Morphological variation among widely dispersed larval populations of anadromous southern hemisphere lampreys (Geotriidae and Mordaciidae)

Larvae of all three southern hemisphere anadromous parasitic lampreys were collected from rivers in Australia, New Zealand and South America. Body intervals were measured, trunk myomeres counted and the frequency of pigmentation in different body regions recorded. Morphometric data were subjected to multiple group principal components analysis (MGPCA) which took into account changes during growth. The components (together with myomere counts) and the pigmentation data were both subjected to discriminant analysis. Ordination and rank correlation tests revealed no evidence for either latitudinal clines or a continuum of circumpolar change amongst larval lamprey populations. Clustering of population centroids clearly distinguished between Mordacia lapicida (Gray) from Chile and M. mordax (Richardson) from south-eastern Australia. Populations of Geotria australis Gray divided into groups representing three geographical regions, namely Argentina, Chile and Australasia (Western Australia, Tasmania and New Zealand). Ammocoetes from Argentina were the most divergent, possessing a more posterior cloaca, taller dorsal fins, a greater gap between dorsal fins, and distinctive pigmentation on the head and caudal fin. Within the Australasian group, Western Australian and New Zealand populations clustered closer than either did with those from Tasmania. The cluster analyses for larval populations of G. australis suggest that, during their marine trophic phase, the adults of this species originating from Argentinian and Chilean rivers follow different migratory routes, whereas those from Western Australia, New Zealand and, to a lesser extent, Tasmania intermix.     

Ovule abortion in white clover (Trifolium repens L.)

Plants of white clover ( Trifolium repens L.) cv. Olwen were grown in an open glasshouse maintained at a mean temperature of 20^oC and ovule growth and seed production measured. Differences in the rate of growth of ovules within ovaries were observed as early as 2 days after pollination. Ovules reached a maximum size after 8 days with the smallest only half the size of the largest. After 8 days, the smallest ovules became flaccid and shrivelled. Ovule position within the ovary had little effect on the frequency of seed set and although there was an apparently higher probability that central ovules produced a seed than those nearer the peduncle or style this was not statistically significant. Inflorescence position and floret position on the inflorescence had a significant effect on the number of seeds per floret and seed weight; the first formed inflorescences and the first florets to be pollinated on each inflorescence had more seeds per floret and heavier seeds and fewer florets with no seed than later pollinated florets. There were also differences between florets within the same whorl. The role of a number of factors which may influence floret site utilisation are discussed.     

Interaction between barley yellow dwarf virus and rust in wheat, barley and oats, and the effects on grain yield and quality

In three separate experiments, the upper leaf surface of the fifth formed leaf of wheat cv. Highbury, the fourth and fifth leaves of barley cv. Julia and the third and fourth leaves of oat cv. Mostyn were inoculated in a spore settling tower with wheat brown rust (Puccinia recondita f. sp. tritici), barley brown rust (P. hordei) or oat crown rust (P. coronata f. sp. avenae), respectively. Fewer pustules developed on distal portions of leaves of plants infected with barley yellow dwarf virus (BYDV) than on similar portions of leaves from virus-free plants. There were no significant differences in the number of pustules on proximal leaf portions. In barley and oats, the number of pustules on distal leaf portions was negatively correlated with the amount of yellowing of the leaf areas scored. In wheat, symptoms of BYDV were mild and leaves were little affected by yellowing. The latent period of rust on wheat and oats was not affected by BYDV. In barley, BYDV reduced the latent period of rust on leaf 5, but not on leaf 4, and reduced it on proximal, but not distal, leaf portions. In other experiments, BYDV reduced the yield of wheat and oats by 44% and 66%, respectively, while BYDV-infected barley was almost sterile. The appropriate rust reduced the yield of wheat, barley and oats by 33%, 13% and 86%, respectively. When infected with both BYDV and rust, yield of wheat and oats was reduced by 63% and 91%, respectively. Neither BYDV nor rust affected the percentage crude protein content of wheat grain, nor did rust affect that of barley. In oats, BYDV and rust each significantly increased crude protein of grain, but rust infection of BYDV-infected plants tended to reduce it.     

Effects of atmospheric environment,before and after treatment,on the toxicity to insects of contact poisons

Experiments were made on the effect of conditions before and after treatment on the toxicity to adult Tribolium castaneum Hbst. of the following contact poisons in the media stated: (i) pyrethrins, (2) lauryl thiocyanate, (3) nicotine-all in aqueous medium, (4) dinitro-o-cresol in ethylene glycol, (5) Wakefield half-white oil, (6) D.D.T. in Wakefield half-white oil.
The difference in environment before spraying did not have any marked effect but, with the exceptions of nicotine and petroleum oil, all the toxicants used were more insecticidal when the beetles were kept under cool conditions after spraying. Nicotine showed little difference due to after-treatment when an inverted filter funnel was used to confine the insects, but seemed markedly more toxic under cooler conditions of after-treatment when the insects were confined in the dishes by means of muslin.
Wakefield half-white oil, a non-volatile petroleum oil, proved more toxic when the insects were kept under warm conditions after treatment than under cool conditions. The increase in toxicity of chemically active contact poisons under cool conditions of after-treatment appeared to occur whatever the nature of the carrier, whether volatile or non-volatile, water or oil.
In the substances tested, with the exception of nicotine under special circumstances, the increase in toxicity under cool conditions of after-treatment occurred whatever the volatility of the poison.
The change in toxicity, when cool conditions were compared with hot, varied with the poison used. With nicotine in aqueous medium the change was relatively small, the toxicity under cold conditions throughout being 1-23 times the toxicity under hot conditions throughout. At the other extreme with pyrethrins and terpineol in aqueous medium there was a large alteration, the toxicity under cold conditions throughout being about 7 times the toxicity under the hot conditions throughout.