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The beet armyworm, Spodoptera exigua (Hubner), is a sporadic but devastating secondary pest of cotton. Scouting cotton for egg masses is commonly recommended for identifying potential outbreaks and for proper timing of insecticide applications. However, there is disagreement regarding where to look on the plant for beet armyworm eggs. We investigated and quantified placement of egg masses by laboratory colony females within cotton and pigweed (a preferred wild host plant) canopies of different heights. In cotton, almost all egg masses were deposited on the undersides of leaves, and ≈80% of the egg masses were consistently located in the upper 50% of the cotton canopy, and horizontally within the inner 50% of the canopy around the central axis. Although this trend was consistent among all categories of plant height tested, variation about the means decreased with increasing height. A smaller sample of wild females indicated similar vertical placement, but horizontal placement extending further distally in the canopy. Our results indicate that scouting for egg masses on the underside of leaves in the upper half of the canopy will recover ≈80% of the egg masses present on the plants. In pigweed, egg masses were commonly laid within the inner 50% of the canopy, but along the upper 80% of the vertical axis. As in cotton, variation about the means was less in taller plants. The number of eggs per egg mass was 29% less in cotton than in pigweed. This positional information will aid in further efforts to investigate, predict, and manage beet armyworm populations in cotton and noncotton hosts.

Longevity, duration of the oviposition period, realized fecundity, potential fecundity, and egg fertility of the beet armyworm, Spodoptera exigua (Hubner), were examined in the laboratory under three different adult diet regimes. All parameters were significantly reduced for the water-only diet compared with 10% honey or sucrose diets, except fertility, which could not be measured after 5 d because of high mortality of water-fed females. Oviposition was highest the night after mating and decreased in a logarithmic manner thereafter. In the carbohydrate-fed moths, 92% of lifetime realized fecundity occurred by the fourth night of oviposition. Although our data indicate that carbohydrates in the adult diet can increase realized and potential fecundity, most of the lifetime complement of oocytes (91%) is present at the time of eclosion from the pupa. Pupal weight was significantly correlated with lifetime potential fecundity, explaining 37–66% of the variation among moths depending on adult diet, and this effect was substantial. Taken together, our results suggest that the bulk of variation in realized fecundity is generated in the larval stage, provided suitable oviposition substrate is available for the adults. This information will be important in understanding population dynamics of beet armyworm and to improving our ability to predict population outbreaks from sampling data.

Despite years of effort, the composition of polar stratospheric clouds (PSCs) is still uncertain. Future studies may be able to use FTIR extinction measurements to determine PSC composition. These studies require accurate optical constants for PSC materials. It has been suggested that accurate infrared (IR) optical constants for aerosols can only be derived from aerosol spectra. We have examined the IR spectra of nitric acid trihydrate (NAT) and nitric acid dihydrate (NAD) films and aerosols formed using a variety of experimental conditions. We conclude that several spectroscopically different types of NAD and NAT may exist. Alternatively, NAT could be birefringent and its spectra depend strongly on crystallographic orientation. The important causes for the different types or orientations seem to be the formation conditions and temperature, rather than whether the material is a film or aerosol.

Laboratory measurements are presented for the freezing kinetics of H 2 O/HNO 3 aerosols over the temperature range of 188-204 K. For 2:1 H 2 O:HNO 3 aerosols crystallizing to NAD we observed a maximum nucleation rate of J= 9.3 x 10 9 cm -3 s -1 at 194 K. This temperature is between the glass point of 161 K [Ji et al., 1993] and the melting point of 235.5 K [Ji et al., 1996]. This can be compared to a previous measurement of J =6.7 x 10 9 cm -3 s -1 at 193 K [Disselkamp et al., 1996] and lower temperature measurements of J 10 10 - 10 12 cm -3 s -1 at 178.8 - 175.8 K [Bertram and Sloan, 1998a]. Measured nucleation rates decrease as the aerosol becomes dilute, but NAD formation is still observable for 2.5:1 H 2 O:HNO 3 at temperatures near 195 K. In contrast, freezing of 3:1 H 2 O:HNO 3 aerosol was not observed for constant temperature experiments throughout this temperature range, yielding an upper limit of J < 1.5 x 10 9 cm -3 s -1 . This is the lowest experimental value determined for 3:1 H 2 O:HNO 3 freezing rates at these temperatures. From the measured freezing rates and knowledge of the free energy of diffusion the average interfacial free energy for NAD in a 2:1 H 2 O:HNO 3 solution was determined to be σ = 25.2 ergs cm -2 . A limit for the interfacial free energy was placed on 3:1 H 2 O:HNO 3 particles, for which freezing was not observed. These data imply that if aerosols reach compositions more concentrated than 3:1 H 2 O:HNO 3 in the atmosphere, NAD may play a role in polar stratospheric cloud formation.

We have determined the infrared optical constants of sulfuric acid solutions at intervals of approximately 5 wt% between 45 and 80 wt% H2SO4 at a temperature near 215 K. The optical constants were determined by first measuring the transmission of infrared light (7000 to 500 cm−1) through sulfuric acid films of varying thickness. An iterative Kramers-Kronig technique was then used to determine the optical constants that yielded the best match between calculated and measured spectra. Finally, a fitting routine was used to create a method for interpolating between the sulfuric acid compositions where optical constants were measured. The optical constants determined here differ considerably from those measured at warmer temperatures using reflection techniques. For some frequencies and compositions, the imaginary refractive index is more than twice as large as was previously measured at 300 K. The change in optical constants has significant implications for retrievals of aerosol mass and composition from satellite measurements.

The crystal structure of [bis(2-diphenylphosphinoethyl)phenylphosphine-P,P',P][bis(diphenylphosphino)-methane-P,P'] carbonylmolybdenum(0), [Mo(dpepp)-(dppm)(CO)] [where dppm = Ph 2 PCH 2 PPh 2 and dpepp = Ph 2 PCH 2 CH 2 P(Ph)CH 2 CH 2 PPh 2 ], is reported. In the distorted octahedral complex, the tridentate ligand adopts a facial arrangement with the monodentate ligand trans to the central P atom. All Mo-P distances are statistically dissimilar.

The crystallization of binary HNO3/H2O aerosols may be an important step in the formation of type Ia polar stratospheric clouds (PSCs). We have used Fourier transform infrared (FTIR) spectroscopy to probe the crystallization kinetics of supercooled 2:1 and 3:1 H2O:HNO3 films to nitric acid dihydrate (NAD) and trihydrate (NAT), respectively. Nitric acid/ice films were grown on a silicon substrate at temperatures near the glass point. The substrate was then warmed to a temperature above the glass point, and the crystallization of the film was measured using FTIR absorption spectroscopy. The temperature dependence of the crystallization rate was used to determine the activation energy for a nitrate ion to cross the liquid−solid phase boundary. The activation energies ranged from 22 to 41 kcal mol-1 for NAD crystallization at temperatures between 177 and 168 K and from 22 to 35 kcal mol-1 for α-NAT crystallization at temperatures between 171 and 161 K. In addition, activation energies at higher temperatures w...

Sub-micrometer sized sulfuric acid H2SO4 particles were generated using a constant output atomizer source. The particles were then exposed to water vapor before being injected into a low temperature cell. Multipass transmission Fourier Transformation Infrared (FTIR) spectroscopy was used to determine the phase and composition of the aerosols as a function of time for periods of up to five hours. Binary H2SO4H2O aerosols with compositions from 35 to 95 wt % H2SO4 remained liquid for over 3 hours at room temperatures ranging from 189-240 K. These results suggest that it is very difficut to freeze SSAs via homogeneous nucleation. Attempts to form aerosols more dilute than 35 wt % H2SO4 resulted in ice formation.