Caterpillar Control
Tricholine b
Trichogramma brassicae
Trichogramma brassicae
Tricholine b is a proprietary product containing the wasp Trichogramma brassicae Bezdenko, Hymenoptera Trichogrammatidae, a parasitoid of Lepidopteran eggs. The species is considered to be synonymous with Trichogramma maidis Pintureau and Voegele and T. evanescens Westwood.
Wasps are provided as pupae within parasitised eggs of the host Ephestia kuehniella, which are supplied attached to cards for distribution within the crop. Each individual card holds sufficient pupae to produce a minimum of 200 adult wasps, and cards are packed as strips of 5, and each unit will produce a minimum of 10,000 adult Trichogramma brassicae.
The females of Trichogramma spp search out suitable host eggs of Lepidoptera and lay eggs within them. When the eggs hatch, the larvae consume the egg contents and then pupate within the empty egg shell or chorion of the host. Small host eggs will contain a single parasitoid larva, but larger eggs may contain more than one.
Thus a proportion of host eggs produce further parasitoid adults, rather than larvae of the host. Crop damage is therefore reduced, but is rarely eliminated completely. The parasitism rates reported in the literature vary widely, with typical reported rates between 40% and 80%. Exceptionally, higher rates are reported, but in field situations part of this parasitism may be caused by naturally occurring egg parasitoids.
Trichogramma spp are the most widely used biological control agents in the world.
Use Trichogramma in any crop where Lepidopteran pests cause significant damage to foliage, fruit, flowers or stems. Not all species are suitable hosts however, and efficacy will vary depending on the habits of the target species. As an example, some species lay eggs singly, whilst others lay in groups of various sizes, or hide their eggs in crevices. Best results will be obtained when the parasitoid adults find freshly laid host eggs. Old eggs may be unsuitable.
Where several generations of the pest occur within a given crop, make releases as early as possible in the season, when pest populations are low. Releases of parasitoids will produce a more significant reduction in total populations of the target pest at this time. Releases of the same number of parasitoids when pest populations are established will produce a much less significant reduction in damage.
Timing can be critical to success. Larvae, pupae and adults of Lepidoptera are not affected in any way by Trichogramma spp, although generally the presence of adults will indicate that eggs are being laid. Where the pest has a long generation time, or closely synchronised generations, it is important to identify those periods when eggs will be present, and not release parasitoids when only larvae and pupae are present.
Ideally, use some monitoring device to identify the periods when adults are active within the crop. For many moths in outdoor crops, pheromone lures and traps are available for exactly this purpose. In glasshouse crops, pheromones may be less effective for monitoring, but an alternative for nocturnal species is to use ultraviolet traps as an indication of pest presence. Where no monitoring is possible, make prophylactic releases during periods when damage is known to occur in the area, based on previous years experience.
Hang cards onto the crop at regular intervals during the risk period. Make sure that the cards are placed amongst foliage, so that they are not directly exposed to sunlight. Repeat releases throughout the period when eggs of the target pest are expected to be present. Individual parasite adults cannot travel far, so it is important to distribute cards as widely as possible throughout the crop area.
Release rates also vary widely depending on crop, but as a guide, release between 10 and 40/mē per week in glasshouse crops.
Do not use Trichogramma when damage levels are already high: there will be no immediate reduction in damage because larvae are not affected. Some reductions may be seen in later pest generations, but very large numbers would be needed to achieve relatively small reductions. Do not use where published information is available which indicates that the target pest is not a suitable host for Trichogramma brassicae.
Releases of Trichogramma will result in reductions in total damage by Lepidopteran pests. The exact extent of reduction will depend on very many factors, including the target host species, level of initial infestation, timing of release, crop history, and climate.
They will not totally prevent damage, even at high release rates.
Trichogramma spp are sensitive to pyrethroids and many other insecticides.