Emergence Flight Research Articles

ACTIVITY PATTERNS OF PARASITOIDS ON THE SWAINE JACK PINE SAWFLY, NEODIPRION SWAINEI (HYMENOPTERA: DIPRIONIDAE), AND PARASITOID IMPACT ON THE HOST

AbstractField studies enabled the identification of some limiting factors to which parasitoids were exposed in exploiting the sawfly host, Neodiprion swainei Middleton, and aspects of their quantitative and qualitative impact on the host population. Emergence patterns and flight activity of parasitoids in the spring indicated that larval parasitoids were vulnerable to hyperparasitism by cocoon parasitoids. Although cocoon parasitoids were limited by a shortage of time in which to exploit the host in the spring they still reduced the overwintered host population by 66% in 1969. All forms of predation caused less than 10% sawfly mortality so parasitoids formed the major mortality factor in the spring. Sawfly in prolonged diapause appeared to be immune from cocoon parasitoid attack and thereby efficiency of these parasitoids was limited. However, cocoon parasitoid activity was selective on sawfly that would normally have emerged early in the season and thus delayed the average development of the host population. The complex food web based on the sawfly host provided a sensitive buffering mechanism to produce a degree of stability in the host–parasitoid interaction. The composition of the parasitoid faunae before and after establishment in N. swainei populations of the introduced Pleolophus basizonus (Gravenhorst) indicates the rapidity with which the parasitoid became influential in the complex.

ACTIVITY RHYTHMS OF LEPIDOPTEROUS DEFOLIATORS: II. HALISIDOTA ARGENTATA PACK. (ARCTIIDAE), AND NEPYTIA PHANTASMARIA STKR. (GEOMETRIDAE)

The 24-hour activity rhythms of a gregarious arctiid (Halisidota argentata Park.) and a geometrid (Nepytia phantasmaria Stkr.) were recorded automatically at different constant temperatures and in naturally varying light and temperatures. Larval activity on foliage, adult emergence, and adult flight were all associated with sunset; eclosion began in the dark hours, but in Nepytia was particularly associated with sunrise. The rhythms were found to be adapted to the different seasonal environments normally experienced by the insects, and activity was influenced by changes in light and temperature. The rhythm of Halisidota larvae, which are active throughout the British Columbia coastal winter as well as in the autumn and spring, undergoes a temperature-related phase reversal, the larvae becoming diurnal in the coldest periods of the winter, though nocturnal in warmer periods. Larval Nepytia are found only in summer; they are generally more active on warm days and have little resistance to cold. The activity of both species of moths is less influenced by low temperatures near sunset than late in the night. The sunrise peak in Nepytia males, which normally fly during autumn nights, is less influenced by low temperatures than the corresponding peak in Halisidota, which fly on summer nights.