Effects of starvation on reproduction of the predaciousmite Neoseiulus californicus (Acari: Phytoseiidae)

Shingo Toyoshima Æ Peter Michalik Æ Giovanni Talarico ÆAnja E. Klann Æ Gerd Alberti

Received: 28 April 2008 / Accepted: 20 October 2008 / Published online: 6 November 2008� Springer Science+Business Media B.V. 2008

Abstract Effects of starvation on gravid females of Neoseiulus californicus were

investigated at 20�C and 85% RH. When females that had been reared with abundant prey

were swapped, just after laying their first egg, to conditions without any prey and water,

they laid 1.8 eggs and survived for 4.3 days. In the body of well-fed females, an egg with

eggshell and/or two oocytes were observed in the ventral and dorsal regions, respectively.

The larger oocyte had two roundish nuclei and abundant yolk granules, and was enveloped

with a vitelline membrane. These two nuclei were not fused but were just close to each

other. The smaller oocyte had a nucleus, but had not yet formed yolk granules and vitelline

membrane. Females after 12 h starvation had an egg in the ventral region and an oocyte in

the dorsal region of the body. After more than 24 h starvation females maintained an

oocyte in the dorsal region of the body, but had no egg in the ventral region. The oocyte

was filled with abundant yolk granules and contained two irregular nuclei when females

were starved for 24 h, but when starved for more than 36 h it contained one irregular

nucleus. These findings suggest that (1) gravid females maintained an oocyte in the dorsal

region after laying two eggs during starvation, (2) the oocyte was not absorbed during

starvation, (3) the oocyte advanced vitellogenesis and the fusion of two nuclei, and (4) the

vitellogenic oocyte was not enveloped with an eggshell and had not started embryogenesis.

Keywords Neoseiulus californicus � Starvation � Survival � Oogenesis �Sex ratio

S. Toyoshima (&)National Institute of Fruit Tree Science, Morioka 020-0123, Japane-mail: toyosin@affrc.go.jp

P. Michalik � G. Talarico � A. E. Klann � G. AlbertiZoological Institute and Museum, Ernst-Moritz-Arndt-University Greifswald,Johann-Sebastian-Bach-Strasse 12/12, 17489 Greifswald, Germany

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Exp Appl Acarol (2009) 47:235–247DOI 10.1007/s10493-008-9211-5

Introduction

Neoseiulus californicus (McGregor) is an important natural enemy to control spider mites

on various crops in the world (e.g., Hoddle et al. 1999; Greco et al. 2005; Gerson and

Weintraub, 2007). In Japan, indigenous populations of N. californicus control spider mites

on pear and citrus trees (Katayama et al. 2006; Kawashima et al. 2006), and a commer-

cially available strain of N. californicus is used for the control of spider mites on

strawberry in the greenhouses (Miyata and Masuda 2006). Since the species does not occur

indigenously in apple orchards (Toyoshima 2003), attempts to control two-spotted spider

mites on apple trees with the commercial N. californicus have been conducted. In the

attempts, continuous and abundant release of the commercial agent was successful in

controlling the mites (S. Toyoshima, unpublished), but control failed when the predators

were released at an economically acceptable rate (Toyoshima and Osakabe 2005).

The present study was performed to explore possible reasons for the failure to establish

effective populations. Perhaps the condition of the mites prior to their release in the

orchards plays a key role. In particular, the nutritional state of the mites may be of

importance. Thus, in this study, the effect of starvation on oogenesis, survival and ovi-

position of N. californicus was investigated, to estimate the survival strategy of

N. californicus under no- or low-prey conditions.

The commercial N. californicus undergoes an extensive journey without prey from the

provider in Europe to Japan. Strong starvation may affect foraging behavior of phytoseiid

mites although the food deprivation elicits ambulatory dispersal of N. californicus (Auger

et al. 1999; Palevsky et al. 1999). The prey source during the journey is only own eggs and

immature stages in the delivery bottle. Some phytoseiid species consume phytoseiid eggs

and immatures to prolong their life span and to sustain egg production (Schausberger

2003). N. californicus also consumed own eggs and immatures, but preferred heterospecific

to conspecific predation (Palevsky et al. 1999; Schausberger and Croft 1999). Since

N. californicus females survived significantly longer (22.4 day, after the first egg was laid)

than the other species when food was short (Williams et al. 2004), females may resorb eggs

in their body to survive prey scarcity. In various insect species, oosorption (resorption of

oocytes) is known as an effective mechanism to save and use resources in the eggs (Bell

and Bohm 1975). Evidence for oosorption has not been found in other phytoseiid species

(Croft et al. 1995), but oosorption in N. californicus was not investigated. If N. californicusfemales would resorb eggs in their body when prey is scarce or absent, they likely would

survive longer without food than unable phytoseiid species. Thus, we investigated whether

oosorption occurs under scarce-food conditions in N. californicus.

Di Palma and Alberti (2001) have explored the detailed structure of the female genital

system in phytoseiid mites. They distinguished four stages of oocyte development in

relation to cell growth and yolk deposition (vitellogenesis) in mated females. Several

oocytes belonging to stages 1 and 2 were located within the ovary. A large stage-3 oocyte

that had just started vitellogenesis was located dorsally in the ovary. A stage-4 oocyte had a

good amount of yolk deposition and was located dorsally and posteriorly in the ovary,

lateral to the stage-3 oocyte. We identified the stages of oocytes in starved females and

compared them with those in the body of well-fed females.

It is also possible that the commercial N. californicus does not establish a population on

apple trees as a result of the low rate of increase just after severe food deprivation. After

deprivation, fecundity and progeny survival of N. californicus were low, and progeny sex

ratio was more male biased (Palevsky et al. 1999). Phytoseiid females conditionally adjust

offspring sex ratio in response to the presence of conspecifics or their cues (Nagelkerke and

236 Exp Appl Acarol (2009) 47:235–247

123

Sabelis 1998) and to the prey consumption rate (Toyoshima and Amano 1998). Several

species of phytoseiid mites usually produce offspring with female-biased sex ratio when

prey is abundant (Sabelis 1985), and decrease the bias of sex ratio gradually into even

another extreme under certain conditions (Friese and Gilstrap 1982; Dinh et al. 1988;

Nagelkerke and Sabelis 1998; Momen 1996). Such sex allocation may be more economical

due to a more efficient use of nutrition. Since the eggs that develop into males (male eggs)

are smaller than eggs that develop into females (female eggs) in Phytoseiulus persimilisand Amblyseius womersleyi (Toyoshima and Amano 1998), N. californicus females thus

may also conserve nutrition by laying more male eggs than female eggs.

If N. californicus females would resorb eggs and manipulate the sex of subsequent eggs

during starvation, they would survive well even when prey is scarce or absent but the

establishment of a population would be delayed. Thus, sex ratios of eggs laid by starved

females were also compared with those laid by well-fed females.

Materials and methods

Phytoseiid mites for experiment

We obtained the commercial product of N. californicus (Spical�: Koppert Biological

Systems, Berkel en Rodenrijs, The Netherlands) and transferred the adult females onto

kidney bean leaflets infested with the two-spotted spider mite Tetranychus urticae Koch.

Neoseiulus californicus were reared in a room with a constant temperature of 22 ± 1�C.

Photoperiod in the room was not controlled but around L15:D9 h during experiments.

Temperature and photoperiod conditions were the same in rearing and experiments.

Survival under no-prey condition

Newly developed adult females were coupled individually with males, and reared on a

leaflet (3 9 3 cm) with an abundance of prey eggs. Under these conditions, the mated

females laid the first egg ca. 24 h after mating and thereafter eggs were laid one by one at a

rate of ca. two eggs per day. Then, females were observed at 3-h intervals during daytime

(6:00–18:00), and females that had already laid an egg at 6:00 h were removed from the

experiment.

Within 3 h after laying the first egg, the females were transferred individually into

rearing cases, each consisting of two yellow micropipette tips, one pressed in the other,

both plugged with a piece of wooden toothpick—the mite was then captured in the ca.

15 mm long space between the two tips. The rearing cases were placed in a plastic

container (3 cm in diameter, 1.5 cm high) along with a wet sponge in order to maintain the

relative humidity inside the container at 85 ± 2%.

The females were kept in the case without prey and water until they died; survival and

oviposition were monitored twice a day. Any eggs in the case were removed when

observed, and dead females were embedded in Hoyer’s medium (Krantz 1978) in order to

confirm whether they held eggs in their bodies. The females were observed under a phase-

contrast microscope (Olympus BX60). Regarding intraspecific consumption (cannibalism)

by adult females, it had been confirmed beforehand that N. californicus females in this

study did not consume own eggs within 24 h, even without prey.

Exp Appl Acarol (2009) 47:235–247 237

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Eggs in the females during starvation

Females were transferred into the rearing case within 3 h after laying the first egg and were

reared for 12, 24, 36, or 48 h without prey and water. They were observed twice a day to

check their oviposition. Ten females with different oviposition history (0, 1 or 2 eggs laid)

were collected in each starvation period and embedded separately into Hoyer’s medium.

Sex ratios of eggs laid by females after starvation treatment

Females were transferred into the rearing case within 3 h after laying the first egg and were

reared for 48 h without prey and water. Females that had laid two eggs in the case were

transferred onto a bean leaflet with abundant prey and reared until they had laid three eggs

on the leaflet. The six eggs laid by each female (one egg before starvation, two in the

rearing case, three after starvation) were reared separately to check their sex. Since the

reproductive activity of starved females was fully recovered only after laying the three

eggs, the sequence of eggs laid could not be distinguished by the observation twice a day.

To compare the sex ratios of eggs produced by starved females with those produced by

well-fed females, eggs were also obtained from the latter females. These females were

reared on the bean leaflet with abundant prey until they had laid more than six eggs. To

obtain the eggs in sequence, oviposition was checked four times a day.

The effect of starvation on the sex ratios was analyzed in eggs in sequence with the non-

parametric Fisher’s exact test (using JMP� software, version 6.0.2, from SAS, Cary, NC,

USA).

Internal observation of females

Females that had laid their first egg were kept separately for 12, 24, 36, 48, 72, or 96 h in

rearing cases without prey and water. Then females were dissected and prefixed overnight

in ice-cold glutaraldehyde (3.5% glutaraldehyde in 0.1 M phosphate buffer; pH 7.4).

Further processes included postfixation with 2% OsO4 for 2 h, rinsing in buffer, dehy-

dration in graded ethanol, and embedding in Spurr’s medium. Semi- and ultrathin sections

were cut using a microtome (Ultracut UCT; Leica Microsystems) with glass knives and a

diamond knife (Diatome), respectively. The semithin sections were stained with Rich-

ardson’s stain and oocytes were observed under a light microscope (Olympus BX60). The

ultrathin sections were stained with saturated uranylacetate (in 70% methanol) and lead

citrate for 10 min each and were examined under a transmission electron microscope

(JEM-1011; JEOL Ltd).

Results

Survival under no-prey condition

Just after laying the first egg, females laid 1.8 ± 0.1 eggs and survived for 4.3 ± 0.7 days

(mean ± SE; n = 30) in the rearing case without prey and water (Fig. 1). Females laid

eggs within 24 h after the beginning of the starvation period, and no female laid more than

three eggs. Starved females held no egg in their body when dead. Maximum period of

survival was 16 days.

238 Exp Appl Acarol (2009) 47:235–247

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Eggs in the females during starvation

When females were mounted after 12 h starvation, 10 females that had not yet laid an egg

did contain an egg in their body, seven females held an egg even if they had already laid an

egg, and three females that had not yet laid an egg contained no egg in their body. When

females were mounted after 24 h starvation or longer, no females contained an egg in their

body, regardless of the number of eggs laid during starvation.

Sex ratios of eggs laid by females after starvation treatment

Females that had starved for 48 h (n = 38) laid an egg within 24 h, but not within 12 h,

after transfer onto the bean leaflet with abundant prey. All eggs that had been laid before,

during and after starvation, were collected in sequence. Sex ratios (number of adult

daughters/number of adult daughters plus sons) are shown in Fig. 2. Sex ratio of the first

eggs laid by the starving females was 11% (strong male-bias). Sex ratio of the second and

third eggs, which were laid in the rearing cases, was 84 and 53%, respectively. Sex ratios

of the fourth, fifth, and sixth eggs, laid on the leaflet after starvation, were 79, 55 and 58%,

respectively.

On the other hand, sex ratio of eggs laid by well-fed females (n = 40) was 8% (1st),

88% (2nd), 60% (3rd), 80% (4th), 73% (5th) and 83% (6th).

Sex ratio of the 1st–5th eggs laid by starvation-treatment females was not significantly

different from that of well-fed females (Fisher’s exact test, n = 1, P = 0.71, 0.75, 0.71, 1.0

and 0.16, respectively). Only the difference in sex ratio between the sixth eggs was sig-

nificant (P = 0.03).

Internal observation of females just before the starvation treatment

Females just before the starvation treatment held an egg and well-developed oocytes in

their body (0 h of starvation in Table 1). Among the nine females, five had a mature egg in

the ventral region and a large vitellogenic oocyte (oocyte at the stage 4) in the dorsal region

of the body. The egg in the ventral region was located in the uterus, and was usually

surrounded by an eggshell (four of the five females). The remaining four females held two

oocytes (stages 3 and 4), both located in the dorsal region of the body (Fig. 3).

0

20

40

60

80

100

0

Sur

viva

l rat

e (%

)

days18 16 14 12 10 8 6 42

Fig. 1 The survival curve ofadult females of Neoseiuluscalifornicus under no-preycondition

Exp Appl Acarol (2009) 47:235–247 239

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0

20

40

60

80

100

1st 2nd 3rd 4th 5th 6th

Fem

ale

ratio

(%

)

The sequence of eggs

Starved females Well-fed females

(A) (B)

Fig. 2 The sex ratios of the first six eggs produced by females reared for 48 h under no-prey condition(starved females; black bar) or by females reared permanently under abundant prey condition (well-fedfemales; white bar). Sex was determined when the eggs had grown into adults. Arrow A indicates when thestarved females were transferred into rearing cases. Arrow B indicates when the starved females weretransferred onto leaflets with abundant prey. The period between A and B was 48 h, and the second and thirdeggs of starved females were laid during this period. The female ratios of the offspring of the sixth eggs laidby the well-fed females were significantly different from those laid by the starved females (Fisher’s exacttest, n = 1, P = 0.03)

Table 1 The number of females with eggs and/or oocytes in their body when starved

Period of starvation (h) No. of eggsa Combination of egg and oocytesb

E ? O4 O4 ? O3 O4 O3

0 – 5 4 0 0

12 0 5 1 1 0

1 3 0 3 0

24 1 0 0 6 0

2 0 0 8 0

36 1 0 0 2 0

2 0 0 6 0

48 1 0 0 3 0

2 0 0 7 0

72 1 – – – –

2 0 0 4 0

96 1 0 0 5 0

2 0 0 5 1

a The number of eggs laid during starving treatmentb Developmental stages of oocytes

E, a matured egg in the uterus at the ventral region of the body; O4, oocyte at stage 4 in the dorsal region;O3, oocyte at stage 3 in the dorsal region. These oocytes were distinguished with a light microscope.Referred to the Fig. 3

240 Exp Appl Acarol (2009) 47:235–247

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It was difficult to observe the detailed structure and embryogenesis in the egg if sur-

rounded with eggshell, because the shell prevented penetration of the fixative into the egg.

Without shell, however, a single nucleus was seen in the center of the egg (Fig. 4a). There

was no evidence for the start of embryogenesis within eggs that lacked the shell.

A single nucleus was detected in the oocyte at stage 3 (not shown in Fig. 4a). Two

roundish nuclei were observed in the large vitellogenic oocyte (stage 4) (Fig. 4b). These

two nuclei were close to each other but not fused (Fig. 4c). The vitellogenic oocyte was

forming a vitelline membrane (Fig. 4d). Also stages 1 and 2 oocytes were detected in the

ovary (Fig. 4e).

Internal observation of females with starvation treatment

Females were collected separately based on duration of starvation and number of eggs laid

during starvation (Table 1). When females laid no egg during 12 h starvation, they held an

oocyte (stage 4) in the dorsal region (n = 1), 2 oocytes (stages 3 and 4) in the dorsal region

(n = 1), or 1 oocyte (stage 4) in the dorsal region along with a mature egg in the ventral

region (n = 5). When females laid an egg during 12 h starvation, they held an oocyte

(stage 4) in the dorsal region (n = 3) or an oocyte (stage 4) in the dorsal region along with

a mature egg in the ventral region (n = 3).

Regardless of the duration of starvation and the number of eggs laid during the star-

vation period, the females with more than 24 h starvation held a large vitellogenic oocyte

(stage 4) in the dorsal region, but no mature egg in the uterus (Table 1; Figs. 5a, 6a). Two

nuclei were observed in the oocyte at stage 4 in the female with 24 h starvation (Fig. 5b,

c). On the other hand, a single nucleus was observed in the stage-4 oocyte in almost all

females with more than 24 h starvation (Fig. 6b, c). In any case, the shape of the nucleus

was not round but irregular, as compared to the nucleus in the oocytes of well-fed females.

Stage-2 oocytes in the ovary had an irregular shaped nucleus (Figs. 5e, 6e) as that in the

lyrate organ (Fig. 5d). The vitelline membrane of the oocyte was formed even in females

with 96 h starvation (Fig. 6d), just as in well-fed females (Fig. 4d).

O3 O4

E

Fig. 3 Schematic illustration of the sagittal section of an adult female of Neoseiulus californicus fixedwithin 3 h after laying of the first egg. The females had one oocyte in the uterus located in the ventral regionand one in the dorsal region, or two oocytes in the dorsal region. The detailed structure of the egg in theuterus could not be observed because it was enveloped by the eggshell that prevented the penetration of thefixative. An oocyte developed up to stage 4 having two nuclei and abundant yolk granules. Another oocytedeveloped up to stage 3 with one nucleus but no yolk granules. Abbreviations: E, mature egg in the uterus;O3, stage-3 oocyte; O4, stage-4 oocyte

Exp Appl Acarol (2009) 47:235–247 241

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Discussion

In this study, N. californicus females did not stock nutrients in their body, but invested

them in egg production, even under no-prey condition. They laid 1.8 eggs without food in

Fig. 4 Internal structures of an adult female that had not been starved. The females were fixed within 3 h afterlaying the first egg. a Sagittal section of an adult female with a mature egg in the uterus. Arrow head shows anucleus of the egg. Light microscopy. Scale bar = 50 lm. b Stage-4 oocyte with two nuclei. Transmissionelectron microscopy (TEM). Scale bar = 10 lm. c Detailed structure of the adjacent two nuclei shown in (b).The two nuclei have not yet fused. TEM. Scale bar = 1 lm. d The boundary between the stage-4 oocyte and theadjacent tissues. The vitelline membrane is being formed (arrowheads). TEM. Scale bar = 2 lm. e The centerof the ovary adjacent to the lyrate organ. Arrowheads show nuclei in the oocytes at stage 2. TEM. Scalebar = 10 lm. Abbreviations: E, mature egg; G, genital opening; L, lyrate organ; N1, N2, nuclei; No, nucleolus;O2, stage-2 oocyte; O4, stage-4 oocyte; Yl, lipid-yolk granule; Yp, protein-yolk granule

242 Exp Appl Acarol (2009) 47:235–247

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the rearing cases. Egg production without food is common in phytoseiid mites (Croft and

Croft 1996), and eggs were sometimes consumed by ovipositing females when food was

absent (Schausberger 2003). In the case of N. californicus, females can prolong their life

Fig. 5 Internal structures of an adult female reared for 24 h under no-prey condition. a Sagittal section ofthe adult female with an oocyte in the dorsal region. Light microscopy. Scale bar = 50 lm. b Stage-4oocyte showing two nuclei. Transmission electron microscopy (TEM). Scale bar = 5 lm. c The detailedstructure of the adjacent two nuclei in (b). The two nuclei are very close to each other but remain separate.TEM. Scale bar = 1 lm. d A part of the lyrate organ. TEM. Scale bar = 2 lm. e The center of the ovary.TEM. Scale bar = 5 lm. Abbreviations: G, genital opening; L, lyrate organ; M, mitochondria; N, N1, N2nuclei; No, nucleolus; NLS, nucleus-like-structure; O2, stage-2 oocyte; O4, stage-4 oocyte; U, uterus; Yl,lipid-yolk granule; Yp, protein-yolk granule

Exp Appl Acarol (2009) 47:235–247 243

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span when feeding on conspecific eggs and larvae (Walzer and Schausberger 1999a), but

normally avoid cannibalism (Walzer and Schausberger 1999b). In our study, females did

not consume eggs laid in a rearing case, because the eggs were removed within 3 h after

oviposition. As a result, they did not encounter any food and survived only 4.3 days. In

Fig. 6 Internal structures of an adult female reared for 96 h under no-prey condition. a Sagittal section ofthe adult female with an oocyte in the dorsal region. Light microscopy. Scale bar = 50 lm. b Stage-4oocyte with a nucleus. TEM. Scale bar = 10 lm. c The detailed structure of the nucleus in (b). TEM. Scalebar = 2 lm. d The boundary between the stage-4 oocyte and the lyrate organ. Formation of the vitellinemembrane was maintained (arrowheads). TEM. Scale bar = 2 lm. e Stage-2 oocyte in the ovary. TEM.Scale bar = 5 lm. Abbreviation: G, genital opening; L, lyrate organ; N, nucleus; No, nucleolus; O2, stage-2oocyte; O4, stage-4 oocyte; Yl, lipid-yolk granule; Yp, protein-yolk granule

244 Exp Appl Acarol (2009) 47:235–247

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previous studies, N. californicus females (after laying the first egg) survived only 1.8 days

when deprived of food and water (Williams et al. 2004), although they survived longer

when deprived of food but supplied with water (Palevsky et al. 1999; Williams et al. 2004).

The females in our study probably would have survived longer if water had been supplied

in the rearing cases.

In the body of 12-h starved females, an egg with eggshell was observed. This egg was

laid during the following starvation period, and no egg with eggshell was observed in

females with more than 24 h starvation. The stage-4 oocyte appeared from 24 h after the

starvation treatment and was maintained for at least 96 h in the dorsal region of the body

(Figs. 5, 6). It seems evident that females do not absorb the egg with shell and stage-4

oocyte to obtain nutrition for further survival. Neoseiulus californicus females may not

need the oosorption because they can prolong their life span when water is supplied

(Palevsky et al. 1999; Williams et al. 2004). They seem to prefer reproduction over

survival even under scarce prey condition. Eggs can hatch if ovipositing females avoid

cannibalism, and then larvae would survive and develop to adulthood if they encounter

prey later on.

Stage-2 oocytes with a single nucleus were observed in females with more than 24 h

starvation, but no stage-3 oocyte was observed (Figs. 5e, 6e). In insects, oosorption

includes cessation of oocyte production in the ovary and formation of a plug at the entrance

of the oviduct (Bell and Bohm 1975). Neoseiulus californicus females may stop producing

vitellogenic oocytes or may absorb oocytes at stage 3 that have just started to grow

between 12 and 24 h of starvation. However, there is no evidence whether stage-3 oocytes

were absorbed or stopped growing in the starved females.

The effect of starvation on gravid females was limited to the oocyte in the ovary.

Starvation treatment did not affect the sex of stage-4 oocytes in the starved females, that

laid these oocytes as the 4th egg when females resumed feeding (Fig. 2). The vitellin

membrane around the stage-4 oocyte (Figs. 4d, 6d) may protect the oocyte against stress

caused by the starvation of the mothers. On the other hand, the sex of oocytes in the ovary

was influenced by the starvation treatment: some of the 6th eggs apparently changed their

sex from female to male (Fig. 2). Since the offspring sex ratio of starved females of N.californicus recovered within 9 days after resuming prey consumption (Palevsky et al.

1999), the sex ratio of later eggs is expected to gradually get back to the female-biased sex

ratio also under the experimental conditions in this study.

The mode of reproduction in phytoseiid mites is known as pseudoarrhenotoky, where

males arise from fertilized eggs that become haploid after inactivation or elimination of the

paternal chromosomes (Nelson-Rees et al. 1980). It is difficult to imagine the sex-deter-

mining mechanism in this mode of reproduction as compared to that in an arrhenotokous

mode (Bull 1983), despite the maintenance of the precise control of the sex ratio in

phytoseiid mites in relation to prey density (Sabelis and Nagelkerke 1993). In the present

study, we found that N. californicus females did not resorb developed oocytes in order to

control the sex ratio of their brood when food is scarce. The oocyte was filled with

abundant yolk granules, and held two irregular-shaped nuclei when females had been

starved for 24 h. The oocyte advanced the fusion of the two nuclei but did not start

embryogenesis. For further discussion, however, a comprehensive study of the oocytes in

the ovary and in the dorsal region of the body is necessary in order to confirm whether the

oocytes are inseminated in the ovary or at another position in the body.

Acknowledgments We thank Mrs. C. Putzar for her skilful technical assistance and Mr. Ard van derMaarel (Koppert Biological Systems) for his kindness to provide N. californicus. We also thank anonymous

Exp Appl Acarol (2009) 47:235–247 245

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reviewers for their advisory comments to this manuscript. This study was financially supported by a grant-in-aid from the National Agriculture and Food Organization of Japan.

References

Auger P, Tixier MS, Kreiter S, Fauvel G (1999) Factors affecting ambulatory dispersal in the predaceousmite Neoseiulus californicus (Acari: Phytoseiidae). Exp Appl Acarol 23:235–250. doi:10.1023/A:1006019014708

Bell WJ, Bohm MK (1975) Oosorption in insects. Biol Rev Camb Philos Soc 50:373–396. doi:10.1111/j.1469-185X.1975.tb01058.x

Bull JJ (1983) Evolution of sex determining mechanisms. The Benjamin/Cummings, CaliforniaCroft BA, Croft MB (1996) Intra- and interspecific predation among adult female pytoseiid mites (ACari:

Phytoseiidae): effects on survival and reprodcution. Environ Entomol 25:853–858Croft BA, Kim SS, Kim DI (1995) Absorption and cannibalism: do phytoseiids conserve egg resources when

prey densities decline rapidly? Exp Appl Acarol 19:347–356. doi:10.1007/BF00052392Dinh NV, Janssen A, Sabelis MW (1988) Reproductive success of Amblyseius idaeus and A. anonymus on a

diet of two-spotted spider mites. Exp Appl Acarol 4:41–51. doi:10.1007/BF01213840Di Palma A, Alberti G (2001) Fine structure of the female genital system in phytoseiid mites with remarks

on egg nutrimentary development, sperm access system, sperm transfer, and capacitation (Acari,Gamasida, Phytoseiidae). Exp Appl Acarol 25:525–591. doi:10.1023/A:1014741808835

Friese DD, Gilstrap FE (1982) Influence of prey availability on reproduction and prey consumption ofPhytoseiulus persimilis, Amblyseius californicus, and Metaseiulus occidentalis (Acarina: Phytoseii-dae). Int J Acarol 8:85–89

Gerson U, Weintraub PG (2007) Mites for the control of pests in protected cultivation. Exp Appl Acarol63:658–676

Greco NM, Sanchez NE, Liljesthrom GG (2005) Neoseiulus californicus (Acari: Phytoseiidae) as a potentialcontrol agent of Tetranychus urticae (Acari: Tetranychidae): effect of pest/predator ratio on pestabundance of strawberry. Exp Appl Acarol 37:57–66. doi:10.1007/s10493-005-0067-7

Hoddle MS, Aponte O, Kerguelen V, Heraty J (1999) Biological control of Oligonychus perseae (Acari:Tetranychidae) on avocado: evaluating release timing, recovery, and efficacy of six commerciallyavailable phytoseiids. Int J Acarol 25:211–219

Katayama H, Masui S, Tsuchiya M, Tatara A, Doi M, Kaneko S, Saito T (2006) Density suppression of thecitrus red mite Panonychus citri (Acari: Tetranychidae) due to the occurrence of Neoseiulus califor-nicus (McGregor) (Acari: Phytoseiidae) on Satsuma mandarin. Appl Entomol Zool (Jpn) 41:679–684.doi:10.1303/aez.2006.679

Kawashima M, Kadono F, Shiota A, Amano H (2006) Can the population size of Neoseiulus californicus(McGregor) (Acari: Phytoseiidae) on Japanese pear trees be estimated by Phyto trap attached to thetwigs? Appl Entomol Zool (Jpn) 41:145–150. doi:10.1303/aez.2006.145

Krantz GW (1978) A manual of acarology, 2nd edn. Oregon State University Book Stores, CorvallisMiyata M, Masuda T (2006) Control of Tetranychus urticae on strawberry by Neoseiulus californicus and

hydrogenated starch hydrolysate. Annu Rep Plant Prot N Jpn 57:174–176 in JapaneseMomen FM (1996) Effect of prey density on reproduction, prey consumption and sex-ratio of Amblyseius

barkeri (Acari: Phytoseiidae). Acarologia 37:3–6Nagelkerke CJ, Sabelis MW (1998) Precise control of sex allocation in pseudo-arrhenotokous phytoseiid

mites. J Evol Biol 11:649–684. doi:10.1007/s000360050112Nelson-Rees WA, Hoy MA, Roush RT (1980) Heterochromatinization, chromatin elimination and haplo-

idization in the parahaploid mite Metaseiulus occidentalis (Nesbitt) (Acarina: Phytoseiidae).Chromosoma Berl 77:263–276. doi:10.1007/BF00286052

Palevsky E, Reuveny H, Okonis O, Gerson U (1999) Comparative behavioural studies of larval and adultstages on the phytoseiids (Acari: Mesostigmata) Typhlodromus athiasae and Neoseiulus californicus.Exp Appl Acarol 23:467–485. doi:10.1023/A:1006187402722

Sabelis MW (1985) Sex allocation. In: Helle W, Sabelis MW (eds) Spider mites, their biology, naturalenemies and control, vol 1B. Elsevier, Amsterdam, pp 83–94

Sabelis MW, Nagelkerke CJ (1993) Sex allocation and pseudo-arrhentoky in phytoseiid mites. In: WrenschDL, Ebbert MA (eds) Evolution and diversity of sex ratio in insects and mites. Chapman & Hall, NewYork, pp 512–541

Schausberger P (2003) Cannibalism among phytoseiid mites: a review. Exp Appl Acarol 29:173–191.doi:10.1023/A:1025839206394

246 Exp Appl Acarol (2009) 47:235–247

123

Schausberger P, Croft BA (1999) Predation on and discrimination between con- and heterospecific eggsamong specialist and generalist phytoseiid mites. Environ Entomol 28:523–528

Toyoshima S (2003) A candidate of predatory phytoseiid mites (Acari: Phytoseiidae) for the control of theEuropean red mite, Panonychud ulmi (Koch), (Acari: Tetranychidae) in Japanese apple orchards. ApplEntomol Zool (Jpn) 38:387–391. doi:10.1303/aez.2003.387

Toyoshima S, Amano H (1998) Effect of prey density on sex ratio of two predacious mites, Phytoseiuluspersimilis and Amblyseius womersleyi (Acari: Phytoseiidae). Exp Appl Acarol 22:709–723.doi:10.1023/A:1006093424452

Toyoshima S, Osakabe M (2005) Effects of artificially released Neoseiulus californicus (Acari: Phyto-seiidae) and naturally occurring Orius minutus (Hemiptera: Anthocoridae) on Tetranychus urticae(Acari: Tetranychidae) population in apple orchard without insecticides. Annu Rep Soc Plant Prot NJpn 56:188–190 in Japanese with an English summary

Walzer A, Schausberger P (1999a) Cannibalism and interspecific predation in the phytoseiid mites Phy-toseiulus persimilis and Neoseiulus californicus: predation rates and effects on reproduction andjuvenile development. Biocontrol 43:457–468. doi:10.1023/A:1009980401662

Walzer A, Schausberger P (1999b) Predation preferences and discrimination between con- and heterospe-cific prey by the phytoseiid mites Phytoseiulus persimilis and Neoseiulus californicus. Biocontrol43:469–478. doi:10.1023/A:1009974918500

Williams MEDC, Kravar-Garde L, Fenlon JS, Sunderland KD (2004) Phytoseiid mites in protected crops:the effet of humidity and food availability on egg hatch and adult life span of Iphieius degenerans,Neoseiulus cucumeris, N. californicus and Phytoseiulus persimilis (Acari: Phytoseiidae). Exp ApplAcarol 32:1–13. doi:10.1023/B:APPA.0000018170.46836.11

Exp Appl Acarol (2009) 47:235–247 247

123