Native perennial planting alongside vegetable crops is increasing the abundance of beneficial insects and spiders to a level where they are providing comparable pest control to a conventional spray programme.
That’s the view of Vegetables New Zealand research and development manager Daniel Sutton, following monitoring undertaken by the Bioeconomy Science Institute (BSI) which showed the biodiversity block consistently supported higher total invertebrate abundance than a comparable conventional site.
As part of the Vegetables NZ-Onions NZ-A Lighter Touch biodiversity project, BSI undertook weekly monitoring of two sites during spring growth of lettuce crops at the demonstration farm, and at another nearby Pukekohe block which was conventionally managed.
“The BSI data also showed that pest numbers at the two sites were not greatly different, even though there were fewer spray inputs on the lettuce crop at the biodiversity block,” Daniel says.
“What this shows is the integrated pest management (IPM)-driven programme at the biodiversity block, utilising the pest control provided by the abundance of beneficials, achieved comparable results to the conventional spray programme used at the comparison block.” Marketable lettuce crops were harvested from both sites.
BSI entomologist Asha Chhagan, who led the monitoring research, found the biodiversity site consistently supported higher total invertebrate abundance than the conventional site. Natural enemies were more abundant and diverse at the biodiversity site across all monitoring methods.
BSI summer student Parekohai Baker (on left) and BSI scientist Frances MacDonald conducting trial work in the lettuce crop. Credit: BSI
Visual monitoring and sticky traps were used to monitor pest and beneficial species in both blocks, with visual monitoring showing a higher abundance of pest species in the biodiversity crop, and sticky traps indicating more pest species flying around the crop in the conventional block. Overall crop infestation levels were generally low at both sites, and key pest groups (thrips and aphids) did not exceed five individuals per plant during assessments.
In the Demo Farm spring lettuce crop, spiders were the most abundant beneficial present, and there were significantly more pests and natural enemies (predators and parasitoids) than in the conventional block. For part of the monitoring period, the sticky traps recorded natural enemy numbers to be more than 200% above that of the conventional block.
Parasitoids and lacewings were abundant on the sticky traps in both blocks, but spiders, hoverflies and ladybirds were also found in both blocks.
Thrips were the most common pest species in crop monitoring, and the sticky traps, at both the biodiversity and conventional sites.
15 sticky traps, at various distances, were assessed each week at each site. Credit: BSI
Sweep netting of the native plants in the moveable insectaries recorded a variety of pest and natural enemy species including pest species such as aphids, thrips, mirids, mites, and moths, while natural enemies collected included parasitoids, lacewings, and spiders.
Interestingly insect predatory thrips (who feed on the larvae of other thrips species), nabids, the spider mite ladybug and predatory mite (Anystis), were also found.
A key objective of the BSI monitoring was to identify beneficial insects and mites in the native plantings and understand how far they would move into an adjacent spring lettuce crop and then compare these observations with a conventionally managed crop without biodiversity planting.
Unfortunately, an accidental herbicide application at the biodiversity block, while many of the native plantings were flowering, resulted in loss of many of the permanent perennial plants, negatively impacting the spatial research on how far the beneficials and natural enemies would move from these plantings into the crop.
A mobile insectary used as a part of the lettuce crop biodiversity block. Credit: BSI.
In addition to the permanent perennial planting, other biodiversity planting components such as annual flower strips, cover crops and mobile insectaries are integrated into the farm system at the biodiversity block and have the potential to also enhance in-crop invertebrate diversity.
The perennial planting is gradually recovering and if possible, a second season of trials, during the spring of 2026 will investigate this spatial aspect to further build understanding of the impact of biodiverse plantings on vegetable crops.
Find more information and grower resources from the Biodiverse planting on vegetable farms project at the project webpage on the ALT website.
