Friday, October 24, 2014

Beneficial Insect Profile - Lacewings

Brown lacewing larva
As the last remaining leaves fall from the trees, I start to think about all the beneficial insects that are seeking shelter under the leaf litter or attached to plant stems for the winter. With leaf blowers dominating the suburban landscape, many gardeners are perhaps not aware that they are eliminating next season's predators and parasitoids when they clean-up their garden in the fall. Eggs, larvae, pupae and adults of beneficial insects are blown or raked up, bagged with the leaves and set out at the curb.

In perennial gardens we don't need to be this fastidious. Leaves, plant debris, and flower stems equal insulation and nesting sites, including nesting sites for cavity-nesting bees and solitary wasps. If you grow apple trees then yes, cleanliness is important so the leaf litter under the trees does not harbor pest populations or fungi such as apple scab.

Green lacewing larva
Lacewings are fascinating insects that belong to the Chyrsopidae and Hemerobiidae families in the insect order Neuroptera. They have been long been recognized for their importance in the control of small or soft-bodied insects such as aphids, thrips, mites, and whiteflies. The larvae of lacewings are voracious predators and have been given several nicknames including 'aphid lions'.

Adult green lacewing feeding
on pollen on Sprengel's sedge
Adult lacewing females lay eggs on the underside of leaves, often where the pest population occurs. Brown lacewings lay their eggs directly onto leaves, green lacewing eggs are suspended from the leaf by long, thread-like stalks. When the larvae hatch, they begin consuming their prey at an impressive rate - up to 400 aphids per week (source: Farming with Native Beneficial Insects).

Adult lacewings feed on pollen and nectar from a variety of plants including forbs and sedges; they also feed on the honeydew created by aphids.

Close up of brown lacewing larva
There are multiple generations of lacewings throughout the growing season in our gardens. The larvae spin cocoons when ready to pupate; these cocoons are attached to leaves or plant stems. Lacewings overwinter in these cocoons; the leaves drop to the ground from perennial foliage in fall and the cocoon remains protected from winter temperatures in the layers of leaf litter. Lacewings can also overwinter as adults and seek shelter under the leaf litter or in another protected site such as behind a loose piece of tree bark. During the growing season, if you have a plant being afflicted by aphids, turn over the leaves and look for lacewing eggs or larvae.

Lacewings are just one of many beneficial insects that need plant debris and leaves left in the garden. Cut down your perennial garden in late spring leaving 12-15" of perennial stem stubble (for cavity-nesting bees). Keep the debris instead of bagging it and use it as a natural mulch (combined with leaves) by laying it on the ground among the emerging perennial plants. The perennials will cover the debris in no time as their new leaves emerge and flower stalks form.


Thursday, May 22, 2014

Ground-Nesting Bee Profile ~ Unequal Cellophane Bee, Colletes inaequalis

The Unequal Cellophane Bee is typically the earliest Colletes species to emerge in the spring in our area. This spring, I found several aggregations of nests on south-facing slopes at a local park.

Females began excavating nests as early as the third week of April (unseasonably cool spring). Other nests not on the exposed slopes were easy to find due to the prairie burn performed the previous fall. Ant nests clustered around the clumps of little bluestem grass, Schizachyrium scoparium in this prairie were dug/sought out by northern flickers in early April. The flickers did not show any interest in the cellophane bee nests.

The cellophane bee nests, besides those in aggregations on the exposed, sandy slope were scattered throughout the flat, open area of the burned portion of the prairie. In late April, on cool days, many females flew low to the ground perhaps searching for new nesting sites or orienting themselves to an existing nest.

Bee flies were active near the bee nesting sites
resting on the ground
Bee flies were also seen near the nesting sites when the nests were being excavated.

During the first week of May when temperatures reached 70 F, there was an increase in nest excavation activity, especially in the sites on the exposed south-facing slopes where soil temperatures were likely warmer.

Cellophane bees secrete a polyester-like substance from their Dufour's gland. This gland secretion is spread over the soil in their brood cells with their tongue. The lining helps protect the larval provisions from bacteria and fungi and because the provisions are liquidy, it helps keep the provisions from leaking out of the brood cell. Unlike many other bee species, instead of the egg being laid on the provisions, these cellophane bees lay the egg suspended above the provisions in the brood cell.

Females were shy and would back
down the nest entrances a few inches but if you waited
long enough, they would come closer to the surface.
Along with the Dufuour's gland secretion, several species of cellophane bees have mandibular gland secretions believed to act as a pheromone to attract a mate, mark food sources and mark male territories. The mandibular gland secretion has a strong citrus odor.

Aggregation of nests on sandy slope
They have one generation per year (univoltine). Males usually emerge first, digging their own exit burrows vertically from their brood cells followed by the females.
Nest Tumulus
When these cellophane bees first emerged there were no plants flowering in the area. Batra (1980) observed these cellophane bees foraging on red maple, Acer rubrum flowers.
Female in Eastern Red Cedar tree
Many females were flying close to or landing on Eastern red cedar, Juniperus virginiana trees, to perhaps warm themselves in the unseasonably cool temperatures but were also observed there a few weeks later after the willows had begun flowering (above). Batra (1980), also observed swarms of these bees around a small pine tree and it was thought that the mandibular gland secretion by the males may have been applied to the pine to attract females for mating.

Willows were the first observed plant that these cellophane bees, both male and female foraged on in the park this spring. Copulation took place while the females foraged on willow flowers.

References:
Batra, S. W. T. (1980). Ecology, behavior, pheromones, parasites and management of the sympatric vernal bees Colletes inaequalis, C. thoracicus and C. validus. Journal of the Kansas Entomological Society, 509-538.