Results from a project trialling the use of natural enemies against thrips in strawberries confirm that any future biocontrol programmes need to target the early life cycle stage of the pest.
The A Lighter Touch-Strawberry Growers NZ (SGNZ) project focused on the control of thrips, in particular the species Frankliniella intonsa (intonsa), which continues to be a challenging pest to control in strawberries in mid-summer in the Auckland and Waikato regions. Barker’s of Geraldine is also supporting the project, and Bioforce through provision of the biological control agents (BCAs).
The project’s initial work involved a landscape survey undertaken by Bioeconomy Science Institute, Manaaki Whenua Landcare Research group. It found that the weed white clover in vegetation surrounding strawberry fields could be acting as a reservoir for thrips, allowing them to repopulate in crops after control measures were implemented. The survey also found that Frankliniella occidentalis, Western flower thrips (WFT), builds up early in the season in West Auckland on strawberries. This observation led to WFT thrips being included subsequent greenhouse trials.
Thrips (Frankliniella intonsa). Credit: Bioeconomy Science Institute, Plant & Food Research group.
The next stage of the project involved testing the efficacy on strawberries in a greenhouse of three different types of predators or BCAs against intonsa and WFT. Conducted at the Bioeconomy Science Institute (BSI) site in Auckland, the greenhouse trials confirmed two commercially available BCAs, the minute pirate bug (Buchananiella whitei) and predatory mite (Neoseiulus cucumeris) reduced the WFT populations in strawberries. Green lacewing was also trialled against WFT populations, but did not reduce this species of thrips in the covered environment.
Mite and insect predators were also released into populations of intonsa in strawberries, but due to the low populations of intonsa available for the predators to feed on, there was no significant effect on the intonsa.
The trials established that both the mite and insect predators prefer the young instar nymph stage of the thrips life cycle. This highlights that successful thrips BCA-control programmes must be focused on early establishment of predators to maintain low reproductive success of thrips, rather than a focus on predating thrips adults.
Based on the trial results, BSI recommended a combination of Neoseiulus cucumeris and minute pirate bugs for thrips control on strawberries as both are commercially available in New Zealand at relatively low costs.
White clover was found to be the main weed host for both thrips species late in the season. Credit: Landcare Research.
SGNZ’s representative on the project, Molly Shaw, of Berryworld, says strawberry growers were hopeful the project might identify an insect predator of adult thrips, as that would provide an “easy fix” for a thrips IPM programme that is proving challenging to achieve.
“The trials did not find that silver bullet, but what is useful, is they confirmed what industry BCA experts would suspect, that a BCA programme needs to focus on early establishment of the predators because of their feeding preference for the young life cycle stages of the thrips. The minute pirate bug predator will eat the adults, but they consume a lot more of the young.”
Molly says these findings mirror what has been learned through other BCA programmes, such as the A Lighter Touch-Tomatoes New Zealand work where the timing of the introduction of the BCAs into the crop is a key component to their success.
Strawberry Growers NZ is now considering next steps for this work. Thrips are also known to be pests of vegetable crops, therefore knowledge gained through this project has the potential to inform biological control options for these crops.
Read more about the landscape survey on the project page of the ALT website.
