There appears to be widely circulated misinformation in the growing community that ladybirds (Adalia bipunctata) are an effective predator of red spider mite (Tetranychus urticae). While they are a popular beneficial insect, we at Dragonfli would like to set the record straight for control of spider mites!
Here are a few reasons ladybirds should not be used in an attempt to control spider mites;
- Although ladybirds may eat a small number of these pests, they are not their preferred food source. This means ladybirds will not feed on spider mites voraciously and are likely to fly away in search of a more favourable food source.
- The ladybird life cycle, from egg to adult can take several weeks, compared to spider mite populations which can double in less than 3 days and increase tenfold within 10 days. The rapid population increase of spider mite, compared with the slow population increase of ladybirds is a total mismatch, preventing any form of control.
- Ladybirds will not eat enough spider mites. Due to the rapid population increase of spider mite infestations, coupled with the ladybirds lack of interest in spider mite as a food source, pest populations can increase rapidly.
- Ladybirds are sensitive to temperature and day length so may go into hibernation or choose to migrate under certain conditions. This may include growth under lights or in heated greenhouses during the winter.
- Ladybirds are expensive. Compared with specially bred spider mite predators ladybirds are very expensive when considering the ratio of spider mites eaten per predator. Phytoseiulus persimilis for example can consume up to 5 adult spider mites and 20 young or eggs per day!