The western corn rootworm, Diabrotica virgifera virgifera LeConte, is an established insect pest of maize (Zea mays L.) in North America.

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To delay evolution of insect resistance to transgenic crops producing Bacillus thuringiensis (Bt) toxins, nearby ''refuges'' of host plants not producing Bt toxins are required in many regions. Such refuges are expected to be most effective in slowing resistance when the toxin concentration in Bt crops is high enough to kill all or nearly all insects heterozygous for resistance. However, Bt corn, Zea mays, introduced recently does not meet this ''high-dose'' criterion for control of western corn rootworm (WCR), Diabrotica virgifera virgifera. A greenhouse method of rearing WCR on transgenic corn expressing the Cry3Bb1 protein was used in which approximately 25% of previously unexposed larvae survived relative to isoline survival (compared to 1-4% in the field). After three generations of full larval rearing on Bt corn (Constant-exposure colony), WCR larval survival was equivalent on Bt corn and isoline corn in greenhouse trials, and the LC50 was 22-fold greater for the Constant-exposure colony than for the Control colony in diet bioassays with Cry3Bb1 protein on artificial diet. After six generations of greenhouse selection, the ratio of larval recovery on Bt corn to isoline corn in the field was 11.7-fold greater for the Constant-exposure colony than the Control colony. Removal from selection for six generations did not decrease survival on Bt corn in the greenhouse. The results suggest that rapid response to selection is possible in the absence of mating with unexposed beetles, emphasizing the importance of effective refuges for resistance management.

Each year the Mythimna separate (Walker), undertakes a seasonal, long-distance, multigeneration roundtrip migration between southern and northern China. Despite its regularity, the decision to migrate is facultative, and is controlled by environmental, physiological, hormonal, genetic, and molecular factors. Migrants take off on days 1 or 2 after eclosion, although the preoviposition period lasts ≈7 d. The trade-offs among the competing physiological demands of migration and reproduction are coordinated in M. separata by the "oogenesis-flight syndrome." Larvae that experience temperatures above or below certain thresholds accompanied by appropriate humidity, short photoperiod, poor nutrition, and moderate density tend to develop into migrants. However, there is a short window of sensitivity within 24 h after adult eclosion when migrants can be induced to switch to reproductive residents if they encounter extreme environmental factors including starvation, low temperature and long photoperiod. Juvenile hormone (JH) titer is low before migration but high titers are associated with termination of migratory behavior and the switch to reproduction. Early release of JH by the corpora allata in environmentally stressed 1-d old adults, otherwise destined by larval conditions to be migrants, switches them to residents. Offspring inherit parental additive genetic effects governing migratory behavior. However, they also retain flexibility in expression of both flight and reproductive life history traits. The insect neuropeptide, allatotropin, which activates corpora allata to synthesize JH, controls adult flight and reproduction. Future research directions to better understand regulation of migration in this species are discussed.

1 The western corn rootworm Diabrotica virgifera virgifera LeConte is a major insect pest of field maize, Zea mays L. Larvae can cause substantial injury by feeding on maize roots. Larval feeding may destroy individual roots or root nodes, and reduce plant growth, stability, and yield. Costs associated with managing corn rootworms in continuous maize are annually one of the largest expenditures for insect management in the United States Corn Belt. 2 Even though D. virgifera virgifera has been studied intensively for over 50 years, there is renewed interest in the biology, ecology, and genetics of this species because of its ability to rapidly adapt to management tactics, and its aggressive invasive nature. 3 This article provides a comprehensive review of D. virgifera virgifera population dynamics, specifically: diapause, larval and adult development, seasonality, spatial and temporal dynamics at local and landscape scales, invasiveness in North America and Europe, and non-trophic interactions with other arthropods. 4 Gaps in current knowledge are identified and discussed especially within the context of challenges that scientists in North America and Europe are currently facing regarding pest dynamics and the need to develop appropriate management strategies for each geographic area.

The mosquito (Aedes aegypti) vitellogenin receptor (AaVgR) is a large membrane-bound protein (214 kDa when linearized) that mediates internalization of vitellogenin, the major yolk-protein precursor, by oocytes during egg development. We have cloned and sequenced two cDNA fragments encompassing the entire coding region of AaVgR mRNA, to our knowledge the first insect VgR sequence to be reported. The 7.3-kb AaVgR mRNA is present only in female germ-line cells and is abundant in previtellogenic oocytes, suggesting that the AaVgR gene is expressed early in oocyte differentiation. The deduced amino acid sequence predicts a 202.7-kDa protein before posttranslational processing. The AaVgR is a member of the low density lipoprotein receptor superfamily, sharing significant homology with the chicken (Gallus gallus) VgR and particularly the Drosophila melanogaster yolk protein receptor, in spite of a very different ligand for the latter. Distance-based phylogenetic analyses suggest that the insect VgRIyolk protein receptor lineage and the vertebrate VgR/low density lipoprotein receptor lineage diverged before the bifurcation of nematode and deuterostome lines.The developing embryo of an oviparous animal draws practically all of its requisite nutrients from a cache of proteins, lipids, and carbohydrates stored within the egg as yolk. Yolkprotein precursors are synthesized extraovarially and transported to the developing egg where they are specifically recognized and bound by membrane-spanning cell-surface receptors. Receptor-ligand complexes accumulate in clathrincoated pits, which pinch-off into the cytoplasm, a fundamental process ubiquitous among cells for internalizing macromolecules referred to as receptor-mediated endocytosis (1, 2). The insect oocyte provides an excellent system for studying receptor-mediated endocytosis because of the high intensity of protein uptake. Mosquitoes are especially useful models in this regard, because a tightly regulated series of physiological events associated with egg maturation is synchronized across all primary oocytes by a blood meal.In the yellow fever mosquito Aedes aegypti (Aa), oocyte size increases more than 300-fold within 36 h of a blood meal (3), largely through the specific accumulation of the major yolkprotein precursor vitellogenin (AaVg). This impressive biological feat depends on the proper interaction ofAaVg with its receptor (AaVgR) on the oocyte surface. In addition to its exceptional value as a model for studying receptor-mediated endocytosis, this system is also a promising target for future novel control strategies. For example, interruption of the receptor-ligand interaction would block egg development, and theAaVgR could serve as a target for an antimosquito vaccine (4). A prerequisite to successful manipulation of this system is a thorough understanding of the proteins involved: their structures, interactions, regulation, and expression. Meaningful progress on all of these fronts hinges on knowledge of the primary structures of both AaVg, which we r...

Microsatellite loci are standard genetic markers for population genetic analysis, whereas single nucleotide polymorphisms (SNPs) are more recent tools that require assessment of neutrality and appropriate use in population genetics. Twelve SNP markers were used to describe the genetic structure of Diabrotica virgifera virgifera (LeConte; Coleoptera: Chrysomelidae) in the United States of America and revealed a high mean observed heterozygosity (0.40 +/- 0.059) and low global F(ST) (0.029). Pairwise F(ST) estimates ranged from 0.007 to 0.045, and all but 2 populations showed significant levels of genetic differentiation (P < or = 0.008). Population parameters and conclusions based on SNP markers were analogous to that obtained by use of microsatellite markers from the identical population samples. SNP-based F(ST) estimates were 3-fold higher than corresponding estimates from microsatellites, wherein lower microsatellite F(ST) estimates likely resulted from an overestimate of migration rates between subpopulations due to convergence of allele size (homoplasy). No significant difference was observed in the proportion of SNP or microsatellite markers loci that were nonneutral within populations. SNP markers provided estimates of population genetic parameters consistent with those from microsatellite data, and their low back mutation rates may result in reduced propensity for error in estimation of population parameters.

The eggs of most oviparous animals are provisioned with a class of protein called vitellogenin (Vg) which is stored as the major component of yolk. Until recently, deduced amino acid sequences were available only from vertebrate and nematode Vgs, which proved to be homologous. The sequences of several insect Vgs are now known, but early attempts at pairwise alignments with vertebrate and nematode Vgs have been problematic, leading to conflicting conclusions about how closely insect Vgs are related to the others. In this paper we demonstrate that insect Vg sequences can be confidently aligned with one another along their entire lengths and with multiple vertebrate and nematode Vg sequences along most of their spans. Although divergence is high, conservation among insect, vertebrate, and nematode Vg sequences is widespread with a preponderance of glycine, proline, and cysteine residues among strictly conserved amino acids, establishing conclusively that Vgs from the three phyla are homologous. Areas of least-certain alignment are primarily in and around insect and vertebrate polyserine domains which are not homologous. Phylogenetic reconstructions of Vgs based on sequence identities indicate that the insect lineage is the most diverged and that the mammalian serum protein, apolipoprotein B-100, arose from a Vg ancestor after the nematode/vertebrate divergence.