Monday, March 30, 2015

Parental Care among Arthropods

You may think that insects are not really good at it while many arachnids are better. But, as long as the offspring survives it’s probably just exactly the amount of care that’s necessary. In many cases the short-lived parental generation is not around to see the eggs hatch anyway. So the care may all be in the careful placement of the eggs on exactly the right food plant or in the protective microclimate of a nest or at the best spot to hitch a ride with the best foster parents …. Or the care may involve tackling a scary giant as a host or a smelly pile of dung rolled into appetizing portions … 

Canthon imitator, Rio Rico, Santa Cruz Co, AZ
 Some dung beetles are 'tumble bugs'. Using their shovel-shaped heads a pair cuts a round ball out of a fresh pile of dung. Then they roll their prize a considerable distance from its origin, bury it, and the female lays eggs inside it. In some species, the parents stay around to protect and feed the offspring while the larvae grow in their dung ball. Why don't the beetles just drop eggs into the fresh dung and leave? Some flies do it that way? That's just it: dung of big vertebrates still contains many nutrients in a very accessible form, so the competition is great. Beetles, flies, worms, all claim their share. Large dung beetles develop more slowly than many smaller competitors. Also, dung attracts predators. So these parents grab there share and then set up house as far away from the source as possible.

Oncideres rhodosticta (Mesquite Girdler)
 Many wood-boring insects have to deal with the trees self-defense mechanisms. If the larvae are feeding in living parts of the tree they are likely to be gummed up by an avalanche of sticky tree sap. That is the reason why bark beetles are so dangerous during droughts: the tree does not have enough sap to spare to fight back.
In Arizona, we have several longhorn beetles whose larvae grow up in twigs. They are rather host specific, so one uses oaks, another species specializes on mesquite and close relatives.  To guarantee the safety of the larvae, the female chews a grove around the twig, all the way through the cambium to interrupt sugar and water transporting vessels. Often a big glob of accumulated sap can be seen on the tree-side of the cut. But the apical part of the twig is now wilting and dying and defenseless.  That's where the beetle is placing her eggs and where the larvae will grow up. Several other species of insects that are usually drawn to freshly dead wood also find those dying branches. So if you collect those dead branches in a raising box you will usually find a number of different insects emerging.

Melanophila consputa
Freshly dead wood is at a premium for the larvae of wood-boring beetles. Adults of a number of species can be found at wood cuttings or wind breaks where they mate and deposit their eggs. A special situation are trees killed by forest fires.   Buprestids in the genus Melanophila  have pits on the mesosternum that actually detect fires. The females are so drawn to this wood that they may come too close to the fire and burn off their tarsi (feet) while ovipositing.

Neuroctenus sp. with offspring, Santa Rita Mts.
Many true bugs stay with their brood and take care of them.. I still remember hearing recordings of acoustic communication between stink bug mothers and their offspring at the University of Ljubljana when I visited the physiology department there in 1981. It was a squeaking sound that she seemed to  generate by stridulating her proboscis in its grove. The kids were quite obedient, they dispersed at one signal and clustered under mom at another. My photo shows a bug from a different family, a Flat Bug (Aradidae) with very young nymphs and eggs

Our Uloborus spiders live indoors with us. They are pretty safe from most predators and, I must admit, from my dusting as well. But they multiply! They build starshaped eggsacks that hang in their cribellate webs until they suddenly burst into fluffy cotton balls, releasing dozens of miniature spiders. Mom allows them to live in her web for a while and then they build their own ones close to hers. So eventually I will have to oust them ..

Spiders often guard eggs and hatchlings in their webs. But few wolf spiders have webs to call home and they need to get around to hunt. These ambulant species have a characteristic way of lugging their egg-sack around under their abdomen. When the young hatch they climb on mom's back for a wile. I would love to see the mother catch prey. I assume the kids get to eat then, too.
By the way, wolf spiders have a good reason to be vigilant. Wasp Mantisflies are waiting to get their own eggs into that egg-sac ...

Brood parasites wait for every tasty clutch of eggs and even more so for eggs that come provisioned with food. So many eggs are deposited deep within nests which are hidden and sealed. Here a Leafcutter Bee is choosing the wall paper for her nursery. Her nest is in a pre-existing hole, maybe a hole from which a wood-boring beetle has hatched. She covers the walls with her circular cut-outs and she uses them to separate the tunnel into several cells. Each will hold provisions (pollen) and an egg. Males develop faster, so those eggs are placed closer to the exit than those that will become females. Leaves may provide moisture and insulation, but most importantly they have some antifungal and antiseptic qualities that may protect the pollen and the egg.

Polistes major castaneicolor, Queen with 2 workers
 More sophisticated than most other care systems is that of the social hymenoptera. A queen (or several) starts the nest in spring. After she's raised a few new workers, she's got help and can concentrate on her main role: to lay more eggs. The larvae will be tended by the workers, who are their sisters. These females need not reproduce themselves because they share at least as many genes with these larvae as they would with their own offspring.
In Arizona I have always seen dark brown Polistes major castaneicolor. But in early spring I found some solitary wasps that I could not fit into any of our Polistes species. Now I see one of them on each of the new nests, in this case accompanied by 2 of the 'castanaeicolor' individuals. I'm guessing that those are the first daughters of the young queen and hatched from the two cells in the center that contain no eggs. New cells are added on the periphery, so those are younger. You can see the eggs inside. If only the overwintered queen is banded in yellow and rust, it's no wonder that I thought that ALL P. major castaneicolor are brown.

Tuesday, March 17, 2015

Mating behaviors among bugs

While sorting the slides for my first ever public talk, a presentation about insects in our local forest in Westphalia, Germany, I found that about 75% of my more interesting photos showed insects in some kind of sexual activity. I was 17, my audience mostly older gentlemen from the local zoological society, and I felt somewhat embarrassed. I got over it and the talk was a success. And think about it: Adult insects, stuck in their stiff exoskeleton...s, aren’t exhibiting too many visually impressive behaviors. They eat or get eaten, or try very hard not to, and they mate and lay eggs. But mating may involve calling, scenting, lekking, courtship and pursuit, dancing and rejection, rape, gift giving, copulating, decapitating, mate guarding …. There is plenty to observe and photograph. And even the most flighty Tiger Beetles tend to slow down for a while … 

Lucaina marginata and Lucaina discoidalis, two species of net-winged beetles
 For animals that do not live in social groups, finding an appropriate partner is the most important part of mating. Pheromones released by one partner may stimulate extremely sensitive olfactory organs of the other gender - and matches are made.
When the Mesquite trees are blooming in the Tucson Mountains I sometimes find the catkins of single trees covered in net-wing beetles. They are nearly all mating pairs. They probably attract each other through pheromones. But there are usually beetles of 2 different species present. Pheromones of closely related species can be similar or identical, so there must be an additional process of mate recognition to match up the correct partners. Lycids are loaded with toxins, so these aggregations may not only allow the beetles to find mates but also protect them against predation.

Collops sp., Melyridae (Soft-winged Flower Beetles), Montosa Canyon, October
Antennae of most insects are the site of incredibly sensitive chemoreceptors but in Melyridae (Soft-winged Flower Beetles), the male's antennae carry big, lumpy extensions. You can see them on the right beetle. Those are not receptors, but producers of stimulating chemicals. On this occasion he was waving them at her, stroking her antennae, doing a whole dance of seduction with them, but she still rejected his advances in the end.

Leaf Beetles Deloyala lecontii
Most biologists define a species as a group of genetically similar individuals that can produce viable offspring by mating under natural conditions. Several beetles in Arizona appear in drastically different color morphs. But they are definitely conspecific because they mate and produce offspring indiscriminately of their color morph.   

Trichodes ornatus (Ornate Checkered Beetle)
Trichodes ornatus (Ornate Checkered Beetle) can sport contrasting black bands on bright yellow or deep red elytra.. Yellow/black may be wasp mimicry while the red/black ones closely resemble a species of blister beetles that occurs on the same flowers where the checkered beetles find their mates.  The threesome in the picture shows a female on the right and 2 males on the left, so the color is by no means gender specific.

Approaching a female can be risky for males of aggressive predatory species that are used to taking prey that is hardly smaller than they themselves. Several groups of diptera (flies) have developed ritualized gift-giving which appeases the female. I am not aware that these big Robberflies actually do that, but this male did successfully grab his chance while the female was busy feeding on a Yellow Jacket.

Desert Firetail pair mating in wheel position
Dragons and Damsel males have secondary sexual organs.
Prior to mating, the male moves sperm from his primary genitalia at the end of his abdomen to the middle of his body where he stores it in a secondary genital location. When he finds a female he grabs her neck/head/eyes with his claspers. Tandem position. She then reaches forward to position her cloaca against his secondary genital opening to receive the sperm. Their bodies now form the mating wheel. 

Hetaerina americana (American Rubyspot
After mating the two may stay together in the tandem position while she lays her eggs. This is mate guarding (against other males) but also allows the female to submerse herself to position the eggs under water while the male hovers above to pull he up.

Leaf-cutter Bees
When I saw the bees swarming a fence post at the Arizona Desert Museum I thought at first that I had found the hive of a social species. But they seemed too frenzied for worker bees. They turned out to be male Leaf-cutter bees waiting for females.
Leaf-cutter bees are solitary, but a good nesting site with many deep tunnels (beetle holes) may attract many females. Each lays multiple eggs in those tunnels, eggs that will become females are placed deeper inside, prospective males more towards the tunnel entrance. The males hatch first. Then they hang around the entrance, waiting for the females to hatch. No matter that some will be their sisters. On thing is certain: no female will run this gauntlet and leave a virgin.

Honey Bees, Apis melifera
Among social bees, only the young queens and few lucky drones mate. A young queen mates only once. She takes off with a part of the old hive's workers to start a new hive. There she will produce thousands of eggs from this one mating.
While the bees are swarming and traveling to a new location they often rest in the open, all clustered tightly around the queen. At this stage the crops of the workers are full of stored honey and they lack aggression. The swarm I found was very small, which might indicate that these were Africanized bees, but I could approach closely without problems.
Drones (males) are recognizable by their large size and their big eyes - I have focused in on one in the right photo. Drones do not forage and don't get fed after the mating flight, so at times they can be found dying under the hive. This is no indication that anything is wrong with the hive in general.

Acromyrmex versicolor pair
 Leafcutter Ant colonies release swarms of winged males and females after generous monsoon rains in late summer. Clouds of alates hover like smoke columns over the nest exits. Young Acromyrmex versicolor queens mate with small-headed males in the air and tumble to the ground together. They lose their wings and the males die soon after. The queens are carrying the beginning of a new fungal garden in their crops with them. Several of them may start a new colony together.

 While scouting in preparation for the BugGuide Gathering in 2013, I was caught in a July thunderstorm in Florida Canyon, Pima Co, AZ. Suddenly many insects were flying in the soft warm rain, most of them tumbling to the ground. There they quickly shed their wings and began running around in pairs. Soon predators like ants an birds began picking them up. But many couples escaped to find new underground nesting sites to begin a new huge family of Termites. Different from ants, wasps and bees, they will have a long fertile life as a couple ahead of them. 

Colliuris pensylvanica, carabids, and Anomola delicate, scarabs
 And what do bugs do instead of on-line dating? Black light dating! Always available during the monsoon months in Arizona and highly recommended ....