Rapid laying by Brown-headed Cowbirds Molothrus ater and other parasitic birds

We compared the length of time parasitic and nonparasitic female birds spent on nests while laying eggs (laying bouts) to evaluate the hypothesis that rapid laving by parasitic Brown-headed Cowbirds Molothrus ater and other parasitic birds is a specialization for brood parasitism. Brown-headed Cowbirds typically spent less than 1 min on host nests while laying (41.0 ± 4.58 [mean ± s.e.] s, n = 21). In contrast, mean laving bouts of six nonparasitic icterine species ranged from 21.5 min to 53.4 min, and laying bouts of 13 other passerine species ranged from 20.7 min to 103.7 min. By spending only a few seconds on the nest while laying, brood parasites probably increase their chances of parasitizing nests unnoticed by hosts or, if noticed, are harassed by hosts for less time. Rapid laying may be adaptive if aggression by hosts can thwart attempted parasitism by chasing away the parasite, preventing the parasite from entering the nest or injuring the parasite. Rapid laying may increase the likelihood that the parasitic egg will be accepted. We tested some of these hypotheses by recording the responses of three frequently parasitized species to a stuffed female cowbird placed on their nests for 1 min. All species attacked the model vigorously; however, the mean time for discovery of the model ranged from 3 min to 17 min, ample time for female cowbirds to parasitize the nests. We concluded that rapid laying by parasitic birds is an adaptation for parasitism and, in Brown-headed Cowbirds, reduces the chances that the parasite will be attacked by hosts.     

Ciliate Ultrastructure: Some Problems in Cell Biology*

SYNOPSIS. Protozoology, along with other cell sciences, has profited immeasurably during the last 25 years from the application of electron microscopy and other new technics to studies of cell structure and function. Protozoa were among the first objects examined with the electron microscope in the 1940's and an extensive literature in protozoan ultrastructure has accumulated since then. Some examples of recent investigations of ciliate cortical ultrastructure are selected to illustrate the importance of protozoan studies to the development of fundamental concepts of cell biology. Ciliates are choice subjects for analysis of ciliary structure and motility and of myoneme contractility. Membrane-limited alveoli contribute to the structure of the characteristic ciliate pellicle and provide evidence of how multiple pellicular membranes may affect cell-surface activities. The striated fibrils and microtubules associated with ciliate kinetosomes resemble those of other cell types but are more highly organized; wherever they occur, these structures appear to be related to the development and maintenance of polarity and asymmetry of cells and organelles. Their stability and the precision of their arrangement in ciliates make them peculiarly suitable for the study of the properties and behavior of such fibrous organelles and also for investigation of the morphogenetic role of the kinetosome.     

The enhanced infectivity of Metarhizium flavoviride in oil formulations to desert locusts at low humidities

Formulation in non-evaporative diluents such as oils is required to exploit the advantages of controlled droplet application methods for biopesticides based on conidial suspensions of entomopathogenic fungi. In laboratory assays on desert locusts (Schistocerca gregaria), formulations of Metarhizium flauoviride conidia in cotton seed oil showed superior performance to water-based suspensions and this was especially pronounced at low humidities (35% r.h.). The LD₅₀s for oil and water suspensions at 5 days were 8900 and > 10⁶ conidia/insect respectively. The dose-mortality regression line for oil was more than four times steeper and median lethal times were typically 76% of those for aqueous suspensions. Formulation in oil improves the efficacy of this fungus and may extend the application of species with lipophilic conidia into less humid agricultural environments.     

Isoprenoid Quinone Composition as a Guide to the Classification of Sporolactobacillus and Possibly Related Bacteria

Menaquinones with seven isoprene units were the major isoprenoid quinones detected in the chloroform-methanol extracts of representative strains of the genera Bacillus and Sporolactobacillus. Neither menaquinones nor ubiquinones were detected in similar extracts of strains of the genus Lactobacillus.     

Aspects of resistance to sweet potato virus disease in sweet potato

In field trials during the first and the second rainy season of 1996 in Uganda, whiteflies were similarly abundant and aphids were absent on three clones of sweet potato (NIS-93–63, cv. Tanzania and cv. New Kawogo) although the three clones differed considerably in their resistance to sweet potato virus disease (SPVD), a complex disease resulting from infection by both the aphid-borne sweet potato feathery mottle virus (SPFMV) and the whitefly-borne sweet potato chlorotic stunt virus (SPCSV). This suggests that vector resistance does not determine the relative SPVD resistance of these genotypes. SPFMV alone had only a low virus titre in sweet potato cvs Tanzania and New Kawogo, became increasingly difficult to detect in plants of these cultivars and was seldom acquired by aphids. However, this resistance to SPFMV was not apparent in plants which were also infected with SPCSV. Plants then had a high SPFMV titre, appeared unable to eliminate SPFMV and provided good sources for aphids to acquire it.