Effects of sub-lethal cold stress on the Western Flower Thrips, Frankliniella occidentalis

In order to establish in a new geographical area, introduced insects must be able to survive any period of adverse conditions such as a temperate winter and be capable of subsequent development to adulthood and/or reproduction. However, this aspect of insect overwintering and cold tolerance has been poorly studied. At high latitudes, Frankliniella occidentalis is typically associated with artificially heated glasshouses, but has some ability to tolerate low temperatures and may survive winter field conditions for short periods, or for longer periods of time during mild winters. The effects of overwintering on the viability of survivors are, however, unknown. In this study, acute and chronic cold exposure regimes were imposed on first instar larvae and adult female Western Flower Thrips, after which the longevity, development and reproductive capacity of the survivors were monitored and compared to those of non-stressed individuals. Survival of cold exposure did not affect subsequent survivorship of immature or adult insects, though cold treated larvae took approximately two days longer to reach adulthood than untreated individuals (at 20°C, 18L:6D). Chill treatment of adult females significantly reduced their rate of reproduction (from 1.45 to 0.93 larvae day^-1), reproductive lifespan (from 13.3 to 9.2 days) and as a result, total reproductive output (from 20.4 to 10.8 larvae), compared to control females. Acute exposure resulted in non-significant decreases of the same parameters. The relevance of the above effects to overwintering of F. occidentalis is discussed.     

Reproductive isolation mechanisms among four closely-related species of Conospermum (Proteaceae)

The effectiveness of geographical isolation, ecological isolation, temporal isolation, mechanical isolation, ethological isolation, cross-incompatibility, hybrid inviability, hybrid sterility and hybrid breakdown as practical barriers to gene flow in the field between Conospermum taxifolium, C. ericifolium, C. ellipticum and C. longifolium has been quantified. The barriers to gene flow between C. ericifolium and C. ellipticum are completely effective, owing to their allopatric distributions. The barriers to gene flow between C. taxifolium and these two species are only partially effective, as their ecological separation breaks down in intermediate habitats, and partially-fertile F₁ plants can grow in the areas of overlap. The barriers to gene flow between C. longifolium and the other three species are almost completely effective, as cross-incompatibility is very high and the F₁ plants are female-sterile.     

The influence of foliar diseases and their control by selective fungicides on a range of groundnut (Arachis hypogaea L.) genotypes

Twenty groundnut genotypes were grown with various spray treatments which controlled either, only rust, or only leaf spot diseases, or all of these diseases or none of them. The genotypes varied in their resistance to these diseases, some having resistance to only one disease and some having resistance or susceptibility to all the diseases. Chemical control of the diseases resulted in variations in leaf area protection and in yield which were specific to each genotype. For some genotypes the diseases had little influence on yield and foliage, while for others yield and remaining green leaf were varied greatly by the control of diseases. For many of the genotypes the yield achieved was well related to variations in the green leaf remaining at maturity as a result of the spray treatments. Genotypes with good levels of genetic resistance did not have high yield potentials while those with the best yields when diseases were controlled were the most susceptible to these diseases.     

Non‐lethal foraging by bell miners on a herbivorous insect: Potential implications for forest health

Tree health is often negatively linked with the localized abundance of parasitic invertebrates. One group, the sap‐sucking psyllid insects (Homoptera: Psyllidae) are well known for their negative impact upon vegetation, an impact that often culminates in the defoliation and even death of hosts. In Australia, psyllid‐infested forest in poor health is also frequently occupied by a native honeyeater, the bell miner (Manorina melanophrys; Meliphagidae), so much so that the phenomenon has been dubbed ‘bell miner‐associated dieback’ (BMAD). Bell miners are thought to be the causative agent behind BMAD, in part because the species may selectively forage only upon the outer covering (lerp) exuded by psyllid nymphs, leaving the insect underneath to continue parasitizing hosts. As bell miners also aggressively exclude all other avian psyllid predators from occupied areas, these behavioural traits may favour increases in psyllid populations. We examined bell miner foraging behaviour to determine if non‐lethal foraging upon psyllid nymphs occurred more often than in a congener, the noisy miner (M. melanocephala; Meliphagidae). This was indeed the case, with bell miners significantly more likely to remove only the lerp covering during feeding, leaving the insect intact underneath. This arose from bell miners using their tongue to pry off the lerp cases, whereas noisy miners used their mandibles to snap at both the lerp and insect underneath. Furthermore, psyllids left behind following a bell miner foraging event were significantly more likely to be viable and regrow a lerp covering than those exposed by noisy miners. Together, this behaviour supports the theory that non‐lethal foraging behaviour of bell miners may contribute to high psyllid abundance, consistent with the mechanisms by which BMAD is thought to develop.     

The allelic isozymes of hexose-6-phosphate dehydrogenase isolated from Fundulus heteroclitus: physical characteristics and kinetic properties

Hexose-6-phosphate dehydrogenase (H6PDH-A2; beta-D-glucose:NAD(P)+ oxido-reductase; E.C. 1.1.1.47) of the teleost Fundulus heteroclitus (L.) shows clinal allelic variation along the east coast of North America. Three of the major allelic isozymes have been purified and compared for native molecular weight, subunit molecular weight, isoelectric point, thermal stability, and steady-state kinetic properties (pH 8.0 and 25 degrees C). Significant differences were found among the allelic isozymes for isoelectric point, thermal stability, and some kinetic parameters. The predominant allelic isozyme in northern populations (H6PDH-AcAc) was found to be more sensitive to heat denaturation than were the predominant homozygous allelic isozymes isolated from southern populations (H6PDH-AaAa and H6PDH-AbAb). The H6PDH-AcAc allelic isozyme had both a significantly greater Km for glucose-6-phosphate than did either of the southern phenotypes and a significantly greater Km for NADP+ and Ki of NAD+ than did one of the southern phenotypes (H6PDH-AaAa). While the allelic isozymes are functionally nonequivalent, it is not yet known whether these differences are reflected at higher levels of biological organization.      

Studies on transmission of Indian peanut clump virus disease by Polymyxa graminis*

The plasmodiophoromycete fungus, Polymyxa graminis was observed in the roots of Sorghum bicolor, S. sudanense, Pennisetum glaucum, Triticum aestivum, Cyperus rotundus, Eleucine coracana, Zea mays, Tridax procumbens and Arachis hypogaea collected from Indian peanut clump virus (IPCV)-infested fields. Examination of roots of IPCV-infected S. bicolor, S. sudanense, P. glaucum and T. aestivum grown in previously air dried field soil also showed the presence of cystosori of P. graminis. IPCV-infested soil stored at room temperature for 3 years transmitted the virus to A. hypogaea, T. aestivum and S. bicolor. Roots extracted from IPCV-infected P. glaucum and S. bicolor containing cystosori, and dried root fragments incorporated into sterile soil, transmitted the virus to A. hypogaea and T. aestivum. The root extracts contained primary zoospores of the fungus, presumably arising from cystosori. Utilising root fragments of S. sudanense containing cystosori as inoculum P. graminis was shown to infect both monocotyledonous and dicotyledonous plants. Profuse cystosorus production in rootlets only occurred in monocotyledonous plants. In dicotyledonous plants, in general, only few rootlets showed cystosori. Indian isolates of P. graminis appear to differ from isolates from temperate soils in that they can infect dicotyledonous plants and have a much wider host range.