Physiological and Ecological Studies on the Pine Bark Beetles

ISHIKUBO, Shigeru

The pine bark beetle is a general term for those beetles which penetrate the barkand live in the bast and sap wood, such as Ipidae, Curculionidae, Cerambycidae and soon. But much in this field is left ecologically unexplored, and the students are by nomeans many. The writer studied th typical species from the standpoint of physiologicalecology and arrived at some conclusions concerning the effect of temperature on theactivities of adult and larva, hatching, growth rate during the period of larva, and the development at every stage of population.

1) Thermal reaction was studied after Motomura's rising temperature method(1938). As a result of experiments, it was revealed that, Ipidae can withstand both highand low temperatures, and show great adaptability. Cerambycidae are affected by low temperatures most easily of all kinds of pine bark beetles, but can withstand hightemperatures.In the case of Curculionidae, adult has a wider range of activity than larva, andthis species stands in between the above-mentioned two species in activity.Their activities in the field were also observed. Ipidae are active both in winterand in midsummer, and are distributed throughout the country. Cerambycidae do muchdamage in high summer, and many kinds are of southern origin. Their distribution islimited to Honsyu and southward. Ceramb ycrdaeaie activ eduring the damp season of May and June. Most of this species are of southern origin and primary harmful insects.Those northern origin are few.

2) Relations between the hatching of Ipidae and temperature were studied usingover-saturated salt solutions of ZWOLLEFER. Hatching took place at temperatures rangingfrom 13°C to 33°C, and relative humidity was 90% with Myelophilus piniperda Linnaeus,and more than 70-80% with Cryphalus fulvus Niijima. A considerably high humidity isrequired. It seems that this is because egg are lacking the controlling mechanismagainst physical loss of water, but since in the field they are laid beneath the barkwhere the humidity is high, it is inferred that the hatching rate is considerably high,The length of time necessary for hatching shortens according as the temperaturesrises, but the length of time is not uniform at low temperatures. In the case ofMyelophilus piniperda Linnaeus, the period of egg stage shortens with a fall in humidity, and in the case of Cryphalus fulvus Niijima, the period of egg stage lengthens with a fall in humidity.

3) Individual breeding of pine bark beetles was carried out, and date for determininginstar were obtained by measuring the head width. Growth rate was apploied tovarious formula, and their adaptability was tested, and at the same time individualvariation was discussed.In the case of Myelophilus piniperda L., the growth rate is almost the same inevery instar, and the growth rate is applicable to GAINES and CAMPBELL's formula the best. In the case of Cryptorrhynchus insidiosus Roelofs, there are the 7th and 8thinstar larvae, and in both cases the growth rate applies to GAINES and CAMPBELL'sformula and Tokunaga's formula the best. In the case of Monochamus tesserulla white,the number of moulting is not definite, but the 7th, 8th and 9th instar larvae are found.It seems that this variation is due to the influence of temperature, humidity andnourishment. The growth rate applied to GAINES and CAMPBELL's formula the best inthe　7th and　8th instar larvae. Myelophilus piniperda L. have the least individualvariations, while Monochamuo tesserul White are most varies both in number ofmoulting and growth rate, and Cryptorrhynchus insidiosus Roelofs stands between the two.

4) The development of population of Ipidae was studied using boxes of　fixedtemperature (30°c, 24°c and 16°c). In the case of Myelophilus piniperda Linnaeus, at24°c, larva group appears 5-20　days later, pupa group 25 days later and new adultgroup appears 35 days later, and then flight hole takes place in 40 days. At 16°c, larvagroup appears 15-45　days later, pupa group 55 days later and adult group appears 65days later, but the process is not uniform. In the case of Cryphalus fulvus Niijima, at30°c, larva group appears after the lapse of 5-15 days, and though pupa group is notmarked because of the short period, adult group appear in some 20 days and at thesame time flight hole takes place. Adults live for about 30 days, and eggs are laid for20 days. At 16°c, larva group appears 5-30 days later, pupa group 35-40 days later andat the same time adult group appears sporadically. Flight hole takes place on the 45th day, but few of the new adults fly out because of the low temperature. Adults canlive for about 40 days, and at the same time eggs are laid little by little.

Physiological and Ecological Studies on the Pine Bark Beetles

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