# The Lacewings Micromus angulatus and Chrysoperla carnea as Predators of the Rhododendron Aphid, Illinoia lambersi, Under Different Temperature Regimes

## TL;DR

This study compares the effectiveness of two lacewing species in controlling a harmful aphid pest on rhododendrons under different temperatures.

## Contribution

The study identifies Micromus angulatus as a promising biological control agent for Illinoia lambersi, especially under cool spring conditions.

## Key findings

- Micromus angulatus larvae and adults effectively reduced aphid numbers across all tested temperatures.
- Female M. angulatus adults were more effective predators than males and maintained consistent predation rates at different temperatures.
- M. angulatus third instar larvae outperformed C. carnea larvae at 15 and 25 °C, and matched them at 20 °C.

## Abstract

The aphid Illinoia lambersi is a key pest of Rhododendron in Northwestern Europe, causing leaf deformation, reduced flowering, and overall loss of plant quality. To support the development of pesticide-reducing strategies, we evaluated the potential of the brown lacewing Micromus angulatus as a biological control agent against this aphid. In laboratory tests, we quantified the predation capacity of M. angulatus larvae and adults at temperatures typical of spring and summer growing conditions (15, 20 and 25 °C), and compared their performance with that of larvae of the widely used green lacewing Chrysoperla carnea. Brown lacewing larvae of the third instar, as well as male and female adults of M. angulatus, consistently reduced aphid numbers across all tested temperatures. At 15 °C, its third-instar larvae performed similarly to those of C. carnea, whereas at 20 °C the green lacewing showed higher predation rates. Predation by female adults of the brown lacewing was similar across all tested temperatures. Female adults of this species were more effective than males. Because M. angulatus is predatory throughout both larval and adult stages, it may provide sustained aphid suppression over longer periods than biological control agents that feed only as larvae, like C. carnea. Our findings highlight the potential of M. angulatus as a biological control agent against I. lambersi, particularly under the cool spring conditions at the start of the rhododendron growing season. Further field validation is needed to confirm laboratory results and assess performance across different rhododendron cultivars.

Illinoia lambersi is a key aphid pest in Rhododendron cultivation in northwestern Europe, where control measures still heavily rely on chemical insecticides. The present laboratory study assessed the predatory potential of the brown lacewing Micromus angulatus on a mix of late instars and adults of I. lambersi across three temperatures (15, 20, and 25 °C) and compared its performance with that of the commonly used green lacewing Chrysoperla carnea sensu lato. Predation rates were measured for third-instar larvae and adults of M. angulatus and for second- and third-instar larvae of C. carnea. Third instars of M. angulatus were highly effective, killing 30–52 aphids per day, with predation significantly increasing at 25 °C. At 15 °C, M. angulatus third instars performed similarly to C. carnea third instars; at 20 °C, C. carnea exhibited higher predation. In all cases, M. angulatus third instars outperformed C. carnea second instars. Female M. angulatus adults maintained steady predation rates (≈30–40 aphids per day) across temperatures, whereas males were less voracious. These findings highlight the potential of M. angulatus as a predator in both its larval and adult stages for integration into IPM programs targeting in particular early-season I. lambersi outbreaks under cool spring conditions. Further field studies are needed to validate laboratory findings and assess the performance of the predator across different Rhododendron cultivars.