Vol. 24 ,No. 2 (1973)
STUDIES O N T H E PUPAL PARASITES O F T H E COMMON CABBAGE BUTTERFLY, PIERIS RAPAE CRUCIVORA
BOISDUVAL AND T H E I R PARASITIC ACTIVITY (II)*
Ryuichi NOGAMI and Hiroshi MATSUZAWA
I n a previous paper in this technical bulletin,
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species of parasitic insects, that is, 4 species of parasitic wasps and 3 species of parasitic flies, were reported by the authors as parasitizing the common cabbage butterfly pupa in Kagawa Prefecture and their parasitic habits and rate of parasitization were briefly presented I n the present report, the results of a survey on the difference in activity of the natural enemies, according to district, carried out in 1971-1972, are presented.Materials and Methods
I n 1971, 3 districts with differing natural environment, Ido, Miki-ch6, Kida-gun (flat country), Nakayama, Nagao-ch6, O k a ~ a - ~ u n (mountain district) and Oishi, Nagao-chb, Okawa-gun (hilly district) were selected as the sites of investigation and common cabbage butterfly pupae were collected in early summer from mid-May to mid-June a t 5-10 days intervals The pupae were brought back to the laboratory, placed separately in glass tubes (2.5 c m x 10 cm), the parasitic insects which later emerged were identified and the rate of parasitization calculated
I n autumn, however, suitable cabbage fields were no longer available in these districts and the SET0 INLAND SEA
HIKAMI* )
*
L
\
TANAKA ?IS1I1 ( ' I\ A
'i
A788Fig 1 Simplified map of the east part of Kagawa Prefecture showing the stations for the research
*
An outline of this study was presented before the 32nd Annual Meeting of The Entomological Society of Japan186 Tech Bull. Fac Agr. Kagawa Univ.
investigation could not be continued so Shionoe, Shionoe-ch6, Kagawa-gun (mountain district) was selected as a supplementary district and pupae collected at intervals of 5--10 days in the period from late September to late October. In 1972, too, no cabbage fields could be found in Ido, Miki-ch6, Kida-gun so the sites were changed to Hikami, Miki-ch6, Kida-gun (flat country), and Tanaka, Miki-ch6, Kida-gun (hilly district) and Oishi and Nakayama district of the previous year for a total of 4 sites. As before, the host pupae were collected at 5-7 days intervals from mid-May to mid-June. The procedure thereafter was carried out in the laboratory as before. The survey sites are presented in the form of a simplified map in Fig 1
Results and Discussion
The rate of parasitism of all the parasitic insects, the rate of parasitism according to species of all the sites and rate of parasitism according to species on each site are presented in Figs. 2-4.
Ephialtes capulifera (B) 01 SH I(B) DISHI(A) C A P t e r omalus puparum
-
i
NAKAYAMA;
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i
30-
I'Iootn,
10-
ID0(I)
DISH1O
1'62;i
13 (MAY) (JUN.) L NAKAYAMA , , & TANAKA O E&ialte/ HIKAMI-
capulifera NAKAYAMA,.--5
$fs"H"FA5
O T a i h i n i d a ~ > . - ~ u ---,--
HIKAMIf
B r a c h y m e ~ i a obscurata (MAY)(JUN.)
Fig 2 Fluctuation of the percent parasitism of each speciesof parasites at each station in early summer
From the results, it can be observed that there was a general trend for the rate of parasitism to be somewhat higher in the mountain district than in the flat country in 1971, as reported by Fuji- moto(l968)but in 1972, this was not the case and the natural enemies were more active and the
Vol.. 24, No. 2 (1973)
Fig 3 Fluctuation of the percent parasitism of all the species of parasites at each station in early summer
188 Tech Bull Fac Agr. Kagawa Univ rate of parasitism higher in the Oishi district close to the flat country, rather than in the mountain district The Oishi district cannot be said to be in the flat country, however, it is a hilly district so that it can be considered in general, that activity of the natural enemies is higher in the moun- tain and hilly districts than in the flat country In the mountain and hilly districts, moreover, Ichneumonid wasps are always present as natural enemies and it can be said that natural enemies are numerous Of the
7
species of natural enemies, Pteromalus puparum and Brachymerza obscurata are especially active and the rate of parasitism tends to be high but close examination of Fig2 reveals that the species and activity of parasitic insects fluctuate quite widely according to the year so a wholly accurate statement cannot be made.
I n recent years, the true natural state cannot be found in Shikoku because of the vigorous engineering enterprises and continuous dusting or spraying of agricultural chemincals and moreover, the agricultural engineering of each individual farmer each year varies widely so that the natural state changes more and more. Therefore, it is believed that the real state must be carefully taken into consideration in this type of investigation.
As stated previously, cabbage was not planted in the flat country in 1971 and data could be obtained only in the mountain district of Shionoe. It can be seen in Fig. 5 that a considerably high rate of parasitization by Complzlura concinnata, which was p o t observed elsewhere, was found in this district while Brachymerza obrcurata, the rate of parasitization of which was high in other districts, was absent here. This observation is limited to 1971 and data is still too small to con- sider this a district-characteristic.
Pteromalus pupar urn
b
,
Ephialtes capulifer aFig..
(SEP.) (OCT.) (SEP.) (OCT.)
5. Fluctuation of the percent parasitism of each species of parasites (right)
and that of three species of parasites (left) a t Shionoe station in autumn.
Finally, here is a question of the species of parasitic wasp and the rate of parasitization of the hibernated pupae of the common cabbage butterfly in the winter season I n th present survey, this was investigated only in the Ikenobe district, Miki-ch6, Kida-gun ,in the flat country. Of 51 hibernating individual hosts, a total of 23 parasitized hosts were found for a rate of parasitiza- tion of 45 1
%.
The natural enemy in this case consisted solely of Pteromalu~ puparum. This find-Vol 24, No 2 (1973) 189
ing suggests that Pteromalus puparum is the main parasitic insect in this district and that there are few other parasitic insects here and moreover, they may spend the winter in the body of hosts other than the common cabbage butterfly
To summarize the findings, the activity of the parasitic insects in each district varies somewhat but in general, Pteromalur puparum and Brachymeria obscurata are the most active and are believed to have a considerable influence on the population dynamics of the common cabbage butterfly
Investigations concerning the life-table of the common cabbage butterfly have been published in Japan by Miyashita, It6 and Gotoh (1956) According to the investigation, the factor which most greatly influence reduction in individual number of the common cabbage butterfly is the activity of predators in the egg stage and young instar larva stage plus some unknown factors together with parasitization in the larval stage by Afanteler glomeratur (A detailed study has been made on this species by Matsuzawa, 1958). This is a n important and noteworthy fact since a major part of the eggs laid by the common cabbage butterfly is already lost before pupa- tion At the pupal stage, furthermore, the parasitic natural enemies described here attack the pupa so that the field population of the common cabbage butterfly can only decline. From this meaning, it can be said that the role of the parasitic natural enemy of the common cabbage butterfly pupa is worthy of interest.
Summary
Several districts ranging from the flat country to the mountains in Kagawa Prefecture were selected as the sites of investigation and a survey made of the difference in parasitic activity according to district in 1971 and 1972. The results were as follows:
1) In the early summer season, the species of natural enemies were, in general, more numerous, rate of parasitism higher and parasitic activity greater in the mountain and hilly districts than in the flat country
2) In autumn, too, the parasitic activity of the various natural enemies is considerably great and rate of parasitism relatively high.
3) In the present survey, parasitic insects were found in the hibernating pupa of the common cabbage butterfly in the winter but in the flat country, parasitism was almost wholly by Ptero- malur puparum
4) Parasitism by Comf~zlura concznnata was found only in Shionoe, in the mountain district, in autumn in the present sutdy Other species of Tachinid flies were also occasionally found in the
flat country.
References
(1) Fujimoto, T : On some pupal parasites of the common cabbage butterfly, Pierzr rapae crwzvora in Kagawa Prefecture, Japan, Kagawa Seibutru (Bull Bzol Soc Kagawa), (4), 10-12 (1968), (in Japanese)
(2) Matsuzawa, H : Ecological studies on the Bra- coid wasp, Apanteles glomeratur, Men Fac Agr.
Kagawa Univ (3), 1-125 (I958), (in Japanese) (3)
-
,
Nogami, R : Studies on the pupalparasites of the common cabbage butterfly, Pzerzr- rapae crwzvora Boisduval and their parasitic activity (I), Tech Bull Fac Agr Kagawa Univ 24(2), 177 -183, (1973).
(4) Miyashita, K , It6, Y , Gotoh, A : Study on the fluctuation of egg and larval populations of common cabbage butterfly and the factors aflect- ing it, &7-konty~ (jour Nzppon SOG A M Ent ),
Tech. Bull. Fac. Agr. Kagawa Univ..
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