Hydrogen Peroxide for Insect and Algae Control in a Lettuce Hydroponic Environment

Insects and algae demonstrate adaptability in hydroponic environments. Algae attract flies, Bradysia spp. (Diptera: Sciaridae) and Scatella stagnalis (Diptera: Ephydridae), called fungus gnats and shore fly, respectively. Flies feed on algae, damaging seedlings radicellae, and may transmit pathogens to lettuce plants. Little information on the management of flies and algae is known. A paradox in the face of the expansion of hydroponics. The objective was to evaluate the potential of hydrogen peroxide (H2O2) as an insecticide and algaecide agent. Entomopathogenic fungi were also evaluated as an alternative control to flies. The experiment was conducted in a commercial hydroponic system under a randomized complete block design with 5 treatments and 4 replicates. The treatments, sprayed on the phenolic foam plates, immediately after lettuce seed deposition, were: H2O2, Beauveria bassiana, Metarhizium anisopliae, Spinosyn and water, as control. The quality of the lettuce seedlings (cv. Brida), the presence of flies and algae evolution in the phenolic foam plates were recorded daily. H2O2 and Spinosyn affected lettuce seed germination, but were able to reduce adult flies on the phenolic foam cells. The highest number of larvae was observed with both fungi, and only water, compared to H2O2. No larvae were found in Spinosyn sprayed phenolic foam cells. However, lettuce seedlings from Spinosyn sprayed plates were those with lower fresh weight. H2O2 severely retained algae infestation in phenolic foam cells over a 15-day observation period. The present work demonstrates the potential that H2O2 can play as an insecticidal and algaecide agent in hydroponic environments.

Efficacy of Beauveria bassiana on Colonized Millet Seed as a Biopesticide for the Control of Shore Flies

Shore flies (Scatella stagnalis) have been implicated as an aerial vector of several soilborne plant pathogens of greenhouse crops. A strain of Beauveria bassiana (Bb), isolated from a shore fly cadaver, was evaluated as a biopesticide for the control of shore flies. Bb was grown on autoclaved millet seed for 2 weeks, air-dried at 24°C for 7 days and stored in paper bags. Dried Bb-colonized millet seeds were broadcast on the surface of pots containing potting medium naturally-infested with larvae and pupae or pots infested only with adult flies. Controls consisted of insect-infested pots amended with autoclaved millet seeds. Pots of the same treatment were placed in insect-proof screen cages. At daily intervals for 15 days, adult fly populations were recorded in each cage. In cages initially containing only larvae and pupae, adult fly populations in the control (no Bb) treatment reached a final population of 70 adults on day 15. In contrast only two adult flies were observed in the Bb-treatment. In cages containing only adult shore flies, the entire population was dead within 10 to 12 days in the Bb-treatment. In the absence of Bb, 65% of the initial population of adults was still alive on day 12.

Preliminary Observations on the Early Stages of Scatella stagnalis Fal. (Ephydridae, Diptera)

The insects, Scatella stagnalis, for the present study were collected from the Marine Biological Laboratory at Plymouth at the kind suggestion of Dr. Allen, F.R.S., the Director of the Laboratory, during my short stay there in the summer of 1929. So far as I can see, no work on the early stages of the genus Scatella is available. This led me to put on record the present account of the different pre-imaginal stages of the insect Scatella stagnalis in the following pages. I have described here only those stages that are exhibited in my hurried collection which may not be complete. A study of its complete biology would be of considerable interest; this, however, requires a constant watch of the species at the spot for a fairly long period.