Development of a combined cold storage and methyl bromide fumigation treatment to control the American serpentine leaf miner Liriomyza trifolii (Diptera:Agromyzidae) in imported chrysanthemum cuttings

Abstract

Individual chrysanthemum cuttings and leaves infested with eggs and larvae of the alien leaf miner Liriomyza trifolii, and batches of pupae, were treated in the laboratory to find an effective quarantine treatment to control the pest in imported cuttings. The laboratory tests were based on a statutory quarantine treatment of 2 days' cold storage at 1-2°C followed by methyl bromide fumigation at 15°C with a concentration time product (CTP) of 54 g h/m3, which is used to control Spodoptera littoralis on imported chrysanthemum cuttings. Treatments of 2 days' storage at 1-2°C followed by methyl bromide fumigation at 15°C with a range of CTPs were used to obtain accurate dose-response lines and estimate the LD99 and LD99.9 for each stage of L. trifolii. The largest estimates of the LD99 for eggs, larvae and pupae up to 3 days old were 40.04, 34.49 and 42.64 g h/m3 respectively. These results indicate that the Spodoptera treatment should give high levels of kill of most stages of L. trifolii. However, the LD99 values for pupae more than 3 days old were greater than those for eggs, larvae and young pupae. Therefore if this treatment were adopted as a quarantine measure against L. trifolii, good prophylactic treatments and rigorous pre-packing inspections in exporting countries would need to be maintained, to minimise any risk of importing pupae. It would also be necessary to ensure that the temperature of the imported cuttings was raised uniformly to 15°C after cold storage and prior to fumigation. The practicality of the technique as a commercial treatment will depend on whether it is possible to achieve this without causing unacceptable phytotoxicity.

Experience of polyphagous alien pests of protected crops in Great Britain1

“…As an example, research on L. trifolii led to the development of in-transit treatments to eradicate this pest from chrysanthemum cuttings before introduction into rooting areas. Mortimer & Powell (1984) proved that a methyl bromide fumigation at 15°C with a CTP of 54 g h m-3 was effective and could be used practically without undue phytotoxiciry. Biological studies proved that natural overwintering in Britain by L. trifolii was highly unlikely (Miller & Isger, P .…”

Control options for eradication campaigns against quarantine pests: what now?1

“…As UK growers were dependent on a limited number of suppliers, this had a severe impact on the industry and prompted investigation of further phytosanitary disinfestation treatments. A pretransit treatment combining cold storage and methyl bromide fumigation was developed by Mortimer & Powell (1984), which was later adopted as an internationally recognized fumigation standard (OEPP/EPPO, 1984a) and became a requirement under UK phytosanitary legislation (Anonymous, 1987). This phytosanitary treatment was subsequently used against Lirioniyzn huidobrensis, when outbreaks first occurred in the UK from 1989.…”

Factors affecting the efficacy of methyl bromide fumigation to control Liriomyza trifolii in imported chrysanthemum cuttings

“…A quarantine treatment of 2 days' cold storage at 1-2°C followed by methyl bromide fumigation at 15°C with a concentration time product (CTP) of 54g h/m3 gave almost complete kill of most stages of L. trifolii in chrysanthemum cuttings cv. Yellow Snowdon (Mortimer & Powell, 1984). The first objective of the present investigation was to ensure that this treatment also controls L. trifolii in cultivars of chrysanthemum other than Yellow Snowdon.…”

“…In commercial practice, if fumigation followed cold storage, it would be difficult to raise the temperature of cuttings enclosed within Polythene wrappers inside boxes from the 1 -2°C cold storage temperature uniformly to 15°C prior to fumigation, without an extensive warming-up period. Studies of the methyl bromide LD99s for eggs, larvae and pupae fumigated at 15°C (Mortimer & Powell, 1984) had indicated that there might be some scope for reducing the fumigation temperature while still obtaining a high degree of kill of L. trifolii. Fumigating at the lowest possible temperature should also minimise the phytotoxic effect of the treatment (Powell, 1979).…”

“…Most of our previous laboratory tests used a constant gas concentration of c. 13.5 g/m3 at the cuttings throughout treatment, varying the duration of fumigation to achieve the different CTPs (Mortimer & Powell, 1984). In commercial practice the concentration of methyl bromide which penetrates the packing and reaches the cuttings gradually increases to a maximum of 9 -12 g/m3 during the required 4 h period under gas, and similarly decreases during the subsequent 4 -6 h airing-off period.…”