Flight responses in a wind tunnel of the parasitoid Microplitis croceipes to three spring and three summer host plants of Heliothis spp.

Flight responses of the parasitoid, Microplitis croceipes (Cresson) (Hymenoptera: Braconidae) to two phenological stages of spring host plants (crimson clover, Trifolium incarnatum L., hairy vetch, Vicia villosa Corbiere, and cutleaf geranium, Geranium dissectum L.) and summer host plants (cotton, Gossypium hirsutum L., sorghum, Sorghum bicolor L., and soybean Glycine max (L.) Merr.) of Heliothis virescens (F.), were measured in a dual choice situation in a wind tunnel. Preflowering clover was more attractive than preflowering geranium, followed by preflowering vetch. Clover was preferred over geranium in flowering stages as well. No within species differences were detected for the two phenological stages. Preflowering and flowering cotton and soybean were preferred over preflowering and flowering sorghum. The findings could be important in pre-determining release sites for M. croceipes in the field.     

Rubus host range of rubus yellow net virus and its involvement with other aphid-borne latent viruses in inducing raspberry veinbanding mosaic disease

After graft inoculation with rubus yellow net virus (RYNV), 12 of 34 Rubus species and cultivars developed noticeable symptoms. R. macraei developed the most conspicuous symptoms and is recommended as an improved indicator plant. In attempts to determine the cause of raspberry veinbanding mosaic, a disease in which RYNV is involved, several European and North American red raspberry cvs were graft-inoculated with RYNV and three other aphid-borne viruses, black raspberry necrosis (BRNV), raspberry leaf mottle (RLMV) and raspberry leaf spot, singly and in all combinations. In periods of up to 4 yr, classical veinbanding mosaic symptoms developed in sensitive cvs only when they contained both RYNV and RLMV. These symptoms were intensified in plants co-infected with additional viruses. Veinbanding mosaic disease did not develop in any of 11 cvs infected with RYNV + BRNV, the combination of viruses previously assumed to be responsible for this disease in Britain and North America.     

Egg laying and host stage preference at constant temperatures inEncarsia tricolor [Hym.: Aphelinidae]

Encarsia tricolor Foërster is a facultative autoparasitoid that develops on the important pestTrialeurodes vaporariorum (Westwood) in outdoor crop conditions, which makes this aphelinid species promising for biological control programs in regions where field and protected crops coexist. In this paper we report the results obtained in the study of daily and totalE. tricolor egg laying and of adult female preference for different host stages in which to lay eggs at constant temperatures in the range 10 to 32 °C. Only whitefly nymphs were present in the searching arena (tomato leaflets). The mean number of eggs laid per female in one day ranged from 4.0 (10 °C and 32 °C) to 15.2 (24 °C). The mean total number of eggs increased with temperature from 10 to 28 °C, reaching a maximum of 123 eggs per female at 28 °C, and decreased sharply from 28 to 32 °C. The relation between the intrinsic rate of increase (r_m) and temperature in the range 10 to 28 °C followed a straight line whose equation was r_m=?0.076+0.011*T (R²=0.99). The r_m ofE. tricolor was greater than the r_m ofT. vaporariorum when temperature was higher than 9.2 °C. The preference for any particular host instar in which to lay eggs was not always significant. However, N4 was the host instar preferred whenever preference was statistically significant.     

Chironomid pupal exuviae and larvae of two storage reservoirs in The Netherlands

For three years chironomid larvae were collected bimonthly with a grab sampler in two deep storage reservoirs in The Netherlands. Chironomid pupal exuviae were collected monthly, from April to November, with a handnet. Net samples yielded more taxa than grab samples. The taxa found in net samples originated from more habitats, than taxa found in grab samples. The relative contribution of Orthocladiinae was much larger in net samples. Based on the results obtained in the two reservoirs, some advantages and disadvantages of both sampling methods are discussed.     

Tree pre-planting at Rutland Water

The aesthetic problems posed by reservoir margins have been recognised for many years. They stem from a complex pattern of action and interaction of several environmental variables — water manipulation patterns, wave action, substrate characteristics, grazing and other factors.These factors usually result in reservoir margins being not only visually unattractive and physically unstable, but also of low ecological diversity.The Natural Environment Research Council and Water Research Centre have, since 1968, together funded a research programme to investigate the use of plant species to combat these problems.In isolated instances in the UK, woody species in particular have succeeded in colonising margins naturally, to very good visual effect (e.g. at Lake Vyrnwy). Biotechnical treatments — using artificially planted shrubs and trees — have been successfully used in large Central European reservoirs to combat soil erosion by waves.Following trials of various woody species on the margins of established reservoirs, 10 species/cultivars were pre-planted above and below the future top water level (TWL) of Rutland Water in 1973, 5 years before reservoir filling was completed. Pre-planting theoretically allows better survival by trees of subsequent partial inundation. The precise siting of pre-planted trees in the vertical dimension should normally be done using modelled predictions of reservoir summer median water level (a variable important to tree survival). The complex factors affecting the operation of Rutland Water made precise prediction impossible; the experimental plot eventually extended from 500 mm above TWL, to 2 000 mm below TWL, in 500 mm steps.252 trees were involved in the plot and their growth has been monitored for the past 7 years. The species being predominantly hydrophytic, drought was a problem in the years prior to reservoir filling. Mulching with grass-cuttings proved to be helpful in this respect. Subsequently, prolonged periods of high water level have been deleterious to tree survival in the lower areas of the plot. Once abstraction/recharging patterns become more cyclic, it is anticipated that tree growth will stabilise.Department of Applied Biology, University of Cambridge     

Quantification and analysis of reverse mutations at the hgprt locus in Chinese hamster ovary cells

We describe an assay for the quantification of reverse mutations at the hypoxanthine-guanine phosphoribosyltransferase (hgprt) locus in Chinese hamster ovary cells utilizing the selective agent L-azaserine (AS). Conditions are defined in terms of optimal AS concentration, cell density, and phenotypic expression time. After treatment, replicate cultures of 10⁶ cells are allowed a 48-h phenotypic expression time in 100-mm plates. AS (10 μM) is then added directly to the growing culture and AS-resistant (AS^r) cells form visible colonies. This assay is used to quantify ICR-191-, ICR-170-, and N-ethyl-N-nitrosourea-induced reversion of independently isolated HGPRT^? clones. The AS^r phenotype is characterized both physiologically and biochemically. All AS^r clones isolated are stably resistant to AS and aminopterin but sensitive to 6-thioguanine. They also have re-expressed HGPRT enzyme. In addition, several revertants are shown to contain altered HGPRT. The data provide further evidence that ICR-191 and ICR-170 cause structural gene mutations in mammalian cells and also suggest that ICR-191, ICR-170, and N-ethyl-N-nitrosourea induce similar types of mutations in Chinese hamster ovary cells.     

Pathological changes in the nephrocytes of the shore crab, Carcinus maenas, following injection of bacteria

The gills of Carcinus maenas were examined by light and electron microscopy following injection of either sterile saline or the bacteria Bacillus cereus and Moraxella sp., to determine any role(s) for the nephrocytes in the host defense reactions. The results showed that although intact bacteria were not sequestered to the nephrocytes, these cells were active in the removal of large quantities of cell debris from the hemolymph. Much of this material was derived from the breakdown of the hemocytes in response to the presence of bacteria and it's accumulation in the central vacuoles of the nephrocytes resulted in the degradation of these cells. It is proposed that while nephrocytes do not phagocytose intact bacteria, they augment the host defenses by clearing much of the hemocyte and associated bacterial debris from the gills, thus preventing blockage of the lamellar sinuses and subsequent impairment of respiration.