NOTULAE ENTOMOLOGICAE - Helda

s. EKIIOI.M, THE I'EÀ MOTII (I.ASPEYRESIA NIGRICANA STEl'II.) 3
Material and methods
S'nce 1946, experimental peas have been cultivated annually at Dickursby,
where insecticide tests have been carried out yearly by the author. In connexion
with these tests, observations have been made with a view to obtaining
a picture of the life habits of the Pea Moth and the fluctuations in its numbers
during the different years. To determine the gregariousness of this species,
200—500 pods were taken from plots for biological investigations the area
of which varied from 10 to 25 m^. In order to obtain some information about
the fluctuations during the experimental years of 19-^6—1962, and earlier
years (1911 — 1945) too, all reports that were sent to the Department of Peast
Investigation since the early years of this century were collected and are here
referred to figures 4 —5. All the values relating to damage given in this paper
are based on the percentage of pods, and not of peas, damaged. When the
percentage of damaged pods is 30, for instance, the percentage of damaged
peas is about 20, and if 10 the pea damage percentage is only 6 (see diagram 1).
Food plants
In England, infestation of some wild pea species is considerable. Thus
WRIGHT and GEERING (1948) report that 26.5 per cent of the pods of Lathyrns
pratensis and 12.5 per cent of those of Vicia cracca were injured by Pea Moth
larvae.
According to REUTER (1899), Laspeyresia dorsana F. occurs in Finland
on Vicia, Orobus and Lathyrus during the month of July.
Larvae of Laspeyresia spp. have been found by the present author on
Vicia cracca, Lathyrus pratensis and Lathyrus maritimus. The last-mentioned
plant species occurs on the islands of the outer archipelago of the Gulf of
Finland, In 1960, among a collection of 200 pods of Vicia cracca and 200 pods
of Lathyrus pratensis taken outside the investigation area, only 11 and 7 larvae
(5.5 and 3.5 per cent), respectively could be found. In 1961,3 adults of A. nigricana
hatched from the pupae of the larvae in question. In Lathyrus maritimus
from Pellinge (province of Nyland) 11 per cent of the pods were parasitized
by Laspeyresia larvae, but none of the larvae developed into adults, and so
the species is still unknown. In 1962, no infestation took place in the pods of
Lathyrus maritimus, probably owing to the unfavourable weather.
The adult moth and its activity
In southern Finland adults emerge towards the end of June and in the two
first weeks of July. The pea moth is active only at high temperatures. Most
moths of related tortricid species are active at dusk, but the Pea Moth is
rarely on the wing at this time. In sunshine the adult becomes active at a
temperature of 17°. Oviposition mostly takes place during hot periods (over