Garrick McDonald

Proteinase inhibitors from Nicotiana alata enhance plant resistance to insect pests

The ornamental tobacco (Nicotiana alata) produces one 6-kDa chymotrypsin inhibitor and four 6-kDa trypsin inhibitors from a single 40.3-kDa precursor protein. Three different approaches have been used to assess the potential of these proteinase inhibitors (PIs) in insect control. The first was an in-vitro approach in which all five inhibitors, the single chymotrypsin inhibitor or three of the four trypsin inhibitors were tested for their ability to inhibit gut protease activity in insects from four orders. The second approach was to incorporate the N. alata PIs in the artificial diet of the native budworm (Helicoverpa punctigera) and the black field cricket (Teleogryllus commodus). H. punctigera larvae and T. commodus nymphs had a significant (P<0.01) reduction in growth after ingestion of the PI and were more lethargic than insects on the control diet. Several of the H. punctigera larvae also failed to complete moulting at the third or fourth instar. The third approach was to express the N. alata PIs in transgenic tobacco under the control of the 35S CaMV promoter. When H. punctigera larvae were fed tobacco leaves expressing the N. alata PIs at 0.2% soluble protein, significant (P<0.01) differences in mortality and/or growth rate were observed.

Migration strategies and outbreaks of noctuid pests in Australia.

Cutworms, semiloopers, budworms and armyworms in the genera Agrotis, Chrysodeixis, Heliothis, Mythimna, Persectania and Spodoptera are important pasture and crop pests in Australia. They comprise both cosmopolitan species, such as A. ipsilon, H. armigera, M. separata and 5. tiexempta and endemic species such as A. infusa, H. punctigera, M. convecta, P. ewingii and P. dyscrila. Although the cosmopolitan species are major pests of parts of Asia and Africa, they are, with the exception of H. armigera, less important agricultural pests in Australia than their endemic counterparts. The latter are widely distributed outside cropping areas, because they breed on a wide range of native host plants as well as on introduced crops and pastures and also have the potential to invade cropping areas from native habitats. The cosmopolitan species are largely confined to tropical and subtropical summer crops and improved pastures of north and east Australia where chronic infestations often develop although major outbreaks and migration out of cropping areas are rare. Periodic outbreaks of endemic species result from an unusually favourable growth of vegetation in early autumn, following drought-breaking rains in the inland. Moths arrive in the rain-affected areas as a result of migration and concentration by rain-bearing troughs and depressions. Southward migration of their progeny occurs in spring on warm northerly airflows produced ahead of eastward-moving cold fronts and results in invasions of temperate crops and pastures. Migration also occurs in anticyclonic conditions, resulting in an extensive redistribution of populations and is adapted to the erratic distribution of rainfall in inland Australia. Among cosmopolitan species, only Spodoptera spp. cause outbreaks which are infrequent and occur with the onset of summer rains in coastal and sub-coastal areas. Most movements of cosmopolitan species are confined within cropping areas although migration from coastal to inland crops, under the influence of prevailing SE winds, and in frontal systems, troughs and storm outflows, is also suspected.RésuméLes larves de Lépidoptères des genres Agrotis, Chrysodeixis, Heliothis, Mythimna, Persectania et Spodoptera sont d’importants prédateurs des cultures et des pâturages en Australie. Elles englobent des espèces cosmopolites, telles que A. ipsilon, H. armigera, M. separata, S. exempta et des espèces endémiques, telles que A. infusa, H. punctigera, M. convecta, P. ewingii and P. dyscrita. Bien que les espèces cosmopolites soient des prédateurs majeurs dans certaines aires d’Asie et d’Afrique, elles sont, à l’exception de H. armigera, moins importantes comme pestes d’agriculture en Australie que les espèces endémiques. Ces dernières sont largement distribuées hors des régions de culture, parce qu’elles se reproduisent sur un grand nombre de plantes indigènes, aussi bien que sur les cultures et les pâturages d’espèces introduites, et elles ont la capacité d’envahir les surfaces cultivées à partir de leurs habitats. Les espèces cosmopolites sont largement resteintes aux cultures d’été des tropiques et des sous-tropiques et aux pâturages améliorés du nord et de l’est d’Australie ou les infestations chroniques se dévèloppent souvent, quoique les pullulations majeures et les migrations hors les aires de culture soient rares. Des pullulations périodique d’espèces endémiques se produisent lorsque le début d’autumne est exceptionnellement favorable à la croissance de la végétation, après les fortes pluies suivànt une période de sécheresse. Les lépidoptères arrivent dans les aires arrosées par les pluies, du fait de trous d’air et dépressions atmosphériques porteurs de pluie, qui en provoquent la concentration et le migration. Ils produisent une nouvelle génération qui migre vers le sud au printemps, transportée par les vents chauds qui se forment à l’avant de fronts froids, et qui se déplacent vers l’est. Ainsi se produit l’invasion des cultures et pâturages des zones tempérées. Les migrations ont aussi lieu en conditions anti-cycloniques causant une redistribution importante des populations. Ceci est une adaptation à l’irrégularité de la répartition des pluies à l’intèrieur en Australie. Parmi les espèces cosmopolites, seule les spodoptères causent des pullations, mais rarement, à l’arrivée des pluies d’été dans les régions côtières et sub-côtières. Les déplacements des espèces cosmopolites sont généralement confinés aux aires de culture bien que les migrations vers l’intèrieur à partir des côtes soient également suspectées, en cas de de vents de sud-est dominants et dans les fronts atmosphériques, les trous d’air ou les courants orageux.

Phenological development and seasonal distribution of the rutherglen bug, Nnysius vinitor Bergroth (Hemiptera: Lygaeidae), on various hosts in Victoria, south-eastern Australia

Populations of Nysius vinitor Bergroth were studied from 1979 to 1982 in two weed hosts, Arctotheca calendula and Polygonum aviculare , and eight irrigated sunflower crops in a summer cropping area of northern Victoria, Australia. The spring generation began with the adults colonizing flowering A.calendula plants in September and concluded with the rapid development of late stage nymphs and an exodus of adults from these plants from mid-November to December. Gradual invasion of sunflowers occurred mostly in late December and reached a peak at flowering, after which nymphs appeared. P. aviculare attracted adults from February and hosted a number of overlapping generations until winter. The weed sustained diminishing numbers of adults through the winter, except in 1982, when a further generation produced an early spring peak. Immigrant populations were regarded as a common source of adults for initiating the spring and summer generations. The rate of development of N. vinitor in spring was more rapid than that predicted by phenological simulation based on ambient temperatures and laboratory-derived day-degree estimates. This was attributed to increased body temperatures through absorption of solar radiation, and the simulation model was adjusted by increasing daily minimum and maximum temperatures by 1·3 and 5·5°C for young and older instars, respectively. This suggested that older nymphs have lower developmental thresholds or are better able to optimize body temperatures.

Soil microflora as hosts of redlegged earth mite (Halotydeus destructor).

The redlegged earth mite,Halotydeus destructor (Tucker) (Acarina: Penthaleidae), is a major pest of pastures and crops in Australia, New Zealand and South Africa (Pescott, 1934; Swan 1934; Wallace, 1970; Ridsdill-Smith, 1997). It can attack virtually all crops, broad-leaved plants, grasses and pastures (Jeppson et al., 1975); and Tucker (1925) stated that with the exception of trees, shrubs and onions, no plant species is resistant. McDonald et al. (1995), however, showed that whileH. destructormay damage most agronomic plants, its true host range, as indicated by life-table and choice studies, is more restricted. Common vetch ( Vicia sativa(L.)), faba beans ( V. faba Harz.) and field peas ( Pisum sativumL.) were suitable hosts; but wheat ( Triticum aestivum(L.)) and narrow-leaf lupins ( Lupinus angustifolius(L.)) were not selected in choice tests, and mites confined on these plants suffered high mortality and produced few offspring. There is clear evidence, however, that the mites breed successfully in field plots of wheat (Merton et al., 1995) and mite-resistant subterranean clover (Trifolium subterraneum(L.)) (Ridsdill-Smith et al., 1995). One suggested reason for this apparent contradiction is that microflora on the soil may provide a food source that maintains the mite population even in ‘monocultures’ of unsuitable host crops (McDonald et al., 1995). This may be why heavy mulching of the soil surface, which can provide a suitable habitat for microflora, increases H. destructor’sfecundity (Thackray et al., 1997).H. destructor’staxonomic relationships too suggest the possibility of its feeding on microflora: at least three of the five families in the superfamily Eupodoidea, to whichH. destructorbelongs, contain litter-dwelling species (Halliday, 1991); the Penthalodidae and Eupodidae occur in moss substrates while other species are specialised fungivores (Krantz & Lindquist, 1979). Indeed, Krantz & Lindquist (1979) suggested that fungivory may have been the ancestral state in some groups of the Eupodoidea. An interaction with microflora could have important implications for control strategies based on hostplant resistance and/or cultural and biological control. In this note we report the results of experiments on the survivorship, growth and reproductive success of H. destructoron soil microflora and on acceptable and unacceptable vascular hosts in the presence and absence of algae and mosses.

The development of the 1983 outbreak of the common armyworm, Mythimna convecta, in eastern Australia.

A large outbreak of common arymworm began in spring 1983, 6 months after the conclusion of a nation-wide drought, and occurred throughout the major cereal-growing regions of E Australia. Probable source areas were in the extensive grasslands of inland Australia, particularly SW and C Queensland. Population increase appeared to follow a complex sequence of overlapping, complementary generations. Although some generations were initiated directly by the drought-breaking rains, others appeared to arise from isolated thunderstorms which preceded them by several weeks in late summer. Moth emergence occurred in early April, late May, late July, and from late August to November. In each case, except late May, it was hypothesized that there were both local and long-range movements of adults on the synoptic airflows, resulting in moths spreading progressively from several isolated sources into the flourishing grasslands of E Australia. Multitemporal satellite data were used to identify areas of potential armyworm habitat in an inland source area of SW Queensland. Very small patches of suitable habitat were identified during the drought whilst, after the drought broke, 36% of the area comprised green grasses ideal for colonization. The subtropical grasses dried off by late winter and emigration by newly emerged moths on prefrontal airflows enabled the spring populations to colonize the temperate grass regions of inland New South Wales.

The role of biotechnology in perennial grass improvement for temperate pastures

Abstract Biotechnology has the potential to complement conventional plant breeding activities and facilitate the production of temperate grasses with improved productivity and persistence. It provides new techniques for generation of gene markers which may greatly enhance the capacity for cultivar discrimination and for tracking particular traits in breeding programmes. Through plant tissue culture and genetic transformation, it is possible to introduce genes from a wide variety of sources into elite breeding lines. This review provides a summary of recent advances in the application of these technologies to temperate grasses. The development of genetic transformation technology has, in general, been much slower for monocots than for dicots. However, all the elements required for production of transgenic plants are now coming into place. Regeneration systems are now available for many of the temperate grass species. Transformation systems have been used to produce transgenic plants of tall fescue and cock...

Factors influencing oocyte development in Mythimna convecta (Lepidoptera: Noctuidae) and their possible impact on migration in eastern Australia

AbstractThe effects of crowding and photoperiod during rearing of Mythimna convecta (Walker) on oocyte development in adult females were measured in the laboratory and field. Most larvae reared under isolated conditions in a Light 12 h: Dark 12 h photoperiod had mature oocytes within 72–84 h of eclosion. Females were slower to mature when reared under longer daylengths. The mean oocyte width in 3–10 days old females was significantly lower for moths reared under long (Light 16 h: Dark 8 h) than equal (Light 12 h: Dark 12 h) daylengths. Crowding of larvae also prolonged the pre-reproductive period. In the laboratory, 47% of females had arrested oocyte development of 3–6 days after eclosion and, in the field during late winter/spring, 48% of females required 3–9 days to mature. Larvae were collected from late spring/summer populations and caged under high and low density conditions. All females emerging from both treatments had arrested oocyte development of at least seven days. In catches from baited moth traps run over the same period, the proportion of immature female M. convecta was lower during spring (18–30%), than in summer (60%) and, in both seasons, mating commenced before oocytes had matured, but after oocyte arrest. Long daylength appears to be only one of several contributing factors causing delays in ovarian development during summer. Delays in achieving reproductive maturity, induced by either crowding or summer conditions, may assist M. convecta to emigrate from unfavourable habitats. This is particularly relevant in the winter rainfall areas of south-eastern Australia where most food plants senesce in summer and suitable habitats are usually confined to the coast.

Simulation models for the phenological development of Mythimna convecta (Walker) (Lepidoptera: Noctuidae).

Larvae of armyworm, Mythimna convecta, were reared under fluctuating temperatures (1-7-degrees; 3-13-degrees; 7-17-degrees; 11-24-degrees; 31-39-degrees-C). Data from these trials were combined with previsouly published data derived from constant-temperature studies (ranging from 15-degrees to 33-degrees-C) to model the effects of temperature on development rate. Temperature-dependent development rates for each of eight immature stages were described by one of three non-linear functions and by a linear model modified to improve the performance about the lower and upper temperature extremes. At the lower and upper thermal limits ( 33-degrees-C) of the species, survival of larvae under fluctuating temperatures was greater than recorded in previously published studies under equivalent constant temperatures. A serious constraint on fitting a model to the later larval instars was the inconsistent appearance of a seventh instar. The two sets of models were evaluated against field development in three winter and one summer experiments. The modified linear model, with capacity to manipulate predicted development at threshold temperatures, provided a marginally better prediction than did the non-linear model. The sine wave method for estimating diurnal temperatures from minimum and maximum temperatures was shown to produce overestimates of development rates. A correction factor for the seasonal conditions in western Victoria was provided.