By Christine Helie

Insects that prey upon other insects are considered beneficial and play an important role in maintaining the health of our landscapes. Supporting populations of beneficial insects or using them to suppress harmful insects is a necessary strategy in any integrated pest management program (IPM).

Since praying mantises are generalist predators, feeding on a variety of insects, we can use them to assist in our natural pest control. When praying mantises are very young they eat small pests such as aphids, leafhoppers, mites, and even small caterpillars that damage leaves and plants. As they grow, praying mantises move on to larger prey such as beetles, wasps, true bugs, or flies.

This year, in an effort to manage several different pest insects, Normand and I released 240 Chinese praying mantises (Tenodera sinensis) on trees throughout the Public Garden, the Boston Common, and on the Commonwealth Avenue Mall.

In January of 2018, I collected several Chinese praying mantis egg cases from a nearby field. Since our goal for the approaching spring and summer was to reduce the populations of smaller pests attacking the trees in the parks, I decided to manipulate the hatching dates of some of these praying mantises and extended their cold period by placing a few egg cases into a refrigerator in mid spring. Delaying their time of emergence enabled us to have tiny mantises, which are best suited for consuming aphids or spider mites, available when we needed them most. This artificial overwintering allowed me to stagger their development and continually release small praying mantises over several weeks.

The addition of praying mantises in the parks has been well received over the past two years. However timing their emergence and growth to coincide with the pest insects we want to control has been challenging. While we appreciate the importance of these beloved predators, there are other beneficial insects that merit our attention. Two natural predators that we should consider releasing in the future are the green lacewings and the brown lacewings. The larvae of each of these insects are predacious. The adult stage of all brown lacewings and green lacewing adults in the genus Chrysopa will also eat insects. Both of these predators are commercially available in species that are already represented in our parks. Most important is that both green lacewings and brown lacewings are little and will pursue the pests we need to control. We are excited about their potential assistance in the ongoing health care of the trees in the three parks.

Areas or Trees in Which Praying Mantises Were Released
June 13, 2018 – Boston Common, B Panel trees; Public Garden, Beacon Street Edge
August 8, 2018 – Boston Common, English Elm En07
August 10, 2018 – Boston Common (near Ballfield), Linden GB
August 13, 2018 – Public Garden, Shadblow 3H2, White Pine, 3F30 Swiss Stone Pine, 3E72 Beech, 3C1 Weeping Beech 2J1; Commonwealth Avenue Mall, Red maple DE6
August 14, 2018 – Boston Common, Linden Jh16, Linden Jh06, Ash Jh02, Slippery elm Jg07, Linden Hb02, Cherry Fa05, Cherry Cf08; Commonwealth Avenue Mall, American elm CD22m
August 23, 2018 – Public Garden, Weeping Beech 1H6