3,5-Dichlorophenoxyacetic acid as a growth retardant

Tomato seedlings, grown in the glasshouse, were sprayed with solutions of 3,5-dichlorophenoxyacetic acid as sodium salt at 2 times 10^-5, 4 times 10^-5 and 10^-4 M. The treated plants became dark-green, dwarfed, and compact. After 6–7 weeks normal growth was resumed. Measurements and analytical data on treated and control plants are presented.     

Fluctuations in populations of wheat bulb fly (Leptohylemyia coarctata) at Rothamsted

Several field experiments at Rothamsted have rotations including plots fallowed before sowing to winter wheat each year, which provide ideal conditions for maintaining infestations of wheat bulb fly (Leptohylemyia coarctata). In eight consecutive years of one experiment, a mean of 13% of the eggs laid on fallows in these rotations eventually survived to become adults. There was a considerable variation between years, ranging from a maximum survival of 28 % to a minimum of 7%. Most deaths occur in the larval stage, and although previous work showed that survival of the larvae increases with the number of shoots available for infestation, much of the variability in survival rates between seasons was apparently caused by other factors, possibly climatic. Eggs laid in fallows were sampled in most years from 1953 to 1972. They varied from 3.57 to 0.02 million/acre (8.81–0.05 million/ha), depending on the season and site; the mean was 1.08 million/acre (2.67 million/ha). Egg populations varied in synchrony at all the three sites studied; there were cycles lasting several years between peaks of abundance or scarcity but there was no consistent tendency for populations to increase or decrease. Fewest eggs were laid when the weather was cold and wet during July and August, i.e. when adults are active. Weather was more closely correlated with the number of eggs laid expressed as a fraction of those laid in the previous year (net reproductive rate) than with the number of eggs laid/acre.     

GENETIC AND CONCHOLOGICAL COMPARISON OF SNAILS (HELIX ASPERSA) DIFFERING IN SHELL DEPOSITION OF LEAD

Populations of snails inhabiting areas with different historiesof Pb contamination differed in their deposition of Pb in shellrelative to soft tissues. Genetic variation, measured usingisozymes, was not related to Pb history nor geographic distancebetween populations. Shell characteristics were significantlydifferent among sites; shell dry weight was strongly relatedto soil calcium levels. Shells of snails from areas with longhistories of Pb contamination were significantly more robust(greater shell width/shell height ratio) than snails from otherlocations. H. asprsa adaptation to Pb contamination may involvesignificant changes in shell characteristics but these do notcorrelate with genetic traits assessed with allozymes (Received 29 December 1994; accepted 15 October 1995)     

Phenotypic plasticity in hoverflies: the relationship between colour pattern and season in Episyrphus balteatus and other Syrphidae

1. The abdominal colour patterns of some multivoltine species of hoverfly are phenotypically plastic and change through the flying season.
2. It was predicted how the abdominal colour pattern of one species, Episyrphus balteatus , should change in the field with season based on a hypothesis that the pattern influences the thermoregulatory capabilities of the animal. The colour patterns were quantified using image analysis. The observed changes in the colour pattern through the year supported the thermoregulation hypothesis.
3. A further three Metasyrphus species were analysed similarly to allow a comparative study of the forms of the plasticities of the above four species and four Eristalis species from a previous study.
4. Whilst it was clear that the abdominal colour patterns of many of the species were plastic, it was also apparent that not all species used the same developmental pathway to control the seasonal colour pattern changes. This suggests convergent evolution towards a general type of plasticity and that abdominal colour pattern plasticity in hoverflies is functional.