Research into stable biological control in mother plant cultivation in East Africa

As part of the PPS Future Proof & Biocontrol-based Chrysanthemum Chain program, WUR Greenhouse Horticulture in Bleiswijk and Chrysant NL are working to strengthen biological control in chrysanthemum mother plant cultivation in East Africa. The goal is to determine how natural enemies, such as predatory bugs and predatory mites, can establish themselves sustainably in the crop, says Jasper van Diemen of Glastuinbouw Nederland.

In East Africa, cuttings are harvested from mother plants almost every day. This removes not only plant material but also part of the natural enemy population from the crop. Within the program, the effect of cutting harvest on natural enemy populations is therefore a key focus. Research at WUR Greenhouse Horticulture showed that up to 25% of Orius laevigatus eggs are laid in young plant parts that are later harvested as cuttings. For Orius albidipennis, this share was lower, at a maximum of 12.5%. Clear differences between cultivars were also observed. These appear to be linked to leaf hairiness: the denser the leaf hair, the fewer eggs are laid in harvestable plant parts.

© Glastuinbouw Nederland

Follow-up research on predatory bugs
In Uganda, five native predatory bug species have already been successfully reared. These will be studied further in the coming months. Which species are best able to build a stable population in a mother plant crop subject to daily cutting harvest? And which predatory bugs are most suitable for maintaining a sustainable “standing army” of natural enemies?

Predatory mite populations
Alongside predatory bugs, the research also focuses on the predatory mite Amblyseius swirskii. Earlier trials in Uganda showed that populations could not sustain themselves on alternative food alone. Weekly re-introductions proved necessary, whereas similar strategies in the Netherlands do lead to stable populations. Several possible causes have therefore been investigated, including temperature, fungicide use, and loss of predatory mite eggs during cutting harvest. High temperatures do not appear to be the sole explanation. Egg loss during harvest remained below 10% and therefore does not seem to be a major cause. Initial results suggest that fungicides may influence predatory mite population buildup, but further research is needed.

Prey mites for predatory mite
Another important line of research involves developing affordable, locally produced alternative food for predatory mites. Earlier trials showed that combining Amblyseius swirskii with alternative food leads to higher numbers of predatory mites in the crop. Several prey mite species are therefore being tested on multiple farms, including Carpoglyphus lactis, Tyrophagus entomophagus, and a locally occurring species. Researchers are examining which prey mite most effectively stimulates predatory mite population growth.

The rearing of prey mites is also being further optimized. A Ugandan PhD candidate is studying, in the Netherlands, how the diet of prey mites can improve their production and nutritional value. Initial results are promising: adding proteins and fats significantly boosts prey mite population growth. The effects on nutritional value for Amblyseius swirskii, and the ultimate contribution to predatory mite populations in the crop, are currently being investigated further.

Source: Glastuinbouw Nederland