Mar 22, 2020

Agapostemon is a bee which belongs to the Halictidae family. The name means “which loves stamen”; stamen being the parts that produce pollen. Their brassy green color has them named “metallic green bees”. There are more green bees in the Halictidae family like the Augochorini, which are covered in a different article.

Agapostemon are only found in the Americas with approximatively 45 species, among which several species are distributed in the Caribbean Islands. The USA and Canada count 14 species. Most of the species are either on the West or on the East, the only exception being A. texanus which can stretch all across the USA.

All Agapostemon are generalist with no particular floral preference, however they will be found preferably on the plants in the sunflower family. This is where I can see them and all pictures show these bess on either wild or cultivated sunflowers.

All species nest in the ground and as they are not social bees, they tend to dig in isolation making their nest difficult to find. This being said, a few species will nest in commune, sharing an entrance but each digging her own tunnel. It is believed to be an opportunistic decision depending whether some other females are nearby. The nest can be built on vertical banks or on flat grounds. Often the nest is surrounded by a Tumulus, see picture below. The tunnel will be vertical on flat grounds or angle in a downslope from a cliff and will bifurcate with each branch ending on a single cell.

Most female are completely green, but a few species, like the female Agapostemon virescens has a green Thorax and a striped abdomen.

Agapostemon distribution is considered low in Mississippi, I believe this is the result of a lack of survey much more than the absence of the insect. It is fairly common in Hudsonville.

The Pennie Hive

Mar 16, 2020

The Pennie hive is a top bar hive made of two half barrels: an inside red cedar chamber floating on a layer of insulation contained in an outer white cypress shell. It is covered with a heavy insulated roof and is supported by a stand at chest level.

The inner chamber is made of a half cylinder 70 cm long for a diameter of 30 cm, which is equivalent to a volume of 25 liters, topped with a straight volume of 10 liters for a total of 35 liters for the whole inner chamber. As usual I tend to build on the lower volume of the natural size which averages 40 liters. I want to make sure the bees are induced to swarm every year thanks to the restricted volume. The swarming is a natural protection to fight proliferation of the varroa mites. My note book describes the dimensions in more details, in particular the half barrel is made of 6 planks 8 cm large cut at 15 degrees angle on both sides.

The inner chamber fits well in the outer shell and the volume in between is filled with home insulation. This insulation is light, cheap (left overs) and efficient.

Once the layer of insulation is in place, wedges will secure the inner chamber within the outer shell.

The top bars are cut in red cedar with a central groove which will hold a wedge coated with bees wax. The bars need to join each other precisely as a continuous roof for the bees. I place a divider board for the first year. I usually leave the divider as the last bar within the hive at the end of the season adding insulation in the back.

The roof sits on top of the bars as shown on the picture, it is also insulated and covered with reclaimed fencing boards. These two pictures do not describe the final version of the roof which proved not to be waterproof. I added at a later stage two full boards of weathered wood, which can be seen on the first picture of the article. The roof is actually heavier than the hive itself. The quality of the roof is very important in a top bar hive which has a large top surface to be protected from the weather as it is a horizontal and not a vertical hive. It also is critical to build the roof wide enough so that rain drips far off the body sides.

The hive is then mounted on a stand. It has been placed at the edge of the woods and will get bees as soon as the swarms start and move.

Megachile bees

Mar 16, 2020

The Megachilidae family is made of bees which characteristics are the front wing with two submarginal cells, large  mandibles and most strikingly the abdominal scopae (collecting hairs) for the female. Hence, unlike other bees, the pollen is not transported along the hind legs but under the abdomen as shows the picture. The name Megachile means ‘large Lipped’ and refers to the characteristic mandibles.

The Megachile bees, one genus of the family Megachilidae, are also called Leafcutter bees due to their habit to cut circular pieces of fresh leaves to coat their nests and separate the cells. The genus counts 1503 referenced species in the world with 144 in US and Canada. 44 species in the East of the US. It is a solitary bee, which cavities can be above the ground (dead trees, plant stems, rock cavities, mud dauber wasps nests), or underground like the Osmia for example. However for their propensity to nest in wood, they are easily transported and can exist in areas where bees are otherwise few and far between. These bees have benefitted from globalization, but also from the trade routes of the last 300 years, among which the slaves trade. Megachile concina for example is thought to have been brought to the United States from the West Indies sometimes after world war II, and may have been brought to the West Indies from Africa sometime in the 1800’s. Also see the article on Megachile sculpturalis (Giant Resin Bee) and how it invaded the USA in the 1990’s.

The sharp mandibles allow the females to cut leaves or petals starting from the edge progressing inward. The females will overlap oval shaped cut leaves to construct cylinders within the nest cavity and will obliterate the cigar with a circular shaped piece of leaf once the nest has been provisioned with pollen and nectar. An analysis run in 2016 on 3 megachile species identified 54 different plant species used, out of which 48 had some antimicrobial properties.

Leaf cutters usually have one generation per year, at least this is verified in the upper North of the US, it is not clear in Mississippi. Females emerge from the nest, mate with males and will look for a suitable nesting site. Most leaf cutters over winter as prepupae (development stage prior the pupa stage, equivalent to chrysalis stage) and will finish their development the following spring emerging mainly late June and July. This being said I can see some species in early May and some late September. I am not capable to identify most of the species I find. Below picture is a female Megachile from Dordogne in France, found by my parents as I was on vacation. All the other pictures have been taken in Holly Springs, Mississippi.

Females present a broad flattened abdomen with rows of scopae (collecting hairs) on the underside. The mandibles are large to cut the leaves and the wings are usually held outward at 45 degrees to the body when foraging. Males will bear a rounded abdomen with the last segment pointing downward. Many males will show long hairs on their forelegs, which they use to cover the eyes of the female when they mate. Special glands oil the males forelegs that will help the female to determine the male identity and suitability. The picture below shows a female on a Butterly milkweed. Unlike most flowers, milkweeds do not produce loose pollen. Waxy masses of milkweed pollen are grouped into sacs called pollinia. Bees don’t collect pollinia to use as food for their larvae the way they do with the loose pollen of other flowers. A visiting insect trying to reach the nectar offered at the top of the star-shaped corona will slip one of its legs or another appendage inside the anther slits between the hoods. The pollinia inside the stigmatic chamber sticks to the insect’s setae or tarsal claws. By pulling its leg out of the slit, the insect extracts the pollinia and carries them off to another milkweed flower. The flower will be pollinated successfully if the donor pollinia remain in the recipient anther slit. the pollinia is visible on the picture attached at the tip of the hind leg of the bee. It also is visible on the picture that the bee has no pad between the tarsal claws (called ariola), which is a distinctive characteristic of the Megachile.

The picture below shows the strong mandibles of the female.

Here below a male Megachile captured by a Crab spider ambushed in a Heliantus. The downward pointing last segment of the abdomen is noticeable. Males lack collecting hairs under the abdomen. Also the pale light colored hair in between segments is typical. Bees in general are subject to predation by spiders, and noticeably crab spiders, at the end of August and September.

The hair adaptation of the megachille makes them capable pollinators and many species are managed by growers to aid in the pollination of several high value crops. The alfalfa leafcutter bee for example (Megachile rotundata) is essential to seed production for alfalfa in the United States.