation released its content immediately. It was thus possible to construct a controlled pesticide release system that prolonged the bioavailability to about eight weeks. © 1999 Society of Chemical Industry

Controlled release of aldicarb from carboxymethyl cellulose microspheres:in vitroand field applications

Aldicarb is a carbamate pesticide that is widely used throughout the world in the protection of crops (eg cotton, nuts, potatoes, onion, tobacco, sugar beet and sugar cane). In Turkey, especially in the Cukurova region, it is used for the control of the cotton white fly (Bemisia tabaci) which attacks cotton plants cultivated in this region. Aldicarb contamination in surface and ground water is a serious problem in several countries, partly due to its high water solubility. It is also highly toxic to mammals. In order to overcome these problems, microspheres of aldicarb were prepared using carboxymethyl cellulose (CMC) as the biodegradable support material cross-linked with aluminium chloride. A strong hysteresis behaviour was observed upon drying and reswelling. Encapsulation efficiency was in the range 12-23% and aldicarb contents of 5.7-10.3 mg per 100 mg of microspheres was achieved. In vitro release was distinctly Fickian, and Higuchi constants were very close to 0.5. Release in pots revealed that only one sample had a release capability for more than four weeks. In the cotton plot much longer durations of release (more than seven weeks) were observed while a commercial granular formulation released its content immediately. It was thus possible to construct a controlled pesticide release system that prolonged the bioavailability to about eight weeks. # 1999 Society of Chemical Industry The control of pests often requires periodic applica- tion of pesticide to the crop using conventional formulations, eg powders, granules, or concentrated emulsions. These lead to significant levels of environ- mental pollution due to the application of extensive quantities of pesticide required to prolong effective- ness. Losses can occur due to wash-out, evaporation, surface run-off and dispersion to unintended regions, 1-3 which also has undesirable economical consequences. Such disadvantages can be overcome by providing low levels of the pesticide over the desired period using a bioactive material release system based on the diffusion of the bioactive compound through a matrix or membrane. 4-6

The influence of normal and low-rate application of insecticides on populations of the cotton whitefly and melon aphid and associated parasites and predators on cucumber

Studies were conducted in cucumber fields to evaluate the standard and reduced dosage rates of 5 insecticides for control the cotton whiteflyBemisia tabaci (Genn.) and melon aphidAphis gossypii Glov. and effect of insecticide application on associated parasites and predators. Eggs of whitefly appeared to be less susceptibility to all treatments (max. 66% reduction) than larval and pupal stages. Populations of larval and pupal stages of whitefly were significantly reduced in all treated plots. For example (larvae on day 10 after treatment with ethiofencarb, diafenthiuron, and chlorpyrifos methyl 67, 50, and 68% pupae 68, 69, and 75%). Two aphelinid parasitoids,Eretmocerus mundus Mercet andProspaltella lutea Masi, were the most primary important parasitoids of the whitefly pupae in all test plots. Percent parasitism, in most treated plots, were slightly affected as a result of insecticide application. However, all tested insecticides and dosage rates caused severe suppression of emergence of adult parasitoids. Moreover, longevity of adult parasitoids were highly decreased.

Variation in biological characteristics and esterase patterns among populations of Bemisia tabaci, and the association of one population with silverleaf symptom induction

AbstractBiological characteristics (oviposition and survival rates) and esterase banding patterns in native PAGE were investigated to evaluate variation among three populations of Bemisia tabaci Gennadius (Homoptera: Aleyrodidae). Reproductive capabilities of whiteflies from cotton (Gossypium hirsutum L.) and pumpkin (Cucurbita maxima Duchesne) populations were similar on the three host plant species tested. These populations, which had the same wild‐type field origin, reproduced better on either cotton and pumpkin than on poinsettia (Euphorbia pulcherrima Willdenow). In contrast, poinsettia whiteflies exhibited relatively similar reproductive capabilities for the three host species tested. Pumpkin and cotton whiteflies had similar esterase banding patterns (‘A’ type), while poinsettia whiteflies yielded a different banding pattern (‘B’ type). In transmission studies, whiteflies from cotton or pumpkin sources did not induce silverleaf (SSL) or white stem (WS) symptoms in Cucurbita spp. tested. In contrast, poinsettia whiteflies were associated routinely with SSL and WS symptoms in Cucurbita spp. following colonization by whitefly adults. From these data, it was possible to correlate a specific esterase banding pattern (A or B) with reproductive capabilities and the ability to induce SSL and WS symptoms.

Resistance to whitefly ( Bemisia tabaci) in cotton ( Gossypium hirsutum) in the Sudan

Over the past 10–15 years, the cotton whitefly ( Bemisia tabaci Genn.) has caused severe damage to cotton in many tropical countries. Effects of three leaf-hair densities (LHD) (high, moderate and low) and three leaf shapes (LS) (normal, okra and super okra) on whitefly numbers were examined in the Sudan in 1982. Resistance was conferred by low LHD and okra or super okra LS, with significant reductions in numbers of whitefly adults per leaf and adults, scales and pupae per unit area. Adults per leaf were lowest on the most resistant line, ORS-13 (exotic Gossypium hirsutum cv., low LHD/okra LS) throughout the season. Pupal parasitism was significantly higher on this line than on a hairy plant of normal leaf shape. Honeydew causing stickiness of lint was reduced to acceptable levels on resistant lines. Leaf shape influenced the microclimate, in that relative humidity was lower and temperature was slightly higher in the canopy of Sudac-K than in Barac (67)B. Fewer whiteflies on Sudac-K may be due to a more adverse microclimate for whitefly and improved host-searching conditions for adult parasites. A breeding programme in the Sudan should be maintained for selection of field-resistant varieties.

Insecticide resistance in the cotton whitefly(Bemisia tabaciGenn.) in the Sudan Gezira

Abstract The results of a survey of insecticide resistance in the cotton whitefly (Bemisia tabaci Genn.) to some of the commonly used insecticides, or insecticide mixtures, in the Sudan Gezira Scheme, disclosed that high levels of resistance exist in the Scheme's whitefly populations. The resistance ratios of the scheme populations, relative to a susceptible strain, for the adults and nymphs, respectively were as follows: dimethoate, 454 × and 257 ×; endosulfan, 364 × and 5 ×; dimethoate/endosulfan mixture, 10 × and 7 ×; methomyl, 8 × and 8 ×; amitraz, 6 × and 2 ×; and amitraz/endosulfan mixture, 5 × and 3 ×. The adults of an out‐of‐season strain of the cotton whitefly exhibited moderate levels of resistance to amitraz (7 ×), amitraz/endosulfan mixture (3×), and endosulfan (3×). The nymphs of this strain showed resistance to dimethoate (25 ×), amitraz (8 ×) and dimethoate/endosulfan mixture (3 ×). Adult whiteflies were always found to be more susceptible than nymphs and the resistance ratio of the adults was generally higher than that of the nymphs.

Serious Increase of Cotton Whitefly and Virus Transmission in Central America

Serious Increase of Cotton Whitefly and Virus Transmission in Central America