NOTULAE ENTOMOLOGICAE - Helda

s. EKIIOI.M, THE PEA MOTH (l.ASPEYKESIA XIGRICANA STEPH.)
pods of cultivated peas contain sufficient food for 3 — 5 larvae, but because
the young larvae are enemies the number of surviving young decreases rapidly
on the pod before it has been occupied. If, on reaching the pod, the young
larva observes another engaged in boring a tunnel in to the pod, the new arrival
attacks the tunnelling larva so fiercely that it dies.
Though numerous eggs may be laid, not more than one larva is generally
found in a pod. In 1960, 5.3 per cent of the 5.873 pods investigated contained
2 larvae and only O.25 per cent 3 larvae. According to IvANGENBUCH (1941),
11 per cent of the pods contained more than one larva.
Normally the larva consumes one pea seed completely and damages 2—3
neighbouring peas. In rather young or small pods with small seeds, the proportion
of damaged seeds becomes rather high in small pods; in older pods,
which are often attacked in cold summers, such as 1952 and 1962, only 2 seeds
may be injured by the larva.
In pea varieties which form new pods over a fairly long period, e.g. garden
peas, infestation principally takes place in the first and intermediate pods.
At normal July temperatures in southern Finland (17 — 18°) new pods develop
every fourth day. Because tlie time taken for the total Pea Moth population to
develop in to adults may be long, owing to the overwintering place of the
"pod storey" (age of pods)
I'igure 2. Infestation of pods of different ages. The oldest pod.s develop normally
from the tenth leaf-axil of the peas in a uniformly growing crop, and the bulk
of these pods are here considered as belonging to pod storey no. 1. The solid
ine gives the number of the pods in the different pod storeys and the dotted
ine the percentage infestation of the pods of corresponding pod storeys. 1.35'.)
pods were investigated. Variety: Sinikka. The rate of infestation of the pods
increased towards the end of the season, and thus the percentage infestation
increased.