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Nipped in the bud!
(Japanese beetles munch rose mallow flowers)
Stage's Pond State Nature Preserve
Pickaway County, Ohio. September 2, 2008
A few of the rose-mallow (Hibiscus moscheutos, family Malvaceae) flowers at Stage's Pond display oddly symmetrical damage to their petals, no doubt inflicted by the Japanese beetle. The day before bloming, rose-mallow flower buds are exerted from the protective calyx. The striking damage pattern is evidentally attributable to a beetle's feeding during this late bud stage, when the petals overlap.
Nipped bud, and partly eaten rose-mallow flower
September 2, 2008, Stage's Pond Stage Nature Preserve, Pickaway County, Ohio.
Rose-mallow and the hibiscus bee
(Hibiscus moscheutos and Ptilothrix bombiformis)
Stage's Pond State Nature Preserve
Pickaway County, Ohio. August, 2008.
Stage's Pond is an isolated pond system formed 17,000 years ago by water that plunged off the edge of the ice sheet covering the landscape. Most of one pond, and all of a second smaller pond, along with approx. 150 acres of wetland, meadow and woods together comprise the Stage's Pond State Nature Preserve. Stage's is a terrific natural area administered by the ODNR's Division of Natural Areas and Preserves. It is approx. 30 miles s. of Columbus, in Pickaway County. Here's an aerial view. The yellow box is where we are.
Stages Pond, aerial view, from Google Maps. The yellow box includes a portion of the rose-mallow population and the nesting site for its principal pollinator, the hibiscus bee (Ptilothrix bombiformis).
Portions of the pond margins and considerable areas adjacent to it are densely occupied by a robust herbaceous perennial marsh plant, common rose-mallow (Hibiscus moscheutos, family Malvaceae).
Shoreline of Stage's Pond (3-picture panorama) August 4, 2008.
Typically, each rose-mallow flower blooms for one day. The plant below shows one perky-looking current flower, and a drooping other one that bloomed the preceeding day.
Common rose-mallow, Stage's Pond State Nature Preserve,
Pickaway County, Ohio, August 14, 2008.
At Stage's Pond, rose mallow flowers occur in an intriguing variety of colors (uniform within each plant but differing among plants). They can be white or pink (of various intensity), and either with or without a red center.
Rose-mallow flowers, showing variability at Stages Pond, August 18, 2008.
The principal rose-mallow pollinator is the "hibiscus bee," Ptilothrix bombiformis (family Anthophoridae), shown below in the process of gathering pollen to provision her nest. Pollen is combed off the anthers and carried on a ridge of long hairs along each hind leg that is termed the "scopa." The scopa (scopae?) seen here are so full of pollen they resemble bulging saddlebags.
Ptilothrix bombiformis gathering pollen (and depositing some as well).
August 14, 2008. Stage's Pond, Pickaway County, Ohio.
Here'a a fuzzy little YouTube video of Ptilothrix foraging on a hibiscus flower for nectar and pollen.
Ptilothrix is a solitary, i.e., non-social, bee. As such, there is no division into reproductive queen/sterile worker castes as occurs in honeybees and bumblebees. Instead, all the females are presumably reproductive. Their nests are placed in hard-packed soil in open areas situated fairly close to both rose mallows and open water. Here at Stage's Pond the bees have chosen to nest in a path through a meadow located approximately 200 feet from the rose-mallow plants, and 500 feet from the pond. There are probably a couple hundred burrows total, aggregated in a few spots along a roughly 100-foot stretch of the path.
Aerial view of Ptilothrix nest site, the rose-mallow marsh, and the open water of Stage's Pond.
Ptilothrix nesting area along path through meadow, Stage's Pond, Pickaway County, August 13, 2008.
Ptilothrix nest area. August 20, 2008, Stage's Pond, Pickaway County, Ohio.
In a detailed study of this bee, R.W. Rust (1980) explained that the female constructs tubular soil burrows terminated by urn-shaped cells lined with a soil-wax mixture. Each cell is provisioned with a chickpea-sized ball of pollen grains pasted together with nectar, and a solitary egg. They're shown about life-size in the left-hand portion of the figure below.
Ptilthrix burrow as depicted in Rust, R.W. 1980. The Biology of Ptilothrix bombiformis (Hymenoptera: Anthophoridae). Journal of the Kansas Entomological Society 53:427-436.
Nest construction begins with the bee moistening the hard-packed surface soil with water she slurped up from the pond. First with her mandibles and then, as the hole gets deeper, with her abdomen, she pushes the soil up and out of the hole. She pirhouetes updside-down while she does this.
Ptilothrix initiating nest-burrow construction, August 13, 2008, Stages Pond, Pickaway County, Ohio.
Here's a blurry little YouTube video showing this early stage of nest burrow construction.
Later in construction of the nest burrow, when it is so deep that the soil cannot simply be pushed away, the bee molds the soil into little dirt-bomb pellets that are tossed away by her hind legs.
Ptilothrix in late stages of nest burrow excavatation. She is doing a head-stand in the tunnel. The motion of her hind legs is evident at 1/500 second exposure. The soil pellet, flying away and to the left, is in mid-air.
Here's 2 more instances of soil-tossing, shown as a flash (.swf) slide show. Use the arrow buttons on the little control panel to move it along quickly, like a flip-book.
Here's an indistinct little YouTube video of the soil-tossing.
When the nest burrow is complete, it is time to provision the cell (or cells) within with a pollen/nectar ball as shown in the Rust (1980) illustration above. This takes place in the morning, when the bees, looking like little yellow pom-poms, can be seen arriving with full loads of pollen and, a couple of minutes later, departing to get more. (The afternoon is apparently spent making additional nest burrows.)
Ptilothrix enters nest with pollen. August 13, 2008, Stage's Pond, Pickaway County, Ohio.
Here's a foggy little YouTube video showing Ptilothrix bringing pollen to the nest site.
Nesting bees are apparently cautious about exiting the nest burrow. They linger at its mouth for some time, and quickly duck back down when something large nearby, holding a camera, moves conspicuously.
Ptilothrix at the mouth of her burrow, about to embark on another pollen-gathering mission. Note the yellow pollen grains littering the entrance. August 19, 2008, Stage's Pond, Pickaway County, Ohio.
After completion --when each cell contains an egg and its pollen/nectar provision -- the burrow is filled with loosely packed soil. The species overwinters as larvae. Adults emerge in the spring.
Nest burrows of Ptilothrix loosely filled with soil.
August 19, 2008, Stage's Pond, Pickaway County, Ohio.
Earlier observations (next")