Sciarid Larvae Research Articles

Characterization of the mitochondrial genomes of Bradysia hygida, Phytosciara flavipes and Trichosia splendens (Diptera: Sciaridae) and novel insights on the control region of sciarid mitogenomes.

Sciarids, also called "fungus gnats" are small, almost entirely dark-coloured insects. Sciarid larvae feed on different substrates and can infest agricultural crops and mushroom nurseries, causing economic losses. Of the 2174 Diptera mitogenome sequences currently available in GenBank, only eight are from the Sciaridae family, none of which are complete circular molecules. Here we describe the mitogenome sequences of three sciarid species: Phytosciara flavipes, Trichosia splendens and Bradysia hygida and provide novel insights on the control region of sciarid mitogenomes. The assembled mitogenomes range from 16,062 bp in P. flavipes to 17,095 bp in B. hygida. All 13 protein coding genes, 22 tRNAs and 2 rRNAs characteristic of insect mitogenomes were identified, but the sequence of the control region could not be determined. Experimental results suggest that the B. hygida control region is about 21 kb long resulting in a 37 kb long mitogenome which constitutes the largest insect mitochondrial genome described so far. Phylogenetic analysis using all Bibionomorpha mitogenome sequences available in GenBank strongly supports the Sciaridae monophyly and led to the identification of species and subfamily specific gene rearrangements. Our study extends the knowledge of this large and diverse insect family that includes agricultural pest species.

A new ecotoxicological test method for genetically modified plants and other stressors in soil with the black fungus gnat Bradysia impatiens (Diptera): current status of test development and dietary effects of azadirachtin on larval development and emergence rate

BackgroundFew suitable and standardized test methods are currently available to test the effects of genetically modified plants (GMP) on non-target organisms. To fill this gap and improve ecotoxicological testing for GMP, we developed a new soil ecotoxicological test method using sciarid larvae as test organisms.ResultsBradysia impatiens was identified as a candidate species. Species of the genus Bradysia occur in high numbers in European agroecosystems and B. impatiens can be reared in the laboratory in continuous culture. A functional basic test design was successfully developed. Newly hatched larvae were used as the initial life stage to cover most of the life cycle of the species during the test. Azadirachtin was identified as a suitable reference substance. In several tests, the effects of this substance on development time and emergence rate varied for different temperatures and test substrates. The toxicity was higher at 25 °C compared to 20 °C and in tropical artificial soil compared to coconut fiber substrate.Conclusions and outlookResults suggest that the developed test system is suitable to enter a full standardization process, e.g., via the Organisation for Economic Co-operation and Development. Such a standardization would not only assist the risk assessment of GMP, but could include other stressors such as systemic pesticides or veterinary pharmaceuticals reaching the soil, e.g., via spreading manure. The use of sciarid flies as test organisms supports recommendations of EFSA, which stressed the ecological role of flies and encouraged including Diptera into test batteries.

The mushroom sciarid fly, Lycoriella ingenua, benefits from its association with green mold disease (Trichoderma aggressivum) in commercial mushroom production

The mushroom fly, Lycoriella ingenua Dufour (Diptera: Sciaridae), is a pest in white button mushroom (Agaricus bisporus) farming in North America. The main risk associated with sciarid flies inside mushroom farms is that the adult can potentially vector mushroom green mold disease caused by the pathogenic fungus Trichoderma aggressivum Samuels & W. Gams (Hypocreales). Flies are attracted to T. aggressivum-infected compost and, through subsequent movement, are suspected to spread the spores. The present study evaluated whether there is a fitness benefit for the sciarid flies from their association with T. aggressivum. Lycoriella ingenua was reared on three substrates: (1) spawned mushroom compost inoculated with the T. aggressivum, (2) spawned mushroom compost and (3) unspawned mushroom compost. Developmental time from larva to adult, adult longevity, adult fecundity and female body size were used as indicators of fly fitness. There was a fitness benefit for the sciarid fly when larvae develop on spawned mushroom compost parasitized by green mold, including higher adult emergence rate, faster development time from larva to adult and larger adult females. Fly fitness declined when the compost was fully colonized by A. bisporus mycelia and T. aggressivum was not present. This suggests that sciarid larvae benefit from the T. aggressivum parasitism on A. bisporus and the green mold. Benefits may include improved nutrition, defense suppression or pre-digestion.

Increased decomposer diversity accelerates and potentially stabilises litter decomposition

Little is known about the effect of decomposer diversity on litter decomposition in alpine areas. Especially under the premise that alpine ecosystems are very sensitive to global change and are currently undergoing extensive land-use changes, a better understanding is needed to predict how environmental change will affect litter decomposition. A mesocosm experiment was conducted to compare the effects of the most common and functionally diverse invertebrates (earthworms, millipedes and sciarid larvae) found in alpine soils on decomposition rates and to assess how decomposer diversity affects litter decomposition. Experimental and estimated (i.e. projected to field decomposer-biomass) litter mass loss was 13–33% higher in the three-species treatment. Notably, the variability in decomposition was greatly reduced when decomposer diversity was high, indicating a portfolio effect. Our results suggest that invertebrate decomposer diversity is essential for sustaining litter decomposition in alpine areas and for the stability of this service.

Prey preference and life tables of the predatory mite Parasitus bituberosus (Acari: Parasitidae) when offered various prey combinations

Parasitus bituberosus Karg (Acari: Parasitidae) is one of the predatory mite species inhabiting mushroom houses. It is known to accept a wide range of prey, suggesting that it may be a promising candidate for the biological control of key pests of mushroom culture. In our study it did not show any prey preference among four groups of small organisms often occurring in mushroom growth medium, namely rhabditid nematodes, pygmephorid mites, and sciarid and phorid fly larvae. Nevertheless, the type of food these predators fed on affects their development. The shortest egg-to-adult development time was obtained on a nematode diet. On a diet of phorid larvae, mite development stopped at the deutonymph stage; none reached adulthood. All other diets sufficed to reach the adult phase. Female fecundity when fed nematodes and sciarid larvae did not differ, but it was much lower when fed pygmephorid mites. Other life table parameters confirmed that pygmephorid mites constituted the worst diet for P. bituberosus. The highest intrinsic rate of population increase (r m = 0.34) was obtained on the nematode diet; when fed sciarid larvae and pygmephorid mites it was 0.25 and 0.14, respectively. Our study provides good reasons to further test P. bituberosus as biocontrol agent of especially sciarid flies and nematodes, especially when the compost is well colonized by mushroom mycelium (which retards nematode growth).

Establishment of an in vitro sciarid fly larvae assay to study plant resistance

AbstractMechanisms underlying natural plant resistance to herbivorous invertebrates are still poorly understood in comparison with bacterial or fungal interactions. One reason is the difficulty in reliably and reproducibly assessing the effects under controlled conditions. This article describes a newly developed in vitro biological assay system that enables the interactions between sciarid larvae and plants, whose roots they feed on, to be studied under highly controlled conditions. The bioassay eliminates the problems created by the often variable environmental factors by providing an aseptic arena where experimental plants can be germinated and grown on agar within a Petri dish. Sciarid fly eggs are then collected, sterilised and added to the Petri dish. The system allows the eggs to hatch and the larvae to feed on the plant roots. A range of developmental parameters can then be recorded over time which can then be correlated with the experimental plant type. This assay system also allows a simultaneous comparison or ‘choice chamber’ between two (or more) different genotypes. The assay should greatly help to facilitate the identification of new components involved in insect resistance mediated pathway via the characterisation of mutant plants.

Toxicity of six commercially formulated insecticides and biopesticides to third instar larvae of mushroom sciarid, Lycoriella ingenua Dufour (Diptera: Sciaridae), in New South Wales, Australia

Abstract Lycoriella ingenua is one of the major pests of cultivated mushrooms, Agaricus bisporus (Lange) Imbach. Insecticide resistance among mushroom sciarid populations has been reported from other countries, and there is a need to determine the toxicity of currently approved and potential pesticides to sustain control of mushroom sciarid populations in Australia. The present study investigated the toxicity of six commercial formulations of insecticides or biopesticides against third instar larvae of L. ingenua using laboratory bioassays. Insecticide treatments were incorporated into the growing medium for sciarid larvae and the concentration of the pesticide, which killed 90% of the test population (LD90) determined the efficacy of selected insecticides. Triflumuron was the most effective insecticide against L. ingenua with an LD90 of 53.12 mg active ingredient (a.i.)/m2 followed by cyromazine (LD90, 179.68 mg a.i./m2) and diazinon (LD90, 261.72 mg a.i./m2). Abamectin and Bacillus thuringiensis ssp. israelensis were ineffective against L. ingenua. Steinernema feltiae, an entomopathogenic nematode, reduced the number of third instar larvae of L. ingenua only when applied at a higher rate (LD90, 732 422 nematodes/m2) than was recommended on the label.

Nomenclatural notes on the names Gaeolaelaps and Geolaelaps (Acari: Laelapidae)

The genus-group names Geolaelaps and Gaeolaelaps (Acari: Laelapidae) are in widespread use in the formal taxonomic literature of acarology, for a genus or subgenus of predatory soil mites. They are also in use in the literature of ecology and agriculture, especially in discussions of the biological control of western flower thrips, Frankliniella occidentalis (Pergande), and sciarid larvae and gnats of the genus Bradysia, in greenhouse vegetables and ornamentals (Zhang, 2003). Examples of usage in mite taxonomy are Karg (1971), Evans & Till (1979) and Casanueva (1993) (Gaeolaelaps), and Karg (1979, 1993) and Xu & Liang (1996) (Geolaelaps). Examples of usage in ecology and agriculture include House et al. (1987) (Gaeolaelaps) and Gillespie & Quiring (1990) (Geolaelaps). There are many other examples of usage of both of these names in both print and internet documents, and there is considerable confusion surrounding their spelling and authorship. The purpose of this note is to resolve that confusion.

Sciaridae in lake sediments: indicators of catchment and stream contribution to fossil insect assemblages

The larval head capsules of Sciaridae (black fungus gnats) are transported into lakes from terrestrial habitats, in most cases via streams or rivers, and preserve well in lake sediments. The abundance of sciarid remains can provide information on the importance of terrestrial and running-water input into fossil insect assemblages in lake sediments if examined in relation to the number of fossils of aquatic insects such as the Chironomidae, Thaumaleidae, Ceratopogonidae, or Simuliidae. Here we describe fossil head capsules of sciarid larvae and provide an example of how these remains can be used to constrain past changes in taphonomic processes that influence fossil chironomid records.

Optimal application strategies for entomopathogenic nematodes: integrating theoretical and empirical approaches

Summary The nematode Steinernema feltiae has been developed commercially as a biocontrol agent and is successful in controlling sciarid flies in mushroom houses. We used a simple model developed in parallel with a series of field trials, to optimize the application strategy of the nematode. The first field trial provided life‐history parameter estimates for both the sciarid flies and the nematodes and showed there to be substantial levels of nematode recycling, leading to high levels of control. Crucially, the field trial showed that by splitting the application into two, and applying half the nematodes at day 0 and half at day 7, the overall number of nematodes (dose) could be substantially reduced from currently recommended levels without sacrificing control success. The model confirmed that there should be a benefit in splitting the dose, if the second application is timed to coincide with the peak in numbers of highly susceptible sciarid larvae. Importantly, the model provided insight into the dynamics of the sciarid larvae, even though the original data set only recorded adult fly numbers. Using a split dose, optimally timed, the model suggested that total doses could be reduced by up to 75% and still achieve control comparable to that found with currently recommended dosages. The timing of the second application of nematodes was crucial in determining the level of control. The model predictions were validated against a second independent field trial with considerably lower fly densities. Even under these different conditions, the predictions were accurate, indicating the robustness of the modelling approach. To date models have rarely provided genuine practical advice to applied agriculturists and biocontrol practitioners. This study shows how a simple model developed in parallel with replicated field trials leads to a better understanding of the biological processes underlying successful control, resulting in improvements in recommended application strategies.

Lasioseius fimetorum: A soil-dwelling predator of glasshouse pests?

Female lifespan and reproduction, in terms of numberof larvae produced, of the soil-dwelling predatorymite Lasioseius fimetorum Karg (Acari:Podocinidae) fed on mould mites (Tyrophagusputrescentiae [Schrank] [Acarina: Acaridae]) wereinvestigated by laboratory experiments at 20 °C,as were the mite's consumption rates of various prey.After a preoviposition period of 10.7 days, L.fimetorum produced progeny at a daily rate of 0.7.The oviposition period lasted 23.6 days and a total of19.4 progeny were produced per female. Females livedfor 38.6 days. Eggs of the Collembola Isotomurusspp. (Collembola: Isotomidae) were consumed in thelargest amount by L. fimetorum followed by mouldmite nymphs, larvae and pupae of thrips (Frankliniella occidentalis [Pergande] [Thysanoptera:Thripidae]), eggs of the Collembola Micrisotomaspp. (Collembola: Isotomidae), Isotomurus spp.nymphs and sciarid larvae (Bradysia pauperaTuomikoski and B. tritici (Coquillet) [Diptera:Sciaridae]). Immature drain flies (Psychoda spp.[Diptera: Psychodidae]) were not consumed by L.fimetorum. The suitability of L. fimetorum forbiological control of glasshouse pests withsoil-dwelling stages is discussed in comparison withanother predatory mite Hypoaspis miles Berlese(Acarina: Hypoaspididae).

Comparison of the Efficacy of Entomopathogenic Nematodes for the Biological Control of the Mushroom Pests Lycoriella auripila (Sciaridae) and Megaselia halterata (Phoridae)

The efficacy of different species of entomopathogenic nematodes was tested against larvae of the mushroom phorid Megaselia halterata (Diptera: Phoridae) and the mushroom sciarid Lycoriella auripila (Diptera: Sciaridae). Sciarid larvae originating from infestations in casing soil during colonization by Agaricus bisporus were almost completely controlled by applications of Steinernema feltiae to the casing soil. When larvae originated from infestations in freshly spawned compost, they could be controlled by compost applications halfway through spawnrunning and by very early casing treatments. The control of phorids in compost was maximally 31% when nematodes were mixed within the infested compost at a concentration of 3 106 nematodes/m2. Only slightly higher reduction rates were obtained at higher concentrations. The control of phorids was more promising in the infested casing layer, in which S. carpocapsae was most successful. At concentrations of 6 and 15 106 nematodes/m2 this species obtained reduction rates of 65 and 73% respectively when it was applied 3 days after the end of the infestation period. These concentrations are, however, too high for practical application.

Control of the mushroom pests Lycoriella auripila (Diptera: Sciaridae) and Megaselia halterata (Diptera: Phoridae) by Steinernema feltiae (Nematoda: Steinernematidae) in field experiments

SummaryThe nematode Steinernema feltiae (Nematoda: Steinemematidae) was tested for its ability to control two main mushroom pests i.e. the sciarid Lycoriella auripila (Diptera: Sciaridae) and the phorid Megaselia halterata (Diptera: Phoridae) in growing‐rooms filled with spawned compost. A clear difference between female and male sciarid control was observed. A nematode application 1 day after casing preceded by an application 1 day before casing on the compost caused an almost complete control (97%) of the F1‐generation of female sciarids. The F2‐generation of females was similarly controlled (95%) by an application 7 days after casing. A dosage of 1 × 106nematodes m‐2was found to be equally effective as higher dosages. Diflubenzuron remained active throughout entire the cropping period with high sciarid mortality rates varying from 72% to 99%.Phorid control was variable and seemed to depend on the presence of sciarids. In one occasion the control rate of F2‐generation phorid larvae was 75% and was possibly caused by the presence of new infective juvenile nematodes recycled in F2‐generation sciarid larvae. Diflubenzuron did not significantly reduce phorid numbers.

The predatory mite Hypoaspis miles: biological and demographic characteristics on two prey species, the mushroom sciarid fly, Lycoriella solani, and the mould mite, Tyrophagus putrescentiae

AbstractThe biology of Hypoaspis miles Berlese (Acarina: Hypoaspidae) fed on mushroom sciarid larvae (Lycoriella solani Winnertz) (Diptera: Lycoriidae) and mould mites (Tyrophagus putrescentiae Schrank) (Acari: Acaridae), was investigated by laboratory experiments at 20 °C, 75% r.h. and LD16:D8 hours. H. miles had a significantly shorter development time and a significantly lower juvenile mortality when fed on sciarid larvae than on mould mites, the development time being 14.5 days and the mortality 3.5% on the former prey. The preoviposition and postoviposition periods of H. miles were not uninfluenced by the prey species and were 5–9 and 32–37 days, respectively. Oviposition periods of 53.2 and 68.5 days and female longevities of 82 and 109.6 days were observed on diets of sciarid larvae and mould mites, respectively. Male longevity (168–219 days) was uninfluenced by the prey species. The egg production of H. miles on sciarid larvae was estimated to be 44.4 ± 4.33 eggs per female, as compared to 22.43 ± 1.79 eggs per female on mould mites. The sex‐ratio of the offspring was significantly influenced by the prey species, the ratios (♀/(♀+♂)) being 0.66 on sciarid larvae and 0.54 on mould mites. The net reproductive rate (R0) for H. miles fed on sciarid larvae was approximately 27 which was three times higher than for mites feeding on mould mites. The innate capacity of increase (rm) was highest (0.0747 day−1) when sciarid larvae served as food, giving a doubling time of 9.3 days as compared to 12.8 days on mould mites. The generation times were 44.28 on sciarid larvae and 40.67 days on mould mites. The daily food consumption rate of juvenile and adult H. miles was 0.24 and 0.86 sciarid larvae and 10.8 and 21.7 mould mites, respectively. In terms of weight consumed, however, the consumption of sciarid larvae was 2–3.5 times the weight of mould mites. The ratio of females to males influenced the oviposition period and egg production of H. miles, with virgin females laying fewer eggs over a longer period of time as compared with females with access to males. The egg production in relation to the sex‐ratio was described by models predicting a maximum number of eggs per female of 22.3 to be attained at a sex ratio of 0.69 (♀/(♀+♂)) and a maximum daily number of eggs per female of 0.33 to be attained at a sex ratio of 0.37 (♀/(♀+♂)).

Comparison of digestive carbohydrases between two forest sciarid (Diptera: Sciaridae) larvae in relation to their ecology

Comparison of digestive carbohydrases between two forest sciarid (Diptera: Sciaridae) larvae in relation to their ecology

Inter‐ and intraspecific variation in infectivity of Steinernema spp. to larvae of the mushroom fly Lycoriella solani

AbstractLaboratory bioassays were done to assess the susceptibility of larvae of the mushroom sciarid fly Lycoriella solani Winnertz (Diptera; Sciaridae) to 16 isolates comprising five species of the entomopathogenic nematode, Steinernema (Nematoda; Steinernematidae). Each isolate was tested by challenging sciarid larvae with single nematodes. Six isolates were also tested in dose‐response experiments. Variations in nematode infectivity occurred (p < 0.001) at both inter‐ and intraspecific levels. Steinernema feltiae (Filipjev) was the most virulent species: two isolates, Nemasys (LD50 = 1.5–3.9) and Sus 94 (1.8–3.9) were superior to the rest. Steinernema kraussei (Steiner) was the least infectious nematode tested as its infection probability never exceeded 0.10. In addition, lethal dose50 values for this species ranged from 9.0–62.6 and two isolates failed consistently to infect any hosts.

Transmission of the mycoparasite Coniothyrium minitans by collembolan Folsomia Candida (Collembola: Entomobryidae) and glasshouse sciarid Bradysia sp. (Diptera: Sciaridae)

Summary Folsomia Candida was maintained on potato dextrose agar (PDA) plates precolonised by the mycoparasite Coniothyrium minitans for 3 yr but the sciarid Bradysia sp. survived for a maximum of only three generations. Collembolans and sciarid larvae from these cultures were able to transmit C. minitans to uninoculated PDA plates through the survival of spores in faecal pellets. Adult and larval sciarids also transmitted C. minitans from PDA culture to uninoculated PDA plates by contamination on the cuticle. In soil and sand both sciarids and collembolans were able to transmit C. minitans from C. m/m'tans‐inoculated to uninoculated sclerotia of Sclerotinia sclerotiorum. Inoculation of sclerotia with C. minitans enabled greater populations of larger collembolans to develop. In the glasshouse where C. minitans had been applied to the soil, one adult sciarid and four collembolans out of 70 and 101 insects collected respectively yielded C. minitans on placement onto PDA + Aureomycin.

Control of Root Gnats (Sciaridae: Diptera) by Tetradonema plicans Hungerford (Tetradonematidae: Nematoda) Produced by a Novel Culture Method

A survey of adult sciarid root gnats in greenhouses at the University of California, Riverside, demonstrated that 9.0% were infected with Tetradonema plicans. The mean number of gravid T. plicans females per infected sciarid adult was 5.1 with a range of 1 to 48 parasites per host fly. Only 1.4% of the maggots collected from pots in the greenhouses were infected. To study the bionomics of T. plicans a simple system for culturing sciarid flies and T. plicans and extraction of T. plicans eggs was developed. Fermented sphagnum moss and cellulose (4:1) with rabbit chow was the basic culture medium. Up to 3 × 10 9 T. plicans eggs were produced from an inoculum of 6 × 10 4 eggs per culture container. Eggs were collected by seiving or sucrose flotation. Infections in 1-liter containers showed that T. plicans (10 T. plicans eggs per sciarid larva) reduced sciarid fly populations by 74 to 80% for 4 months. Steinernema carpocapsae had no effect on sciarid flies, but in contrast, Heterorhabditis bacteriophora (10 juvenile nematodes per host larva) decreased sciarid populations by 60%. At 100-fold higher infection level all sciarid larvae were killed, but H. bacteriophora was unable to reproduce in the sciarid larvae.

Dabbing and shooting of benzo- and naphthoquinone secretions: Defensive strategies of bark-inhabiting aleocharine (col.: Staphylinidae) and tenebrionid (col.: Tenebrionidae) beetle larvae

The abdominal glands of three bark-inhabiting larvae of generaBolitochara, Leptusa (Staphylinidae), andHypophloeus (Tenebrionidae) were studied chemically and morphologically. Behavior of the larvae indicated that secretion is emitted only after severe disturbance of the larvae. These mechanical contacts may also occur incidentally with coinhabiting nonpredatory arthropods when the beetle larvae move within small interstices under bark. Depending on the species, the secretions contained 1,4-benzoquinone derivatives and three 6-alkyl-naphthoquinones dissolved within various alkanes, alkenes, ethyl-, isopropyl-, and isoamylesters. More erratically distributed gland constituents also detected were acetophenone, benzyl propionate, and methyl hydroxybenzoate. In the laboratory, synthetic quinone-containing solutions simulating those found inLeptusa andBolitochara larvae acted as strong topical irritants and caused further damage to last-stageCalliphora vomitoria larvae if hydrocarbons or esters were used as solvents. The natural secretions ofHypophloeus versipellis elicited considerable mortality in two subcortical sciarid larvae cooccurring with tenebrionid larvae. Bioassay and secretion chemistry of the Staphylinidae/Tenebrionidae larval secretions indicated that they are typical defensive secretions that act topically. Morphological data characterized Bolitocharini larvae as possessing protuberant abdominal tergites supplied with an interiorly situated gland reservoir. After mechanical contact, the defensive secretion is topically applied to other arthropods by dabbing this tergal protuberance on targets. The defensive gland ofHypophloeus versipellis is unusual in possessing a movable reservoir opening situated at the anterior border of tergite IX. By this peculiar gland morphologyHypophloeus larvae are capable of shooting secretion droplets frontally from their slightly depressed dorsal abdominal surface without bending their abdominal tips dorsally. This seems an adaptation to the interstitial habitat of the larvae. The types of defensive glands and their phylogenetic value in Aleocharinae/Tenebrionidae larvae are discussed.

Effects of Application Rates ofSteinernema feltiae(Nematoda: Steinernematidae) on Biological Control of the Mushroom FlyLycoriella auripila(Diptera: Sciaridae)

The potential of Steinernema feltiae for the biological control of Lycoriella auripila was tested in commercial mushroom‐growing conditions. The nematodes, applied at rates of 1.5, 3, 6 or 12 x 10 6 infective juveniles per 34 kg tray of spawn‐run compost, were mixed into the casing material before it was spread over the compost surface. When compared with untreated control trays, any rate of nematode application significantly reduced fly emergence. Insecticides significantly reduced mushroom yields; nematodes significantly increased them. At a rate of 3 x 10 6 infectives/tray S. feltiae elicited mean total increases in the weight and numbers of mushrooms produced of 8% and 11% respectively. The nematodes also reduced the incidence of mushrooms spoiled by tunnelling sciarid larvae. The early decline in the numbers of nematodes persisting in casing was a trend that was reversed later, when evidence was obtained that S. feltiae was recycling in insects that had been killed. When applied at a rate of 3 ‐106in...