Quantitative sampling method for fungus gnat (Diptera: Sciaridae) eggs in soilless growing media

A simple method is described for separating fungus gnat eggs from soilless growing media. The flotation/extraction method primarily involves the use of a MgSO4 solution (density 1.065 g cm(-3)) and a series of sieving procedures. Bradysia sp. nr. coprophila Lintner eggs were collected in an isolation chamber containing adult fungus gnats. Three soilless growing media were used: Metro-Mix 560 with Scott's Coir, Sunshine LC1 Mix, and Universal SB 300 Mix. Each growing medium was inoculated with 100 fungus gnat eggs. Growing medium samples were processed using separatory funnels and a MgSO4 solution. Eggs were washed through a 250-microm sieve and collected on a 53-microm sieve, and then the eggs were rinsed into glass petri dishes. The sieving process separated fungus gnat eggs from the larger growing medium particulates (perlite, bark, and peat), providing a sample consisting of water, eggs, and fine growing medium particulates (peat). Using a vortex for 60 s increased the number of fungus gnat eggs recovered (37.4 +/- 3.7-67.1 +/- 1.9 [mean +/- SEM]) for all three growing media. The mean number of fungus gnat eggs recovered from the three soilless growing media was significantly different, with the growing medium containing coir (Metro-Mix 560) having the highest recovery rate of 61.0 +/- 2.1. For all three growing media, there was > 50% recovery of fungus gnat eggs. In addition to fungus gnat eggs, this method also may prove useful for quantitative recovery of shore fly (Scatella sp.) eggs and the eggs of other arthropods from soilless growing media.     

Egg-laying preference of female fungus gnat Bradysia sp. nr. coprophila (Diptera: Sciaridae) on three different soilless substrates

Fungus gnats, Bradysia spp., are major insect pests in greenhouses. Adult female fungus gnats prefer to lay eggs in growing medium that is microbially active or that contains high amounts of peat moss or hardwood bark. However, egg-laying preference has not been demonstrated quantitatively. This study was designed to determine whether fungus gnat Bradysia sp. nr. coprophila females prefer any of the three soilless growing media provided. The three soilless growing media tested were Metro-Mix 560 with Scott's Coir, Sunshine LC1 Mix, and Universal SB 300 Mix. Initially, the egg-laying potential of the fungus gnat species used in this study was assessed by dissecting mated females after 24, 48, and 72 h. For the egg-laying preference experiment, adults that emerged from pupae were aspirated into a plastic vial, sexed, and then allowed to mate for 24 h. Individual mated females were released into an experimental chamber (15 by 15 by 5-cm plastic container) consisting of four 6-cm petri dishes, three of which contained soilless growing media and one with filter paper (control). In total, there were 50 experimental chambers, with each chamber representing a replication. Females remained in the experimental chambers for 48 h after which the growing media were processed using a flotation/extraction method. The number of eggs laid by female fungus gnats ranged from 21 to 217 with most eggs recovered after 48 h (141.0 +/- 9.3). There were no significant differences among the three soilless growing media in terms of number of eggs laid, although all three growing media were significantly different from the filter paper with higher numbers of eggs laid in the soilless growing media than the filter paper. Despite no significant difference among the growing media in the number of eggs laid, fungus gnat females tended to lay eggs more often, based on the number of petri dishes in which at least one egg was laid, in Metro-Mix 560 (86%) than Sunshine LC1 (66%), Universal SB 300 (52%), or filter paper (18%). Based on the results of this study, female fungus gnats may not prefer a specific growing medium for oviposition. However, fungus gnat females may rely on other factors not tested in this study such as moisture content and volatiles emitted from growing media in their decision where to lay eggs.     

Effect of diatomaceous earth and Trichoderma harzianum T-22 (Rifai strain KRL-AG2) on the fungus gnat Bradysia sp. nr. coprophila (Diptera: Sciaridae)

This study, consisting of three experiments, was designed to assess whether diatomaceous earth, when applied to the surface of growing media, reduces adult fungus gnat Bradysia sp. nr. coprophila (Diptera: Sciaridae) emergence or inhibits the females from laying eggs; and whether fungus gnat adults are attracted to the fungus Trichoderma harzianum T-22 (Rifai strain KRL-AG2) under laboratory conditions. In the first two experiments, diatomaceous earth was applied at two different thicknesses (3.1 and 6.3 mm) and conditions (dry and moist) to the surface of a growing medium (Universal SB 300 Mix) after the growing medium had been artificially inoculated with second or third instars of fungus gnats, or before female fungus gnat adults were released into each deli squat container. In the third experiment, preparations of the fungus T. harzianum at the highest recommended label rate (0.889 kg/m3) were amended into the growing medium and processed 24, 48, or 72 h before use in a series of three two-choice trials with a two-armed experimental arena. In the first two experiments, the dry or moist layers of diatomaceous earth, in general, did not affect fungus gnats in terms of preventing adult emergence or egg laying by the females. During the course of these experiments, we observed that the diatomaceous earth dry treatments expanded as a result of absorbing moisture from the growing medium, creating fissures that allowed the fungus gnat larvae to pupate and females to lay eggs. In the third experiment, fungus gnat adults were not attracted to the T. harzianum treatments in any of the trials.     

Fungus gnats, Bradysia spp. (Diptera: Sciaridae), and other arthropods in commercial bagged soilless growing media and rooted plant plugs

Fungus gnats, Bradysia spp., in greenhouses cause economic losses to horticultural producers by damaging young root systems during plant propagation, by spreading soilborne diseases, and by reducing the marketability of the crop. In a greenhouse cage study, our observations suggested that bagged soilless growing media or rooted plant plugs from wholesale distributors may be sources for the introduction of fungus gnats into commercial greenhouse facilities. To evaluate these possibilities, carefully collected samples of bagged soilless growing media stored in the greenhouse, as well as bagged soilless growing media and rooted plant plugs delivered from midwestern wholesale distributors, were incubated under controlled conditions in the laboratory. Fungus gnats emerged from soilless media stored in the greenhouse, soilless media delivered from wholesale distributors, and from rooted plant plugs delivered from wholesale distributors. These results demonstrate that pasteurization of even bagged soilless media may be essential to effectively managing greenhouse populations of fungus gnats. However, pasteurization is not an option for responding to contamination of rooted plant plugs. Preliminary evidence is provided that application of entomopathogenic nematodes may offer potential as a method for managing fungus gnats in plant plugs, so long as treatment is early. Other arthropods found contaminating soilless media and rooted plant plugs included the western flower thrips, Frankliniella occidentalis (Pergande), Collembola, Acari, Formicidae, Staphylinidae, Psychodidae, and other Diptera.     

Effect of growing media and their constituents on fungus gnat, Bradysia sp, nr, coprophila （Lintner） adults

This study was conducted to determine the attractiveness of two growing media, commonly utilized in greenhouses, to fungus gnat, Bradysia sp. nr. coprophila adults. The constituents of the most attractive growing medium tested were determined by gas chromatography analysis using a steam-distillation procedure. We found that fungus gnat adults were more attracted to the growing medium, SB300 Universal Professional Growing Mix, which contains composted bark, than to another growing medium （Sunshine LC1 Mix） and their components when tested in a series of laboratory experiments using multiple-choice experimental arenas. A higher percentage of fungus gnat adults were attracted to moist SB300 （92%） than SB300 growing medium that had been oven dried （8%）. In addition, fungus gnat adults preferred SB300 although they had been reared on Sunshine LC1 Mix. When comparing the SB300 fresh from the bag to growing medium that had been pasteurized and moistened with water, gas chromatographic-mass spectroscopic data showed there were declines in several terpenoid constituents as well as an increase in fatty acids and cyclosulfur. The results of this study indicate that B. sp. nr. coprophila adults prefer certain growing media, which may assist greenhouse producers in managing fungus gnats in crop production systems.     

Persistence of Metarhizium anisopliae incorporated into soilless potting media for control of the black vine weevil, Otiorhynchus sulcatus in container-grown ornamentals

The objective of this study was to determine the persistence of Metarhizium anisopliae (F52), measured as infectivity against black vine weevil larvae, in a soilless potting medium at six wholesale nursery locations across the Willamette Valley, Oregon. A granule formulation (0.30 and 0.60 kg/m(3)) was incorporated into media at planting and fungal persistence determined over two growing seasons. The fungus persisted in the potting media over the duration of the experiment with 50-60% of the larvae exposed to treated media becoming infected at the end of the experiment. The percentage of infected larvae gradually declined from > or = 90% on week 3 to 40-60% by week 19. Larval infection rebounded over the fall and winter months of 2004 to 75-80% followed again by a slow decline over the course of the second growing season.     

Repellency of naturally occurring volatile alcohols to fungus gnat Bradysia sp. nr. coprophila (Diptera: Sciaridae) adults under laboratory conditions

This study, conducted under laboratory conditions, was designed to determine the repellent activity of 10 naturally occurring volatile alcohol constituents against adults of the fungus gnat, Bradysia sp. nr. coprophila (Lintner) (Diptera: Sciaridae). The essential oil constituents were octanoic acid, furfural, acetophenone, benzaldehyde, dimethoxybenzene, borneol, menthol, 1-octen-3-ol, and 7-hydroxycitronellol, and alpha-terpineol. alpha-Terpineol, octanoic acid and furfural were tested at several concentrations, whereas the remaining seven were tested at only one concentration. The essential oil constituents' menthol, 1-octen-3-ol, and borneol displayed the most repellent activity. The mean percentage of fungus gnat adults recovered from the test compound petri dishes associated with the three essential oil constituents was between 6 and 15% compared with between 36 and 50% for the petri dishes with distilled water. The mean +/- SEM number of fungus gnat adults present in the sample compartments associated with menthol (10.4 +/- 2.6), 1-octen-3-ol (18.8 +/- 2.4), and borneol (23.4 +/- 5.6) was statistically lower than those in the petri dishes containing distilled water (60.9 +/- 7.4, 49.8 +/- 4.0, and 79.7 +/- 13.5), respectively. Only the highest concentration of alpha-terpineol (8.0 micromol) displayed significant repellent activity against fungus gnat adults. The other essential constituents tested, including octanoic acid (all three concentrations), furfural (both concentrations), acetophenone, dimethoxybenzene, and 7-hydroxycitronellol, were not statistically different from the distilled water control. The results of this study indicate that certain essential oil constituents repel fungus gnat adults, which may be useful, from a practical standpoint, in deterring adults from laying eggs into growing media.     

Food preference of the rove beetle, Atheta coriaria Kraatz （Coleoptera： Staphylinidae） under laboratory conditions

A study, involving laboratory choice tests, was conducted to determine the feeding behavior, based on food preference, of the adult and larval stage of the rove beetle, Atheta coriaria Kraatz when presented with both fresh moistened oatmeal and second instar fungus gnat, Bradysia sp. nr. coprophila （Lintner） larvae in Petri dishes. Rove beetles used in this study came from a laboratory-reared colony. A rating scale from 1 to 5, based on percent missing （1 = 0 to 10%, 2 = 11 to 30%, 3 = 31 to 50%, 4 = 51 to 75%, and 5 = 76 to 100%）, was used to objectively assess the amount of oatmeal and number of fungus gnat larvae consumed by each rove beetle adult and larva. In all the choice tests, A. coriaria adults and larvae preferred to feed on fungus gnat larvae （78% and 69%, respectively） significantly more so than oatmeal （9% and 5%, respectively） based on the amount of oatmeal and number of fungus gnat larvae consumed after 4 and 6 hours. There were relatively minimal differences in the amount of food consumed for both adults and larvae after 4 and 6 hours. The results of this study indicate that oatmeal may be an inexpensive supplemental food source, during the rearing process, which will not inhibit the effectiveness of rove beetles to control fungus gnat larvae when released into greenhouses.     

Detection of Rhagoletis indifferens (Dipt., Tephritidae) larvae using brown sugar flotation and hot water methods

The brown sugar flotation and hot water methods are accepted procedures for detecting larval western cherry fruit fly, Rhagoletis indifferens Curran, in sweet cherry [Prunus avium (L.) L.] and could be included in a systems approach, a combination of all steps involved in cherry production, for showing the absence of larvae in fruit. The methods require crushing cherries and then submerging them in brown sugar solution or hot water to extract the larvae. Larvae are visually detected when they float to the surface of the brown sugar solution or sink in the hot water. The objective of this study was to test the efficacy of these two methods. Both methods detected at least one larva in all 288 moderately to heavily infested cherry samples. The brown sugar flotation and hot water methods detected 89.6–94.7% and 83.0–85.9% of total larvae, respectively, from cherry samples on each of three dates. Significantly higher percentages of 1st instars were detected using the brown sugar than hot water method on two dates, of 3rd instars on one date and of total larvae on two dates. Percent detection of 3rd instars was higher than that of 1st instars using both methods. For both methods, greater percentages of split whole cherries with seeds and non‐split cherries had larvae than split whole cherries with no seeds and halved cherries. Results show that both methods were equally efficacious in detecting the presence of R. indifferens larvae in cherry samples, but brown sugar flotation was more efficacious than the hot water method in detecting a higher percentage of total larvae present and could be integrated into a systems approach for R. indifferens.     

Fungus gnats vector Fusarium oxysporum f.sp. radicislycopersici1

Fungus gnat adults transported Fusarium oxysporum f.sp. radicis-lycopersici from Petri dish culture and infected host plants to the roots and hypocotyls of healthy tomato and bean plants. The source of the fungus did not affect the ability of fungus gnats to transport the fungus to healthy hosts. The presence of fungus gnat larvae in media in which young tomato plants were grown did not increase the incidence of plant infection by the pathogen. Fungus gnat adults appear to aid in the dissemination of F. oxysporum f.sp. radicis-lycopersici.     

Steinernema carpocapsae (Rhabditida: Steinernematidae) as a biological control agent against the fungus Gnat Bradysia agrestis (Diptera: Sciaridae) in propagation houses

A recently introduced fungus gnat, Bradysia agrestis, has caused serious problems in Korean propagation houses where vegetable seedlings are produced for transplant into the fields. Although chemical insecticides are available against this pest, alternate control measures are needed. A Korean isolate of the entomopathogenic nematode, Steinernema carpocapsae Pocheon strain, was tested against this insect in the laboratory and propagation house. In the laboratory, S. carpocapsae affected oviposition, with the untreated females laying an average of 121±25 eggs, whereas the treated females averaged 7±2 eggs. The infectivity of S. carpocapsae to the fungus gnat was affected by the developmental stage and temperature, with highest mortality observed with the third and fourth instars and pupal stage. Nematode mortality in the second instar fungus gnat ranged between 23 and 35%, but showed no significant differences among the temperatures tested. The egg and first instar were not infected by the nematode. In nematode dispersal studies, adult female fungus gnats alone dispersed S. carpocapsae from the nematode-treated area to the control area at a higher rate than male and female gnats or male gnats alone. In the propagation house experiments with watermelon seedlings, no significant difference was observed in fungus gnat larval reduction at S. carpocapsae concentrations of 5, 10, or 20 infective juveniles (IJs)/g of soil at 7, 14, and 21 days after treatment. In comparison with the control, the S. carpocapsae treatments significantly reduced B. agrestis larval numbers. When the watermelon seed was treated with S. carpocapsae at sowing, the larval density of B. agrestis was significantly reduced, that is, the number of B. agrestis larvae ranged from four to eight and from five to eight in the nematode-treated plots compared with 26 and 30 in the control plots on the 17th and 34th day post-treatment, respectively. In the chemical insecticide treatments, diflubenzuron and chlorpyrifos were significantly more effective than S. carpocapsae and diazinon in reducing larval populations of the fungus gnat. Our data show that, although some of the chemical insecticides were more effective than S. carpocapsae Pocheon strain, the nematode was still an effective tool for management of the fungus gnat larvae and in protecting seedlings from damage in propagation houses.     

Biotic and abiotic parameters associated with an epizootic of Coelomomyces punctatus in a larval population of the mosquito Anopheles quadrimaculatus.

Biotic and abiotic parameters associated with an epizootic of the fungus Coelomomyces punctatus in larval populations of the mosquito Anopheles quadrimaculatus were investigated for three mosquito breeding seasons (1986-1988) in two adjacent farm ponds in North Carolina. In the first pond, the prevalence of infected larvae averaged 42% (range 0-85%) for collections made weekly from May 1 to November 20, 1986, but larvae did not occur in this pond in 1987. Infection rates in the adjacent pond, sampled during the mosquito breeding seasons of 1987 and 1988, declined from 10.9% (range 0-27.5%) in 1987 to 2.5% (range 0-14.2%) in 1988. Correlation analyses between the number of female copepods and fungal infection rates in sentinel mosquitoes were significant (P < 0.01) for Acanthocyclops robustus but insignificant for eight other species. Infections obtained in sentinel larvae placed in the ponds for 3 hr intervals indicated that C. punctatus infected larvae around sundown. Infection rates for field-collected larvae increased with the stage of larval development. However, experiments with sentinel larvae showed that early instars were more susceptible to infection than later instars, suggesting that the higher infection rates in late instars resulted from individual larvae being infected by two or more zygotes during larval development. Standard multiple regression analyses, used to determine the relationship between seasonal infection rates and water chemistry, weather variables, and the abundance of early and late instar larvae, showed that the abundance of late instars was the only independent variable common to linear models. The models only accounted for 20 and 9% of the variation in larval infection rates for 1987 and 1988, respectively. These results indicate that of the parameters examined, the seasonal abundance of the copepod, A. robustus, was the most important factor (or variable) correlated with the prevalence of mosquito infection.     

Activity of an essential oil derived from Chenopodium ambrosioides on greenhouse insect pests

This study involved both greenhouse and laboratory experiments evaluating the effect of an essential oil product (QRD 400) derived from Chenopodium ambrosioides variety nr. Ambrosioides L. (Chenopodiaceae) on greenhouse insect pests that feed on different plant parts: citrus mealybug, Planococcus citri (Risso); longtailed mealybug, Pseudococcus longispinus (Targioni Tozzetti); western flower thrips, Frankliniella occidentalis (Pergande), and fungus gnats (Bradysia spp.). Treatments were applied to coleus, Solenostemon scutellarioides plants; transvaal daisy, Gerbera jamesonii flowers; or growing medium, depending on the insect pest. The essential oil was most effective, based on adult emergence, on both the second and third instars of the fungus gnat Bradysia sp. nr. coprophila when applied as a drench to growing medium. In addition, there was a significant rate response for QRD 400 on fungus gnats. The QRD 400 treatment had the highest percentage of mortality on longtailed mealybug (55%) compared with the other treatments. However, the essential oil was less effective against citrus mealybug (3% mortality) and western flower thrips adults (18-34% mortality) compared with standard insecticides, such as acetamiprid (TriStar) and spinosad (Conserve), which are typically used by greenhouse producers. This lack of efficacy may be associated with volatility and short residual properties of the essential oil or with the essential oil taking longer to kill insect pests. Other insecticides and miticides evaluated, including sesame oil, garlic, paraffinic oil, and Bacillus thuringiensis subsp. israelensis, provided minimal control of the designated insect pests. In addition, adult rove beetle Atheta coriaria Kraatz adults were not effective in controlling the larval instars of fungus gnats when applied at a rate of five adults per container.     

Improvements in Assays for Soil Populations, of Pythium ultimum and Macrophomina phaseolina

The method of Stanghellini and Hancock to enumerate Pythium ultimum Trow, populations in soil was modified by distributing 1 ml dilutions of soil containing the pathogen into 100–120, 2.5 mm diam. Wells made in 2% water agar in 9 × 15 mm Petri dishes. The modified method was more sensitive than the original method m which droplets or soil dilutions are placed on agar, it permitted the use of lower soil dilutions, and was rapidly performed. Sclerotia of Macrophomina phaseolina (Tassi) Goid. (=M. phaseoli [Maubl.] Ashby) were recovered by flotation using 60% sucrose, collected by aspiration onto nylon filters, and surface-sterilized. The viable Sclerotia were enumerated by counting colonies growing on a selective medium. Efficiency of recovery was 95–97% of Sclerotia added to soil. Large numbers of samples could be processed rapidly by this method which utilized readily available materials, and gave higher counts than earlier methods, which involved only sieving or flotation.     

Virus infection decreases the attractiveness of white clover plants for a non-vectoring herbivore

Plant pathogens and insect herbivores are prone to share hosts under natural conditions. Consequently, pathogen-induced changes in the host plant can affect herbivory, and vice versa. Even though plant viruses are ubiquitous in the field, little is known about plant-mediated interactions between viruses and non-vectoring herbivores. We investigated the effects of virus infection on subsequent infestation by a non-vectoring herbivore in a natural genotype of Trifolium repens (white clover). We tested whether infection with White clover mosaic virus (WClMV) alters (1) the effects of fungus gnat feeding on plant growth, (2) the attractiveness of white clover for adult fungus gnat females, and (3) the volatile emission of white clover plants. We observed only marginal effects of WClMV infection on the interaction between fungus gnat larvae and white clover. However, adult fungus gnat females clearly preferred non-infected over WClMV-infected plants. Non-infected and virus-infected plants could easily be discriminated based on their volatile blends, suggesting that the preference of fungus gnats for non-infected plants may be mediated by virus-induced changes in volatile emissions. The compound β-caryophyllene was exclusively detected in the headspace of virus-infected plants and may hence be particularly important for the preference of fungus gnat females. Our results demonstrate that WClMV infection can decrease the attractiveness of white clover plants for fungus gnat females. This suggests that virus infections may contribute to protecting their hosts by decreasing herbivore infestation rates. Consequently, it is conceivable that viruses play a more beneficial role in plant-herbivore interactions than generally thought.     

Greenhouse application of <Emphasis Type="Italic">Steinernema yirgalemense</Emphasis> to control fungus gnats, <Emphasis Type="Italic">Bradysia impatiens</Emphasis>

Bradysia impatiens Johannsen (Diptera: Scaridae) has recently been identified as a pest, in various greenhouse-cultured crops in South Africa. The control potential for different concentrations of a local entomopathogenic nematode (EPN), Steinernema yirgalemense Nguyen, Tesfamariam, Gozel, Gaugler and Adams, on a natural population of B. impatiens was determined in a cucumber greenhouse. Additionally, the effect of potting media on nematode movement to control an artificial population of fungus gnats was tested. Doubling the EPN dosage, from that recommended by a commercial product (5?×?10⁵ IJs m^?2), reduced the fungus gnats significantly after 21 days. The three different types of potting media, consisting of pine sawdust, coco coir, and a mixture of both coir bale and vermiculite, all had a positive effect on the movement of S. yirgalemense. A significant mortality was achieved for the introduced fungus gnat larvae.     

Studies on the biology of Chaoborus flavicans (Meigen) (Diptera: Chaoboridae) in a fish-free eutrophic pond,Japan

Population dynamics of Chaoborus flavicans larvae of various instars was studied from November 1986 to December 1987 in a eutrophic, fish-free pond, Japan. First and 2nd instar larvae were observed from late April to late October, indicating a reproductive period of about half a year. C. flavicans overwintered in the 4th instar larvae. In water column samples, total density of all instars was 680–23680 m^-2, and pupal density 0–2600 m^-2; larvae of the 1st, 2nd, and 3rd instars showed 5–6 density peaks in 1987, suggesting that 5–6 generations occur during a year (peaks of the 4th instar larvae were not clear, probably due to their longer development than those of younger instars). In sediment samples, no 1st and 2nd instar larvae were found, 3rd instar larvae were found occasionally but density of the 4th instar larvae was 280–18600 m^-2, and pupal density varied between 0–502 m^-2. Fouth instar larvae accumulated in sediment in the cold season and in the water column in the warm season; high temperature and low oxygen concentration were the most important factors limiting the distribution of larvae in the sediment in summer in the NIES pond. The dry weight of total C. flavicans larvae was 0.08–4.2 g m^-2 in sediment samples and 24–599 μg l^-1 (0.10–2.40 g m^-2) in water column samples. Comparisons of maximum densities in the NIES pond in different years and in waters of different trophic status show that density is generally higher in eutrophic than in oligotrophic habitats. This revised version was published online in July 2006 with corrections to the Cover Date.     

Prey attraction by luminous larvae of the fungus gnat Orfelia fultoni

Abstract. 1. Bioluminescence in predacious larvae of the fungus gnat Orfelia filtoni attracts potential prey.
2. Transparent traps placed over larvae caught more arthropods than opaque traps put over neighbouring conspecifics.
3. Small Diptera are particularly vulnerable to light lures, while apterous soil arthropods are seemingly unaffected.     

Development and reproduction of Stratiolaelaps scimitus (Acari: Laelapidae) with fungus gnat larvae (Diptera: Sciaridae), potworms (Oligochaeta: Enchytraeidae) or Sancassania aff. sphaerogaster (Acari: Acaridae) as the sole food source

Stratiolaelaps ( = Hypoaspis) miles (Berlese) (Acari: Mesostigmata: Laelapidae) is a polyphagous soil-dwelling predatory mite that is widely marketed for use in greenhouse production systems to manage populations of dark-winged fungus gnats, Bradysia spp. (Diptera: Sciaridae) and for supplemental control of thrips. The suggestion by Walter and Campbell (2003, Biol. Control 26: 253–269) that North American commercial cultures of S. miles may actually be S. scimitus was confirmed. The development and reproduction at 21–23 °C of S. scimitus provided ad libidum with one of three different prey – the fungus gnat Bradysia aff. coprophila (Lintner), potworms (Enchytraeidae), or Sancassania aff. sphaerogaster (Zachvatkin, 1937) (Acari: Astigmata: Acaridae) – were compared. Developmental duration of the egg and non-feeding larval stages were 2.47 and 1.11 days, respectively; mortalities were 8.3 and 5.5%. Stratiolaelaps scimitus failed to develop beyond the protonymphal stage when provided with S. aff. sphaerogaster alone, although some feeding was observed. Development and reproduction of S. scimitus was successful on both fungus gnat larvae and enchytraeids, with no influence of prey on protonymphal duration (4.70 days) and mortality (8.3%), or on deutonymphal duration (4.61 days) and mortality (6.1%). Adult female S. scimitus feeding on potworms, compared to those feeding on fungus gnat larvae, had a significantly shorter pre-oviposition period (2.69 vs. 4.59 days). However, diet did not influence other adult female developmental or reproductive characteristics (oviposition period, 18.6 days; post-oviposition period, 6.2 days; total adult longevity, 27.3 days; total number of eggs, 26.5). S. scimitus reared on potworms tended (p = 0.06) to have a higher intrinsic rate of increase, a higher finite rate of increase and a shorter doubling time (r _m = 0.142 day⁻¹, λ = 1.153, Dt = 4.85 days) than those reared on fungus gnat larvae (r _m = 0.105 day⁻¹, λ = 1.110, Dt = 6.58 days), but differences in net reproductive rate (R ₀) and generation time (G) were not significant.     

Interactions between Nosema pyrausta (Microsporidia: Nosematidae) and Bacillus thuringiensis subsp. kurstaki in the European corn borer (Lepidoptera: Pyralidae).

Larval susceptibility to Bacillus thuringiensis was determined for Nosema pyrausta-infected and uninfected European corn borers, Ostrinia nubilalis (Hübner), in bioassays using a commercial formulation of B. thuringiensis subsp. kurstaki, Dipel ES, incorporated into diet. LC50 values for N. pyrausta-infected larvae were significantly lower (P<0.0001) than for uninfected larvae and declined with increasing levels of infection. LC50 values for a 15-d bioassay using field-colony first instars were 0.006 and 0.027 mg of Dipel ES/kg of diet for larvae moderately infected by N. pyrausta and uninfected larvae, respectively. Nosema pyrausta-infected larvae reared on Dipel ES-amended diets produced 70-fold fewer spores (P<0.0001) than larvae reared on standard diet. For example, 15 d after placement as first instars on standard diet, infected field-colony larvae produced 7.6-8.7 million N. pyrausta spores per larva; similar larvae placed on diet containing 0.09 mg of Dipel ES/kg of diet produced 85-103 thousand spores per larva. Infected larvae also weighed less and failed to mature on Dipel ES-amended diets. Increased susceptibility of N. pyrausta-infected larvae to Dipel ES and reduced N. pyrausta spore production in larvae feeding on diet containing Dipel ES suggest that Bt corn will have a direct adverse effect on the survival and continual impact of N, pyrausta as a regulating factor on European corn borer populations.