Effects of experimentally enhanced flows on fishes of a small Texas (U.S.A.) stream: assessing the impact of interbasin transfer

1. Completion of a large interbasin water transfer system in northern Texas (U.S.A.) provided the opportunity to test the effects of pre-planned, experimental increases (≈×30) in flow on the fish fauna of a small, low-gradient, natural stream that was included as part of the conveyance system. Water from Lake Texoma (Red River basin) was pumped via a 16-km pipeline to the headwaters of Sister Grove Creek (Trinity River basin), which then carried the donor water 50 km downstream to Lake Lavon.
2. Baseline (pre-transfer) data on the composition of fish assemblages at seven stations on the creek or at its confluence with the receiving reservoir were collected monthly for 3 years, and similar data were collected for 2 years during and after trial flows of Lake Texoma water to Sister Grove Creek. We also documented fish abundance at five creek stations immediately before and after three trial flow periods of 10–14 days each in summer and autumn.
3. Multivariate analysis of all routine monthly samples over the 5-year pre- and post-transfer period showed moderate changes in the fish fauna of the creek after initiation of the trial flows. Samples taken within a week before and after the artificial high flows showed little overall change in abundance of individual fish species, but at some stations the quantitative or qualitative change in composition of the local assemblage was substantial.
4. The trial flows lasted 2 weeks or less. Long-term effects of water transfer on the fish fauna of Sister Grove Creek can only be determined after the conveyance system goes into normal operation, with periods of artificial flow of longer duration.     

Role of chemical cues and natal rearing effect on host recognition by the parasitic wasp Melittobia digitata

Parasitoids are expected to have the ability to find, recognize, and perhaps to discern potential hosts that can best support the development of their progeny. Melittobia Westwood (Hymenoptera: Eulophidae) are gregarious ectoparasitoids, which primarily attack mud daubers (Hymenoptera: Sphecidae). How Melittobia females locate their host is not well known, but the process may involve host‐related chemical signals. In this study, we investigated the roles of host chemical cues and natal rearing effect in host recognition by Mel. digitata Dahms. In an olfactometer that contained prepupae of Trypoxylon politum Say (Hymenoptera: Sphecidae), Megachile rotundata (Fabricius) (Hymenoptera: Megachilidae), puparia of Neobellieria bullata (Parker) (Diptera: Sarcophagidae), empty or intact host cocoons, or nest mud, Mel. digitata females spent significantly more time in air fields that contained T. politum (prepupae + cocoon) and Meg. rotundata (prepupae + cocoon) than in N. bullata and control fields. Nest mud and natal host had no attraction for parasitoid host choice. Most first and last choices of Mel. digitata females in the olfactometer were not consistent, suggesting an initial random dispersion, although they responded positively towards hosts in cocoons.     

Seed Development in the Recalcitrant Species Quercus robur L: Water Status and Endogenous Abscisic Acid Levels

Water status and endogenous ABA levels were measured duringthe development of the embryonic axis and cotyledons in fruitsof Quercus robur L. As dry matter accumulated in the embryoduring development, both moisture content and osmotic potential(     

FACTORS AFFECTING THE PRODUCTION OF LOCAL LESIONS BY PLANT VIRUSES

Beans inoculated with tobacco necrosis virus were kept in the dark at different temperatures for 1 hr. before and 1 hr. after inoculation; in this experiment the number of lesions increased with temperature over the range 55–82° F.
The effect of 30 min. periods of darkness before or after inoculation depended on the time of day, the number of local lesions usually being decreased. Prolonging the night period before inoculation sometimes increased the number of lesions.
Light appeared to be more important than temperature in controlling the daily variation in susceptibility. However, in a test over a 30 hr. period this variation continued even when plants were placed under constant conditions before and after inoculation.
When plants that had been kept in the dark were exposed to light of about 800 f.c. intensity for 1 min. immediately before inoculation the number of local lesions was doubled.