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.

And the beak shall inherit - evolution in response to invasion

The increased demographic performance of biological invaders may often depend on their escape from specifically adapted enemies. Here we report that native taxa in colonized regions may swiftly evolve to exploit such emancipated exotic species because of selection caused by invaders. A native Australian true bug has expanded it host range to include a vine imported from tropical America that has become a serious environmental weed. Based on field comparisons and historical museum specimens, we show that over the past 30-40 years, seed feeding soapberry bugs have evolved 5-10% longer mouthparts, better suited to attack the forest-invading balloon vines, which have large fruits. Laboratory experiments show that these differences are genetically based, and result in a near-doubling of the rate at which seeds are attacked. Thus a native biota that initially permits invasion may rapidly respond in ways that ultimately facilitate control.

Isolation and characterization of microsatellite loci from mother-of-millions, Bryophyllum delagoense (Crassulaceae), and its hybrid with Bryophyllum daigremontianum, 'Houghton's hybrid'

Nine microsatellite loci were developed, and are transferable, across the Madagascan succulents Bryophyllum daigremontianum, Bryophyllum delagoense (mother-of-millions) and their horticultural hybrid (Houghton's), from enriched libraries of the later two species. For B. delagoense, a tetraploid, three to 13 alleles per locus were found for native Madagascan (H-O = 0.4-1.0), and one to nine in invasive Australian (H-O = 0.0-1.0) samples. In addition for 91 Australian samples, only five multilocus genotypes were found (95% of individuals were of two genotypes), suggesting extensive clonality in its introduced range. These loci will be used to examine genetic diversity, hybrid origin and mating system in natural and introduced populations.

First record of Passalora calotropidis in Australia and its generic position

Passalora calotropidis has been found for the first time in Australia on rubber bush (Calotropis procera) in northern Queensland where it was associated with a damaging leaf spot disease. Analysis of sequence data of the ITS region indicated that P. calotropidis belonged to a group that consisted of species of Pseudocercospora. The generic position of P. calotropidis and its potential for biological control are discussed.

Bioactivity of Fusarium oxysporum f. sp glycines and Sclerotium rolfsii filtrates on egg hatching, survival and infectivity of juveniles of Meloidogyne incognita race 2

The effects of culture filtrates of Fusarium oxysporum and Sclerotium rolfsii on egg hatching and juvenile survival of Meloidogyne incognita in vitro and impact of these filtrates on infectivity of M. incognita were investigated on soybean seedlings. Five- and 10-day-old filtrates of F. oxysporum caused 65 and 54% egg-hatching inhibition, while that of S. rolfsii caused 61 and 49% inhibition, respectively. Juveniles of M. incognita died within 6 days when incubated in 5-day-old filtrate of F. oxysporum, while the similar filtrate of S. rolfsii caused 100% juvenile mortality on the fifth day. Filtrates reduced root galling, egg population, number of adult females in soybean plants at harvest and also soil population. Culture filtrates could be used as source of biological nematicides.

Possible incompatibility between transgenic cottons and parasitoids

We investigated the rates of egg and larval parasitism in transgenic and non-transgenic, conventional cottons. Sentinel eggs and larvae of the cotton bollworm, CBW, Helicoverpa armigera Hubner, were released and collected at regular intervals across the cotton growing season, and the relationship between parasitism and different cotton cultivars determined. Egg and larval parasitism were significantly lower in the transgenic cottons than in the non-transgenic conventional cottons. The egg parasitoid recovered was Trichogramma confusum Viggiani and the predominant larval parasitoids were Campoletis chlorideae Uchida and Meteorus pulchriconis (Wesmael). Our studies indicate a potential negative interaction between transgenic cottons and parasitoids of CBW but need to be interpreted with caution because no within-year replication was used and treatments were not spatially randomised across years.

Identification and characterization of non-pathogenic Fusarium oxysporum capable of increasing and decreasing Fusarium wilt severity

Fusarium wilt of banana is a potentially devastating disease throughout the world. Options for control of the causal organism, Fusarium oxysporum f.sp. cubense (Foc) are limited. Suppressive soil sites have previously been identified where, despite the presence of Foc, Fusarium wilt does not develop. In order to understand some aspects of this disease suppression, endophytic Fusarium oxysporum isolates were obtained from banana roots. These isolates were genetically characterized and compared with an isolate of Fusarium oxysporum previously identified as being capable of suppressing Fusarium wilt of banana in glasshouse trials. Three additional isolates were selected for glasshouse trials to assess suppression of Fusarium wilt in two different cultivars of banana, Cavendish and Lady Finger. One isolate (BRIP 29089) was identified as a potential biocontrol organism, reducing the disease severity of Fusarium wilt in Lady Finger and Cavendish cultivars. Interestingly, one isolate (BRIP 45952) increased Fusarium wilt disease severity on Cavendish. The implications of an isolate of Fusarium oxysporum, non-pathogenic on banana, increasing disease severity and the potential role of non-pathogenic isolates of Fusarium oxysporum in disease complexes are discussed. (c) 2006 Published by Elsevier Ltd on behalf of The British Mycological Society.

Parthenium weed: a potential major weed for agro-ecosystems in Pakistan

Parthenium weed (Parthenium hysterophorus L.) is a new and potentially major weed in Pakistan. This weed, originating from central America, is now a major weed in many regions of the world including Eastern Africa, India, parts of South East Asia and Australia. Presumably its recent arrival in Pakistan has been due to its movement from India, but this has yet to be established. In Australia it has been present for about 50 years, in which time it has spread from isolated infestations to establish core populations in central Queensland with scattered and isolated plants occurring south into New South Wales and north-west into the Northern Territory. Its spread in Pakistan is likely to be much more rapid, but lessons learnt in Australia will be of great value for weed managers in Pakistan. This annual herb has the potential to spread to all medium rainfall rangeland, dairy and summer cropping areas in Pakistan. In Australia its main effect is upon livestock production, but it is also causing health concerns in regional communities. However, in India it has also had a significant impact in cropping systems. To help coordinate actions on its management in Australia, a National Weeds Program has created a Parthenium Weed Management Group (PWMG) and under this group a Parthenium Weed Research Group (PWRG) has been formed. Funding coming from this national program and other sources has supported the PWRG to undertake a collaborative and technology exchange research program in two main areas: 1) biology and ecology and 2) management; while the PWMG has focused on community awareness and the production of various extension and management packages. Research in the area of biology and ecology has included studies on the evaluation of competitive plants to displace parthenium weed, the use of process-based simulation models to monitor and predict future spread and abundance under present and future climate conditions, the effect of the weed on human health and the ecology of its seed bank. Management research has focussed on the development of biological control approaches using plant-feeding insects and pathogens. The effectiveness of biological control is also being monitored through long term studies on seed bank size and dynamics. The use of fire as another potential management tool is also being evaluated. In addition to this important research, an effort has also been made to spread the most important findings and management outcomes to the wider community through an extension and education program driven by the PWMG. These developments within Australia, in parthenium weed management, will be of great help to P