Bacillis thurigiensis
- A programme of weekly sprays of Bacillus thuringiensis (Bt) throughout the egg hatch period gives fairly good control, though control may not be as good as that achieved with conventional or Insect Growth Regulator insecticides (see below).
- Bt has to be ingested to act and is most effective in warm weather when caterpillars are feeding actively.
- The bacterium produces a crystalline toxin. The insect dies from the effects of this toxin rather than from pathogenesis due to the bacterium.
- Bt is of short persistence as it is degraded by heat and UV light.
- It is most effective against newly hatched larvae before they form leaf rolls in which they feed internally and are inaccessible to sprays.
- The first spray should be applied at the onset of egg hatch which should be determined from pheromone trap catches and egg development sums calculated from the daily maximum and minimum air temperature (see ‘Forecasting’ ).
- Bt is not detected by conventional pesticide residue analysis.
Viruses
- Three baculoviruses of summer fruit tortrix moth have been tested for use in the field in Europe including a nucleopolyhedrovirus (AoNPV) and a granulovirus (AoGV).
- AoNPV can control summer fruit tortrix very effectively and is highly host-specific but the virus is uneconomic to produce and is not available commercially.
- AoGV has a very slow pathogenesis. Newly hatched larvae become infected in the first instar development stage and only die when they reach the final development stage.
- They can live longer than uninfected larvae and larval damage to fruit may not decrease in the short term.
- In the longer term, a high degree of control can be obtained. The virus may persist for several generations.
- A commercial formulation is produced in Switzerland but is not registered for use in the UK.