Effective concentrations of garlic distillate (Allium sativum) for the control of Tetranychus urticae (Tetranychidae)

The two-spotted spider mite, Tetranychus urticae Koch, is a worldwide
pest that feeds on a large variety of plant families. Because its resistance
to acaricides is spreading rapidly, the development of new biological
control tactics for population management is crucial. Plant extracts, such
as garlic extract (Allium sativum Linn.), may represent viable alternatives,
because they are currently considered to be minimum-risk pesticides.
Although garlic is known for its acaricidal properties, the extract
concentration that provides the most efficient control has not yet been
precisely determined.
In this study, we conducted a series of laboratory experiments to
determine the susceptibility of adult females to different concentrations
of garlic extract. Fresh garlic cloves were steam-distilled and sprayed
using a Potter spray tower. Mortality and fecundity were measured
upon treatment with garlic extract concentrations ranging from 0.46 to
14.4 mg/l. Female mortality increased with concentration, with LD50
and LD90 values of 7.49 and 13.5 mg/l, respectively. Reduced fecundity
was previously observed at concentrations of 0.36 and 0.74 mg/l.
The chemical composition of the Allium sativum distillate was characterized by reversed-phase high-performance liquid chromatography coupled with photodiode array detection, GC/MS and Fast GC-FID against
an authentic standard (Standard, Bioextract).Vinyl dithiin, diallyl disulphide, diallyl trisulphide and methyl allyl trisulphide were identified
based on their mass spectra. Sesquiterpenoids were identified by their
retention index.