Spatial Distribution of Preimaginal Bemesia tabaci (Homo-ptera: Aleyrodidae) in Cotton

ABSTRACT
Studies were conducted to examine the distribution of preimaginal Bemesia tabaci (Gennadius) in cotton, Gossypium hirsutum L. at various locations in 1996 and 1997. The number of eggs and nymphs were counted on the underside of leaves from the top, middle and bottom thirds of the plants. Fifty to one hundred leaf samples were taken from each field at weekly intervals. Fields were selected from commercial crops with conventional spray programmes and from research fields with controlled conditions. The number of eggs and nymphs per leaf increased considerably towards the end of the season in all three strata in each field but the proportion of eggs was consistently higher in the upper stratum. The nymphs took higher proportions of the populations on leaves in the middle and bottom strata. This became more evident late in the season. The proportion of nymphs was always higher in the middle than the bottom stratum.

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Mass Rearing and Use of a New Species of Chrysoperla (NeuropteraL Chrysopidae) in Cotton Crops in Argentina

ABSTRACT
In the larval stage, Chrysoperla (Steiman) species feed on various agricultural pests. So far, only Chrysoperla externa had been recorded on cotton crops in Argentina. Towards the end of 1994, Chrysoperla chaquensis was discovered in the province of Salta, being predominant in the western region of the Argentinian cotton area, while C. externa is abundant in the eastern region. Efforts at rearing both species were successful, with higher production levels in C. chaquensis, showing the advantage of a shorter life cycle than C. externa. A daily yield of 500,000 eggs was reached for C. chaquensis that were used for inundative and inoculative releases on cotton crops aimed at the control of aphids and the eggs and first instar larvae of bollworm and leafworm. Cotton yields for areas treated parcels with this predator, supplemented with two treatments of Bacillus thuringiensis, were comparable to those reached in fields with 11 – 12 conventional insecticide treatments.

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The Influence of Host Plants on the Mating Success of the Cotton Bollworm,

ABSTRACT
The chances of a moth mating successfully may depend on the type of crop or other vegetation surrounding it. Mating trays were used to determine the mating success of Helicoverpa armigera (Hübner) in various crops in the Darling Downs, Queensland, Australia during the 1996/97 and 1667/98 seasons. Moth abundance was assessed with pheromone and light traps. A series of comparisons of three or four crops was used, including mature maize (corn), immature, flowering and post flowering cotton and pre flowering and post flowering sunflower, sorghum and soybeans and fallow land. Laboratory reared virgin females with their wings clipped were placed in mating trays in the various crops and remained there until they were mated. The studies indicate that host plants did not significantly influence the chance of being mated, despite substantial variation in moth abundance between crops. Preliminary studies included a comparison of wing-clipping methods. The removal of the right fore and hind wings proved most effective. No consistent pattern emerged suggesting the multiple moths could be used in each tray. A comparison of females aged two to five days old showed no significant effect of moth age on the chance of being mated. The response of females to host volatiles and male response to females in the presence of host volatiles is being investigated in laboratory studies

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Survival and Control of the Boll Weevil, Anthonomus grandis, Around Overwintering Habitat in the United States

ABSTRACT
A field and a laboratory experiment were performed to evaluate factors that influence the overwinter survival of boll weevil, Anthonomus grandis Boheman, populations. Spring surveys of boll weevil densities were conducted as indicators of overwintering survival in 1994, 1995, 1996 and 1997 in four Arkansas counties. Approximately 1000 traps were placed adjacent to defined overwintering habitats near cotton fields. Traps near forested habitats consistently contained the highest average boll weevil catches among habitat types, while grassy field borders generally had the lowest mean trap captures. Trap captures near tree-line and brushy field border habitats were moderate. Larger and more significant differences between habitat types occurred during springs following colder winters. In the laboratory experiment, diapause-conditioned boll weevils were subjected to freezing temperatures within containers submerged in a cold circulation bath and held for one to eight hours. Results showed that temperature, duration of exposure, moisture and substrate were significant factors in boll weevil mortality. Mortality increased with temperature reduction and exposure time. The presence of dry substrate significantly improved weevil survival over those in empty containers at -10.0 and -12.5oC and over those in moist substrate at -5.0 to -12.5oC. Over 70% of weevils were able to survive temperatures of -2.5oC for eight hours, in either moist or dry substrate, while high (>75%) mortality occurred at -10oC or colder temperatures in moist substrate, even for short (1 hour) exposures. These results indicate that temperature and litter type within overwintering habitat microsites are important indicators of boll weevil survival.

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Seasonal Ecology of Deraeocoris pallens (Hemiptera: Miridae) in Cotton

ABSTRACT
Deraeocoris pallens Reut. is the most commonly observed predator in cotton fields of Çukurova region in Turkey. Population developments D. pallens and other cotton pests were monitored in four different cotton fields in 1992 and 1993. The number of aphids, spider mites, thrips and whiteflies were counted on fifteen cotton leaves randomly taken from each field at weekly intervals. D. pallens populations were monitored by using insect net and vacuum samples. In both years, adults of D. pallens were first observed alongside the increase of aphid populations, reaching a peak by late June and then declining as aphid populations declined. Populations of D. pallens stayed at low levels in the absence of aphid populations and then started to increase again with the population increases of thrips, whiteflies, and spider mites. Winter surveys indicated that D. pallens overwintered as adult on various plants, including citrus and pine trees, winter vegetables, and some other wild flora

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The Status of Bemesia as a Cotton Pest: Past Trends and Future Possibilities

ABSTRACT
Bemesia tabaci was first recognized as a cotton pest in India early in the 20th Century. Between 1970 and 1980, severe outbreaks occurred in Sudan, Turkey and Israel, followed by California, on vegetable crops and cotton. In 1989-90, epidemic infestations occurred on cotton in the USA, followed by Mexico and then South America and Asia. They were attributed to a new whitefly called B. tabaci strain B or B. argentifolii. Bemesia damage to cotton is expressed in direct crop loss, contamination with honeydew leading to stickiness problems in the spinning mill and transmission of viral diseases. The latter is primarily a problem in Pakistan and India where cotton leaf curl virus has taken on very serious proportions. Bemesia suppression relies heavily on chemical control, leading to excessive use followed by resistance and failure of control measures. Population levels are influenced by cultivar, environmental factors and the efficacy of natural enemies. Heavily infested cotton fields may exist near lightly infested fields where less susceptible cultivars, cultural practices and natural enemies suppress the infestation. Effective whitefly management should utilize suitable cotton cultivars, insecticide resistance management (IRM) to reduce insecticide use, improved natural enemy efficacy and effective grower/extension worker co-operation. Supporting research is essential to provide explanations for favourable plant/whitefly associations and success or failure of natural enemy activity.

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Parasitism and Other Mortality in the Cotton Boll Weevil Anthonomus grandis Boh. (Coleoptera:Curculionidae) in Paraguay

ABSTRACT
Boll weevil (Anthonomus grandis Boh.) parasitism by 2 hymenopterous parasites, tentatively identified as Catolaccus sp. and Bracon sp., was found in the San Pedro province, Paraguay, in 1995-96 to reach astonishingly high levels often killing 100 % of the immature host population. Another key mortality factor was egg non-viability; 27% of the eggs did not hatch. Parasitism in Anthonomus grandis appears to be much higher in Paraguay where the boll weevil was introduced recently in 1992, than in other countries where it is native. This is a case where a foreign pest reaching a new geographical region found efficacious natural antagonists already in place.

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Movement of Boll Weevils in Three Areas of Texas Relative to Cotton Plant Phenology

ABSTRACT
This investigation was conducted in three separate areas of Texas using baited traps around cotton fields and in all four directions one mile apart, up to five miles from the test site, to define the movement and mechanism of boll weevil survival during the cotton season. Generally, more boll weevils were captured at sites away from cotton fields. Boll weevil captured in remote sites during the entire cropping season indicated that they may enter cotton fields from adjacent areas at any time during the summer. In two of the three areas, 50 % or less of the overwintering boll weevils entered cotton fields by the one third grown square. Evidence is presented suggesting that a portion of the F1 boll weevils leave cotton and move to remote areas even though there is ample food and oviposition sites in the cotton field. Pollen analyses determined alternative foraging resources of boll weevil adults in the three locations. Eighty percent of the captured weevils contained a total of 311 pollen types, representing 52 families, 97 genera and 31 species. These studies demonstrate that boll weevil in Texas use a wide range of foraging resources for survival in the spring and summer.

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Capture of Alabama argillacea Hübner (Lepidoptera: Noctuidae) Adults in Light Traps in Cotton,

ABSTRACT
In cotton crop management it is important to carry out periodic scouting to evaluate the
degree of infestation with lepidopteran pests, which can be captured at the adult stage
with light traps and/or specific pheromones. The objective of this study was to try to
identify an association between Alabama argillacea adults captured in light traps and
eggs and larvae that infest the crop. A light trap was established in a cotton field at Sáenz
Peňa, Chaco, Argentina. Daily capture of A. argillacea adults in light traps was
determined, and periodic eggs and larvae counts of that species in plants of neighbour
fields were carried out. There is a positive association between the number of adults
captured and the presence of larvae in the crop the following week (r = 0.62 significant
at p =0.05). This suggests that the capture of adults could be useful means of alerting
farmers to scout their cotton to establish the degree of infestation in the crop and the
right timing for control decisions.

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Morphophysiological Changes of Cotton under Saline Stress in the Presence of Fusarium oxysporum sp

ABSTRACT
Fusarium wilt in cotton causes the greatest damage on sandy soil, acid, potassium deficient and saline soils. Because Fusarium wilt is more virulent under saline stress, the morphophysiological variations predisposing cotton plants under saline stress to the disease were evaluated. Seed of two cotton (Gossypium hirsutum L.) cultivars, Coker 304 (susceptible to wilt) and Acala SJ-2 (wilt resistant but susceptible in saline soils) were cultivated in hydroponic culture with non-saline nutrient solution (control group) or a range of nutrient solutions containing only FOV or only NaCl to EC 20mS/cm, or NaCl plus FOV. After 61 days, two transverse sections were cut from each plant of the four groups, one from the collar and one from the stem. From each sample, two characteristic were determined in the SEM, the average diameter of the xylem vessels (random selection, enlargement x156) and the total number of vessels per unit area. The experimental data (LSD test p<0.05) showed that the saline groups of plants had a lower diameter of the xylem vessels but a larger number of vessels per unit area. Both the greater number of vessels and the reduced lymph flow through these narrower vessels seem to be a precondition for cotton plants to be more susceptible to wilt.

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