Is the distribution of Fiji leaf gall in Australian sugarcane explained by variation in the vector Perkinsiella saccharicida?

Fiji leaf gall (FLG) is an important virally induced disease in Australian sugarcane. It is confined to southern canegrowing areas, despite its vector, the delphacid planthopper Perkinsiella saccharicida, occurring in all canegrowing areas of Queensland and New South Wales. This disparity between distributions could be a result of successful containment of the disease through quarantine and/or geographical barriers, or because northern Queensland populations of Perkinsiella may be poorer vectors of the disease. These hypotheses were first tested by investigating variation in the ITS2 region of the rDNA fragment among eastern Australian and overseas populations of Perkinsiella. The ITS2 sequences of the Western Australian P. thompsoni and the Fijian P. vitiensis were distinguishable from those of P. saccharicida and there was no significant variation among the 26P. saccharicida populations. Reciprocal crosses of a northern Queensland and a southern Queensland population of P. saccharicida were fertile, so they may well be conspecific. Single vector transmission experiments showed that a population of P. saccharicida from northern Queensland had a higher vector competency than either of two southern Queensland populations. The frequency of virus acquisition in the vector populations was demonstrated to be important in the vector competency of the planthopper. The proportion of infected vectors that transmitted the virus to plants was not significantly different among the populations tested. This study shows that the absence of FLG from northern Queensland is not due to a lack of vector competency of the northern population of P. saccharicida.

Negative regulation of prophenoloxidase (proPO) activation by a clip-domain serine proteinase homolog (SPH) from endoparasitoid venom

Most parasitic wasps inject maternal factors into the host hemocoel to suppress the host immune system and ensure successful development of their progeny. Melanization is one of the insect defence mechanisms against intruding pathogens or parasites. We previously isolated from the venom of Cotesia rubecula a 50 kDa protein that blocked melanization in the hemolymph of its host, Pieris rapae [Insect Biochem. Mol. Biol. 33 (2003) 1017]. This protein, designated Vn50, is a serine proteinase homolog (SPH) containing an amino-terminal clip domain. In this work, we demonstrated that recombinant Vn50 bound P. rapae hemolymph components that were recognized by antisera to Tenebrio molitor prophenoloxidase (proPO) and Manduca sexta proPO-activating proteinase (PAP). Vn50 is stable in the host hemolymph-it remained intact for at least 72 It after parasitization. Using M. sexta as a model system, we found that Vn50 efficiently down-regulated proPO activation mediated by M. sexta PAP-1, SPH-1, and SPH-2. Vn50 did not inhibit active phenoloxidase (PO) or PAP-1, but it significantly reduced the proteolysis of proPO. If recombinant Vn50 binds P. rapae proPO and PAP (as suggested by the antibody reactions), it is likely that the molecular interactions among M. sexta proPO, PAP-1, and SPHs were impaired by this venom protein. A similar strategy might be employed by C rubecula to negatively impact the proPO activation reaction in its natural host. (C) 2004 Elsevier Ltd. All rights reserved.

Isolation and characterization of a Cotesia rubecula bracovirus gene expressed in the lepidopteran Pieris rapae

Polydnaviruses are endogenous particles that are crucial for the survival of endoparasitoid wasps, providing active suppression of the immune function of the lepidopteran host in which wasp larvae develop. The Cotesia rubecula bracovirus (CrBV) is unique in that only four gene products are detected in larval host (Pieris rapae) tissues and expression of CrBV genes is transient, occurring between 4 and 12 h post-parasitization. Two of the four genes, CrV1 and CrV3, have been characterized. CrV1 is a secreted glycoprotein that has been implicated in depolymerization of the actin cytoskeleton of host haemocytes, leading to haemocyte inactivation; CrV3 is a multimeric C-type lectin that shares homology with insect immune lectins. Here, a third CrBV-specific gene is described, CrV2, which is expressed in larval P. rapae tissues. CrV2, which is transcribed in haemocytes and fat body cells, has an ORF of 963 bp that produces a glycoprotein of approximately 40 kDa. CrV2 is secreted into haemolymph and appears to be internalized by host haemocytes. CrV2 has a coiled-coil region predicted at its C-terminus, which may be involved in the formation of putative CrV2 trimers that are detected in haemolymph of parasitized host larvae.

A novel venom peptide from an endoparasitoid wasp is required for expression of polydnavirus genes in host hemocytes

Maternal factors introduced into host insects by endoparasitoid wasps are usually essential for successful parasitism. This includes polydnaviruses (PDVs) that are produced in the reproductive organ of female hymenopteran endoparasitoids and are injected, together with venom proteins, into the host hemocoel at oviposition. Inside the host, PDVs enter various tissue cells and hemocytes where viral genes are expressed, leading to developmental and physiological alterations in the host, including the suppression of the host immune system. Although several studies have shown that some PDVs are only effective when accompanied by venom proteins, there is no report of an active venom ingredient(s) facilitating PDV infection and/or gene expression. In this study, we describe a novel peptide (Vn1.5) isolated from Cotesia rubecula venom that is required for the expression of C. rubecula bracoviruses (CrBVs) in host hemocytes (Pieris rapae), although it is not essential for CrBV entry into host cells. The peptide consists of 14 amino acids with a molecular mass of 1598 Da. In the absence of Vn1.5 or total venom proteins, CrBV genes are not expressed in host cells and did not cause inactivation of host hemocytes.

Life history parameters and biocontrol potential of the mealybug parasitoid Coccidoxenoides peregrinus (Timberlake) (Hymenoptera: Encyrtidae): Asexuality, fecundity and ovipositional patterns

Properties relevant to the ovipositional activity and lifetime productivity of Coccidoxenoides peregrinus (Timberlake) were assessed in the laboratory, to determine the potential of this species as a biocontrol agent against the citrus mealybug, Planococcus citri (Risso). In general, this species has not performed well in orchards, except for a few localities on different continents. The mode of reproduction of C peregrinus is almost entirely thelytokous, with males produced sporadically and at low frequency. The females have both pro-ovigenic and synovigenic traits, which raises questions of the utility of this distinction. The females have a high reproductive potential with 10-20 eggs per day available within the first two days (after a short (12 h) pre-oviposition period), and 80-150 eggs per day thereafter until death at about eight days. Mean lifetime fecundity was 239.2 +/- 34.3 eggs. C peregrinus oviposits across a range of P. citri instars, but productivity relies predominantly on second instar hosts. Second stage (N2) hosts received most eggs in choice (about 52%) and no-choice (about 50%) tests. Most eggs deposited into N2 hosts (82%) reached adult stage whereas only a few of those deposited into N1 and N3 (about 5% each) developed successfully. The haemolymph of parasitised reproductive mealybugs contained granular structures and no parasitoid eggs were found 24 h after exposure to ovipositing wasps. Also, no wasps emerged from parasitised adult hosts that were kept alive. Parasitoid eggs deposited into adult hosts were presumed encapsulated and destroyed, as control mealybugs (not exposed to female wasps) had no granular structures in their haemolymph. Wasps exposed to an abundance of hosts soon started ovipositing, but only for a relatively short time each day (about 2.5 h out of a 7 h exposure). They stopped ovipositing despite eggs judged to be mature in their ovaries. The reproductive output of C peregrinus is discussed in relation to the ecological factors that could influence this output, and the implications for biocontrol are discussed. (C) 2003 Elsevier Inc. All rights reserved.

Biology and phenology of the eriophyid mite, Floracarus perrepae, on its native host in Australia, Old World climbing fern, Lygodium microphyllum

The biology and phenology of the eriophyid mite, Floracarus perrepae Knihinicki and Boczek,a potential biological control agent of Lygodium microphyllum (Cav.) R. Br., was studied in its native range - Queensland, Australia. F. perrepae forms leaf roll galls oil tile subpinnae of L. microphyllum. It has a simple biology, with females and males produced throughout the year. Tile Population was female biased at 10.5 to 1. The immature development time was 8.9 ± 0.1 and 7.0 ± 0.1 days; adult longevity was 30.6 ± 1.6 and 19.4 ± 1.2 days and mean fecundity per female was 54.5 ± 3.2 and 38.5 ± 1.6 eggs at 21 and 26 ° C, all respectively. Field studies showed that tile mite was active year round, with populations peaking when temperatures were cool and soil moisture levels were highest. Two species of predatory mites, Tarsonemus sp. and a species of Tydeidae, along with the pathogen Hirsutella thompsonii, had significant effects oil all life stages of F. perrepae. Despite high levels of predators and the pathogen, F. perrepae caused consistent damage to L. microphyllum at all the field sites over the entire 2 years of the study.

Presence of a novel small RNA-containing virus in a laboratory culture of the endoparasitic wasp Venturia canescens (Hymenoptera : Ichneumonidae)

Parasitoid wasps use a variety of mechanisms to alter their host's physiology to the benefit of the developing endoparasite inside the host larva. Association of certain wasps with viruses and virus-like particles (VLPs) that contribute to their success in parasitism is one of the fascinating evolutionary adaptations conferring active or passive protection for the endoparasite from the host immune system. Venturia canescens has been shown to produce VLPs that provide protection for the developing parasitoid egg inside the host, Ephestia kuehniella. Here, we report on the presence of a novel small RNA-containing virus from V. canescens, designated as VcSRV, occurring in the ovaries of the wasp. The virus particles are found together with VcVLPs in the lumen of the calyx region of the ovaries and are injected together with the egg and VcVLPs into E kuehniella larvae where they enter hemocytes. Alignment of the RNA-dependent RNA polymerase gene of VcSRV indicates that the virus most likely belongs to the recently described genus Iflavirus. (c) 2004 Elsevier Ltd. All rights reserved.

Why is Coccidoxenoides perminutus, a mealybug parasitoid, ineffective as a biocontrol agent - Inaccurate measures of parasitism or low adult survival?

Coccidoxenoides perminutus achieves only low levels of parasitism of its host Planococcus citri in southeast Queensland citrus. Two possible causes were investigated. Adult survival under natural conditions was assessed to determine whether providing adult food sources could enhance survival. Behavioural changes of hosts, induced by C perminutus parasitism, was also investigated to establish if parasitised P. citri move from their feeding site to seek protected shelters some distance away and are thus not accounted for in field assessments of parasitism rates. Unparasitised mealybugs placed in the field for two periods were retrieved before the effects of parasitism were manifested and parasitism rates were still low (0.3% at 5 days and 1.2% at 10 days). Levels of locomotion of P. citri exposed to C perminutus were compared with those of unexposed ones. Parasitised mealybugs, regardless of instar, undergo behavioural changes. In comparison to unparasitised controls, the mealybugs become highly active 7-14 days after exposure to wasps. All parasitised mealybugs undergo physical changes, their body becomes cylindrical, their legs go so rigid that the mealybugs become immobile, and this signifies the typical mummy appearance. All mealybugs that became mummies eventually fell from the host lemon fruit because of impaired locomotion and were caught on sticky traps that had been placed beneath the lemons. Consequently, their final site of mummification was not established. C perminutus adults provided with nectar or honey survived longer (about 5 days) in the field than those without food (about a day). Nectar from two plant species, Alpinia zerumbet and Datura candida, proved to be good sources of food for the adult wasps, and were comparable in quality to honey. The low level of parasitism achieved by C perminutus in southeast Queensland citrus thus appears to be a consequence of the short adult life and the negative effects of a harsh environment. Provision of a suitable food source (e.g., nectar) may well enhance levels of parasitism in the field. (c) 2005 Elsevier Inc. All rights reserved.

Water quality monitoring: A combined approach to investigate gradients of change in the Great Barrier Reef, Australia

For the managers of a region as large as the Great Barrier Reef, it is a challenge to develop a cost effective monitoring program, with appropriate temporal and spatial resolution to detect changes in water quality. The current study compares water quality data (phytoplankton abundance and water clarity) from remote sensing with field sampling (continuous underway profiles of water quality and fixed site sampling) at different spatial scales in the Great Barrier Reef north of Mackay (20 degrees S). Five transects (20-30 km long) were conducted from clean oceanic water to the turbid waters adjacent to the mainland. The different data sources demonstrated high correlations when compared on a similar spatial scale (18 fixed sites). However, each data source also contributed unique information that could not be obtained by the other techniques. A combination of remote sensing, underway sampling and fixed stations will deliver the best spatial and temporal monitoring of water quality in the Great Barrier Reef. (c) 2004 Elsevier Ltd. All rights reserved.

Cannibalistic feeding of larval Trichogramma carverae parasitoids in moth eggs

Wasps of the genus Trichogramma parasitise the eggs of Lepidoptera. They may deposit one or many eggs in each host. Survival is high at low density but reaches a plateau as density increases. To reveal the mechanism by which excess larvae die we chose a lepidopteran host that has flattened, transparent eggs and used video microscopy to record novel feeding behaviours and interactions of larval Trichogramma carverae (Oatman and Pinto) at different densities. Single larvae show a rapid food ingestion phase, followed by a period of extensive saliva release. Ultimately the host egg is completely consumed. The larva then extracts excess moisture from the egg, providing a dry environment for pupation. When multiple larvae are present, the initial scramble for food results in the larvae consuming all of the egg contents early in development. All larvae survive if there is sufficient food for all to reach a threshold developmental stage. If not, physical proximity results in attack and consumption of others, continuing until the surviving larvae reach the threshold stage beyond which attacks seem to be no longer effective. The number of larvae remaining at the end of rapid ingestion dictates how many will survive to emerge as adults.

Pollination of Australian Macrozamia cycads (Zamiaceae): Effectiveness and behavior of specialist vectors in a dependent mutualism

Complementary field and laboratory tests confirmed and quantified the pollination abilities of Tranes sp. weevils and Cycadothrips chadwicki thrips, specialist insects of their respective cycad hosts, Macrozamia machinii and M. lucida. No agamospermous seeds were produced when both wind and insects were excluded from female cones; and the exclusion of wind-vectored pollen alone did not eliminate seed set, because insects were able to reach the cone. Based on enclosure pollination tests, each weevil pollinates an average 26.2 ovules per cone and each thrips 2.4 ovules per cone. These pollinators visited similar numbers of ovules per cone in fluorescent dye tests that traced insect movement through cones. Fluorescent dye granules deposited by Cycadothrips were concentrated around the micropyle of each visited ovule, the site of pollen droplet release, where pollen must be deposited to achieve pollination. In contrast, Tranes weevils left dye scattered on different areas of each visited ovule, indicating that chance plays a greater role in this system. Each weevil and 25 thrips delivered 6.2 and 5.2 pollen grains, respectively, on average, to each visited ovule per cone, based on examination of dissected pollen canals. In sum, the pollination potential of 25 Cycadothrips approximates that of one Tranes weevil.