Mark M. Stevens

Effects of different management regimes on aquatic macroinvertebrate diversity in Australian rice fields

The maintenance of invertebrate diversity within agricultural environments can enhance a number of agronomically important processes, such as nutrient cycling and biological pest control. However, few Australian studies have been undertaken which specifically address the effects of commercial management regimes on rice field biodiversity. In this study, we compared aquatic macroinvertebrate communities within Australian rice fields cultivated under three commercial management regimes: conventional-aerial (agrochemicals applied, aerially sown), conventional-drill (agrochemicals applied, directly drill-sown) and organic-drill (agrochemical-free, directly drill-sown). These comparisons were undertaken using a combination of community assessment approaches, including morphospecies richness, abundance, diversity and community composition. In general, greater biodiversity existed within macroinvertebrate communities that developed under organic management regimes than under conventional regimes (i.e., higher morphospecies richness and Shannon diversity). Although there were significant differences in several parameters across management regimes early in the rice-growing season, as the growing season progressed the invertebrate communities that developed in the different management regimes became more similar. Only community composition analyses showed significant differences late in the growing season, with functional differences across aquatic faunal assemblages suggested by increased predator abundance in communities sampled from the organic management regime. In order to improve biodiversity within these aquatic environments, management techniques need to be examined individually and the most disruptive processes identified. Alternative management procedures can then be developed that minimise biodiversity loss whilst still delivering required agronomic outcomes.

Fine‐needle aspiration biopsy for the diagnosis of lymphoma: A perspective

Fine‐needle aspiration (FNA) has become a widely used diagnostic tool and it remains one of the most rapid and cost‐effective methods of assessing a variety of pathologic conditions. However, FNA as a method of evaluation of enlarged lymph nodes has been approached with a greater degree of caution and reservation, largely because Hodgkins disease and the non‐Hodgkins lymphomas represent a diverse group of neoplasms, which is mirrored by a large range of histopathologic and cytologic appearances. For these reasons, adjunctive techniques such as immunohistochemical staining, cytogenetics, and molecular techniques have been introduced to improve the diagnostic accuracy. While such procedures have made significant contributions to the identification and typing of lymphomas, there is still a requirement for a simple and rapid diagnostic procedure for the patient who presents with persistent lymphadenopathy. Light microscopic examination of FNA smears fulfills this role, provided its limitations and pitfalls are recognised. Diagn Cytopathol 1996;15:352–357.

Within-plant distribution of onion thrips (Thysanoptera: Thripidae) in onions.

Abstract Two aspects of the within-plant distribution of Thrips tabaci Lindeman (Thysanoptera: Thripidae) on onion, Allium cepa L., plants were investigated: 1) diurnal variations in the distribution of adults and larvae between basal and upper sections of onion leaves, and 2) between-leaf and within-leaf distribution of the eggs. The diurnal investigations showed that higher proportions of larvae than of adults congregated at the basal sections of plants, particularly when plants were young and thrips density was low. As plants matured and thrips density increased, the larvae became more dispersed. Regardless of plant size, there were always more adults in the upper than basal plant sections. There were no clear time-windows during the 24-h diurnal cycle when more thrips were in the upper plant parts. T. tabaci eggs were laid everywhere in the plant. Leaves of intermediate ages had more eggs than older or younger leaves. Within leaves, the white leaf sheath received the least eggs and leaf tips received slightly more eggs than leaf sheaths. The highest egg density was found between the green leaf base and the leaf tips. Regardless of plant size, more than half of all eggs were laid above the basal sections. The percentage increased to >95% in mature plants. Except when plants were small the outer leaves were preferred over inner leaves and upper leaf sections preferred over lower leaf sections as egg-laying sites by adults. Implications of the results in the management of T. tabaci are discussed.

Toxicity of Bacillus thuringiensis var. israelensis formulations, spinosad, and selected synthetic insecticides to Chironomus tepperi larvae.

ABSTRACT Three Bacillus thuringiensis var. israelensis (BTi) formulations, the bacterial metabolite spinosad, and 7 synthetic insecticides were bioassayed against 4th instars of Chironomus tepperi, a serious pest of rice in southern Australia. The BTi formulations returned 48-h product median lethal concentration (LC50) values (25 ± 1°C) of between 0.59 mg/liter (VectoBac® water-dispersible granule [WDG], 3,000 international toxic units [ITU]/mg) and 2.15 mg/liter (Teknar® suspension concentrate [SC], 1,200 ITU/mg). When LC50 values were adjusted to reflect nominal ITU values of the 3 products, there was still substantial variation, with LC50 values ranging from 1,770 ITU/liter (VectoBac WDG) to 2,580 ITU/liter (Teknar SC). Aquabac® SC (1,200 ITU/mg) showed intermediate activity. Differential activity between formulations may reflect faster settling rates in the more active formulations, which may be a beneficial characteristic when controlling benthic species such as C. tepperi. Spinosad (24-h LC50=28.9 μg active ingredient [AI]/liter) and the synthetic insecticides we evaluated were all substantially more active than BTi. The highest activity was shown by the neonicotinoid compounds thiacloprid, acetamiprid, and clothianidin, which all returned 24-h LC50 values between 1 and 3 μg AI/liter. Indoxacarb and thiomethoxam showed the lowest activity of the synthetic compounds evaluated.

Developmental toxicity of two common corn pesticides to the endangered southern bell frog (Litoria raniformis)

To examine the link between corn agriculture and the observed decline of the endangered southern bell frog (SBF), the effects of two corn crop pesticides on larval growth and development were investigated. Tadpoles were exposed to terbufos sulfone (10 μg/L), a major breakdown product of the insecticide terbufos, and the herbicide atrazine (25 μg/L) individually and as a mixture until the completion of metamorphosis. Atrazine did not interact synergistically with terbufos sulfone or result in significant effects on growth and development alone, although there was some indication of accelerated metamorphosis in the pilot study. Terbufos sulfone alone and as a mixture (terbufos/atrazine) significantly slowed larval development and ultimately delayed metamorphosis. The observed developmental effects from an environmentally relevant concentration of terbufos sulfone indicates a risk posed by this persistent degradation product to the endangered SBF, which breeds and develops in the rice bays adjacent to corn fields treated with pesticides.

The acute toxicity of fipronil to two non-target invertebrates associated with mosquito breeding sites in Australia

Mosquito-borne arboviruses are a significant health issue in the irrigation areas of south-eastern Australia. Fipronil, a pyrazole insecticide with strong activity against larval Culex species, was tested for its acute effects on Simocephalus elizabethae (Daphniidae) and Polypedilum nubiferum (Chironomidae), two non-target invertebrates associated with Australian rice field mosquito habitats. Technical and formulated fipronil were assessed in the presence or absence of particulate artificial diets in 48 h static bioassays. LC(50) values for neonate S. elizabethae ranged from 11.13 to 19.12 μgl(-1) whilst those for final instar P. nubiferum ranged from 0.89 to 2.18 μgl(-1). Feeding during exposure significantly reduced the susceptibility of P. nubiferum to both technical and formulated fipronil. The effect of feeding was less consistent in Simocephalus bioassays, where much less food was present. We investigated whether adsorption to unconsumed food particles may have limited fipronil bioavailability by using solid-phase microextraction and gas chromatography to measure the available fipronil from fed and unfed systems 24h after establishment. Differences between the systems were not significant (P>0.05). The significantly higher LC(50) values in the fed Polypedilum bioassays do not appear to be a consequence of reduced fipronil bioavailability. Observed differences in toxicity probably reflect increased stresses associated with food deprivation in the unfed bioassays. Our results support published data on the toxicity of fipronil to aquatic invertebrates which suggest that the use of this material as a mosquito larvicide may cause disruption to aquatic ecosystems.

Simultaneous determination of niclosamide and its degradates in water by LC-MS/MS

A new method for the analysis of niclosamide (NIC) and its primary degradates 2-chloro-4-nitroaniline (2C4NA), aminoniclosamide (AN), hydroxyniclosamide (HN) and 5-chlorosalicylic acid (5CSA) in water was developed using direct injection LC-MS/MS. Methanol and acetonitrile mobile phases were compared. Methanol was superior for both separation and sensitivity for all chemicals. LLoQs for all chemicals were 3–50 times better in methanol than in acetonitrile, and baseline separation was observed for HN and 5CSA in methanol but not acetonitrile. The LLoQ for NIC in the current study was approximately 20 times lower than that previously reported using LC-MS/MS methodology, and 10–250 times lower for all chemicals than obtained by HPLC-UV/visible detection. The method reported in the current study relies upon smaller injection volumes and direct injection of water, eliminating time consuming clean-up steps and increasing sample throughput. The current method is also more selective for all four chemicals than existing HPLC-UV/visible methods, and is not susceptible to spectral interferences from DOM. The use of a shorter LC column with core shell particles resulted in shorter run times and lower mobile phase consumption than previously reported methods for NIC, which rely on traditional porous particle columns.

Evaluation of a commercial Bacillus thuringiensis var. israelensis formulation for the control of chironomid midge larvae (Diptera: Chironomidae) in establishing rice crops in south-eastern Australia

A commercial formulation of Bacillus thuringiensis var. israelensis (B.t.i.) was evaluated for its potential to control chironomid midge larvae in newly sown rice crops in south-eastern Australia. Two replicated small-plot field trials were conducted using product application rates of 0.5-6 kg/ha. In trial 1 application rates between 2 and 6 kg product/ha all significantly (P<0.05) reduced populations of target Chironominae/Orthocladiinae by between 71% and 93% over the 19 day post-treatment monitoring period. Trial 2 was conducted using lower application rates (0.5-2 kg product/ha) and only the 2 kg product/ha rate significantly (P<0.05) reduced numbers of the target group (81% reduction) despite lower application rates resulting in target group suppression of 38-62%. Identification of larvae to species level from selected samples indicated that populations of Chironomus tepperi, the principal pest species that attacks the roots of rice seedlings, were reduced at all application rates; elimination of C. tepperi was achieved in trial 1 at an application rate of 2 kg/ha. Consistent with other studies, non-target Tanypodinae were not adversely affected by B.t.i., and in some treatments populations of Tanypodinae exceeded control levels by up to 73%. In the first trial, which was conducted under relatively high pest pressure, plant establishment was significantly (P<0.05) increased (120-157%) by Vectobac® WDG application rates of 2-6 kg/ha. No significant increase in plant establishment relative to the controls was identified in the second trial, when pest pressure was substantially lower and minimal damage occurred in the control bays. Overall, our results demonstrate that B.t.i. may be an economically viable alternative to broad-spectrum synthetic pesticides for the control of phytophagous midge larvae in establishing rice crops where members of the Chironominae, the group most susceptible to B.t.i., are the principal species of concern. The high specificity of B.t.i. for nematoceran Diptera should lead to reduced impacts on non-target organisms.

Screening of tropical isolates of Metarhizium anisopliae (Hypocreales: Clavicipitaceae) for virulence to the sweet potato weevil, Cylas formicarius (Coleoptera: Brentidae)

The sweet potato weevil (SPW), Cylas formicarius, is a serious pest of sweet potato in Australia and Papua New Guinea. Ten strains of Metarhizium sp. isolated from Australian soil samples were evaluated for their growth characteristics and screened for virulence to adult SPW under laboratory conditions. All isolates except QD62 (48.6%) had moderate to high germination (66–97%), and all took 2 to 4 days to sporulate at 25 °C. The optimal temperature for radial growth for the majority of isolates was 30 °C, and there was a significant interaction between isolate and temperature (P < 0.05). Isolate QS155 showed the fastest radial growth at 30°C. The internal transcribed spacer sequences showed slight variations among the isolates; however, all isolates were shown to be Metarhizium anisopliae. Isolates varied greatly in their virulence. At 10 days after inoculation (DAI) by immersion in a suspension of 1 × 107 conidia/ml, 9 of the 10 isolates were virulent, causing 80-100% mortality of adult SPW. Only two isolates (QS001-6 and QS155) caused more than 50% mortality at 5 DAI. In dose-mortality bioassays, isolate QS155 had the lowest 20-day LC50 and LC90 values; however, there were no statistically significant differences in mortality among the three most promising isolates tested (QD66, QS001-6 and QS155). These results show that M. anisopliae isolate QS155 has potential as a microbial control agent for SPW, and that further evaluation under glasshouse and field conditions is warranted.

Attraction of Parastethorus nigripes and other insect species to methyl salicylate and ( Z )-3-hexenyl acetate dispensers in a citrus grove and vineyard in south-eastern Australia

Herbivore-induced plant volatiles (HIPVs) play an important role in tritrophic interactions, and have the potential to attract beneficial arthropods into crops to enhance biological control of target pests. We conducted field trials in citrus and grapes to evaluate the response of abundant insect species to two HIPVs, methyl salicylate (MeSa) and (Z)-3-hexenyl acetate. Micromus tasmaniae (Hemerobiidae) showed significant attraction to MeSa, but only in the vineyard trial. Parastethorus nigripes (Coccinellidae) was also attracted to MeSa in the vineyard, but in the second citrus trial the treatment response was just outside the nominal 5% significance level. In the first citrus trial where P. nigripes was not separated taxonomically from the closely related coccinellid Stethorus vagans, a combined analysis was undertaken and significant attraction of both coccinellid species to MeSa was also observed. There was also a significant positive combined response of P. nigripes and S. vagans to (Z)-3-hexenyl acetate in the first citrus trial. Other predatory insect species did not respond to MeSa or (Z)-3-hexenyl acetate. As compared with the vineyard trial, weaker attraction of some insect species in the citrus trials may reflect high levels of background odour in the citrus orchard that could have interfered with normal insect olfactory responses. Our results support previous studies demonstrating coccinellids in the tribe Stethorini are often strongly attracted to MeSa. Deploying MeSa dispensers in vulnerable crops could attract increased numbers of P. nigripes, enhancing the biological control of pest tetranychid mites in Australian horticultural systems and reducing or eliminating the need for miticide applications.