Bionomics of thrips on apples and nectarines

Mass rearing of two known pest thrips species, namely Western Flower Thrips (Frankliniella occidentalis) and Kromnekthrips (Frankliniella schultzei) was achieved during the course of this project.  In future, this will enable researchers to conduct very specific exposure trials with these thrips species.

The causal agents of different types of fruit damage have been ascertained. Nectarine russet damage are caused primarily by F. occidentalis.  Nectarine silvering is caused mainly by F. occidentalis, as well as F. schultzei.  It is still unknown which of the two species is the more damaging.  Dimpling in apples is caused by F. schultzei, while pansy spot in apples is caused by F. occidentalis.

Management strategies were proposed for thrips damage in apples and nectarines.  These should be updated regularly according to export requirements.

Research in future should be focused on Western Flower Thrips as this thrips species is singularly the most detrimental to deciduous fruit of all thrips.  Kromnekthrips, causing dimpling malformation in apples and silvering to nectarines, should also be examined.  Silvering damage to nectarines and possible thrips damage to plums are the two most reported problems concerning this pest and should be researched.

Through long-term monitoring it was established that thrips populations follow the same trend each season.  This appears to be of little significance, since no correlation between damage and thrips numbers was found by any researcher, both locally and in other countries.  F. occidentalis and F. schultzei populations showed different dynamics to total thrips populations. The peaks for these two species differed in different areas.  It appears to be related to climatic conditions rather than crop phenology.

Recommendations for future research.

• Research focus should be on Western Flower Thrips primarily as well as Kromnekthrips.
• A damage prediction model should be developed instead of a population prediction model.
• Apple, nectarine, peach and plum cultivars should be screened for susceptibility to thrips damage.
• Severe damage to plums, attributed to thrips, needs to be researched.