Biochemical identification and comparative insecticidal activity of nucleopolyhedrovirus isolates pathogenic for Heliothis armigera (Lep., Noctuidae) larvae

Three Nucleopolyhedrovirus (NPVs) originally isolated from Heliothis armigera larvae, collected from Portugal (HearNPV-PO) and two places in Spain (HearNPV-SP1 and HearNPV-SP2), and three previously described NPVs were compared biochemically and biologically. Restriction endonuclease analysis of the virus genome with several enzymes revealed that isolates HearNPV-SP1 and HearNVP-SP2 are unique but closely related genotypes which represent two new strains of the NPVs of H. armigera. The DNA fragment profiles of HearNPV-PO were distinct from those of the HearNPV-SP1 and HearNPV-SP2, with all the enzymes used, while they were identical to the Mamestra brassicae NPV strain present in the commercial product MAMESTRIN^®. Bioassays in third-instar H. armigera larvae showed that the LD₅₀ value obtained for HearNPV-SP1 (68 occlusion bodies/larva) was about two- and six-times lower than those of HearNPV-SP2 and a Russian isolate, HearNPV-RU, respectively. The corresponding LT₅₀ values were not found to differ significantly between these three virus isolates at comparable doses.     

Effective Size of Nonrandom Mating Populations

Nonrandom mating whereby parents are related is expected to cause a reduction in effective population size because their gene frequencies are correlated and this will increase the genetic drift. The published equation for the variance effective size, Ne, which includes the possibility of nonrandom mating, does not take into account such a correlation, however. Further, previous equations to predict effective sizes in populations with partial sib mating are shown to be different, but also incorrect. In this paper, a corrected form of these equations is derived and checked by stochastic simulation. For the case of stable census number, N, and equal progeny distributions for each sex, the equation is [formula: see text], where Sk2 is the variance of family size and alpha is the departure from Hardy-Weinberg proportions. For a Poisson distribution of family size (Sk2 = 2), it reduces to Ne = N/(1 + alpha), as when inbreeding is due to selfing. When nonrandom mating occurs because there is a specified system of partial inbreeding every generation, alpha can be substituted by Wright's FIS statistic, to give the effective size as a function of the proportion of inbred mates.     

Epizootics caused by a nuclear polyhedrosis virus in populations of spodoptera exigua in southern Spain

A nuclear polyhedrosis virus (NPV) has been identified as the etiological agent causing epizootics in natural populations of Spodoptera exigua in the south of Spain. The incidence of this NPV has been determined from samples of larvae collected from sunflower fields and vegetable greenhouses at two sites located 500 km apart. The NPV was the only disease agent identified at both sites. Through the period surveyed the percentage of NPV‐infected larvae increased from 4.3% to 23% and from 22.5% to 100% in S. exigua larvae collected from sunflower fields and vegetable greenhouses respectively. No mortality attributed to the NPV was found in Spodoptera littoralis, Heliothis armigera, Peridroma saucia and Plusia gamma larvae collected in the same survey from the same sites. This is the first report of epizootics caused by NPV in S. exigua populations in field and greenhouse crops in Europe.     

Molecular and Regulatory Properties of the Nitrate Reducing Systems of Rhodobacter

Phototrophic bacteria of the genus Rhodobacter possess several forms of nitrate reductase including assimilatory and dissimilatory enzymes. Assimilatory nitrate reductase from Rhodobacter capsulatus E1F1 is cytoplasmic, it uses NADH as the physiological electron donor and reduced viologens as artificial electron donors, and it is coupled to an ammonium-producing nitrite reductase. Nitrate reductase induction requires a high C/N balance and the presence of nitrate, nitrite, or nitroarenes. A periplasmic 47-kDa protein facilitates nitrate uptake, thus increasing nitrate reductase activity. Two types of dissimilatory nitrate reductases have been found in strains from Rhodobacter sphaeroides. One of them is coupled to a complete denitrifying pathway, and the other is a periplasmic protein whose physiological role seems to be the dissipation of excess reducing power, thus improving photoanaerobic growth. Periplasmic nitrate reductase does not use NADH as the physiological electron donor and is a 100-kDa heterodimeric hemoprotein that receives electrons through an electron transport chain spanning the plasma membrane. This nitrate reductase is regulated neither by the intracellular C/N balance nor by O₂ pressure. The enzyme also exhibits chlorate reductase activity, and both reaction products, nitrite and chlorite, are released almost stoichiometrically into the medium; this accounts for the high resistance to chlorate or nitrite exhibited by this bacterium. Nitrate reductases from both strains seem to be coded by genes located on megaplasmids. Received: 17 April 1996 / Accepted: 28 May 1996     

Relationship Estimation from Whole-Genome Sequence Data

The determination of the relationship between a pair of individuals is a fundamental application of genetics. Previously, we and others have demonstrated that identity-by-descent (IBD) information generated from high-density single-nucleotide polymorphism (SNP) data can greatly improve the power and accuracy of genetic relationship detection. Whole-genome sequencing (WGS) marks the final step in increasing genetic marker density by assaying all single-nucleotide variants (SNVs), and thus has the potential to further improve relationship detection by enabling more accurate detection of IBD segments and more precise resolution of IBD segment boundaries. However, WGS introduces new complexities that must be addressed in order to achieve these improvements in relationship detection. To evaluate these complexities, we estimated genetic relationships from WGS data for 1490 known pairwise relationships among 258 individuals in 30 families along with 46 population samples as controls. We identified several genomic regions with excess pairwise IBD in both the pedigree and control datasets using three established IBD methods: GERMLINE, fastIBD, and ISCA. These spurious IBD segments produced a 10-fold increase in the rate of detected false-positive relationships among controls compared to high-density microarray datasets. To address this issue, we developed a new method to identify and mask genomic regions with excess IBD. This method, implemented in ERSA 2.0, fully resolved the inflated cryptic relationship detection rates while improving relationship estimation accuracy. ERSA 2.0 detected all 1^st through 6^th degree relationships, and 55% of 9^th through 11^th degree relationships in the 30 families. We estimate that WGS data provides a 5% to 15% increase in relationship detection power relative to high-density microarray data for distant relationships. Our results identify regions of the genome that are highly problematic for IBD mapping and introduce new software to accurately detect 1^st through 9^th degree relationships from whole-genome sequence data.