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Sphenoptera
jugoslav/ca Obenb.
(Coleoptera:
Buprestidae)
Table 30
Evaluation of Control Attempts
Centallrea diffllsa Lam. and C. maclllosa Lam. s. lat., 133
contain an average 17 seeds compared with the 9-10 seeds for C. vallesiaca in the Swiss
Rhone Valley. Only one M. paucipunctella larva develops in a head and destroys
approximately four seeds or about one quarter of the production in a head at Westwold.
However, at Westwold, M. paucipunctella does coexist in the same heads with U.
quadrifasciata and there was no significant difference in the number of galls in heads
with and without M. paucipunctella. Certainly U. quadrifasciata is adding to the seed
destruction by M. paucipunctel/a but the moth larvae destroy U. affinis galls in the head.
The biology and host specificity of S. jugoslavica were studied by Zw61fer (1976). The
beetle is indigenous to the Balkans where it is found only on C. diffusa and C. jurineafolia.
The adults feed on the knapweed foliage and do relatively minor damage. The female
oviposits between the bases of tightly appressed rosette leaves, and if rosette growth
occurs during the egg stage, the larva is unable to penetrate into the root crown. Thus the
beetle is restricted to regions with a reliable summer drought during this stage. From the
root crown a single larva bores into the root leaving a cylinder of cortex undamaged. The
rosette continues to live, but in Europe often does not flower in the following year and so
is subject to a second attack by S. jugoslavica. Up to 70% of the larvae in Europe are lost
to parasitoids, predators, and competitors, but they were able to coexist with insects
that feed on the outside of the knapweed roots. The beetle is univoltine and produces
33-65 eggs/female.
S. jugoslavica was released at Grandforks (51 adults) and White Lake, British
Columbia (188 adults) in 1976 (Table 32). No survivors were found at Grandforks, but
the colony at White Lake increased to infest 25-50"10 of the rosettes within a 250 m
radius in 1981, and over half the flowering plants had been attacked (Table 30).
Proportion of diffuse knapweed plants, C. diffusa L., attacked by Sphenoplera at the
White Lake Observatory release site.
Year Distance From Release Site Total·
II 3m 6m 10 m 13 m 26 m 39 m 52 m 65 m
Stem
PlantslO.25 ml X ±S.D. n
1977 .13 (40)··
1978 .38 (52) .29 (17) .07 (41)
1979 .39 (18) .SO (5) .29 (7) .05 (20)
1980 .40 ( 5) .SO (34) .46 (13)
1981 .59 (94)in 23 quadrates 0-250 m
• Ungrazed area only
•• Number of flowering plants
10.11
3.1
.SO (IS) .52 (23) .57 (21) .29 (14) .33 (9) 6.5
4.3
Predictions of the eventual effects of the knapweed gall flies, U. affinis and U. quadri·
fasciata, are conflicting. The immediate effects of the flies on the study sites at Kamloops
have been a decline in seed production from around 25 000 to 1 SOO/m l and a reduction in
the biomass of the weed, but the number of plants per unit area has remained the same.
Obviously any effects of seed destruction would be masked for several years by the seed
bank in the soil which, under dense stands of knapweed, is massive. Survivorship
studies by Roze (1981) indicate that 1 500 seedslm l should be enough to maintain the
7.6
3.5
4.2
1.8
11
IS
8
23