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Effect of temperature and photoperiod on the induction of diapause in the mite Metaseiulus occidentalis
J. Insect Physiol., 1975, Vol. 21, pp. 605 to 611. Pergamon Press. Printed in Great Britain
EFFECT OF TEMPERATURE AND PHOTOPERIOD ON THE INDUCTION OF DIAPAUSE IN THE MITE METASEIULUS OCCIDENTALIS MARJORIE
A. HOY”
Division of Biological Control, University of California, Berkeley 94720, U.S.A. ((Received 22 January
1974)
Abstract-Diapause in a predaceous mite, Metaseiulus occidentalis, from a Californian vineyard population is a photoperiodically induced, facultative, adult reproductive diapause in females. The laboratory-determined critical photophase at 19°C was estimated at 11.2 hr. At 16”C, the critical photophase under laboratory conditions was approximately 11.6 hr. Temperature influenced the photoresponse of M. occidentalis so that diapause was entirely averted at temperatures of 22, 2.5, and 30°C. Aestival diapause at higher temperatures and long photophases was lacking. Development was continuous under constant darkness at all the temperatures tested. Diapause termination in laboratory-reared mites occurred spontaneously under the inductive conditions. Under constant 19°C temperatures, females responded to photophases so that diapause was terminated most rapidly under a 16 hr photophase (in 18.6 days) ; the 12 and 8 hr photophases, at this temperature, were next in their effectiveness, with 27.9 and 73.0 days, respectively, required for termination. INTRODUCTION
CONSIDERABLE interest has been directed recently towards understanding
and augmenting the effectiveness of predators of spider mites, the Tetranychidae. Thus, numerous biological and systematic papers have been published about members of the predatory mite family Phytoseiidae (reviews by HUFFAKER et al., 1969,197O; MCMURTRY et al., 1970). Diapause is an important aspect of a species’ population dynamics and phenology. In addition, laboratory rearing is facilitated if diapause can be manipulated. Studies on the physiological condition of overwintering phytoseiid mites have been meagre until recently. SAPOZHNIKOVA (1964) reported a photoperiodically induced diapause in the phytoseiid Typhlodrmus similis (Koch) at Leningrad. This species has an adult diapause of the long-day type under laboratory conditions at 18°C when mites are reared under short photophases. The critical day length (when 50 per cent of all adult females enter diapause) for this species was 11.5 hr. However, higher temperatures (25°C) eliminated the photoperiodic effect so that diapause was not evident, even with a 9 hr photophase. * Present address: The Connecticut Agricultural Experiment Station, P.O. Box 1106, New Haven, CT. 06504. This study was supported, in part, by N.S.F. Grant No. GB-7322 to Dr. C. B. Huffaker. 605
MARJORIE A. HOY
606
Since 1964 a number of workers have reported a facultative adult diapause in several phy toseiid females [HOY and FLAHERTY, 1970, Metaseiulus occidentah (Nesbitt); CROFT, 1971, M. occidentalis; ROCK et al., 1971, Neoseiulus fallacis Garman; KNISLEYand SWIFT, 1971, Amblyseius umbraticus (Chant)]. Males were not observed to diapause under any conditions. Diapause can be terminated spontaneously in M. occidental& (HOY and FLAHERTY, 1970). If laboratory-reared females are maintained under induction conditions they eventually oviposit. For example, diapause termination may occur as soon as 27 days or as long as 129 days under the same conditions. Chilling is not necessary to terminate diapause (HOY and FLAHJZRTY, 1970). On the other hand, temperature and photophase may interact to terminate diapause much more quickly, for when diapausing M. occidentalis females were reared at 19°C under an 8 hr photophase and held for 3 weeks, they oviposited within 5 days subsequent to transfer to 25°C and a 16 hr photophase (HOY and FLAHERTY,1970). These facts led to a test to determine if diapausing females terminate diapause in response to longer photophases when temperature is held constant. Another objective of this study was to determine how temperature and photoperiod interact in the induction of diapause in M. occidentalis under laboratory conditions, MATERIALS
AND METHODS
This research was conducted at two different locations during two different time intervals. It was initiated during 1969 and continued through 1970 at Reedley, California, and was concluded during 1972 at Albany, California. Two different predator colonies were used. The equipment used also differed somewhat. Colony sources and culture methods The laboratory colony of M. occidentalis used during 1969 and 1970 originated from 30 to 40 adult females collected from grape foliage on 1 April 1969 near Fresno, California. Studies conducted during 1972 were made with mites from a colony collected in early March 1972 near Fresno, originally consisting of approximately 150 females from under grape bud scales. Both colonies were held under continuous light and ambient temperatures which fluctuated between 22 and 27°C. They were fed all stages of the two-spotted spider mite, Tetranychus urticae Koch, which was obtained from a colony of the Division of Biological Control, Albany, California. This prey was reared either on soybeans or on celery at Reedley and on celery only at Albany, and also under continuous light and ambient temperature conditions as above. The predator colonies were kept on paraffin-coated paper disks that rested on water-soaked cotton, and fed all stages of T. urticae. When the predator colony became excessively large (about once a month), approximately one-quarter of it (200-300 mites of all stages) was used to start a new colony. Experimental equipment For tests conducted
at Reedley, mites were placed in two Percival growth
INDUCTION
OF DIhiUSE
IN
i%?ETASEIULlJS OCCIDENTALIS
607
chambers, Model I-30L. Continuous recording hygrothermographs were kept in the chambers during the tests. Lighting was by two cool-white 20 W fluorescent bulbs, which produced about 300 ft-c of light at the shelf level. Timer clock mechanisms turned light on and off. In Albany, tests were conducted either in two Percival chambers as above or in four specially constructed constant-temperature chambers. These chambers were adjusted to produce as closely as possible the conditions in the Percival chambers. Temperature was, however, continuously recorded for the duration of the experiments by means of thermocouples that directly touched the leaf surfaces. The temperature recorded closely represented that directly experienced by the mites, and varied 1°C about the desired temperatures. Relative humidity in both types of chambers averaged about 75%, but on the leaf surfaces the mites probably experienced higher humidities. Experimental
techniques and scoring
Experiments at Reedley were conducted with individually reared predator females. These females were isolated from the colony as eggs tind reared (1 egg/ disk) to adulthood on detached grape leaf disks supported on water-soaked cotton. Leaf disks were checked each 1 to 2 days with a dissecting microscope; notes were made of the developmental stage, appearance, and behaviour of the predator as well as the abundance of prey. At maturity, the females were mated with males from the stock colony,’ If progeny were -produced by the experimental females, they were counted and removed, usually in the egg stage. Data were gathered during the photophase of the photoperiod and time out of the chamber was held to 15 to 30 min. Females reared under 0 hr light were placed into the dark as eggs and not examined again until they were adults. For experiments conducted in the Albany laboratory, rearings were generally made of 35 to 50 predator females en masse from the egg stage. Mass-reared females mated spontaneously. Failure to oviposit by females was the major criterion of diapause and was based on observations lasting a minimum of 1 week after mating. Observations were usually continued until diapause terminated. Females reared individually were scored as non-diapause if eggs were observed on the leaf disks. In the group study, diapausing females were distinguishable because they were quiescent, non-gravid, and pale in colour in contrast to the active, pink, gravid, nondiapausing females. On a few occasions, mass-reared females were isolated to ascertain their reproductive status. RESULTS
AND
DISCUSSION
Photoresponse and critical daylength at 19°C A photoresponse curve was developed for individually reared mites using constant temperatures of 19°C and photophases of 8, 10, 11, 12, 13, 16, and 18 hr. Mites were reared individually on grape leaf disks; numbers tested under each photophase averaged 19, with a range from 5 to 26. 20
MARJORIE A. HOY
608
In Fig. 1, the percentage of adult females in diapause is plotted against daylength. This yielded a curve typical for arthropods that enter diapause in response to short photophases (BECK, 1968). The critical daylength (mean response) at 19°C was estimated as 11.2 hr. 100
r
9
lo
Photophase,
FIG. 1.
II
I2
.1?,
14
l?i
16
17
IS
IS
hr ot 19*C
Photope~odic response curve for M. o&den&&s ~~vidua~y reared at 19°C.
At any given daylength and temperature each mite or insect will or will not enter diapause, depending on its individual response threshold, generally genetically determined. If Fig. 1 is compared with other species’ photoresponse curves (BECK, 1968), the response of the Fresno colony of M: OC~~~UZ~Schanges rather gradua1Iy with increasing daylength. According to BECK (1968), this indicates the population may be rather variable genetically for diapause induction response. Comparison of photoresponses at 19°C obtained dziring 1970 and 1972 In 1972, a second photoresponse curve was obtained, again using a 19°C constant temperature and the same photophases as above so that a comparison could be made between individually reared mites vs mass-reared mites and between the two stocks. The photoresponse curve obtained in Albany in 1972 with mass-reared mites was compared to that obtained at Reedley in 1969 with The Mann-Whitney U-test (U = 18.5) was not individually reared mites. significant and thus supports the hypothesis that both stocks adequately represented the same Fresno, California vineyard population and that the two experia mental procedures yielded comparable data.
INDUCTION OF DIAPAUSE IN METASEIULUS
OCCIDENTALLY
609
Temperature and photophase efsects on induction To study the effect of temperature on the critical daylength and photoresponse curve, mass-reared mites were tested at constant temperatures of 16, 19, 22, 25, and 30°C. Photophases tested were: 0, 10, 11, 12, 13, 16, 18, and 24 hr of light. Two rearing units of 35 or 50 mites were placed into each combination of temperature and photophase tested. A check was included in each temperature series to indicate if genetic changes or seasonal effects influenced results. Since 25°C was not expected to provide any diapausing females except possibly at the extra-long, 18 hr photophase (HoY, unpublished data), two 30°C trials were substituted for two of the 25°C photophases. At 3O”C, 18 and 24 hr photophases were tested to detect a potential aestival diapause. Table 1 lists the test results for temperature and photophase interactions in M. occidentalis. For 16 and 19°C the results are similar although the lower temperature yielded a more sharply defined critical daylength estimate. Again the critical daylength is between 11 and 12 hr; at 16”C, it is about 11.6 hr. TABLE ~--THE
INFLUENCE OF TEMPERATUREON THE PHOTORESPONSESOF REAREDFROM EGGS DURING 1972
M. occidentalis MASS-
o/0females in diapause under photophases tested (hr) Temperature (“C)
16 19 22 25 30
Sequence of test
Check at 0
10
11
12
13
16
18
24
19”C, 10 hr
Fourth (&*
&
&
(5:)
(4;)
(6:)
-
-
(203)
(E,
(Z)
(5:)
(5;)
(2:)
(2:)
-
(E,
(300)
(3;)
(4:)
(3:)
(2;)
(2:)
-
-
(E,
$I,
(3:)
-
-
(2;)
(1:)
(2:)
-
(E)
-
-
-
-
-
-
First Second Third Third
(1:)
(27)
* The number of females tested in each category is shown in parentheses.
Diapause induction was exhibited only within a quite narrow temperature range. Diapause was not evident under the 22, 25, or 30°C temperatures under any photophases tested. No sign of aestival diapause due to long photophases at high temperature (30°C) was noted. Developmental success was poor at longer photophases, but survivors were reproductively active. Under continuous darkness and under continuous light, diapause was absent at all temperatures tested, indicating that M. occidentalis has a Type III diapause response (BECK, 1968).
MARJORIEA. HOY
610
The ‘check’ results suggest that neither genetic photophases influenced the results (Table 1).
changes nor lengthening
Photophase effects on diap&se termination in laboratory-reared mites An experiment was conducted to determine if photophase alone influences diapause termination when temperature is held constant. The adult females used were reared individually at 19°C under an 8 hr photophase. They were mated and observed for 1 week to determine that they were in diapause (i.e. that they did not oviposit). Those in diapause were split into three groups: one was transferred to a long photophase (16 hr) ; one to a 12 hr photophase; and the other kept under the 8 hr rearing condition. Temperature was held constant at 19°C. Females were checked each 2 to 3 days to determine when oviposition began. It was hypothesized that females in diapause when transferred to the 16 hr photophase would terminate diapause quickly; those transferred into the 12 or 8 hr photophases should follow, .in that order. The results are shown in Table 2. TABLE ~-TIME REQUIREDFOR SPONTANEOUS DIAPAUSETERMINATIONBY FEMALESHELD UNDER8, 12, AND 16 hr PHOTOPHASES AT 19°C 1 week AFTER MATING*
Photophase (hr) under which termination occurred 16 12 8
Mean No. of days after transfer to first oviposition f S.D. 18.6 k 2.3 27.8 5 4.7 73.0 + 32.7
Range in No. of days
No. of mites
No. of unusual females excluded from mean
15-20 23-41 29-147
11 14 9
3i 1X 3§
* Females were reared at 19°C under an 8 hr photophase. -1_These three females died 56, 82, and 126 days after mating without ovipositing. They had mated, but were sterile or in diapause. 3 This female died 160 days after mating without ovipositing ; this longevity in a non-diapausing mite is unusual. 6 Three females apparently ‘switched’ from a non-diapause state into diapause, with a subsequent termination and resumption of oviposition. For example, one female deposited 2 eggs on day 5 and then remained inactive 72 days before producing an additional 7 eggs. The two other females behaved similarly.
The mean number of days to first oviposition followed a trend that supports the above hypothesis (Table 2). Thus, those females with the longest preoviposition period (73 days) were the ones held under rearing conditions (i.e. the 8 hr photophase at 19’C). The next longest mean time (27.8 days) occurred in the 12 hr photophase, and the quickest termination occurred under the long-day photophase of 16 hr. Thus, M. occidentalis can respond to long photophases while in diapause; this means that laboratory manipulation of diapause is easy with this stock from Fresno, California.
INDUCTION OF DIAPAUSE IN METASEIULUS
OCCIDENTALS
612
Table 2 shows that several females were excluded from the calculations of the means, however. The unusual behaviour of 3 females transferred into the 8 hr photophase was interpreted to be due to a ‘switch-over’ by adults from an initial non-diapause state to a diapause condition. Eventual spontaneous diapause termination then occurred with resumption of oviposition. These three females’ history suggests that induction might occur in the adult stadium. This possibility has been studied (HoY, 1975). Acknowledgements-NIy appreciation is extended to Dr. CARL B. HWFAKER for his inspiring and valued discussions. Professor P. S. MESSENGERand Mr. CHARLESKENNETT kindly made constant temperature chambers available for this study. Dr. D. L. FLAHERTY offered valuable advice during the course of the research. REFERENCES BECK S. D. (1968) Insect Photoperiodism. Academic Press, New York. CROFT B. A. (1971) Comparative studies on four strains of TyphZodromus occidentalis (Acarina: Phytoseiidae)-V. Photoperiodic induction of diapause. Ann. ent. Sot. Am. 64,962-964. HOY M. A. (1975) Diapause in the mite Metaseiulus occidentalis: stages sensitive to photoperiodic induction. r. Insect Phyiol. In press. HOY M. A. and FLAHERTYD. L. (1970) Photoperiodic induction of diapause in a predaceous mite, Metaseiulus occidentalis. Ann. ent. Sot. Am. 63, 960-963. HUFFAKERC. B., VAN DE VRIE M., and MCMURTRYJ. A. (1969) The ecology of tetranychid mites and their natural control. A. Rev. Ent. 14, 125-174. HUFFAKERC. B., VAN DE VRIE M., and MCMURTRY J. A. (1970) Ecology of tetranychid mites and their natural enemies: A review-II. Tetranychid populations and their possible control by predators: an evaluation. Hilgardia 40, 391-458. KNISLEY C. B. and SWIFT F. C. (1971) Biological studies of AmbZyseius umbraticus (Acarina: Phytoseiidae). Ann. ent. Sot. Am. 64, 813-822. MCMURTRY J. A., HUFFAKER,C. B., and VAN DE VRIE M. (1970) Ecology of tetranychid mites and their natural enemies: A review-I. Tetranychid enemies: their biological characters and the impact of spray practices. Hilgardia 40, 331-390. ROCK C., YEARGAND. R., and RABB R. L. (1971) Diapause in the phytoseiid mite, Neoseizdus (T.) fallacis. J. Insect Physiol. 17, 1651-1659. SAPOZHNIKOVA F. D. (1964) Photoperiodic response of the mite Typhlodromus (AmbZyseius) similis (C. L. Koch) (Acarina: Phytoseiidae). ZooZ. Zh. 43, 1140-1144.
EFFECT OF TEMPERATURE AND PHOTOPERIOD ON THE INDUCTION OF DIAPAUSE IN THE MITE METASEIULUS OCCIDENTALIS MARJORIE
A. HOY”
Division of Biological Control, University of California, Berkeley 94720, U.S.A. ((Received 22 January
1974)
Abstract-Diapause in a predaceous mite, Metaseiulus occidentalis, from a Californian vineyard population is a photoperiodically induced, facultative, adult reproductive diapause in females. The laboratory-determined critical photophase at 19°C was estimated at 11.2 hr. At 16”C, the critical photophase under laboratory conditions was approximately 11.6 hr. Temperature influenced the photoresponse of M. occidentalis so that diapause was entirely averted at temperatures of 22, 2.5, and 30°C. Aestival diapause at higher temperatures and long photophases was lacking. Development was continuous under constant darkness at all the temperatures tested. Diapause termination in laboratory-reared mites occurred spontaneously under the inductive conditions. Under constant 19°C temperatures, females responded to photophases so that diapause was terminated most rapidly under a 16 hr photophase (in 18.6 days) ; the 12 and 8 hr photophases, at this temperature, were next in their effectiveness, with 27.9 and 73.0 days, respectively, required for termination. INTRODUCTION
CONSIDERABLE interest has been directed recently towards understanding
and augmenting the effectiveness of predators of spider mites, the Tetranychidae. Thus, numerous biological and systematic papers have been published about members of the predatory mite family Phytoseiidae (reviews by HUFFAKER et al., 1969,197O; MCMURTRY et al., 1970). Diapause is an important aspect of a species’ population dynamics and phenology. In addition, laboratory rearing is facilitated if diapause can be manipulated. Studies on the physiological condition of overwintering phytoseiid mites have been meagre until recently. SAPOZHNIKOVA (1964) reported a photoperiodically induced diapause in the phytoseiid Typhlodrmus similis (Koch) at Leningrad. This species has an adult diapause of the long-day type under laboratory conditions at 18°C when mites are reared under short photophases. The critical day length (when 50 per cent of all adult females enter diapause) for this species was 11.5 hr. However, higher temperatures (25°C) eliminated the photoperiodic effect so that diapause was not evident, even with a 9 hr photophase. * Present address: The Connecticut Agricultural Experiment Station, P.O. Box 1106, New Haven, CT. 06504. This study was supported, in part, by N.S.F. Grant No. GB-7322 to Dr. C. B. Huffaker. 605
MARJORIE A. HOY
606
Since 1964 a number of workers have reported a facultative adult diapause in several phy toseiid females [HOY and FLAHERTY, 1970, Metaseiulus occidentah (Nesbitt); CROFT, 1971, M. occidentalis; ROCK et al., 1971, Neoseiulus fallacis Garman; KNISLEYand SWIFT, 1971, Amblyseius umbraticus (Chant)]. Males were not observed to diapause under any conditions. Diapause can be terminated spontaneously in M. occidental& (HOY and FLAHERTY, 1970). If laboratory-reared females are maintained under induction conditions they eventually oviposit. For example, diapause termination may occur as soon as 27 days or as long as 129 days under the same conditions. Chilling is not necessary to terminate diapause (HOY and FLAHJZRTY, 1970). On the other hand, temperature and photophase may interact to terminate diapause much more quickly, for when diapausing M. occidentalis females were reared at 19°C under an 8 hr photophase and held for 3 weeks, they oviposited within 5 days subsequent to transfer to 25°C and a 16 hr photophase (HOY and FLAHERTY,1970). These facts led to a test to determine if diapausing females terminate diapause in response to longer photophases when temperature is held constant. Another objective of this study was to determine how temperature and photoperiod interact in the induction of diapause in M. occidentalis under laboratory conditions, MATERIALS
AND METHODS
This research was conducted at two different locations during two different time intervals. It was initiated during 1969 and continued through 1970 at Reedley, California, and was concluded during 1972 at Albany, California. Two different predator colonies were used. The equipment used also differed somewhat. Colony sources and culture methods The laboratory colony of M. occidentalis used during 1969 and 1970 originated from 30 to 40 adult females collected from grape foliage on 1 April 1969 near Fresno, California. Studies conducted during 1972 were made with mites from a colony collected in early March 1972 near Fresno, originally consisting of approximately 150 females from under grape bud scales. Both colonies were held under continuous light and ambient temperatures which fluctuated between 22 and 27°C. They were fed all stages of the two-spotted spider mite, Tetranychus urticae Koch, which was obtained from a colony of the Division of Biological Control, Albany, California. This prey was reared either on soybeans or on celery at Reedley and on celery only at Albany, and also under continuous light and ambient temperature conditions as above. The predator colonies were kept on paraffin-coated paper disks that rested on water-soaked cotton, and fed all stages of T. urticae. When the predator colony became excessively large (about once a month), approximately one-quarter of it (200-300 mites of all stages) was used to start a new colony. Experimental equipment For tests conducted
at Reedley, mites were placed in two Percival growth
INDUCTION
OF DIhiUSE
IN
i%?ETASEIULlJS OCCIDENTALIS
607
chambers, Model I-30L. Continuous recording hygrothermographs were kept in the chambers during the tests. Lighting was by two cool-white 20 W fluorescent bulbs, which produced about 300 ft-c of light at the shelf level. Timer clock mechanisms turned light on and off. In Albany, tests were conducted either in two Percival chambers as above or in four specially constructed constant-temperature chambers. These chambers were adjusted to produce as closely as possible the conditions in the Percival chambers. Temperature was, however, continuously recorded for the duration of the experiments by means of thermocouples that directly touched the leaf surfaces. The temperature recorded closely represented that directly experienced by the mites, and varied 1°C about the desired temperatures. Relative humidity in both types of chambers averaged about 75%, but on the leaf surfaces the mites probably experienced higher humidities. Experimental
techniques and scoring
Experiments at Reedley were conducted with individually reared predator females. These females were isolated from the colony as eggs tind reared (1 egg/ disk) to adulthood on detached grape leaf disks supported on water-soaked cotton. Leaf disks were checked each 1 to 2 days with a dissecting microscope; notes were made of the developmental stage, appearance, and behaviour of the predator as well as the abundance of prey. At maturity, the females were mated with males from the stock colony,’ If progeny were -produced by the experimental females, they were counted and removed, usually in the egg stage. Data were gathered during the photophase of the photoperiod and time out of the chamber was held to 15 to 30 min. Females reared under 0 hr light were placed into the dark as eggs and not examined again until they were adults. For experiments conducted in the Albany laboratory, rearings were generally made of 35 to 50 predator females en masse from the egg stage. Mass-reared females mated spontaneously. Failure to oviposit by females was the major criterion of diapause and was based on observations lasting a minimum of 1 week after mating. Observations were usually continued until diapause terminated. Females reared individually were scored as non-diapause if eggs were observed on the leaf disks. In the group study, diapausing females were distinguishable because they were quiescent, non-gravid, and pale in colour in contrast to the active, pink, gravid, nondiapausing females. On a few occasions, mass-reared females were isolated to ascertain their reproductive status. RESULTS
AND
DISCUSSION
Photoresponse and critical daylength at 19°C A photoresponse curve was developed for individually reared mites using constant temperatures of 19°C and photophases of 8, 10, 11, 12, 13, 16, and 18 hr. Mites were reared individually on grape leaf disks; numbers tested under each photophase averaged 19, with a range from 5 to 26. 20
MARJORIE A. HOY
608
In Fig. 1, the percentage of adult females in diapause is plotted against daylength. This yielded a curve typical for arthropods that enter diapause in response to short photophases (BECK, 1968). The critical daylength (mean response) at 19°C was estimated as 11.2 hr. 100
r
9
lo
Photophase,
FIG. 1.
II
I2
.1?,
14
l?i
16
17
IS
IS
hr ot 19*C
Photope~odic response curve for M. o&den&&s ~~vidua~y reared at 19°C.
At any given daylength and temperature each mite or insect will or will not enter diapause, depending on its individual response threshold, generally genetically determined. If Fig. 1 is compared with other species’ photoresponse curves (BECK, 1968), the response of the Fresno colony of M: OC~~~UZ~Schanges rather gradua1Iy with increasing daylength. According to BECK (1968), this indicates the population may be rather variable genetically for diapause induction response. Comparison of photoresponses at 19°C obtained dziring 1970 and 1972 In 1972, a second photoresponse curve was obtained, again using a 19°C constant temperature and the same photophases as above so that a comparison could be made between individually reared mites vs mass-reared mites and between the two stocks. The photoresponse curve obtained in Albany in 1972 with mass-reared mites was compared to that obtained at Reedley in 1969 with The Mann-Whitney U-test (U = 18.5) was not individually reared mites. significant and thus supports the hypothesis that both stocks adequately represented the same Fresno, California vineyard population and that the two experia mental procedures yielded comparable data.
INDUCTION OF DIAPAUSE IN METASEIULUS
OCCIDENTALLY
609
Temperature and photophase efsects on induction To study the effect of temperature on the critical daylength and photoresponse curve, mass-reared mites were tested at constant temperatures of 16, 19, 22, 25, and 30°C. Photophases tested were: 0, 10, 11, 12, 13, 16, 18, and 24 hr of light. Two rearing units of 35 or 50 mites were placed into each combination of temperature and photophase tested. A check was included in each temperature series to indicate if genetic changes or seasonal effects influenced results. Since 25°C was not expected to provide any diapausing females except possibly at the extra-long, 18 hr photophase (HoY, unpublished data), two 30°C trials were substituted for two of the 25°C photophases. At 3O”C, 18 and 24 hr photophases were tested to detect a potential aestival diapause. Table 1 lists the test results for temperature and photophase interactions in M. occidentalis. For 16 and 19°C the results are similar although the lower temperature yielded a more sharply defined critical daylength estimate. Again the critical daylength is between 11 and 12 hr; at 16”C, it is about 11.6 hr. TABLE ~--THE
INFLUENCE OF TEMPERATUREON THE PHOTORESPONSESOF REAREDFROM EGGS DURING 1972
M. occidentalis MASS-
o/0females in diapause under photophases tested (hr) Temperature (“C)
16 19 22 25 30
Sequence of test
Check at 0
10
11
12
13
16
18
24
19”C, 10 hr
Fourth (&*
&
&
(5:)
(4;)
(6:)
-
-
(203)
(E,
(Z)
(5:)
(5;)
(2:)
(2:)
-
(E,
(300)
(3;)
(4:)
(3:)
(2;)
(2:)
-
-
(E,
$I,
(3:)
-
-
(2;)
(1:)
(2:)
-
(E)
-
-
-
-
-
-
First Second Third Third
(1:)
(27)
* The number of females tested in each category is shown in parentheses.
Diapause induction was exhibited only within a quite narrow temperature range. Diapause was not evident under the 22, 25, or 30°C temperatures under any photophases tested. No sign of aestival diapause due to long photophases at high temperature (30°C) was noted. Developmental success was poor at longer photophases, but survivors were reproductively active. Under continuous darkness and under continuous light, diapause was absent at all temperatures tested, indicating that M. occidentalis has a Type III diapause response (BECK, 1968).
MARJORIEA. HOY
610
The ‘check’ results suggest that neither genetic photophases influenced the results (Table 1).
changes nor lengthening
Photophase effects on diap&se termination in laboratory-reared mites An experiment was conducted to determine if photophase alone influences diapause termination when temperature is held constant. The adult females used were reared individually at 19°C under an 8 hr photophase. They were mated and observed for 1 week to determine that they were in diapause (i.e. that they did not oviposit). Those in diapause were split into three groups: one was transferred to a long photophase (16 hr) ; one to a 12 hr photophase; and the other kept under the 8 hr rearing condition. Temperature was held constant at 19°C. Females were checked each 2 to 3 days to determine when oviposition began. It was hypothesized that females in diapause when transferred to the 16 hr photophase would terminate diapause quickly; those transferred into the 12 or 8 hr photophases should follow, .in that order. The results are shown in Table 2. TABLE ~-TIME REQUIREDFOR SPONTANEOUS DIAPAUSETERMINATIONBY FEMALESHELD UNDER8, 12, AND 16 hr PHOTOPHASES AT 19°C 1 week AFTER MATING*
Photophase (hr) under which termination occurred 16 12 8
Mean No. of days after transfer to first oviposition f S.D. 18.6 k 2.3 27.8 5 4.7 73.0 + 32.7
Range in No. of days
No. of mites
No. of unusual females excluded from mean
15-20 23-41 29-147
11 14 9
3i 1X 3§
* Females were reared at 19°C under an 8 hr photophase. -1_These three females died 56, 82, and 126 days after mating without ovipositing. They had mated, but were sterile or in diapause. 3 This female died 160 days after mating without ovipositing ; this longevity in a non-diapausing mite is unusual. 6 Three females apparently ‘switched’ from a non-diapause state into diapause, with a subsequent termination and resumption of oviposition. For example, one female deposited 2 eggs on day 5 and then remained inactive 72 days before producing an additional 7 eggs. The two other females behaved similarly.
The mean number of days to first oviposition followed a trend that supports the above hypothesis (Table 2). Thus, those females with the longest preoviposition period (73 days) were the ones held under rearing conditions (i.e. the 8 hr photophase at 19’C). The next longest mean time (27.8 days) occurred in the 12 hr photophase, and the quickest termination occurred under the long-day photophase of 16 hr. Thus, M. occidentalis can respond to long photophases while in diapause; this means that laboratory manipulation of diapause is easy with this stock from Fresno, California.
INDUCTION OF DIAPAUSE IN METASEIULUS
OCCIDENTALS
612
Table 2 shows that several females were excluded from the calculations of the means, however. The unusual behaviour of 3 females transferred into the 8 hr photophase was interpreted to be due to a ‘switch-over’ by adults from an initial non-diapause state to a diapause condition. Eventual spontaneous diapause termination then occurred with resumption of oviposition. These three females’ history suggests that induction might occur in the adult stadium. This possibility has been studied (HoY, 1975). Acknowledgements-NIy appreciation is extended to Dr. CARL B. HWFAKER for his inspiring and valued discussions. Professor P. S. MESSENGERand Mr. CHARLESKENNETT kindly made constant temperature chambers available for this study. Dr. D. L. FLAHERTY offered valuable advice during the course of the research. REFERENCES BECK S. D. (1968) Insect Photoperiodism. Academic Press, New York. CROFT B. A. (1971) Comparative studies on four strains of TyphZodromus occidentalis (Acarina: Phytoseiidae)-V. Photoperiodic induction of diapause. Ann. ent. Sot. Am. 64,962-964. HOY M. A. (1975) Diapause in the mite Metaseiulus occidentalis: stages sensitive to photoperiodic induction. r. Insect Phyiol. In press. HOY M. A. and FLAHERTYD. L. (1970) Photoperiodic induction of diapause in a predaceous mite, Metaseiulus occidentalis. Ann. ent. Sot. Am. 63, 960-963. HUFFAKERC. B., VAN DE VRIE M., and MCMURTRYJ. A. (1969) The ecology of tetranychid mites and their natural control. A. Rev. Ent. 14, 125-174. HUFFAKERC. B., VAN DE VRIE M., and MCMURTRY J. A. (1970) Ecology of tetranychid mites and their natural enemies: A review-II. Tetranychid populations and their possible control by predators: an evaluation. Hilgardia 40, 391-458. KNISLEY C. B. and SWIFT F. C. (1971) Biological studies of AmbZyseius umbraticus (Acarina: Phytoseiidae). Ann. ent. Sot. Am. 64, 813-822. MCMURTRY J. A., HUFFAKER,C. B., and VAN DE VRIE M. (1970) Ecology of tetranychid mites and their natural enemies: A review-I. Tetranychid enemies: their biological characters and the impact of spray practices. Hilgardia 40, 331-390. ROCK C., YEARGAND. R., and RABB R. L. (1971) Diapause in the phytoseiid mite, Neoseizdus (T.) fallacis. J. Insect Physiol. 17, 1651-1659. SAPOZHNIKOVA F. D. (1964) Photoperiodic response of the mite Typhlodromus (AmbZyseius) similis (C. L. Koch) (Acarina: Phytoseiidae). ZooZ. Zh. 43, 1140-1144.