27. Dates of Insect Appearance and Activity
TH Sparks and IP Woiwod

Dates of insect appearance and activity in Britain shown in relation to temperature variables.

The average time of appearance of the common footman moth in Britain in relation to mean May-July temperatures in Central England

When the orange tip butterfly was most active (the peak timing) in Britain in relation to mean January-April temperatures in Central England

When the peach-potato aphid was first seen at Rothamsted, Herts, in relation to mean January-February temperatures at Rothamsted

Specific Indicators
Aphids and large moths have been monitored since the 1960s by catching then in suction or light traps throughout Britain within the Rothamsted Insect Survey. Butterflies have been monitored visually throughout Britain since the 1970s by the Institute of Terrestrial Ecology. From these extensive records, three specific indicators were chosen which show how warm temperatures promote the early appearance of insects. They are: (i) the first appearance of aphids at Rothamsted, (ii) the peak flight time of the orange tip butterfly in Britain, and (iii) the average timing of activity of the common footman moth in Britain.
[Source: Rothamsted Research, Rothamsted, Harpenden, Hertfordshire AL5 2JQ; Centre for Ecology & Hydrology, Monks Wood, Abbots Ripton, Huntingdon, Cambridgeshire PE17 2LS]

Relevance
Insect species include pests of agriculture, horticulture and forestry, carriers of human and animal disease and some aesthetically attractive and endangered species. Thus the time when insects first appear or are most active can have many implications. The three variables reported here are the first appearance of the peach-potato aphid (Myzus persicae) in the Rothamsted suction trap (Harpenden, Herts), the peak flight timing of the orange tip butterfly (Anthocharis cardamines) from the ITE Butterfly Monitoring Scheme, and the average (median) timing of the common footman moth (Eilema lurideola) from the Rothamsted Insect Survey light traps. The first of these is a serious pest of crops such as sugar beet, the male orange tip is easily recognisable and both this species and the common footman are widespread in Britain.

Sensitivity to climatic and other factors
The timing of insect activity is very weather dependent. Indeed, butterfly monitoring is only done in warm conditions when butterflies are active. The time to complete insect development to the adult stage is temperature dependent and can often be equated to day-degrees.
All three of the species selected show high sensitivity to temperatures. The timing of the first appearance of the peach-potato aphid is strongly negatively correlated with mean January-February temperatures taken from the Rothamsted meteorological station. The peak timing of the orange tip butterfly is similarly negatively related to mean January-April temperatures in Central England and the common footman moth is negatively related to mean May-July temperatures in Central England. That is, for all three species, warmer temperatures result in earlier flight times.

Change over time
There is some suggestion that the appearance and activity of species have been getting earlier in response to an upward trend in temperature. However, more prominent is the pattern of early appearance in warm springs and late emergence in cold springs - for instance the late appearance of the peach-potato aphid and orange tip in 1979 and 1986. The common footman is more dependent on summer temperatures - 1972 and 1976 displaying extremes of lateness and earliness.
 
The relationships with temperature suggest that a 1degree C increase in temperature is associated with a 16-day advancement in the first appearance of peach-potato aphid, a 6-day advance in peak flight time of the orange tip butterfly and an 7-day advancement in the average time of activity of the common footman moth. Thus, in the event of climate warming we would expect all three species to make considerably earlier appearance, particularly the peach-potato aphid.