Re-evaluating the Economic Injury Level for Alfalfa Weevil (Coleoptera: Curculionidae) Control in Low Desert Irrigated Alfalfa.

Alfalfa (Medicago sativa L.) dominates cropping systems in the Western United States and is first in terms of acreage planted in Arizona. The alfalfa weevil, Hypera postica (Gylenhall) and/or Hypera brunneipennis (Boheman), respectively, is the most destructive pest in terms of yield loss in low desert-grown alfalfa hay. The current economic threshold of 15-20 larvae per sweep, established in California in 1975, is currently not suitable or adopted by growers in the western U.S. low desert. Here, we conducted 4 yr of field trials to re-evaluate this economic threshold. Supporting observations of agricultural growers and professionals in the region, our results indicate that the economic threshold established in 1975 is too high. Specifically, one to three large larvae often cause a significant decrease in yield justifying weevil control based on current hay prices and costs of insecticide application. These results are discussed in the context of sustainable alfalfa production in the western U.S. low desert.

Evaluation of Trap Cropping for Control of Diamondback Moth (Lepidoptera: Plutellidae) in a Broccoli Production System.

Trap cropping, in which a trap crop is planted near a cash crop, has been used successfully for reducing pest damage in some agricultural systems. We used a meta-analysis of extensive data on two trap cropping systems, diamondback moth, Plutella xylostella (Linnaeus), exploiting cabbage and Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) exploiting maize, to show that oviposition preference for, and high larval mortality on trap crops are important indicators of effectiveness of trap cropping systems. We then evaluated Indian mustard (Brassica juncea var. juncea L. Czern.) (Capparidales: Brassicaceae) and yellow rocket (Barbarea vulgaris W. T. Aiton) (Brassicales: Brassicaceae) as trap crops for protecting broccoli (Brassica oleracea var. italica Plenck) (Capparidales: Brassicaceae) against diamondback moth in Yuma, AZ, using planting configurations compatible with current practices for commercial production and without use of insecticides. In oviposition choice tests, both yellow rocket and Indian mustard were highly preferred over broccoli in the field. Furthermore, the number of larvae and pupae was significantly lower on yellow rocket and Indian mustard compared to broccoli, indicating relatively high mortality on these trap crops. Nevertheless, during the fall and spring growing seasons, no significant differences in the number of individuals on broccoli or proportion of broccoli crowns infested at harvest occurred between plots with trap crops relative to plots exclusively planted to broccoli. Thus, with the plant density and planting patterns used and without use of insecticides, there was no evidence that trap cropping was effective for reducing diamondback moth infestation of broccoli.

Assessing transmission of crop diseases by insect vectors in a landscape context.

Theory indicates that landscape composition affects transmission of vector-borne crop diseases, but few empirical studies have investigated how landscape composition affects plant disease epidemiology. Since 2006, Bemisia tabaci (Gennadius) has vectored the cucurbit yellow stunting disorder virus (CYSDV) to cantaloupe and honeydew melons (Cucumis melo L.) in the southwestern United States and northern Mexico, causing significant reductions in yield of fall melons and increased use of insecticides. Here, we show that a landscape-based approach allowing simultaneous assessment of impacts of local (i.e., planting date) and regional (i.e., landscape composition) factors provides valuable insights on how to reduce crop disease risks. Specifically, we found that planting fall melon fields early in the growing season, eliminating plants germinating from seeds produced by spring melons after harvest, and planting fall melon fields away from cotton and spring melon fields may significantly reduce the incidence of CYSDV infection in fall melons. Because the largest scale of significance of the positive association between abundance of cotton and spring melon fields and CYSDV incidence was 1,750 and 3,000 m, respectively, reducing areas of cotton and spring melon fields within these distances from fall melon fields may decrease CYSDV incidence. Our results indicate that landscape-based studies will be fruitful to alleviate limitations imposed on crop production by vector-borne diseases.

Mating behaviour, life history and adaptation to insecticides determine species exclusion between whiteflies.

1. Negative interspecific interactions, such as resource competition or reproductive interference, can lead to the displacement of species (species exclusion). 2. Here, we investigated the effect of life history, mating behaviour and adaptation to insecticides on species exclusion between cryptic whitefly species that make up the Bemisia tabaci species complex. We conducted population cage experiments independently in China, Australia, the United States and Israel to observe patterns of species exclusion between an invasive species commonly referred to as the B biotype and three other species commonly known as biotypes ZHJ1, AN and Q. 3. Although experimental conditions and species varied between regions, we were able to predict the observed patterns of exclusion in each region using a stochastic model that incorporated data on development time, mating behaviour and resistance to insecticides. 4. Between-species variation in mating behaviour was a more significant factor affecting species exclusion than variation in development time. Specifically, the ability of B to copulate more effectively than other species resulted in a faster rate of population increase for B, as well as a reduced rate of population growth for other species, leading to species exclusion. The greater ability of B to evolve resistance to insecticides also contributed to exclusion of other species in some cases. 5. Results indicate that an integrative analysis of the consequences of variation in life-history traits, mating behaviours and adaption to insecticides could provide a robust framework for predicting species exclusion following whitefly invasions.

Analyzing haplodiploid inheritance of insecticide resistance in whitefly biotypes.

We developed new methods for analyzing inheritance of insecticide resistance in haplodiploid arthropods and applied them to elucidate resistance of the whitefly Bemisia tabaci (Gennadius) to an insect growth regulator, pyriproxyfen. Two invasive biotypes of this devastating crop pest, the B biotype in Arizona and the Q biotype in Israel, have evolved resistance to pyriproxyfen. Here, we incorporated data from laboratory bioassays and crossing procedures exploiting haplodiploidy into statistical and analytical models to estimate the number of loci affecting pyriproxyfen resistance in strains of both biotypes. In tests with models of one to ten loci, the best fit between expected and observed mortality occurred with a two-locus model for the B biotype strain (QC-02) and for one- and two-locus models for the Q biotype strain (Pyri-R). The estimated minimum number of loci affecting resistance was 1.6 for the B biotype strain and 1.0 for the Q biotype strain. The methods used here can be applied to insecticide resistance and other traits in haplodiploid arthropods.

Susceptibility of Helicoverpa armigera (Lepidoptera: Noctuidae) to Cry1Ac and Cry2Ab2 insecticidal proteins in four countries of the West African cotton belt.

Transgenic cotton, Gossypium hirsutum L., producing Cry1Ac and Cry2Ab2 insecticidal proteins from Bacillus thuringiensis (Bt) was first planted in Burkina Faso (West Africa) in 2008. Here, we provide the first baseline data on susceptibility of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) populations collected in West Africa (Benin, Cameroon, Nigeria, and Chad) to Cry1Ac and Cry2Ab2 toxins incorporated separately or in combination in a semisynthetic diet. For populations collected in 2006 and 2008, dose-response curves were used to estimate mortality (LC50), growth inhibition (IC50), and stunting (EC50) of larvae. For each of these parameters, susceptibility respectively varied 44-, 23-, and 37-fold for Cry1Ac; 10-, 40-, and 25-fold for Cry2Ab2; and 37-, 11-, and nine-fold for the mixture. Country or laboratory of testing did not significantly affect susceptibility to Cry1Ac and Cry2Ab2. LC50 was significantly higher in 2008 than in 2006 for Cry1Ac, possibly due to variation in experimental conditions. LC50 and IC50 (but not EC50) were positively correlated and presented similar precision and variability across regions. However, IC could provide a more practical indicator of resistance than LC, because measuring LC and IC was equally labor intensive but estimating IC required lower amounts of toxins. Cry1Ac was two- to three-fold more toxic than Cry2Ab2 and no cross-resistance occurred among populations. Incorporation of both toxins in diet had an additive effect on mortality and growth inhibition. Our results provide a basis to establish resistance-monitoring for H. armigera before the widespread use of Bt cotton in West Africa.

Delaying evolution of insect resistance to transgenic crops by decreasing dominance and heritability.

The refuge strategy is used widely for delaying evolution of insect resistance to transgenic crops that produce Bacillus thuringiensis (Bt) toxins. Farmers grow refuges of host plants that do not produce Bt toxins to promote survival of susceptible pests. Many modelling studies predict that refuges will delay resistance longest if alleles conferring resistance are rare, most resistant adults mate with susceptible adults, and Bt plants have sufficiently high toxin concentration to kill heterozygous progeny from such matings. In contrast, based on their model of the cotton pest Heliothis virescens, Vacher et al. (Journal of Evolutionary Biology, 16, 2003, 378) concluded that low rather than high toxin doses would delay resistance most effectively. We demonstrate here that their conclusion arises from invalid assumptions about larval concentration-mortality responses and dominance of resistance. Incorporation of bioassay data from H. virescens and another key cotton pest (Pectinophora gossypiella) into a population genetic model shows that toxin concentrations high enough to kill all or nearly all heterozygotes should delay resistance longer than lower concentrations.

Predicting spring moth emergence in the pink bollworm (Lepidoptera: Gelechiidae): implications for managing resistance to transgenic cotton.

Cultural control methods have been central in the southwestern United States for reducing pink bollworm, Pectinophora gossypiella (Saunders), damage to cotton. Nevertheless, it is not clear at present how such methods could be integrated within the novel pest management framework allowed by introduction of cotton producing a toxin from Bacillus thuringiensis (Bt) for pink bollworm control. Using statewide pheromone trapping and climatic data in conjunction with deterministic simulation models, we investigated whether manipulation of cotton planting date and use of other cultural control methods could represent valuable tactics for control of the pink bollworm in Arizona. Accumulation of heat units from one January accurately predicted the rate of pink bollworm emergence from diapause in 15 cotton-producing regions. Significant variation in rate of emergence from diapause was present among regions, with earlier emergence at higher altitudes. Most adults emerge from diapause too early to reproduce successfully on cotton, a phenomenon known as suicidal emergence. A method for prediction of the fraction of suicidal emergence resulting from adoption of a given cotton planting date is presented. Results from simulation models suggest that manipulation of planting date and implementation of other control cultural methods reduce the rate of application of insecticides and delay the evolution of resistance to Bt cotton in the pink bollworm.

Effects of Bt cotton and crylac toxin on survival and development of pink bollworm (Lepidoptera: Gelechiidae).

We evaluated the effects of Bacillus thuringiensis (Bt) toxin CrylAc on survival and development of a susceptible strain and laboratory-selected resistant strains of pink bollworm, Pectinophora gossypiella (Saunders). For susceptible and resistant strains tested on artificial diet, increases in CrylAc concentration reduced developmental rate and pupal weight. In greenhouse tests, survival of resistant larvae on transgenic cotton that produces CrylAc (Bt cotton) was 46% relative to their survival on non-Bt cotton. In contrast, Bt cotton killed all susceptible larvae tested. F1 hybrid progeny of resistant and susceptible adults did not survive on Bt cotton, which indicates recessive inheritance of resistance. Compared with resistant or susceptible larvae reared on non-Bt cotton, resistant larvae reared on Bt cotton had lower survival and slower development, and achieved lower pupal weight and fecundity. Recessive resistance to Bt cotton is consistent with one of the basic assumptions of the refuge strategy for delaying resistance to Bt cotton. Whereas slower development of resistant insects on Bt cotton could increase the probability of mating between resistant adults and accelerate resistance, negative effects of Bt cotton on the survival and development of resistant larvae could delay evolution of resistance.

Overwintering cost associated with resistance to transgenic cotton in the pink bollworm (Lepidoptera: Gelechiidae).

Fitness costs associated with resistance to transgenic crops producing toxins from Bacillus thuringiensis (Bt) may have important effects on the evolution of resistance. We investigated overwintering costs in pink bollworm, Pectinophora gosypiella (Saunders), strains with different degrees of resistance to Bt cotton. Frequency of resistant individuals in a strain was not associated with induction of diapause or emergence from diapause in early winter. Emergence from diapause in the spring was 71% lower in three highly resistant strains than in two heterogeneous strains from which the resistant strains were derived. This underestimates the overwintering cost because the frequency of the resistance allele was relatively high in the heterogeneous strains. Emergence in the spring in hybrid progeny from crosses between the resistant and heterogeneous strains was greater than in resistant strains but did not differ from susceptible strains, showing that the overwintering cost was recessive to some extent.

Reversing insect adaptation to transgenic insecticidal plants.

The refuge-high-dose strategy for delaying insect adaptation to transgenic plants produces non-transgenic plants that enable survival of susceptible individuals. Previous theoretical work has suggested three requirements for success of the refuge-high-dose strategy: a low initial frequency of the resistance allele, extensive mating between resistant and susceptible adults and recessive inheritance of resistance. In order to understand an observed decrease in resistance frequency and improve the potential for managing resistance better, we used analytical and simulation models for exploring the conditions that prevent or reverse the evolution of resistance, even when resistance is not rare initially. Assuming random mating and recessive or nearly recessive inheritance of resistance, the factors favouring reversal of resistance are non-recessive costs of resistance, low initial resistance allele frequency, large refuges, incomplete resistance and density-independent population growth in refuges.

Large-scale management of insect resistance to transgenic cotton in Arizona: can transgenic insecticidal crops be sustained?

A major challenge for agriculture is management of insect resistance to toxins from Bacillus thuringiensis (Bt) produced by transgenic crops. Here we describe how a large-scale program is being developed in Arizona for management of resistance to Bt cotton in the pink bollworm, Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae), and other insect pests of cotton. Financial support from growers makes this program possible. Collaboration between the Arizona Cotton Research and Protection Council, the University of Arizona, and government agencies has led to development of resistance management guidelines, a remedial action plan, and tools for monitoring compliance with the proposed guidelines. Direct participation in development of resistance management policies is a strong incentive for growers to invest in resistance management research. However, more research, regularly updated regulations, and increased collaboration between stakeholders are urgently needed to maintain efficacy of Bt toxins in transgenic crops.

Genetics of pink bollworm resistance to Bacillus thuringiensis toxin Cry1Ac.

Laboratory selection increased resistance of pink bollworm (Pectinophora gossypiella) to the Bacillus thuringiensis toxin Cry1Ac. Three selections with Cry1Ac in artificial diet increased resistance from a low level to >100-fold relative to a susceptible strain. We used artificial diet bioassays to test F1 hybrid progeny from reciprocal crosses between resistant and susceptible strains. The similarity between F1 progeny from the two reciprocal crosses indicates autosomal inheritance of resistance. The dominance of resistance to Cry1Ac depended on the concentration. Resistance was codominant at a low concentration of Cry1Ac, partially recessive at an intermediate concentration, and completely recessive at a high concentration. Comparison of the artificial diet results with previously reported results from greenhouse bioassays shows that the high concentration of Cry1Ac in bolls of transgenic cotton is essential for achieving functionally recessive inheritance of resistance.

Constraints on the evolution of thermal sensitivity of foraging in Trichogramma: genetic trade-offs and plasticity in maternal selection.

Negative genetic correlation between performance at different temperatures or temperature-dependent mutations may promote evolution of thermal specialization in ectotherms. The first hypothesis implies that a selective change in performance at one temperature simultaneously results in change in performance at others, while the second implies a delay before observing such indirect responses. Comparison of the direction of evolution among Trichogramma lines selected for improvement of parasitization capacity at low, medium, or high temperatures indicated that a change in performance at one temperature concurrently resulted in opposite changes at distant temperatures. Unexpectedly, selection at high temperatures resulted in a decrease in adult fitness components, while adult performance expressed at cold temperatures simultaneously increased. The relationship between maternal fecundity and offspring fitness components varied across the thermal range. No correlation between these traits was present at cold or medium temperatures, but negative relationships appeared at high temperatures. We show that maternal selection resulting from a conflict between adult and offspring fitness components may have resulted in reversed evolution of the adult traits at the high end of the thermal range. Thus, genetic trade-offs in performance at different temperatures and phenotypic plasticity in maternal selection may constrain evolution of the thermal niche in Trichogramma.

Fitness costs and maternal effects associated with resistance to transgenic cotton in the pink bollworm (Lepidoptera: Gelechiidae).

Transgenic cotton producing a Bacillus thuringiensis (Bt) toxin is widely used for controlling the pink bollworm, Perctinophora gossypiella (Saunders). We compared performance of pink bollworm strains resistant to Bt cotton with performance of their susceptible counterparts on non-Bt cotton. We found fitness costs that reduced survival on non-Bt cotton by an average of 51.5% in two resistant strains relative to the susceptible strains. The survival cost was recessive in one set of crosses between a resistant strain and the susceptible strain from which it was derived. However, crosses involving an unrelated resistant and susceptible strain indicated that the survival cost could be dominant. Development time on non-Bt cotton did not differ between the two related resistant and susceptible strains. A slight recessive cost affecting development time was suggested by comparison of the unrelated resistant and susceptible strains. Maternal effects transmitted by parents that had eaten Bt-treated artificial diet as larvae had negative effects on embryogenesis, adult fertility, or both, and reduced the ability of neonates to enter cotton bolls. These results provide further evidence that fitness costs associated with the evolution of resistance to Bt cotton are substantial in the pink bollworm.

Frequency of resistance to Bacillus thuringiensis in field populations of pink bollworm.

Strategies for delaying pest resistance to genetically modified crops that produce Bacillus thuringiensis (Bt) toxins are based primarily on theoretical models. One key assumption of such models is that genes conferring resistance are rare. Previous estimates for lepidopteran pests targeted by Bt crops seem to meet this assumption. We report here that the estimated frequency of a recessive allele conferring resistance to Bt toxin Cry1Ac was 0.16 (95% confidence interval = 0.05-0.26) in strains of pink bollworm (Pectinophora gossypiella) derived from 10 Arizona cotton fields during 1997. Unexpectedly, the estimated resistance allele frequency did not increase from 1997 to 1999 and Bt cotton remained extremely effective against pink bollworm. These results demonstrate that the assumptions and predictions of resistance management models must be reexamined.

Sequential sampling plans for the hairy chinch bug (Hemiptera: Lygaeidae).

Two sequential sampling plans were developed to produce tools to reduce the use of pesticides for the control of the hairy chinch bug, Blissus leucopterus hirtus Montandon, on turfgrass lawns in the cool-humid region of Quebec, Canada. A first plan based on Wald's method was shown to be too conservative in a validation conducted on infested lawns. The second plan developed using Iwao's method yielded good results. The difference between the two plans may have occurred because no common k could be found for the negative binomial functions describing chinch bug distribution on lawns, thereby violating an essential assumption of Wald's approach. Application of the Iwao plan, which is based on visual sampling of 0.1-m2 quadrats, requires approximately 20 min when lawn evaluation is conducted by a single person. Estimation of the occurrence of chinch bug infestations (28% infested lawns in the regions of Montreal and Quebec cities), and results from validation of the Iwao plan on infested lawns, indicate that the error rates alpha and beta of the plan are lower than an upper limit of 0.05 and 0.14, respectively. The adequate precision and practicality of this plan suggest that it could become an essential tool for management of turfgrass lawns in regions where the hairy chinch bug completes less than two generations per growing season.

Lawn parameters influencing abundance and distribution of the hairy chinch bug (Hemiptera: Lygaeidae).

Management of lawns that promotes conditions detrimental to the development of insect pests may represent a valuable environmentally benign turfgrass management strategy. In the cool-humid region of Quebec, Canada, we investigated 45 lawns infested with hairy chinch bug, Blissus leucopterus hirtus Montandon, to identify lawn parameters related to its distribution and abundance. Kentucky bluegrass, creeping bentgrass, and perennial ryegrass, respectively, accounted for 55.8, 19.6, and 9.3% of the grass species. Chinch bug population density was associated positively with abundance of perennial ryegrass, whereas it was marginally negatively related with the abundance of creeping bentgrass. An index of the severity of chinch bug infestation was obtained for each lawn by combining estimates of number of infested patches per lawn, average size of the patches, and chinch bug number per patch. The index was associated positively with abundance of Kentucky bluegrass and perennial ryegrass. There was evidence that abundance of creeping bentgrass was associated negatively with the number of infested patches per lawn, area of the patches, and number of chinch bugs within those patches. The number of infested patches increased, whereas patch area and chinch bug number per patch tended to decrease, when broad-leaf weeds were more abundant on a lawn. No significant relationship was found between thatch thickness and patterns of chinch bug abundance and distribution. These results suggest that management of lawns to respectively increase and decrease abundance of creeping bentgrass and perennial ryegrass could facilitate control of hairy chinch bug populations in cool-humid regions.

[The economic welfare and health of Quebec seniors]. / Le bien-etre economique et la sante des personnes agees au Quebec.

PIP: "The current aging of Quebec's population is expected to intensify in the beginning of the next century. By 2031, seniors could represent 25 percent of the total population, or nearly two million individuals. It is vital that policy-makers more fully grasp the multiple aspects of this much-feared eventuality. To this end, the aim of this study is to shed new light on one facet of the problem. Using data from the 1986 Health and Activity Limitation Survey (HALS), the authors analyze the correlation between the income and health status of Quebec seniors aged 65 and over living in private households." (EXCERPT)^ieng

The coadaptation of female morphology and offspring size: a comparative analysis in crickets.

Few studies of invertebrates have considered combinations of morphological and life history traits in the context of the evolution of reproductive strategies. Cricket species that exploit habitats harsh with respect to egg survival have evolved a long ovipositor, presumably because laying deep in the soil reduces egg mortality. Yet hatchling mortality increases with laying depth, and the ability of hatchlings to climb through the soil increases with egg size. Thus a conflict may exist between survival of the egg and that of the hatchling, inducing a positive covariation between egg size and ovipositor length across species evolving under contrasting selective habitats. We used the phylogenetic autocorrelation method and a path analysis to assess whether egg size coevolved with ovipositor length across 40 species of crickets, and whether egg size was affected by body size or ecological factors that influence egg mortality. Body size and ovipositor length were affected by taxonomic association, whereas common ancestry had no significant effect on egg size, diapausing strategy, and oviposition preference for soil types. The path model indicated that 29.11% of the variance in egg size was explained by independent evolution. As expected, ovipositor length was positively correlated with egg size, and species diapausing in the egg stage produced larger eggs than crickets diapausing in the nymphal stage or with no diapause. Ovipositor length and diapausing strategy were the first and second most important traits, respectively, in term of the proportion of variance in egg size explained by specific values. These results support the hypothesis that the ability of hatchlings to climb through the soil, and variation in diapause strategies, are general selective factors affecting the evolution of egg size in crickets. Phylogeny explained 51.01% of the variance in egg size. Egg size in a current cricket species, however, was not directly determined by egg size in its ancestor. Instead, it was strongly related to the phylogenetic values of body size and ovipositor length. Such indirect phylogenetic effects of body size and ovipositor length may have arisen because clades originating from ancestors with different ovipositor lengths experienced different selective pressures on egg size.