Collembolan trophic preferences determined using fatty acid distributions and compound-specific stable carbon isotope values

The trophic preferences of soil invertebrates such as Collembola are often determined by the analysis of gut contents, or through visual observations of the location of individuals. As an alternative approach, two species of Collembola, Folsomia candida and Proisotoma minuta, were offered a choice of the soil fungus Cladosporium cladosporioides or the bacterial feeding nematode Panagrellus redivivus; each exhibited distinct fatty acid profiles and stable carbon isotopic compositions. Over 21 days, the fatty acids i15:0, i17:0, 18:1(n-7) and 18:2(n-6) all increased in abundance in both collembolan species consistent with direct routing from the nematode dietary choice which contained a high concentration of these components. Collembolan fatty acid δ¹³C values increased by between 5.7 and 21.6‰ over 21 days reflecting those of the nematode diet. Therefore, both fatty acid profiles and δ¹³C values were consistent with a strong feeding preference of F. candida and P. minuta for the nematodes over the offered fungi. In fact, neither collembolan species consumed any detectable amount of C. cladosporioides. Comparison of the δ¹³C values of the 16:0 and 18:0 fatty acids (which are biosynthesised by the Collembola as well as directly incorporated from the diet) and the 16:1(n-7) and 18:2(n-6) components (which are not biosynthesised by the Collembola) demonstrated that the input of distinct pools of C can lead to large shifts in δ¹³C values between diet and consumer. The fatty acids that were not biosynthesised by Collembola better reflected the δ¹³C values of the diet helping to differentiate between biosynthesised and directly incorporated compounds; an important prerequisite in the interpretation of compound-specific δ¹³C values in trophic behaviour tests. The combination of fatty acid distributions and δ¹³C values is a significant improvement on traditional methods of examining feeding preferences, since it determines directly the assimilated dietary carbon rather than relying on indirect observations, such as the proximity of individuals to a defined food source.     

Temperature and size effects on the accuracy of estimating postlarval shrimp populations

The common practice in estimating postlarval penaeid shrimp populations for stocking ponds is volumetric subsampling with subsequent extrapolation. This procedure can lead to considerable undercounting, which, if not recognized, will result in overstocking with accompanying underfeeding and depressed growth. Postlarval blue shrimp Penaeus stylirostris counts derived from volumetric subsampling in a container of known volume and shrimp density were checked for accuracy. Counts were made of three sizes of shrimp (4, 6 and 10·5 mm total lengths) at four temperatures (18, 22, 26 and 30°C). Water temperature and shrimp size both had highly significant (p < 0·0001) effects on the mean catch, which tended to decrease with increasing shrimp sizes and water temperatures.The population estimates ranged from 100% of the actual population for 4 mm postlarvae at 18°C to 57% for 10·5 mm postlarvae at 30°C.     

Influence of gonadotropins on insulin- and insulin-like growth factor-I (IGF-I)-induced steroid production by bovine granulosa cells

To determine the effect of gonadotropins on insulin- and insulin-like growth factor (IGF-I)-induced bovine granulosa cell functions, granulosa cells from bovine ovarian follicles were cultured for 2 days in the presence of 10% fetal calf serum (FCS), and then cultured for an additional 2 days in serum-free medium with added hormones. In the presence of 0 or 1 ng/mL of insulin or IGF-I, FSH had little or no effect (P>0.05) on estradiol production by granulosa cells from both small (1–5 mm) and large (≥8 mm) follicles. However, in the presence of ≥3 ng/mL of insulin, FSH increased (P<0.05) estradiol production by granulosa cells from small and large follicles such that the estimated dose (ED₅₀) of insulin necessary to stimulate 50% of the maximum estradiol production was decreased by 2- to 3-fold from 22 to 28 ng/mL in the absence of FSH to 7–14 ng/mL in the presence of FSH. Similarly, in the presence of ≥3 ng/mL of IGF-I, FSH increased (P<0.05) estradiol production by granulosa cells from small and large follicles such that the ED₅₀ of IGF-I for estradiol production was decreased by 4- to 5-fold from 25 to 36 ng/mL in the absence of FSH to 5–6 ng/mL in the presence of FSH. In the presence of FSH, the maximal effect of insulin on estradiol production was much greater than that of IGF-I (137- versus 12-fold increase) and were not additive; when combined, 100 ng/mL of IGF-I completely blocked the stimulatory effect of 100 ng/mL of insulin. In the absence of FSH, the maximal effect of insulin and IGF-I on estradiol production was similar. Concomitant treatment with 30 ng/mL of LH reduced (P<0.05) insulin-stimulated estradiol production by 52% on day 1 and 19% on day 2 of treatment. Insulin, IGF-I and FSH also increased (P<0.05) granulosa cell numbers and progesterone production but their maximal effects were less (i.e., <4-fold increase) than their effects on estradiol production. In conclusion, insulin and IGF-I synergize with FSH to directly regulate ovarian follicular function in cattle, particularly granulosa cell aromatase activity.     

Residues of endosulfan in the tissues of lactating goats

SUMMARY: The sites of tissue accumulation in lactating goats of the organochlorine insecticide endosulfan were studied. Twelve lactating goats were dosed orally with endosulfan (1 mg/kg body weight per day) for 28 days. Groups of 3 animals were killed on days 1, 8, 15, and 21 after endosulfan treatment ended and their tissues examined for the presence of endosulfan. Total residues of α and β endosulfan and endosulfan sulphate (mg/kg) were detected in kidney (0.29), gastro-intestinal tract (0.20), liver (0.12), brain (0.06), muscle and spleen (0.04), lung and heart (0.01) and milk (0.02) on the flrst sampllng day but within 15 days, concentrations had fallen to < 0.01 mg/kg in all tissues except kidney (0.20). Endosulfan could not be detected in animals 21 days after dosing had ceased. The residue in milk could only be detected on day 1 of sampling. This study indicates that kidney rather than fatty tissue should be used to monitor the presence of endosulfan in animals intended for human consumption.     

The sor gene of HIV-1 is required for efficient virus transmission in vitro

The genome of the human immunodeficiency virus HIV-1 contains at least eight genes, of which three (sor, R, and 3' orf) have no known function. In this study, the role of the sor gene was examined by constructing a series of proviral genomes of HIV-1 that either lacked the coding sequences for sor or contained point mutations in sor. Analysis of four such mutants revealed that although each clone could generate morphologically normal virus particles upon transfection, the mutant viruses were limited in their capacity to establish stable infection. Virus derived from transfection of Cos-1 cells (OKT4-) with sor mutant proviral DNA's was resistant to transmission to OKT4+ "susceptible" cells under cell-free conditions, and was transmitted poorly by coculture. In contrast, virus derived from clones with an intact sor frame was readily propagated by either approach. Normal amounts of gag-, env-, and pol-derived proteins were produced by all four mutants and assays in both lymphoid and nonlymphoid cells indicated that their trans-activating capacity was intact and comparable with wild type. Thus the sor gene, although not absolutely required in HIV virion formation, influences virus transmission in vitro and is crucial in the efficient generation of infectious virus. The data also suggest that sor influences virus replication at a novel, post-translational stage and that its action is independent of the regulatory genes tat and trs.     

Control of three major bollworm pests of cotton in Pakistan by a single application of their combined sex pheromones

Abstract

In the Punjab province of Pakistan, cotton is subject to attack by three major bollworm pests: Pectinophora gossypiella, Earias vittella and £ insulana. Because of the difficulty of controlling these pests once their larvae have penetrated the bolls, early season control is essential. A non‐toxic method is desirable if beneficial insects are not to be destroyed. Tests with a Mitsubishi ‘twist‐tie’ pheromone formulation containing the major components of Pectinophora and the two Earias spp. achieved almost complete trap suppression of all three species for up to eight weeks duration following a single application at the pin‐square stage. Visual observations confirmed a complete lack of moth activity indicating that control by mating disruption was attainable.     

Distribution of earthworms and influence of soil properties across a successional sand dune ecosystem in NW England

An investigation of earthworms across a sand dune system in NW England examined species distribution and abundance with respect to soil physico-chemical conditions and management. Replicated 0.1 m² quadrats were examined every 50 m along 700 m transects across areas of vegetation succession and samples were then taken every 10 m where earthworms were first encountered. A translocation of Aporrectodea longa assessed the ability of this species to live in soils with a high sand content and laboratory work examined growth, maturation and survival of this species in soils with increasing proportions of sand (0–100%). Nine earthworm species were found on the dunes, but none in yellow dunes where organic matter (OM) content was <1%. Dendrobaena octaedra and Lumbricus rubellus were located 300 m from the strand line in grey dunes with an OM content of 3.9%. Allolobophora chlorotica and Lumbricus castaneus occurred within a wet dune slack at 340 m (OM content 11%). In areas of human disturbance (dune car park), A. longa, Aporrectodea caliginosa and Lumbricus terrestris were present, and in soil below pine trees L. castaneus and L. rubellus were present in litter. Laboratory growth of A. longa demonstrated significant (p < 0.05) increases in growth (2–2.75 g) with 25 and 50% sand compared with 0, 75 and 100% over 24 weeks and a greater rate of maturation. Initial results show earthworm colonisation to be influenced by dune successional stage. Laboratory findings suggested A. longa could exist in higher sand content areas but experimental design needs development. The translocation was unsuccessful. Future investigations could examine soil properties more closely and undertake monitoring on site throughout the year.     

Echinococcus granulosus in the Northern Territory,Australia: hydatid disease reported in beef cattle from the region

Hydatid disease in beef cattle has been reported to be widespread throughout Australia, but cattle bred and raised in the Northern Territory were previously believed to be free of the disease. Between 2010 and 2016, 1061 cattle from the Northern Territory were slaughtered at a New South Wales abattoir and inspected for hydatid disease. The proportion of cattle reported infected with hydatid disease was 3.5%. Individual cattle identification numbers indicated that the cattle included in the study had most likely remained within the Northern Territory from birth until immediately prior to slaughter, so were assumed to have become infected within the region. We suspect that the sylvatic cycle of Echinococcus granulosus transmission could be responsible for infection of cattle in this region.