Pesticides have played a significant role in traditional crop protection during the last five decades. Consequently, high yields have been harvested from treated crops. However, man's eagerness for inventing these much needed chemicals has not allowed for ample establishment of risk reduction measures against their possible adverse effects on non-target organisms. This occurred mostly because crop production was given top priority, and partly because of the poor research and development (R&D) resources in the past. After many years of pesticide use, it is now recognized that application of broad spectrum and non-selective pesticides could pose high risks to beneficial organisms, especially among mite and insect species which usually regulate pest population(s) under natural conditions. Selective pesticides will always be needed in sustainable integrated pest management (IPM) for commercial-crop(s) pests. Pesticide testing methods to determine the effects of pesticides on beneficial mite and insect species are gaining priorities in R&D because of their vital importance to crop protection. In this review paper we examine pesticide testing methods and their evaluation and interpretation on beneficial mite and insect species. The limitations and implications of pesticide effects in IPM and their future prospects are also discussed.

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The aedeagal length, body size and number of pecten setae of the peach fruit fly, Bactrocera zonata, in Egypt were measured and compared with the sympatric species, B. dorsalis and B. correcta in Thailand. The body size of B. zonata was intermediate between B. dorsalis and B. correcta, with some overlap at each end. Aedeagal length of B. zonata was also intermediate between B. dorsalis and B. correcta, with no overlap. These results indicate that the 3 sympatric species can be distinguished by measurement of the aedeagal length. Because B. zonata recently invaded Egypt, it was expected that variability of morphological traits of this population would be smaller than what might be found in an indigenous Bactrocera population. However, coefficients of variation (CV) for body size, aedeagal length and number of pecten setae were similar to those for an indigenous population of B. correcta, indicating that the founder B. zonata population in Egypt had already acquired significant variation in these traits despite having passed through a presumed bottleneck situation. It was remarkable that the CV for aedeagal length was less than one half that for other traits, supporting the notion of stabilizing selection.

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Adults of the sweet potato weevil, Cylas formicarius, were allowed to lay eggs on a 150 g tuberous root of sweet potato for 3 days under conditions of 27°C, 60% RH, and 14L:10D. The number of progeny increased with the increase of parental density, and reached the saturation level. The number of progeny per parental female showed a peak at 30–100 pairs of parents. The density response mode of this insect characterizes it as the Allee type. At very low density, the mortality of eggs and larvae was high, which might have been due to the unfavorable conditions of the tuberous root, the quality of which had not yet been improved by the frano-inducing factor secreted during feeding by the larval and adult weevil. Comparatively more eggs were laid on the tuberous root conditioned by adult-feeding or oviposition. Size of adult progeny became smaller with the increase of parental density. The duration of their development was shortened, and variation of the time period until their emergence from the tuberous root became smaller with the increase of parental density. Optimal parental density for mass-rearing was found to be 65 pairs per tuberous root of 150 g for 3-days oviposition.

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Studies were conducted in two commercial cucumber greenhouses to examine thrips' seasonal and spatial patterns on Cheju Island, Korea, in 1996. Leaf and flower samples were taken to determine the thrips species and stage complexes inhabiting cucumber plants. Adult thrips (54–55%) were the most dominant stage on flowers and the majority of adult species was Frankliniella occidentalis (Pergande), whereas immature (82–84%) was the dominant stage on leaves. To determine the spatial distribution patterns of thrips, at least 63 leaf samples which were regularly spaced within a greenhouse were visually inspected from among the 1st, the 7th and the 15th leaves assigned from the top plant canopy. The leaf positions were located at 1.8, 1.0 and 0.3 m above ground level, respectively. Taylor's power law indicated that the counts of thrips on leaves were aggregated, regardless of thrips stage and leaf position. Autocorrelation analysis, which is based on the relative position of samples revealed the different spatial distribution patterns among the leaf positions. In general, the counts of thrips were nonrandomly distributed on the 7th leaf position, whereas the counts were randomly distributed on the 1st and 15th leaf positions. Correlograms suggested the presence of single or multiple gradients within the sample portion of the greenhouse, depending on thrips stage. Our results suggest that Taylor's power law cannot detect the spatial relationship in data sets accurately, and testing correlograms for significance is more accurate for describing the spatial distribution patterns of thrips.

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Pre-calling behavior of female adults of Helicoverpa armigera reared on artificial diet (Insecta LF) during the larval stage and fed on water and honey solutions (5, 10 and 20%) was observed. The quality of the adult diet did not influence the distribution of the pre-calling period (PCP). However, the calling rate was significantly higher in the three honey-fed groups (100%) than in the water-fed group (87.5%). In the next experiment, pre-calling behavior of female adults that were reared on Insecta LF during the larval stage and fed on 10% honey solution starting from different days after emergence was observed. The delay of adult feeding did not influence the calling rate, although the PCP was slightly prolonged in individuals which were not fed on honey solution until the onset of night 3 or night 5 (night 0=night of adult eclosion). In the experiment in which larvae were fed on different qualities of food (cotton leaf, okra fruit and Insecta LF), the calling rate varied greatly depending on the adult diet. When fed on honey solution, almost all adults called irrespective of their larval diet. However, when fed on water only, the calling rate of adults fed on Insecta LF during the larval period was 60.4%, while those of adults fed on cotton leaf and okra fruit were only 16.7% and 33.3%, respectively. These results indicate that most female adults of H. armigera can attain reproductive maturity even without feeding on nutritious diets when provided with highly nutritious diets during the larval period, and most female adults can not attain reproductive maturity without feeding on nutritious diets when provided with low nutritive value diets during the larval period.

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Precopulatory guarding behavior in males of Tetranychus urticae occurs because only the first mating is effective for females. Sufficient copulation duration to fertilize females in the laboratory is shorter than it is in nature. This finding leads to the hypothesis that the copulation duration of T. urticae is prolonged by postcopulatory guarding which prevents the female from remating with other males. To test this hypothesis, we manipulated the interval between the first and second copulations of a female. A significant positive correlation was detected between the mating interval and the proportion of daughters fathered by the first male of each brood. Males using postcopulatory guarding are successful when other males disturb the mating pair to take over from the mating male. These results demonstrate that males gain from prolonged copulation that prevents a female from remating until their sperm precedence is assured. Thus, males of T. urticae increase their paternity not only by precopulatory guarding but also by the postcopulatory guarding.

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Using GC-MS, we studied the time course of Tetranychus urticae-induced kidney bean plant volatile production during the period from foundation to collapse of the T. urticae colony. The density of T. urticae females showed a unimodal curve, which was followed by the production of T. urticae-induced plant volatiles. The intensity of the olfactory response of the predatory mite Phytoseiulus persimilis to the induced volatiles in a Y-tube olfactometer correlated with the amount of volatiles per plant. In the period before the increase of the second generation of female T. urticae, the infested plant did not attract predatory mites. Such a period can be considered to constitute a temporary enemy-free period for T. urticae.

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At 20°C, only 0–19% of newly emerged females of Argopistes coccinelliformis laid eggs under short-day conditions (LD 13.5 : 10.5, 13 : 11 and 12 : 12), but all females laid eggs within 30 days after emergence under long-day conditions (LD 14.5 : 9.5 and 15 : 9). The critical photoperiod was between LD 13.5 : 10.5 and 14 : 10. At 25°C, 27–39% of females laid eggs within 60 days after emergence even under short-day conditions (LD 12.5 : 11.5 and 12 : 12). All females laid eggs under long-day conditions (LD 14.5 : 9.5 and 15 : 9), but the preoviposition periods were longer than those at 20°C. The critical photoperiod was between LD 14 : 10 and 14.5 : 9.5 when it was estimated on the 20th day from emergence and between LD 12.5 : 11.5 and 13 : 11 when it was estimated on the 60th day. At 28°C, 41–73% of females laid eggs within 60 days after emergence under short-day conditions (LD 13 : 11, 12.5 : 11.5 and 12 : 12), but 14–33% of females did not lay eggs, even under long-day conditions. The critical photoperiod could not be determined. From the past and the present data, I concluded that A. coccinelliformis might produce 4 generations per year around Tokyo, central Japan, if new sprouts of host plants are available beyond the spring. The best season for trimming host plants would be late autumn–early winter to control the flea beetle population.

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The phagocytosis of five established cell lines, IPLB-Sf-5-5C, UCR-Se-1, NTU-Sl-1A, NTU-Pn-HH, and IPLB-Ld-652Y was examined by fluoresbrite carbosylate particle uptake. The phagocytic action of the Sf-5-5C cells was highly efficient compared to other cells, while Pn-HH cells showed no phagocytic action. Sf-5-5C, Se-1 and Sl-1A engulfed readily the OBs of AcMNPV, a virus to which they are susceptible, while they did not engulf the OBs of the non-susceptible virus, PenuNPV. These findings suggested that these insect cell lines would be useful for studying phagocytosis in vitro. Thus, Sf-5-5C cells were selected for the advanced study of phagocytosis. Three types of Sf-5-5C cells, non-basophilic cells, light basophilic cells and basophilic cells, were distinguished by morphology, toluidine blue staining, and electron microscopic staining. The non-basophilic cells acted as the main phagocytic cells in OB uptake, while the phagocytic activity of the light basophilic cells was weak. Inside the phagosome, the OBs were digested in the cytoplasm. The titration of AcMNPV in the culture media of Sf-5-5C cells after OB uptake was examined. The results implied that AcMNPV may be released from the engulfed OBs.

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Three EAG-active components were detected in the GC-EAD analyses of the hexane extracts of abdominal tips from virgin females of Acrolepiopsis nagaimo Yasuda (Lepidoptera: Acrolepiidae). These components were identified as (Z)-11-hexadecenyl acetate (Z11-16:Ac), (Z)-11-hexadecenal (Z11-16:Ald) and (Z)-11-hexadecen-1-ol (Z11-16:OH) at 1.8, 0.6, and 0.2 ng/female, respectively, by subsequent GC-MS analyses and chemical derivatization. In a field test conducted at Daiei-cho, Tottori in 1998, more males were captured with blends of Z11-16:Ac and Z11-16:Ald (0.1 mg/septum) at ratios of 50 : 50 and 75 : 25 than with two 2- to 3-d-old virgin females while the effect of an addition of Z11-16:OH to the blends was unclear.

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2-Hydroxy-6-methylbenzaldehyde (2,6-HMB) was identified as the female sex pheromone from the acarid mite, Cosmoglyphus hughesi. Although the sex pheromone functioned to stimulate males to tap females and then mount, it was detectable as a major component of hexane extracts not only from females but also from males and protonymphs. Its contents were estimated to be 283.1±49.4 ng per female, 135.2±25.5 ng per male and 3.8±0.4 ng per protonymph. Sexual activity was induced in males by exposure of a filter paper impregnated with 100 ng of synthetic 2,6-HMB. Behavioral observation demonstrated that the male could not distinguish females from males upon attempt to mate.

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The feeding activity of Nilaparvata lugens (Stål) (Homoptera: Delphacidae) was compared on the barnyard grass, Echinochloa Crus-galli var. oryzicola, which contains an antifeedant, (E)-aconitic acid, and on resistant (bph4) and susceptible rice varieties using an AC electronic monitoring system (EMS). N. lugens made more frequent probes on the barnyard grass and the resistant rice than on the susceptible rice. Mean duration of probes tended to be the shortest and the percentage of probes that consisted of the primarily salivation phase only was the highest on the barnyard grass, followed by the resistant rice. The most distinct difference in N. lugens feeding activities between the barnyard grass and the resistant rice was the frequency of the primarily ingestion phase. On the barnyard grass, the insect was rarely successful in achieving the primarily ingestion phase, indicating that probing was interrupted before the arrival of the stylets at the sieve elements. On the other hand, on the resistant rice the primarily ingestion phase was observed as frequently as it was on the susceptible rice. However, it stopped within 5 min on the resistant rice in most cases. Probing activities were strongly inhibited by 1% (E)-aconitic acid diluted with distilled water. The inhibitory effect was considerably mitigated when diluted with 15% sucrose. These results suggest that on the barnyard grass, interruption of probing activity by (E)-aconitic acid can occur in stylet pathway tissues rather than in ingestion tissues (e.g. the phloem where sucrose is located).

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To evaluate the effect of predation on spider mite populations in the field, we identified the predator species that caused the death of the eggs of Panonychus species using scanning electron micrographs of their feeding traces. The predator species could be distinguished from the shape of the feeding traces, which showed clear differences among the species studied. We evaluated the predation of individual predator species on Panonychus citri eggs from their feeding traces in comparison with their abundance on pear in Tsukuba, eastern Japan. The proportion of feeding traces by Oligota spp. was dominant, although both Oligota spp. and Scolothrips takahashii Priesner showed high population densities. Stethorus japonicus H. Kamiya with a low population density, showed a similar proportion of feeding traces to that of S. takahashii. These differences seemed to be due to differences in predation capacity among the species. Therefore, this study revealed the impact of individual predator species on Panonychus species more directly than simple population dynamics analyses in the field.

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The influence of host pupal age on host preference and host suitability in Brachymeria lasus (Walker) was examined. Rice armyworm, Mythimna separata (Walker), pupae of different ages, i.e., 0–1, 2–3, 4–5, 6–7 and 8–9 d old were used as hosts. The females accepted the host pupae equally for oviposition among 5 age groups, suggesting that female B. lasus does not discriminate hosts of different ages. However, the rate of progeny emergence was lower in old (6 to 9 d old) hosts. The adult parasitoid progeny produced from young (0 to 5 d old) hosts were heavier in body weight than those from old hosts. The developmental time of the immature stages of progeny was not significantly affected by host pupal age. Adult progeny with heavier body weight emerged earlier than lighter ones when reared on 0- to 5-d-old hosts. However, there was no correlation between the progeny body weight and developmental time of the immature stages when reared on 6- to 9-d-old hosts. Most of the progeny were females and no effect of host age was found on progeny sex ratio, which may be due to the low oviposition rate they experienced.

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In order to evaluate the efficiency of an indigenous aphid parasitoid Aphidius gifuensis as a biological control agent against Myzus persicae, its oviposition rate, developmental time and survival rate on M. persicae were investigated in the laboratory. The oviposition rate was 84.9% at 25°C, and no aphids in which more than one A. gifuensis progeny were oviposited by one A. gifuensis female were observed. The survival rates and developmental times of immature A. gifuensis were examined at four constant rearing temperatures of 15, 20, 25 and 30°C with a photoperiod of 16L–8D. The survival rates from egg to adult emergence were more than 80% at all temperatures tested. The developmental times decreased with increasing temperatures in both sexes, except that the periods at 30°C were slightly longer than those at 25°C. The lower developmental threshold (T₀) and total effective temperature (K) of A. gifuensis were 5.5°C and 188.6 degree-days for the females, and 5.7°C and 181.0 degree-days for the males. The oviposition rate, survival rates and the developmental times were similar to those of commercially produced Aphidius colemani.

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Continuous rearing of the brown planthopper, Nilaparvata lugens (Stål), was achieved on a chemically defined diet D-97 developed in this laboratory. The performance of N. lugens reared on D-97 was much better than that on a previously reported artificial diet MMD-1, although it was inferior to the susceptible rice variety TN1. N. lugens can not finish a complete generation on MMD-1 due to poor fecundity and unhatchability of eggs, but it has been successfully reared for more than 6 generations on D-97. In comparison with TN1-reared N. lugens, D-97-reared insects had a longer nymphal period (more than 3 days longer for males and 5 days longer for females), lighter weight (over 25% lighter for males and 35% lighter for females) and lower fecundity (over 50% less). Of the six generations on D-97, the first two generations had a significantly higher rate of emergence and hatchability. The possible factors influencing rearing efficiency and the potential applications of this diet are also discussed.

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An entomopathogenic fungus, Beauveria bassiana was tested against the rice weevil Sitophilus oryzae. Bioassays were conducted by introducing 25 adult insects on 50 g of B. bassiana mixed rice in glass jars maintained at 28±2°C, and 70% RH. Mortality was monitored at five-day intervals until 25 days. At higher doses (7.6 log conidia/ml), B. bassiana produced a higher percentage of mortality up to 75.8% and F₁ adult emergence was reduced by 86.2%. At lower concentrations B. bassiana was not effective against S. oryzae. The study stresses the need for higher numbers of conidial inoculation for maximum mortality.

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Early-, mid-, and late-stadium Helicoverpa zea larvae were fed on a diet which was surface-treated with occlusion bodies (OB) at rates from 0.1 to 1, 000 OB/mm² for periods ranging from 0.25 to 72 h. Fifty-percent of early-stadium larvae fed 0.1, 1, 10, and 100 OB/mm² eventually died after they had fed for 7.5, 4.5, 2.3, and 0.3 h, respectively, and then were transferred to virus-free diet. Greater than 98% mortality occurred, regardless of the viral rate, after 24 h of feeding. Less than 0.5 h of feeding at the highest rate (1, 000 OB/mm²) resulted in 100% mortality. Using mid-stadium larvae, 50% mortality at 0.1, 1, or 10 OB/mm² occurred when larvae had fed for 11.0, 3.5 or 0.3 h, respectively, and then were transferred to virus-free diet. Viral rates of 100 or 1, 000 OB/mm² resulted in >90% mortality after only 0.25 h of feeding. All mid-stadium larvae fed the highest rates (10, 100 or 1, 000 OB/mm²) for at least 12 h and then transferred to virus-free diet, eventually died of a virus infection. One-hundred percent mortality, however, was never reached when larvae were fed for 72 h at the two lowest rates of 0.1 and 1.0 OB/mm². Within each viral rate it did not seem to matter whether late-stadium larvae had fed for 1 or 72 h on virus-treated diet. Mortality of late-stadium larvae was never greater than 75% regardless of the viral rate or feeding time. Mortality of early-, mid-, or late-stadium larvae not fed virus never exceeded 2%.

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Mid-stadium larvae of Helicoverpa zea were equally susceptible to either the wild-type (Wt) or recombinant (RcHzLqh) strain of HzSNPV. There was, however, a significant difference (1.8-fold) in the rate of mortality between the two strains. The LT₅₀ for the Wt and Rc strain was 3.4±0.1 days and 1.9±0.2 days, respectively. In contrast, there was a significant difference in both the rate and extent of mortality of mid-stadium larvae of H. virescens fed either the Wt or Rc strain of HzSNPV (LC₅₀: Wt, 11.4±0.6 OB/cm²; Rc, 42.2±8.2 OB/cm². LT₅₀: Wt, 4.1±0.1 days; Rc, 2.8±0.2 days). An 8-fold increase in the viral rate of the WtHzSNPV was needed (800 OB/mm²) to match the effectiveness of the RcHzLqh strain at 100 OB/cm². Increasing the RcHzLqh rate above 100 OB/cm² did not significantly reduce the LT₅₀ or larval feeding as measured by frass weight. All viral rates of the Rc strains significantly reduced (ca. 6- to 12-fold) mid-stadium larval feeding over that of the control. Differences between the Rc and Wt strains of HzSNPV, using late-stadium H. zea larvae, showed the same tendency as that using mid-stadium larvae, but the differences were not as great (< 2-fold). Mid-stadium larvae of H. virescens were ca. 3-fold more susceptible to RcAcLqh than to either the WtAc or RcAcAa. Both RcAcLqh and RcAcAa strains killed larvae quicker (1.5- to 1.7-fold) and reduced feeding more (1.6- to 1.9-fold) than the WtAc strain. A combination of RcAcLqh and RcAcAa at 5 OB/cm² had no additive effect on mortality of H. virescens larvae and the combination was less effective than either Rc strain at 10 OB/cm². Unexpectedly, the known level of susceptibility of semi-permissive larvae of H. zea to WtAcMNPV, as measured by percent mortality, LT₅₀, and feeding, was significantly enhanced (ca. 2-fold) when H. zea larvae were fed the RcHzLqh strain. In contrast, expression of the Lqh-toxin by RcHzLqh did not significantly increase the susceptibility of H. subflexa, larvae previously reported as being highly resistant to WtHzSNPV.

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Three populations of the western flower thrips, Flankliniella occidentalis (Pergande), were collected from commercial greenhouses (strawberry, rose and gerbera) in Wakayama Prefecture, Japan. Four females were transferred onto a kidney bean leaf, Phaseorus vulgaris L., floated on 0.5% agar gel in a plastic petri dish. The petri dish, which contained 40–80 larvae 2 to 3 days after hatching, was sprayed with 6 ml of insecticides through a spraying tower. Of the organophosphates, dichlorvos, sulprofos, profenofos, prothiofos, malathion, chlorpyrifos-methyl, chlorfenvinphos, fenthion and phenthoate were toxic with more than 90% of corrected mortality. Most carbamates except for methomyl and pyrethroids were less toxic. Of the IGRs, lufenuron, chlorfluazuron and flufenoxuron were effective. Chlorphenapir and spinosad achieved 100% mortality. There was no remarkable difference in sensitivity to the insecticides among the populations except for acrinathrin. The Kishigawa and the Inami populations collected from rose and gerbera, respectively, were more tolerant to acrinathrin than the Iwade population collected from strawberry.

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The efficacy of four plant extracts, Alpinia galanga Sw. (Zingiberaceae), Amomum cardamomum Auct. (Zingiberaceae), Cyperus rotundus L. (Cyperaceae), and Gomphrena globosa L. (Amaranthaceae) were evaluated against the diamondback moth, Plutella xylostella L. and the cabbage webworm Crocidolomia binotalis Zeller larvae on cultivated cabbage. Treatments with 0.5% A. galanga and G. globosa extracts significantly reduced P. xylostella larval density, and the percentage of infested plants, proving to be more effective than a standard insecticide Decis7 2.5EC (deltamethrin). Moreover, G. globosa significantly reduced the intensity of cabbage damage caused by P. xylostella. Treatment with 0.5% A. cardamomum extract reduced the percentage of P. xylostella-infested plants and the intensity of cabbage damage. However, the plant extracts did not effectively reduce C. binotalis larval density, the percentage of infested plants or the intensity of cabbage damage. Phytotoxic effects on cabbage plants were not observed in any extract treatment.

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The species assemblage and seasonal activity of carabids were investigated in a cabbage field, an adjacent fallow field, and the field boundary during 1994 and 1995 by pitfall trapping. Trap catches indicated that Amara and Harpalus species were generally active in every habitat during the 1st (May to July) and 2nd (August to September) growing seasons, respectively. Small species such as Bembidion morawitzi Csiki were active in the 3rd growing season (November to March), especially in the cabbage plot. The adults of the beneficial species Chlaenius micans (F.) were active in the 1st and 2nd growing seasons and their larvae were found on cabbage heads in the 1st growing season. The adults of another beneficial species, Campalita chinense (Kirby), were active in the 2nd growing season; the larvae were trapped during the 1st and 2nd growing seasons. Although the seasonal activity patterns of these beneficial species varied spatially and temporally, they consistently preferred the cabbage plot to the boundary. The timing of the peak activity of the beneficial species coincided to some extent with the peak density of lepidopteran larvae. The activity pattern of the beneficial carabid species could enhance their value as biological control agents for cabbage pest insects.

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A small scale experiment was carried out to eradicate the sweet potato weevil, Cylas formicarius (Fabricius) by the sterile weevil release method from 1994 to 1996 on the islet, Kiyamajima, 35 ha, of the Amami Islands, Kagoshima Prefecture, Japan. Weevils were mass-reared with fresh sweet potato roots at 27°C and roots filled with the weevils were irradiated with gamma ray, 80 Gy on the 27th to 28th days after oviposition (newly eclosed adult). Sterile weevils were stained with fluorescent dyes and released by hand on host plant foliages. Monitoring was done by both pheromone traps and root traps throughout the experimental period. From 11 January, 1994 to 19 July, 1994, ca. 32,000 sterile weevils were released every 10 d as a rule all over the island. This trial suggested the necessity of a denser release of sterile weevils for successful eradication. Thus, for intensive release ca. 16,000 sterile weevils were released every 10 d as a rule from 29 July, 1994 to 5 September, 1995 in a restricted area, 13 ha, as the release zone. The wild population in the release zone was controlled to zero or at least nearly to zero after summer in 1995. Only a few unmarked males were captured by pheromone traps for one year after the final release of sterile weevils on 5 September, 1995, which was probably immigrants from outside of the release zone. No weevils were found in the reexamination of root traps and dissection of wild host plants carried out in September in 1996.

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The overwintering ecology of two species of spider mites was studied on three different host plants in central Wakayama Prefecture, southwestern Japan. Laboratory diapause-inducing experiments showed that populations of Tetranychus urticae on peas and chrysanthemums both had a very low inherent capacity for diapause, and the population on chrysanthemums continued development and reproduction throughout the winter. On the other hand, populations of T. kanzawai had a genetically strong diapause capacity, regardless of the host species on which they occurred. However, the proportion of field-induced diapause females was lower in the population occurring on Akebia quinata, an evergreen host that had ample fresh leaves throughout the winter, than the populations on peas and Clerodendrum trichotomum, a deciduous tree, the leaves of both of which deteriorated or defoliated in winter. The low incidence of diapause on A. quinata seemed due to weak diapause induction and/or earlier diapause termination in the plastic response to ample food conditions. On A. quinata, high proportions of eggs and immatures remained throughout the winter, suggesting that development and reproduction are possible throughout the winter in this area under ample food conditions.

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The incidence of diapause in the polyphagous spider mite Tetranychus kanzawai was determined for 65 populations derived from deciduous and herbaceous hosts and for 33 populations from tea, at 3 temperatures under short-day conditions. Most populations on the four main islands of Japan, irrespective of the host species on which they occurred, expressed more than 90% diapause at 15°C, whereas populations on the Okinawa islands exhibited a very low incidence or no diapause. The incidence of diapause decreased when temperature was increased from 18 to 20°C in populations from warmer areas such as southern Kyushu and Honshu. This temperature-dependent decline in diapause incidence was most conspicuous in populations from Tanegashima and Yakushima Islands. The incidence of diapause at 20°C tended to be lower in populations derived from tea than those from deciduous hosts in the same, warmer areas, showing that the former have a lower capacity for diapause. The present results, together with previously published data for T. urticae, showed that the lower temperature threshold for diapause induction was higher in T. kanzawai than in T. urticae and thus the clinal decrease in diapause percentage occurred at much lower latitudes in the former at 20°C.

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