Influence of Environment and Genotype on the Expression of Host Plant Resistance in Sweet Potato to the Sweet Potato Weevil, Cylas Formicarius (Fab.).

Field and laboratory experiments were conducted to study the influence of environment and genotype on the expression of sweetpotato resistance to the sweetpotato weevil (SPW), Cylas formicarius (Fab.). Roots of four genotypes ( W-244 , W-250 , Beauregard , Centennial ) were evaluated for SPW feeding and oviposition at three different storage times. Roots from Louisiana, South Carolina and Mississippi were also evaluated. Genotype had a significant effect on feeding and oviposition. Storage time and production sites appeared to affect resistance expression; the outcomes depend on the genotypes. The effect of nitrogen on sweetpotato resistance to SPW was studied. Four genotypes were grown in the field under three nitrogen regimes (0, 45 and 135 kg N/ha). Harvested roots were evaluated for SPW feeding, oviposition, larval survival, and pupal weight. Significant nitrogen effects were found on oviposition. Genotype significantly affected feeding, oviposition, and larval survival where W-244, Excel and Sumor had lower rates than Beauregard and W-250. No significant nitrogen and genotype interaction was found. The effects of drought and manual defoliation on SPW feeding, oviposition, larval survival and pupal weight were studied on Beauregard and Excel. Drought, stressed plants received significantly more SPW feeding punctures and eggs than non-stressed plants, but had lower larval survival. Manual defoliation (67% of leaf area at different growth stages) had a significant effect on oviposition, but not on feeding, larval survival or pupal weight. Experiments were conducted to investigate the effect of root and foliage feeding by other insects on sweetpotato resistance to SPW using four genotypes. In the field, banded cucumber beetle (BCB), Diabrotica balteata LeConte, and armyworm, Spodoptera latifascia (Walker), were released into cages (1.8 x 1.8 x 1.8m) placed over sweetpotato plants, and were allowed to feed and deposit eggs throughout the growing season. Harvested roots were evaluated for SPW feeding, oviposition, larval survival, and pupal weight. Root feeding by BCB and defoliation by armyworm tended to increase SPW feeding and oviposition, but had no effect on larval survival and pupal weight. Genotype had a significant effect on feeding, oviposition, and larval survival, suggesting both antixenosis and antibiosis as resistance mechanisms

Relative Extensions of Modules and Homology Groups

We introduce the concepts of relative (co)extensions of modules and explore the relationship between the relative (co)extensions of modules and relative (co)homology groups. Some applications are given.Введено поняття відносних (спів)розширень модулів та вивчено взаємозв'язок між відносними (спів)розширеннями модулів та відносними (ко)гомологічними групами

On w-copure projective modules

Let $R$ be a commutative ring. An $R$-module $M$ is said to be $w$-split if Ext$_{R}^1(M,N)$ is a GV-torsion $R$-module for all $R$-modules $N$. It is known that every projective module is $w$-split, but the converse is not true in general. In this paper, we study the w-split dimension of a flat module. To do so, we introduce and study the so-called $w$-copure (resp., strongly $w$-copure) projective modules which is in some way a generalization of the notion of copure (resp., strongly copure) projective modules. An $R$-module $M$ is said to be $w$-copure projective (resp., strongly $w$-copure projective) if Ext$_{R}^1(M,N)$ (resp., Ext$_{R}^n(M,N)$) is a GV-torsion $R$-module for all flat $R$-modules $N$ and any $n\geq1$.Comment: 13 page

Formosan subterranean termite (Isoptera: Rhinotermitidae) soldiers regulate juvenile hormone levels and caste differentiation in workers

A caste structure is maintained in termite societies and juvenile hormone (JH) is generally regarded as the most important regulator in these termite colonies. Here, we demonstrate that the soldier caste regulates JH in workers of Coptotermes formosanus Shiraki. Worker termites (80-100 individuals) were placed in petri dishes with 0, 5, 10, or 20% soldiers. JH III titers of groups of these workers were monitored at 14, 28, 42, and 56 d. Any changes in soldier caste proportions also were noted at each sample date. On the first sample date, the JH levels in workers were similar among treatments with different initial soldier proportions, and no new soldiers were formed. Over the next three sample dates, the worker JH levels were higher for low initial soldier proportion treatments and vice versa. Concurrently, soldier formation increased with lower initial soldier proportions. JH titers in workers showed a positive and statistically significant relationship to soldier numbers until a certain soldier proportion was reached. These results provide evidence that soldier caste proportions regulate JH levels and thereby caste differentiation in workers. The means by which this regulatory mechanism may proceed is discussed. © 2005 Entomological Society of America