Population Dynamics of Greenhouse Thrips ( Heliothrips haemorrhoidalis ) on Avocado Under Single and Combined Predator Releases

The greenhouse thrips, Heliothrips haemorrhoidalis (Bouché, 1833), is an important avocado pest in New Zealand, where repeated infestations reduce leaf quality and tree vigour. To assess biological control stability under different predator assemblages, this study evaluated thrips population dynamics and predator survival across two sequential phases using four treatments: lacewings, Mallada basalis (Walker, 1853), only; predatory mites, Amblydromalus limonicus (Garman & McGregor, 1956), only; combined predator releases; and a predator‐free control. After the initial release, thrips abundance declined rapidly in all predator treatments, with the strongest early reduction observed in the lacewing‐only treatment, but populations later rebounded. During the later part of the first phase, the combined treatment maintained lower thrips densities than single‐predator treatments. In the second phase, following predator rerelease, treatment differences became clearer: suppression remained weak in the mite‐only treatment, whereas lacewing‐only and combined treatments produced sustained declines, with the combined treatment providing the most consistent control overall. Predator survival declined over time in all treatments; mite survival was lower under combined release during the second phase, while lacewing survival differed only modestly. Correlation analyses showed strong alignment between single and combined survival trajectories in the first phase but weaker consistency for mites in the second phase. The observed thrips rebound probably reflects egg protection within leaf tissue and density‐dependent defensive secretions that reduced predator foraging efficiency. These findings suggest that repeated or sustained combined releases timed to target vulnerable thrips stages may improve suppression stability.