Summary 1.A high dose ⁄ refuge strategy has been adopted in the USA to manage the risk of Bacillus thuringiensis (Bt) resistance in target pests such as the cotton bollworm (CBW), Helicoverpa zea (Boddie) in transgenic Bt cotton Gossypium hirsutum L. Structured refuges, consisting of non-Bt cotton, have been a mandated part of this strategy to produce non-selected insects that are temporally and spatially synchronous with insects from the Bt crop, diluting Bt resistance alleles through mating. However, the bollworm is highly polyphagous and exploits a large number of crop and weedy hosts concurrently with Bt cotton. 2. A study was carried out in five major US cotton-producing states during 2002 and 2003 using the ratios of 13 C to 12 C in bollworm moths to estimate the proportions of the population originating from C 3 or C 4 plants. A separate study measured gossypol residues in moths from four states in 2005 and 2006, enabling the identification of moths whose natal hosts were cotton rather than other C 3 hosts. 3. C 4 hosts served as the principal source of bollworm moths from mid-to-late June to early September, depending on the state. Beginning in late August ⁄ early September and lasting 1-4 weeks, the majority of moths exhibited isotopic compositions characteristic of C 3 hosts. During this period, however, the minimum percentage of moths that developed as larvae on C 4 hosts was typically >25%. By mid-September and through October and November, the majority of the bollworm population exhibited C 4 isotopic compositions. 4. Between late June and early August, cotton-derived bollworm moths (moths with gossypol residues) comprised <1% of moths in all states, and remained below this level throughout the season in North Carolina. In other states, cotton-derived moths increased between early August and early September to peak at an average of 19AE1% of all moths. 5. Synthesis and applications. Data on 13 C ⁄ 12 C ratios and gossypol residues in CBW moths were used to assess the importance of structured non-Bt cotton refuges for the management of Bt resistance risk in H. zea. Weekly estimates of bollworm breeding on cotton, C 3 plants other than cotton and C 4 plants showed that, throughout the season, the majority of bollworm moths caught in pheromone traps adjacent to cotton fields did not develop as larvae on cotton. This result implies that management practices in cotton such as the use of structured cotton refuges will play a relatively minor role -particularly compared with maize Zea mays L. -in managing potential resistance to Bt cotton in populations of the CBW in the US Cotton Belt.

Selection pressure on bollworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), by cotton, Gossypium hirsutum (L.) (Malvaceae), that produces one or more Bacillus thuringiensis Berliner (Bt) proteins is reduced by plantings of non‐Bt refuge cotton that produce non‐selected individuals. However, the contributions of non‐Bt, non‐cotton crop hosts to the overall effective refuge for H. zea on Bt cotton have not been estimated. A 2‐year, season‐long study was conducted in five US cotton‐producing states to assess the spatial and temporal population dynamics and host use of H. zea. Helicoverpa zea larval estimates in commercial crop fields demonstrated that non‐cotton crop hosts, such as maize, Zea mays L. (Poaceae), grain sorghum, Sorghum bicolor (L.) Moench (Poaceae), peanut, Arachis hypogaea L. (Fabaceae), and soybean, Glycine max (L.) Merrill (Fabaceae), collectively support much larger larval populations than cotton throughout the season. Larval populations were almost entirely restricted to maize in the middle part of the season (June and portions of July), and were observed in non‐cotton crop hosts more frequently and typically in larger numbers than in cotton during the period when production would be expected in cotton (July and August). Numbers of H. zea larvae produced in replicated strip trials containing various crop hosts paralleled production estimates from commercial fields. In contrast, the number of H. zea adults captured in pheromone traps at interfaces of fields of Bt cotton and various crop hosts rarely varied among interfaces, except in instances where maize was highly attractive. With the exception of this early season influence of maize, moth numbers were not related to local larval production. These data demonstrate that H. zea adults move extensively from their natal host origins. Therefore, non‐cotton crop hosts, and even relatively distant hosts, contribute significantly to effective refuge for H. zea on Bt cotton. The results presented here demonstrate that substantial natural refuge is present for Bt‐resistance management of H. zea throughout the mid‐South and Southeast portions of the US cotton belt.

A deterministic two-locus model was used to examine how small fitness costs to individuals carrying resistance alleles could impact the risk of panmictic insect pest populations adapting to crop varieties that produced two distinct toxins. Parameters examined were (1) level of toxicity of each toxin, (2) initial frequencies of alleles for adaptation to the toxins, (3) percentage of population feeding on nontoxic plants, and (4) level of fitness cost associated with adaptation to each of the two toxins. Resistance to each toxin was assumed to be biochemically independent, controlled by a resistance coding allele at a single locus, and inherited as a partially recessive trait in the field. When plants are extremely toxic to the pest, effective refuge size is 10%, and there is a fitness cost to resistance alleles only when in homozygous form (5%), the pest population is never predicted to adapt to either toxin as long as the initial frequencies of the resistance alleles are below 0.05. Even if the initial frequency of the allele for adapting to one toxin is 0.95 when a two-toxin cultivar completely replaces a one-toxin cultivar, the model predicts that a low equilibrium allelic frequency will develop for both resistance alleles, as long as the frequency of the allele for adapting to the second toxin is initially 0.001 or less. If cultivars with one and two toxins are planted, the model predicts that resistance will develop. Nonrandom mating and stochastic variation within subpopulations also could lead to evolution of resistance.

Raw flax goes through a long and dusty preparation to make the yarn from which linen is woven. The flax workers of Northern Ireland have been known for many years to be specially liable to respiratory disease,`' but the condition received little attention during the first half of this century until J. A. Smiley4 and J. S. Logan' renewed interest in it. The flax workers' respiratory disorder is similar to that seen in the cotton industry investigated by R. S. F. Schilling and his colleagues.6 A prescribed industrial disease in the cotton industry, regulations have now been introduced to make it one in the flax industry. Byssinosis is of world-wide occurrence,7 and now a detailed epidemiological survey in flax workers has been completed by the Department of Social and Preventive Medicine at the University of Belfast.8The most typical feature of byssinosis is the " Monday syndrome." Diagnosis in this survey was made from a questionary to patients on the presence of breathlessness, tightness of the chest, or wheezing coming on a few hours after returning to work on the first day of the week, and, in the early stages, confined to that day. In addition, details of all other respiratory symptoms were obtained,9 and the one-second forced expiratory volume and forced vital capacity were measured as tests of ventilatory capacity. It was not found possible to diagnose byssinosis by clinical examination, for the physical signs and the radiological appearances are those of chronic bronchitis and emphysema.The Belfast authors found a significant association between the prevalence of byssinosis and the job performed in the flax mill. There were 111 cases of byssinosis among the 205 workers who were engaged on the early preparation and carding of the fibres, and so most heavily exposed to dust. There was no clear-cut trend of prevalence with age over the age of 35, but the prevalence under 35 was much lower, though the condition could develop within two or three years of starting work. The youngest worker with the most severe grade of byssinosis was 22 years old.Workers in the dusty preparing processes had a higher prevalence of bronchitis and exertional dyspnoea than workers in the less dusty departments. In a group of men who had left the industry those who had had byssinosis were more breathless on exertion at the time of interview, though the majority who had experienced symptoms improved after exposure to the dust had ceased. Workers with byssinosis and those in the dusty processes without byssinosis, as defined in the survey, were more likely to have impaired ventilatory function than those not so exposed. The results of the respiratory function tests indicated that exposure to flax dust can cause prolonged or permanent impairment of ventilatory capacity.Measurements of the concentration of airborne dust showed that the prevalence of byssinosis was directly related to the concentration. Since improved ventilation in two of the mills was followed by a reduction in dust levels, the authors, citing the experience of C. B. Mc...

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Soil arthropods were sampled from untreated and phorate-treated conventionally tilled soybean (Forrest cv) systems at the Tidewater Research Station, Plymouth, NC. Arthropods larger than 420 microns (U.S. Std. 40 mesh) were collected in 10-cm diameter by 15-cm depth soil cores and extracted through an elutriation process. Microarthropods larger than 149 microns (U.S. Std. 100 mesh) were collected in 5-cm diameter by 5 cm-depth soil cores and extracted using a salt flotation technique. Soybean root weight, root damage, nodulation, and yield were also quantified. Coleopteran larval number in early-planted soybean was positively correlated with root weight (r = 0.404, P &lt; 0.01) and nodulation, yet soybean yields were higher (P &lt; 0.05) in phorate-treated than in untreated plots. Adult Ataenius spp. number was higher (P &lt; 0.05) in phorate-treated than in untreated plots in 1984 and 1985, suggesting higher arthropod decomposer activity in phorate- than in untreated soil. Predaceous centipede number was positively correlated with the number of Chrysomelidae larvae (r = 0.478, P &lt; 0.001) and other Coleoptera larvae (r = 0.357, P &lt; 0.01) in late-planted soybean. Similar nodulation levels between phorate-treated and untreated plants suggests compensatory or possibly stimulatory growth in response to low levels of soil arthropod feeding.

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