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Foster and Kreitzman - Seasons of Life - The life cycle of the Winter moth
Identifier
014193
Type of Spiritual Experience
Background
So how do the eggs know when to hatch – how do they know when the tree is due to burst its buds? How does the pupae know it is November and time to emerge?
System – and interacting systems.
The diagram below has been drawn from the rather approximate evidence of the research so far [and this is not criticising the research]. We know that there is a complex web of interaction between the systems in which temperature [air systems], the tree system, the winter moth system and the great tit system all interact. The key finding here is that this is NOT MECHANICAL. All this is the interaction of ‘software processes’ to use the analogy.
A description of the experience
Seasons of Life – Russell G Foster and Leon Kreitzman
The winter moth is a pest in northern Europe and increasingly so in North America. As a green caterpillar, it munches on leaves and buds and is particularly fond of apple and cherry, but more or less any deciduous tree will do, and it is quite partial to oak leaves.
The moth itself usually emerges from the soil in late November and can be active into January. The male moths have four wings but the female is wingless and cannot fly. She gets her mate by emitting a pheromone that often attracts clouds of male moths. After mating, the female crawls up a tree and deposits an egg cluster on tree trunks, on branches, in bark crevices and under bark scales. The adult moth then dies and the eggs overwinter.
Eggs hatch in spring, just before bud burst and leaf opening of most of the host plants. The caterpillars feed voraciously for 4 to 8 weeks and then spin a thread to lower themselves to the woodland floor, where they pupate in the litter. They stay in the soil in the pupal stage until they emerge in late November as adult moths.
Visser knows from records collected by his predecessor that the caterpillar must hatch at almost precisely the time of bud burst. If it hatches more than about 5 days early it may starve. More than 2 weeks too late and it will also starve, because oak leaves become infused with inedible tannin. Either circumstance leads to a lower weight at pupation or to a longer larval period, resulting in a higher probability of being eaten. There is also an increased risk of falling victim to a parasitic fly...................
Great tits are keenly tuned to the timing of the moth’s life cycle. The great tit is usually a single brood bird and only gets one annual go at breeding, so it has to make the most of it. And there is no better food for fledgling chicks of the great tit than protein rich winter moth caterpillars. Great tits have eight or nine chicks in a brood, and each will eat about 70 caterpillars a day, which is about 90% of their food intake. It takes about 18 days for the eggs of the great tit to incubate and hatch, so to make the most of the caterpillar spurge the timing becomes critical. If moths and birds get the timing right, the caterpillars emerge at just the right time, they can guzzle on the new oak leaves and their population peaks just as the hungry chicks need feeding. If the parent chicks are a bit late, or to put it another way, if the caterpillars are early, then the chicks hatch after the caterpillar biomass has peaked and is on the wane, so the food is less abundant.