Ron Wilson

Ron Wilson

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Insect Word of the Week: Diapause - Curtis Young

Anyone who lives in Ohio knows that there are times of the year that can be extremely harsh, cold and devoid of potential food for critters that live outdoors. This is true for the vast majority of insects that live in Ohio. Thus, it is logical to ask, what happens to all of the insects that live in Ohio during the times when conditions are not conducive to living outdoors (i.e., late fall through early spring)? Do they all die and have to be replaced by immigrants the following year? The answer for some species is that they do all die and have to be replaced with new immigrants (e.g., potato leafhoppers, black cutworm moths, fall armyworm moths, and secondary screwworm flies). But for most species, the answer is DIAPAUSE.

Female bagworm (Thyridopteryx ephemeraeformis) pupal case inside of bag constructed by female larva. Photo Credit: Joe Boggs

Female bagworm (Thyridopteryx ephemeraeformis) pupal case inside of bag constructed by female larva cut open to reveal diapausing eggs that will overwinter. Photo Credit: Joe Boggs

Definition: Diapause is defined as a physiological state of arrest in development in response to regular and recurring environmental stimuli that are predictive of impending, adverse environmental conditions.

Chinese praying mantid (Tenodera sinensis) egg mass laid in the fall, filled with diapausing eggs which will overwinter to the following spring before hatching. Photo Credit: Curtis E. Young

These European corn borer (Ostrinia nubilalis) larvae spent the winter as diapausing, fifth instar caterpillars in corn stalk residue in corn fields. Photo Credit: Curtis E. Young

Diapause is a form of animal dormancy that is exhibited by insects and other arthropods. It is similar, but not entirely equivalent to hibernation exhibited in a number of mammals. Diapause allows insects and their relatives to survive through periods of unfavorable, harsh environmental conditions. During these periods of harsh environmental conditions such as the winter months in the northern climates, temperature extremes and/or the lack of available food resources would lead to the death of the insect without diapause.

Cecropia moth (Hyalophora cecropia) cocoon inside of which a cecropia moth pupa spent the winter in diapause. Photo Credit: Curtis E. Young

Boxelder bugs (Boisea trivittata) aggregating on a house foundation preparing to enter a hiding place to diapause as adults in a protected location. Photo Credit: Curtis E. Young

Diapause is typically stimulated and initiated well in advance of the onset of these harsh conditions. In Ohio, the signal to initiate the onset of diapause is photoperiod, the length of night verses the length of day. The stage of the insects life cycle that is sensitive to the photoperiod stimulus is often not the same stage in which diapause occurs (e.g. flesh flies (GenusSarcophaga) are signaled in the larval stage (maggot) and diapause as pupae). Across the insect world, diapause occurs in all stages of the life cycle (eggs, larvae, nymphs, pupae and adults), however in a particular species of insect, diapause only occurs in one stage of its life cycle. For example, in the bagworm,Thyridopteryx ephemeraeformis, diapause always occurs in the egg stage, in the European corn borer,Ostrinia nubilalis, diapause always occurs in the late fifth instar larva, and in the elm leaf beetle,Xanthogaleruca luteola, diapause always occurs in the adult stage.

A mated, bald-faced hornet (Dolichovespula maculata) queen preparing to diapause by herself under the loose bark of a log lying on the ground in a metro park. Phot Credit: Curtis E. Young

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