A core set of microsatellite markers for western corn rootworm (Coleoptera: Chrysomelidae) population genetics studies

Interest in the ecological and population genetics of the western corn rootworm, Diabrotica virgifera virgifera LeConte, has grown rapidly in the last few years in North America and Europe. This interest is a result of a number of converging issues related to the increasing difficulty in managing this pest and the need to characterize and understand gene flow in the context of insect resistance management. One of the key components needed for successful population genetics studies is the availability of suitable molecular markers. Using a standard group of microsatellite markers enables researchers from different laboratories to directly compare and share their data, reducing duplication of effort and facilitating collaborative work among laboratories. We screened 22 candidate microsatellite loci against five criteria to create a core set of microsatellite markers for D. v. virgifera population genetics studies. The criteria for inclusion were moderate to high polymorphism, unambiguous readability and repeatability, no evidence of null alleles, apparent selective neutrality, and no linkage between loci. Based on our results, we recommend six microsatellite markers to be included as a core set in future population genetics studies of D. v. virgifera along with any other microsatellite or genetic markers. As more microsatellites are developed, those meeting the criteria can be added to the core set. We encourage other groups of researchers with common interests in a particular insect species to develop their own core sets of markers for population genetics applications.     

Utility of EST-derived SSRs as population genetics markers in a beetle

Microsatellite, or simple sequence repeat (SSR), loci can be identified by mining expressed sequence tag (EST) databases, and where these are available, marker development time and expense can be decreased considerably over conventional strategies of probing the entire genome. However, it is unclear whether they provide information on population structure similar to that generated by anonymous genomic SSRs. We performed comparative population genetic analyses between EST-derived SSRs (EST-SSRs) and anonymous SSRs developed from genomic DNA for the same set of populations of the insect Diabrotica virgifera, a beetle in the family Chrysomelidae. Compared with noncoding, nontranscribed regions, EST-SSRs were generally less polymorphic but had reduced occurrence of null alleles and greater cross-species amplification. Neutrality tests suggested the loci were not under positive selection. Across all populations and all loci, the genomic and EST-SSRs performed similarly in estimating genetic diversity, F(IS), F(ST), population assignment and exclusion tests, and detection of distinct populations. These findings, therefore, indicate that the EST-SSRs examined can be used with confidence in future genetic studies of Diabrotica populations and suggest that EST libraries can be added as a valuable source of markers for population genetics studies in insects and other animals.     

Potential for transport of boll weevils (Coleoptera: Curculionidae) to the cotton gin within cotton modules

There is concern that cotton gins located in boll weevil, Anthonomus grandis grandis Boheman, eradication zones serving customers in adjacent infested zones may serve as a site for boll weevil reintroductions if weevils are transported alive inside cotton modules. We surveyed fields in three distinct areas of Texas and found that weevils can be present in large numbers in cotton fields that have been defoliated and desiccated in preparation for harvest, both as free adults and as immatures inside unopened bolls. Harvested cotton taken from module builders indicated that approximately = 100-3700 adult boll weevils were packed inside modules constructed at the sampled fields. Marked weevils were forced through a laboratory field cleaner (bur extractor) commonly mounted on stripper-harvesters, and 14% were recovered alive in the seed cotton fraction and lived at least to 24 h. Survival of weevils placed inside modules declined over time up to 7 d, but the magnitude of the decline varied with experimental conditions. In one experiment, 91% of the weevils survived to 7 d, whereas under harsher environmental conditions, only 11% survived that long. Together, our results indicate that when cotton is harvested in an infested area, boll weevils likely will be packed alive into cotton modules, and many will still be alive by the time the module is fed into the gin, at least up to 7 d after the module's construction.     

Boll weevil (Coleoptera: Curculionidae) survival through the seed cotton cleaning process in the cotton gin

There is concern that gins located in boll weevil, Anthonomus grandis grandis Boheman, eradication zones may become points of reintroduction when they process cotton grown in a neighboring infested area. We estimated boll weevil survival through two typical machine sequences used in commercial cotton gins to clean and dry the seed cotton in advance of the gin stand, as well as separately through two incline cylinder cleaners or one or two tower dryers operating at different temperatures. Large numbers of laboratory-reared adult boll weevils were marked with fluorescent powder, fed into the test system, and recovered with the assistance of blacklights. We found no evidence of survival through the seed cotton cleaning systems even when the dryers were not heated, or when passed separately through the two incline cleaners alone. Upper confidence limits (95%) were calculated for the observed zero recoveries based on sample size and the binomial distribution, and these represent the statistical worst-case (i.e., highest) survival potential. Survival through heated tower dryers declined rapidly to zero at higher temperatures, especially when two dryers were running. Although we conclude that the potential for survival of weevils in the seed cotton to the gin stand is zero or close to zero, a small percentage of live weevils was recovered in the green boll/rock trap, which may represent the greatest threat of reintroduction at the gin. Escape of live weevils with the gin trash is also possible, and studies addressing this issue will be presented elsewhere.     

Effects of burial and soil condition on postharvest mortality of boll Weevils (Coleoptera: Curculionidae) in fallen cotton fruit

Effects of soil condition and burial on boll weevil, Anthonomus grandis grandis Boheman, mortality in fallen cotton, Gossypium hirsutum L., fruit were assessed in this study. During hot weather immediately after summer harvest operations in the Lower Rio Grande Valley of Texas, burial of infested fruit in conventionally tilled field plots permitted significantly greater survival of weevils than in no-tillage plots. Burial of infested squares protected developing weevils from heat and desiccation that cause high mortality on the soil surface during and after harvest in midsummer and late summer. A laboratory assay showed that burial of infested squares resulted in significantly greater weevil mortality in wet than in dry sandy or clay soils. Significantly fewer weevils rose to the soil surface after burial of infested bolls during winter compared with bolls set on the soil surface, a likely result of wetting by winter rainfall. A combination of leaving infested fruit exposed to heat before the onset of cooler winter temperatures and burial by tillage when temperatures begin to cool might be an important tactic for reducing populations of boll weevils that overwinter in cotton fields.     

Size-dependent feeding and reproduction by boll weevil (Coleoptera: Curculionidae)

The considerable variation in adult size of the boll weevil, Anthonomus grandis grandis Boheman, has been well documented, but the influences of adult size on reproductive rate are not known. We examined the relationship between the size of boll weevils and their feeding and oviposition. Weevils weighed to the nearest milligram were grouped into five categories based on pupal weight: < or =5, 6-10, 11-15, 16-20, and >20 mg. Numbers of lifetime punctures produced in flower buds (squares) of cotton, Gossypium hirsutum L., by both sexes of adults tended to increase with pupal weight. Boll weevil females with pupal weights >10 mg produced progeny with significantly higher survival to adulthood and also produced a higher percentage of female progeny than those with pupal weights < or =10 mg. The population growth indices for females having pupal weights >10 mg averaged 1.8-fold higher than those of females weighing < or =10 mg. Survivorship of adults of both sexes also tended to increase with pupal weight. The percentage of females laying eggs on any given day averaged 2.1 times higher when their pupal weights were >10 mg than when their pupal weights were < or =10 mg. Although small size negatively affected female reproductive potential, even extremely small females produced some viable offspring. However, the penalties of small adult size, in terms of longevity and reproductive potential, suggest that cultural practices that result in the production of small adults may be used to impact weevil populations.     

Colonization history of the western corn rootworm (<Emphasis Type="Italic">Diabrotica virgifera virgifera</Emphasis>) in North America: insights from random forest ABC using microsatellite data

First described from western Kansas, USA, the western corn rootworm, Diabrotica virgifera virgifera, is one of the worst pests of maize. The species is generally thought to be of Mexican origin and to have incidentally followed the expansion of maize cultivation into North America thousands of years ago. However, this hypothesis has never been investigated formally. In this study, the genetic variability of samples collected throughout North America was analysed at 13 microsatellite marker loci to explore precisely the population genetic structure and colonization history of D. v. virgifera. In particular, we used up-to-date approximate Bayesian computation methods based on random forest algorithms to test a Mexican versus a central-USA origin of the species, and to compare various possible timings of colonization. This analysis provided strong evidence that the origin of D. v. virgifera was southern (Mexico, or even further south). Surprisingly, we also found that the expansion of the species north of its origin was recent—probably not before 1100 years ago—thus indicating it was not directly associated with the early history of maize expansion out of Mexico, a far more ancient event.     

Thermal feedback in Raynaud's phenomenon secondary to systemic lupus erythematosus: long-term remission of target symptoms

Thermal feedback shows promise when applied to Raynaud's phenomenon secondary to systematic lupus erythematosus (SLE). A female subject was followed over an 8-year period that included initial training, 1-year follow-up, and 8-year follow-up. Peripheral circulation was initially very poor, as evidenced by low basal fingertip temperatures and trophic lesions at the fingernails. An intensive 5-week training regimen in thermal self-regulation yielded evidence of hand warming, followed by an increase in basal finger temperature. Reported vasospasms were markedly reduced and the lesions healed in the ensuing weeks. As of the 1-year follow-up, the skill was intact. Symptoms remained in substantial remission throughout the 8-year period during which the subject practiced somatic relaxation and hand warming without electronic feedback. Objective temperature measurement at the 8-year juncture yielded results similar to the initial acquisition, gradual manifestation of control over the first 4 days. The subject also reported diminution of vascular headache, another symptom of SLE. While much of the biofeedback literature is focused on stress-related disease, research of this kind affirms the value of self-regulatory technique in illnesses whose causes are primarily physical.     

Accelerated and Synchronized Oviposition Induced by Flight of Young Females May Intensify Larval Outbreaks of the Rice Leaf Roller

Physiological management of migration-reproduction trade-offs in energy allocation often includes a package of adaptions referred to as the oogenesis-flight syndrome. In some species, this trade-off may be overestimated, because factors like flight behavior and environmental conditions may mitigate it. In this study, we examined the reproductive consequences induced by different flight scenarios in an economically-important Asian migrant insect, Cnaphalocrocis medinalis. We found that the influences of flight on reproduction are not absolutely positive or negative, but instead depend on the age at which the moth begins flight, flight duration, and how many consecutive nights they are flown. Adult flight on the 1st or 2nd night after emergence, flight for 6 h or 12 h nightly, and flight on the first two consecutive nights after emergence significantly accelerated onset of oviposition or enhanced synchrony of egg-laying. The latter can contribute to subsequent larval outbreaks. However, flight after the 3rd night, flight for 18 h at any age, or flight on more than 3 consecutive nights after adult emergence did not promote reproductive development, and in some scenarios even constrained adult reproduction. These results indicate that there is a migration/reproduction trade-off in C.medinalis, but that it is mitigated or eliminated by flight under appropriate conditions. The strategy of advanced and synchronized oviposition triggered by migratory flight of young females may be common in other migratory insect pests.