In lieu of an abstract, here is a brief excerpt of the content:

7. Blights and Diseases of Cretaceous Plants Pterosaurs gliding above an expanse of the araucarian forest passed over a bronze swath that cut across the otherwise verdant landscape. Conifers within that reddish-brown patch stood denuded of foliage and their gracious branches had turned hard and brittle. All around the periphery of this stark graveyard of dead trees were diseased ones destined for the same fate, their foliage already turning various shades of yellow and red. A little bark beetle scrambled over the trunk of a still-healthy kauri tree, looking for a place to bore through the bark and construct galleries for her brood. She passed similar beetles that had searched with the same zeal, but were now being suffocated by droplets of resin the tree poured out through their drilling holes. It was the tree’s main line of defense against such attacks. But along with many others, this beetle was finally successful, and every completed mission was marked by scatterings of wood dust under a small entrance hole in the bark. As soon as the female reached the tender plant cells under the bark, she began to eat away at the wood, instinctively constructing long, narrow tunnels punctuated with lateral egg galleries. The wood borings and frass left over from construction were shoved backwards into passages or dumped to the outside through small borings in the bark. At night the air was filled with a cracking sound emanating from the concerted chewing of bark and wood by thousands of such beetles. After finishing a main gallery, the beetle fashioned some lateral egg galleries where a few small white eggs were deposited. While excavating, minute spores of a symbiotic fungus were released from her body. Within a few days, the fungus grew hyphae along the surface of all the tunnels and provided food for the young. Devouring the fungal-riddled wood, the legless larvae grew rapidly, and when their development was nearly finished, they built an enlarged pupal chamber just under the bark. Life appeared safe and secure in those galleries sealed off from the world of outside predators. But other beetles the same shape and size of bark beetles had entered some of the tunnels and ate many of the developing stages there. Those pupae that escaped the marauders changed into soft yellow-brown adults and waited until their exoskeletons hardened before they chewed out of their domiciles. As they left, they carried in cracks and crevices on their bodies the spores of the symbiotic fungus that was so necessary for their development. The fungus infection they left behind in their abandoned homes produced a blue stain in the wood as the disease progressed and gradually spread throughout the tissues of the tree, sealing its fate. Leaves of the infested araucarian first turned yellow, then slowly withered and died until only a lifeless trunk remained. In another part of the forest, a female siricid wood wasp was preparing to implant eggs into the stem of a conifer. She used a saw-like ovipositor to bore through the bark and then deposited about a dozen creamy white eggs in the deep recess, where they would be protected from predators. When laying eggs, spores and fungal fragments stored in compartments at the base of her abdomen were also released. Survival of the larval wood wasps depended on the growth of that symbiont which ironically would eventually destroy the tree. Over the course of the next few months as the succeeding generations of wood wasps spread the disease, large tracts of conifers yellowed, turned brown, and died. Meanwhile along the riverbeds, palms dropped their fruits prematurely . Flowers turned black and fell off the stalks, while their leaves, beginning with lower ones, progressively turned yellow, then brown. Small, colorful leafhoppers feeding on the diseased 64 – CHAPTER SEVEN plants picked up the microscopic agents that were responsible for this viral disease and at subsequent feedings unknowingly distributed them far and wide. These plant diseases were an integrated part of the forest’s life cycle. The Cretaceous was a moldy world, not that much different from the tropical regions today. Fungi parasitized other fungi, and these in turn were parasitized by still others.345 Having lived in the tropics, we know what it is like to find masses of long gray filaments emerging from shoes left in the closet a few days, spots spreading over various parts of your skin, spores clogging your respiratory system, and delicate strands etching the surfaces of microscope...

Share