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ACCEPTABILITY OF LOTUS CORNICULATUS AND LOTUS ULIGINOSUS
AS A FOOD SOURCE FOR NON-PEST BUTTERFLY LARVAE
The potential effects of sown legumes on the wildlife of agricultural
ecosystems is a subject that has received scant attention. In
the United Kingdom sown Lotus is still of negligible agricultural
importance, though wild lotus is a constituent of semi-natural
grasslands where it is an important food source for the larvae
of several butterfly species. As many butterfly species have declined
markedly in recent decades as a result of intensive agriculture,
many are now widely regarded as important 'emblematic' species
and targets for conservation measures in, for example, biodiversity
action plans. However, agricultural cultivars of L. corniculatus
have been reported to be unsuitable food plants for at least one
butterfly species, the Common Blue (Polyommatus icarus)
(Pollard and Yates, 1995). In this research we investigated the
feeding preferences of three butterfly species which use lotus
as food plants, Common Blue, Wood White (Leptidea sinapsis)
and Clouded Yellow (Colias croceus), for native and cultivated
varieties of lotus.
MATERIALS AND METHODS
Plants of Lotus corniculatus (cv. Leo and a local English
wild type), and of L. uliginosus (cv. Maku) were grown
from seed, in 10cm diameter pots, in potting compost. The pots
were held outside, under ambient conditions, until required. Butterfly
species were obtained as early and late instar larvae (late only
for Common Blue) from a commercial supplier, and kept in separate
insect cages in the laboratory until required. While the larvae
were in the cages white clover was provided as the food source.
Entire leaves were excised from each plant and placed singly on
moist filter paper in a 9 cm. petri-dish, together with one larva.
Ten replicates were set up for each of the plant varieties and
each butterfly species. The leaves were chosen so that they were
of a similar size and maturity for each plant species. The dishes
were then sealed and stored at 20(2oC in an incubator with a 16h
light period, for 24h. After 24h the dishes were removed from
the incubator and the leaves removed. The area of leaf eaten by
the larvae was assessed with a grid of mm squares. The fresh weight
of plant material eaten was determined by weighing known areas
of leaf on a microbalance immediately after excision.
RESULTS AND DISCUSSION
For each butterfly species there was a wide variation in the leaf
dry matter intake. The larvae of both Common Blue and Wood White
consumed more of cv. Leo than either wild lotus or cv. Maku, whilst
Clouded Yellow consumed significantly less of cv. Leo than either
wild lotus or cv. Maku, at both stages of larval development (Table
1.).
Table 1. Mean weight (mg/d) and SEM of lotus leaf consumed by
three species of butterfly larvae
wild | cv Leo | cv Maku | |
| Wood White (Late instar) | |||
| Wood White (Early instar) | |||
| Clouded Yellow (Late instar) | |||
| Clouded Yellow (Early instar) | |||
| Common Blue (Late instar) |
An important finding was that carbon assimilation by Clouded Yellow
differed between lotus varieties. Investigation of the excretory
products revealed that for the wild lotus the larvae were able
to assimilate a high proportion (44%) of their carbon intake,
whereas for cv. Maku the proportion assimilated was much lower
(25%). Thus, the larvae were consuming plant material but they
were able to assimilate less of it. This may possibly be related
to the differences in amount of condensed tannins (not measured
in this study). This could be of major consequence for the conservation
of this species if lotus were to become a widely sown forage.
REFERENCES
Pollard E and Yates T J. (1995) Monitoring butterflies for ecology
and conservation. The British butterfly monitoring scheme. Peterborough:
JNCC/ ITE.
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