Summary
Fertility schedules of Unaspis yanonensis on citrus leaves were investigated from 1962 to 1971 for the first generation and from 1964 to 1971 for the second generation, at the Okitsu Branch of the Fruit Tree Research Station in Shizuoka Prefecture. The fertility curves were commonly characterized by a first major peak and a few subsequent minor peaks, although their shapes differed from year to year. Models estimating these fertility curves of each generation were constructed in relation to the fluctuations in average daily temperature, on the assumption that the curve was composed of two peaks, i.e., bimodal. Estimated curves were well fitted to observed ones.
Overwintering eggs of aphids on citrus trees were studied over two winter seasons from 1976 to 1978. Three aphid species, namely the black citrus aphid Toxoptera citricidus (KIR-KALDY), the green citrus aphid Aphis citricola VAN DER GOOT, and the cotton aphid Aphis
Summary
A mathematical model was constructed describing population dynamics of the arrowhead scale, Unaspis yanonensis Kuwana. The population occurrence patterns simulated by the model from 1971 to 1976 were relatively consistent with the actual findings in the field.
The effects of control tactics for this pest were examined on the basis of the model.
Effective timing of insecticide (petroleum oil and organophosphorous insecticide) application was indicated to be 40 days after the initial appearance of 1st‐instar nymphs in both the 1st and 2nd generations of the host.
The number of overwintering adult females in May of the next year (i.e., the starting point of the next year's population) decreased linearly with the increment in the degree of insecticide coverage. The pest populations were expected to be kept to low densities by petroleum oil sprays alone for the 1st generation when overall, complete coverage was accomplished.
Examination of the effects of two introduced parasitoids, Aphytis yanonensis and Coccobius fulvus, showed that they were able to control the scale population by themselves when more than 70% parasitism was achieved. When petroleum oil was applied to overwintering adults (termed winter petroleum oil) at the degree of coverage of 0.8, host populations were reduced by ca. 60% parasitism. When the winter petroleum oil was combined either with additional petroleum oil 40 days after the initial appearance of 1st‐instar nymphs of the 1st generation or with an organophosphorous insecticide 40 days after the initial appearance of 1st‐instar nymphs of the 2nd generation (degree of coverage=0.8 in each case), 40% parasitism led the reduction of the pest population.
The most desirable control program was considered to be one in which winter petroleum oil was used every year and additional petroleum oil or an organophosphorous insecticide was also used in those years when host density was high.
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