Friday, April 29, 2016

Sexual dimorphism of Centris Bees

 For Arizona, this April morning  (4/26/2016) was rather cool and very windy. At 72 degrees Fahrenheit and gusts up to 40 mi per hour, the only insects flying seemed to be big, strong Centris bees visiting our Foothills Palo Verdes (Parkinsonia microphylla). The big bees were actually flying in wind so strong that it ripped one of our swamp coolers off its foundation.


At around 8 am, and just about 70 degrees Fahrenheit, many Centris Bees were actively collecting among the bright yellow flowers that are just beyond their prime by now. But equally many were still asleep, clinging to twigs with their tarsi, but even more firmly with their strong mandibles.


Most insects are ectotherm, meaning that their body temperature depends completely on environmental factors and fluctuates. They can only regulate it somewhat through their behavior. Birds and mammals produce and regulate their body temperature actively through endogenous mechanisms (shivering, panting, sweating, addipose tissue metabolism), which makes them endotherm (this is not to say that they do not use behavioral means of thermoregulation in addition).


But there are exceptions among insects. Big hairy bees and big active sphingid moths, as well as some big beetles and Robber Flies (my own observation) are able to elevate their body temperature using muscle activity that does not translate into movement or at least locomotion, just like their avian and mammalian counterparts who shiver to get warm.

Birds are highly effective thermoregulators, they can shiver and increase their insulation when it's cold
Birds and mammals maintain high body temperatures almost constantly. Times of  hibernation and nightly torpor phases in some few species are the exceptions.  In contrast,  facultatively endotherm insects are ectotherm most of the time. That saves a lot of energy. They actively increase their body temperature only when needed. Flight is a very demanding way of locomotion, and the flight musculature of most insects is only operational when warm enough. Maintaining this high temperature requires a great energy investment, especially in small organisms with a less than optimal body-mass-to-surface-area ratio. Note that all part-time endotherm insects are comparatively big and hairy, at least as insects go!

Promachus albifacies buzzing its wings to warm up before it can actually fly
 So even those big hairy bugs don't keep their temperature up constantly. B. Heinrich found that bumblebees only fly at cold environmental temperatures when their investment yields a  worthwhile return - meaning that they fly among nectar-rich flowers, but stop, rest and crawl if the available flowers are of minor quality. While the flying bumblebees maintained high body temperatures, body temperature of the crawling ones quickly fell to the level of the environmental temperature. And before they could fly again, they first had to warm up.

Male Centris pallida
So on this cool morning, the palo verde flowers, a little past their prime, were a still worthwhile investment to most of our bees, but not to all of them. And those who were not flying and active were still really cold and unresponsive.

female Centris pallida
There were sleeping females as well as  males, debunking the myth that females always sleep in their nest burrows. They may do so, often, because they often spend the sunset time digging (own observation). So when it gets dark and cold they just stay in the burrows. But they also camp out among the flowers when that's where nightfall catches them.

The sleeping bees do not warm up quickly. While it is usually difficult to get a close look at those constantly hovering Centris Bees, this is an opportunity to study them.

Male on theft, female on the right
Sexual dimorphism is in the details. While both sexes have big green eyes in this species, the area between the eyes is white in males. It looks like the reason is the much larger clypeus. This feature is shared with many bees,  and interestingly some male beetles also have more white in their faces.
The faces of the female bees are more fuzzy and grey.
Another difference: his eyes are bigger and more bulging. Male Centris bees are extremely eager suitors, to the point that they try to dig up their late-born sisters to mate with them. Much of that activity is pheromone driven. But often, the males also relentlessly pursue flying females. Those big bulging eyes - to better see her in three-dimensional space?

Centris bee digging her brood chamber
Only females build nests and collect provisions in form of pollen and flora oils, a specialty of Centris (and Epicharis), so only females show special adaptations for the transport of those substances. Their hind tibiae are covered with long, dark hairs densely covering the hind leg - the scopa. There are also long bristles arranged like a comb on the front legs. I often see Centris Bees hover and use their front legs in grooming motions - probably combing pollen and oils from all over the body and stuffing it into those hind-tibia brushes.  Maybe that comb of setae is also useful to dig in the loose sand?

Scopa of the hind leg and setae brush on the front legs of the female
The hairy tibia of Centris and Epicharis is considered the evolutionary precursor of the corbicula (pollen basket) of the apidae (orchid, honey, carpenter, bumblebees).

Corbicula, a bare concavity into which moist pollen is crammed, on the hind leg of a Honey Bee
 "The corbicula is a glabrous, concave baskets on the hind tibia of Apidae, and represents a key evolutionary innovation, allowing efficient transport of plant resins and large pollen/nectar loads and freeing the corbiculate clade from dependence on oil-offering flowers" (Martins AC et al., 2014)




Here is another look at the male Centris pallida - he does not have those brushes of long hairs on the hind tibiae.

Lastly, he also has no ovipositor and that means no stinger. I have handled individuals of both sexes when they were still too cold to fly and none tried to sting me, but I'm too careful to find out whether that is the rule for Centris Bees. They are certainly not as aggressive as social bees and wasps but the females probably can sting.


Literature quoted: The corbiculate bees arose from New World oil-collecting bees: implications for the origin of pollen baskets. Martins AC, Melo GA, Renner SS,Mol Phylogenet Evol. 2014 Nov;80:88-94. doi: 10.1016/j.ympev.2014.07.003. Epub 2014 Jul 15.

Thursday, April 21, 2016

Deceiving No-see-ums, Pollination of the Pipe Vine

Pipevine Swallowtail (Battus philenor) nectaring on ButtonBush, not Pipe Vine
Our most common desert Swallowtail is called after it's foodplant Aristolochia, the Pipe Vine. It is a A trailing or climbing vine with stems up to 3 feet (0.9 m) long. The 1 inch (2.5 cm) long, arrow-shaped leaves are usually dark brownish-green when growing in full sun.

Southwestern Pipevine Aristolochia watsonii
 The tubular-funnel form flowers are about 1¼ inches (3.8 cm) long, green with brown spotting.Supposedly the flowers reminded earlier botanists of the pipes that Dutch sailors used. As the great grand daughter of a German pipe smoker, I can see the similarity.  By the way, the Swallowtail lays its eggs on the plant, but it does nothing to pollinate the flowers. Pollination is left to much less obvious little insects.

Ear of a packrat left,  pipe vine flower right
It would be much more fitting to call those fluted flowers Mouse Ears. Even a human eye can see a physical similarity. More interestingly, there is a smell that is musty, and, well, similar to the inside of a rodent ear. This is the olfactory stimulus that attracts  flies of the family Ceratopogonidae (Biting Midges)

No-see-um, Ceratopogonidae (Biting Midges)
 They are small, blood sucking insects, some of the no-see-ums that pester humans and other animals on warm, humid summer days and often seek access to the bloodvessels in rodent ears that are especially highly vascularized in desert species (thermoregulation!).
The Pipe Vine grows usually in the shady, humid micro climate under shrubs -ideal micro habitat for the little flies. Drawn by odor and ear-like shape of the flower, and expecting a blood meal, the midges enter.   The shape of the flower and inward-directing hairs in its narrowed throat  trap the flies temporarily, often over night when pollen release is at its peak.. In their attempts to escape the flies dislodge pollen and transfer the pollen they may have already bought with them to the stigma. In the morning the pollinated flower releases the captives. Because the flowers provide super-stimuli, the flies' instinctual reaction is to fall for the same deceit over and over.

The fruit of Southwestern Pipevine Aristolochia watsonii, and Swallowtail caterpillars feeding
 So this is another striking example how plants secure the pollination services of insects. No reward (nectar) is offered in this case.  

Thank you to lepidopterist Fred Heath who reminded me of this interesting story during our recent nature walk in Sabino Canyon. Also see Mark Dimmit https://www.desertmuseum.org/books/nhsd_aristolochiaceae.php

Tuesday, April 19, 2016

Mid April in Picture Rocks

Since my last blog I took a great trip to the Californian Desert over Easter and there will be a write-up about that later. Since then I've been through one of the more difficult times I can remember and the last three days of trying to finish our taxes in time in spite of everything were the most easy and pleasant part.

Desert Iguana,
But now I'm taking a deep breath, of course outside with dogs, looking at flowers, birds and bugs. It's early morning, and big Desert Iguanas are only half out of their burrows, basking and warming up their sluggish bodies. Their favored environmental temps are above those of Spiny, Side-blotched and Zebra-tail lizards.  Over the last 10 years, the numbers of the Iguanas seemed to go up while the others declined.


Ornate Tree Lizards also used to be much more common, but today I find one that is fascinated by a bunch of male Leaf-cutter Bees dancing around  a tree hole where virgin females must be ready to emerge.

Red Tail Hawks and Common Ravens
Right at the border between our land and the State Trust Land, long before we have entered the usual sensitive area around the Red-tail nest, I hear the scream of the Dark Female. Above us rages an aerial battle. Both hawks and three Common Ravens, also residents that have been around for years, are dive bombing and chasing each other high above our heads. I can't tell if the ravens are closer to the camera than the hawks or if they are actually as big or bigger than even the female. At least the male hawk has shown up for this - I rarely get to see him.

Red Tail Hawk Chicks 2016
 By the time we reach the nesting saguaro, Dark Female has shaken the company and is screeching at me by herself, as usual. I have stayed at a save distance from the nest while she was sitting on eggs and small chicks, but now that she is usually up hunting I go close enough to finally get a glimpse. At least 2 chicks, already changing out of their fluffy down stage.


We are very lucky to have these hawks here: they have been using 2 nests in neighboring saguaros at least since 2010. The female is such a rare dark morph that she is easily and individually recognizable. She has raised 2 or three chicks to the fledgling stage every spring. For months afterwards we can even follow the young hawks around while their activity radius grows wider and wider.


I'm heading for some blooming Cat-claw Acacias now but the dogs are getting adamant: they are hot and thirsty and hide in the shade whenever I stop. So soon we had back for the bathtub on our patio.

Aaahhhh!

Monday, March 14, 2016

A Western diamondback rattlesnake in the garage, again



Coming back from Cortaro with a trunk full of veggies and library books, we had to park by the side of the garage because my new car now resides inside, together with my art show van. We carried our haul through the side door. Then Randy went out again to return the cooler to his car, but instead he came to get me with the words 'come, he's back!' No idea who's back, but I'm always curious and we live a lonely life out here.


The rattler in the garage door hadn't just moved in. He obviously came out of the garage to bask in the sunshine in the open door. Of course he did not want to move all the way out, but retreated back in, between all those stored butterfly nets, beating sheets and collecting buckets and what else we store there. Too much stuff! After pushing him back and forth between us, mostly out of sight under the shelves, I finally managed to grab him behind his head with my snake stick and carefully pull him out.


He was released right there again, on the other side of our main entrance under a great Ironwood tree and in the company of a metal quail family that my friend Mary Lee made.


We noticed how docile he was - he never rattled through the whole ordeal and then patiently waited to have his picture taken. I wonder how long he lived in the garage ... we have a pack rat problem there.


We released him also very close to our first blooming hedgehog cactus. Maybe that will make him want to stay outside?


Sunday, March 13, 2016

Birds around the house in early March


The Hooded Oriol was very conspicuous for about three days, chattering and scolding. He discovered a hummingbird feeder on the patio  and still likes our Aloes.

 As usual, he has to share those with the Gila Woodpeckers. They are claiming saguaro cavities and use our old antenna as a sounding board.


Pyrrholoxia male and female are calling after we have not seen them all winter long. I hope they'll stay around. Maybe we should bring out some sunflower seeds.


Ladderback Woodpeckers show up from time to time, they especially still like the old dead peppertree, but I have never seen nesting attempts.


The Gilded Flickers are interested in several existing cavities. It would be nice if they could use one instead of hammering out a new hole. We have so many in our saguaros that some  arms and even center trunks are breaking off. I have sold the boots that develop as scar tissue around the nests to an artist friend, but I prefer healthy saguaros.


Roadrunners are also preparing to nest, we hear their unnh-unnh-unnh calls all morning during breakfast.


I hope the Roadrunners don't catch our patio Desert Magister - we saw her grow up over several years after our dogs and cats wrecked havoc among the population when they were young. That seems to be under control now ...


White-winged Doves just showed up, only to find the invading Eurasian Collared Doves already in residence and on eggs    


Turkey Vultures have been arriving for at least a couple of weeks now, but today the dogs got really upset and chased a pair of Black Vultures through the property. Those are rare here, but until my camera was ready, they had already gained so much height that they hardly show up in the pictures. Too bad, they were circling each other like they were courting.


Good news from the Dark Female: Our resident Red-tailed Hawk is again using one of her saguaro nests, this time the one closer to us. I'll have to check my records, but it seems that she's been raising her broods here now for at least 5 years, if not longer.


The Kestrels are also very territorial around their chosen saguaro, so there are probably eggs in the nest as well.


There is a constant din from the metallic songs of white-crowned and Black-throated Sparrows. They are everywhere, but not very eager to sit for photos. Phainopeplas are better - sitting pretty on top of trees - we did not pull down mistletoe  for a couple of years and those silky guys are happy.

Friday, March 11, 2016

Marbles in Florida Canyon

One day after my birthday we - Randy, the pack and I - hiked up Florida Canyon Trail towards the saddle. A beautiful, if slightly muggy day.


From the highest point, we had great views all the way over downtown Tucson to the Pinal mines and Green Valley.


On the way up I told some birdwatchers to look for Montezuma Quail and when we met them again higher up, they proudly reported that they actually saw some: 'and suddenly two rocks began to move!'


Heading down I let go of  Mecki because he kept getting in my way on the steep trail with loose rocks. He stayed nicely on the trail until he saw the quail too. He is usually no hunter, but this time he ran. I normally trust our dogs to be smart enough to find us again, but this time we had to wait ominously long. We called and whistled and felt rather bad that he was running free and anxious that he was lost, or worse. There were signs posted along the trail warning of a dead horse that might attract predators. We saw neither carcass nor pumas ...
and Mecki eventually turned up behind us on the path, panting and wet. Very tired, too.


There were only some Blue Dicks and a few Sand Verbenas blooming and we saw few insects with exception of very active Carpenter Bees that constantly droned across our path.We did find some interesting butterflies, though, mating pairs of Desert Marbles, Euchloe lotta.

Looking down from the trail into the Santa Rita Research Station I recognized some familiar figures with beating sheets and nets: Charlie and Lois O'Brien and their Canadian guest Robert Anderson were searching for weevils. So our hike concluded with  a nice visit with them and station manager Mark Heitlinger.

Wednesday, March 9, 2016

Insect photography in canine company


Today I hiked the De Anza Trail. Well, I followed in the footsteps of that Spanish explorer for at least a couple of miles. And I had my own army to organize. Because Randy was working on a paper, I took all 4 dogs, even though I still don't trust Mecki and Frodo to be friends or at least peaceful. So in the car, Mecki sits in the passenger seat and the others in back.


Then, to hike, they get organized in pairs- Mecki and Bilbo and Laika and Frodo share leashes. To add to the confusion, Bilbo was bitten by either neighbor dog or Javelina, licked the wound until its size quadrupled and was turned into an inverse cone-head with the help of an Elizabethan collar. That thing swings from side to side with every step, and since he's decided to just ignore its existence,  he bangs it into legs, car doors and dog noses as if he enjoys it.

 The sandy path along the Santa Cruz in Marana used to produce a multitude of natural and planted spring flowers, but in this deceptive el Nino year they are few and far in between. Even sparser  are  the insects that are usually attracted to the flowers. But I anyway brought my camera and the dogs are getting their training in photography-cooperation.



Some metallic Sweat Bees collect pollen from Desert Marigolds, joined by a Buffalo Treehoppers (Ceresa)  


Some nice Anthophora Bees are visiting Parry's Penstemon but they prove very difficult to photograph.

The blooming Brittlebush has nothing to offer except a big hover fly Copestylum apiciferum which probably grew up in a decomposing cactus in the less cultivated parts of this river park.


A tiny beetle is perched on a petal of a surprisingly white desert Primrose. The beetle turns out to be Lytta auriculata, not even half as big as  these beetles usually are. Most likely it grew up as a brood parasite in the nest of a bee that only stored a minimal amount of provisions.   The plant seems to be The Dune Evening Primrose which is out of place here, but as I said, some flowers were obviously put here by well meaning city gardeners and are not quite native to the Sonoran Desert


My dogs quickly learn not only to sit quietly around the wildflower spots but they even begin to determinedly walk towards them. They know that a reward follows every successful photo session.