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Temperature at immature and adult stages differentially affects mating duration and egg production of Neoseiulus californicus females mated once (Acari: Phytoseiidae)
Journal of Asia-Pacific Entomology 13 (2010) 65–68
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Journal of Asia-Pacific Entomology j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / j a p e
Temperature at immature and adult stages differentially affects mating duration and egg production of Neoseiulus californicus females mated once (Acari: Phytoseiidae) Thao T.P. Nguyen, Hiroshi Amano ⁎,1 Graduate School of Horticulture, Chiba University, Matsudo, Chiba 271-8510, Japan
a r t i c l e
i n f o
Article history: Received 11 September 2009 Revised 9 October 2009 Accepted 12 October 2009 Keywords: Developmental stages Temperature Mating duration Fecundity N. californicus
a b s t r a c t A series of experiments was conducted to investigate whether temperatures of 18 °C, 25 °C, 30 °C, and 35 °C and a photoperiod of 16L:8D at immature and adult stages would differentially affect the mating duration and egg production of Neoseiulus californicus females mated once. Mating duration was strictly determined by ambient temperature at the time of mating, regardless of the temperatures under which they were raised. Compared with a consistent 25 °C condition, total fecundity of females decreased when temperature conditions of 18 °C, 30 °C, and 35 °C were applied during any life stage (immature, mating, and oviposition periods) or a combination of different stages. In general, however, if mites were raised in conditions of ≤ 25 °C, and mated and oviposited at conditions of ≥ 25 °C, total egg production was relatively high. Based on these results, the adaptation of mites to thermal environments was discussed. © Korean Society of Applied Entomology, Taiwan Entomological Society and Malaysian Plant Protection Society, 2009 Published by Elsevier B.V. All rights reserved.
Introduction Our first paper revealed that the duration of copulation and total egg production of Neoseiulus californicus mated once were significantly affected by temperature, which was kept constant throughout the mite's life (Nguyen and Amano, 2009). Pairs copulated for the longest duration when they were maintained at 18 °C and for the shortest duration at 30 °C and 35 °C. However, females produced the fewest eggs at 18 °C; egg production peaked at 25 °C and dropped at 30 °C and 35 °C. We concluded that the optimum reproductive temperature for N. californicus females was 25 °C, while lower or higher temperatures reduced their reproductive ability. (Constant) temperature conditions are well-known to determine mating duration and egg production of phytoseiid mites. As temperatures rise, the duration of copulation becomes shorter; this negative relationship between temperature and mating duration has been demonstrated in many species of phytoseiid mites such as Typhlodromus tiliae Oudemans (Herbert, 1956), Typhlodromus pyri Scheuten (Zaher and Shehata, 1971), and N. californicus (Nguyen and Amano 2009). Temperature also significantly affects N. californicus egg production, and the reproductive ability of this species is reduced when it is maintained at low or high temperatures (Gotoh et al., 2004; Canlas et al., 2006). The same trend has been reported for other phyto-
⁎ Corresponding author. Tel.:/ fax: +81 75 753 6135. E-mail address: [email protected] (H. Amano). 1 Present address: Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan.
seiid species, such as Euseius stipulatus (Athias-Henriot), Typhlodromus phialatus Athias-Henriot (Ferragut et al., 1987), Amblydromalus limonicus (Garman and McGregor) (McMurtry and Scriven, 1965), Neoseiulus cucumeris (Zhang et al., 2000), Phytoseiulus longipes Evans (Ferrero et al., 2007), Phytoseiulus fragariae Denmark and Schicha (Vasconcelos et al., 2008), Typhlodromus swirskii Denmark, and Typhlodromus athiasae Porath and Swirski (Momen and Abdel-Khalek, 2008). However, little is known about the total effects of a combination of different temperatures during immature and adult stages on mating duration and egg production of phytoseiid females. Researchers are now interested in identifying which stage of the life cycle of N. californicus is sensitive to temperature and responsible for observed differences. We carried out a series of experiments on the mating and reproductive behavior of N. californicus mites that were subjected to various temperatures during immature, mating, and oviposition periods to investigate thermal effects and possible mechanisms underlying any temperature-related effects. Materials and methods The materials and basic observation methods of copulation and oviposition in this study were the same as those described in Nguyen and Amano (2009). The N. californicus population was collected at Ichihara, Chiba, Japan, in 1995 and was maintained at the Laboratory of Applied Entomology and Zoology, Chiba University, at a temperature of 25 °C and a photoperiod of 16L:8D. Prey for the mites was the greenform of the two-spotted spider mite Tetranychus urticae Koch reared on kidney bean plants Phaseolus vulgaris L. Predaceous mites were always kept in vials with abundant prey and during the experiments,
1226-8615/$ – see front matter © Korean Society of Applied Entomology, Taiwan Entomological Society and Malaysian Plant Protection Society, 2009 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.aspen.2009.10.002
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T.T.P. Nguyen, H. Amano / Journal of Asia-Pacific Entomology 13 (2010) 65–68
vials were transferred between chambers maintained at specific temperatures: 18 °C, 25 °C, 30 °C, and 35 °C. Mating duration was observed every 5 or 10 min and any subsequent egg production was checked daily. Experimental details are described below under separate headings. Throughout the text, we use the generic names proposed by Chant and McMurtry (2007). Mating duration and estimated transferred sperm volume Immature mites that developed at temperatures of 18 °C, 25 °C, 30 °C, and 35 °C were transferred to a chamber with identical or differing temperature conditions and kept there for one day. Each mite engaged in a single mating. Table 1 lists the combinations of temperature conditions during immature development and during mating, by experimental code. A total of 16 different combinations (Exp. codes) were used in the study. To estimate the volume of sperm ejaculated into the female spermatheca (female mites each have a pair of spermathecae inside their body cavity) immediately after copulation was completed, females were killed and mounted on Hoyer's medium. The size of the spermatophore (or the mass of sperm and seminal fluid) injected by each male was estimated by measuring the size of the inflated vesicle of the female spermatheca, using a micrometer attached to a phasecontrast microscope. Previous research has demonstrated a positive relationship between spermatophore size and the resultant total egg production (Amano and Chant, 1978; Schulten et al., 1978).
Table 2 Total egg production of N. californicus females under different temperature regimes. Exp. Code
111 211 212 121 122 221 222 223 224 322 323 422 424 232 233 333 242 244 444
Temperature (°C) at different stages Immature
Mating
Oviposition
18 25 25 18 18 25 25 25 25 30 30 35 35 25 25 30 25 25 35
18 18 18 25 25 25 25 25 25 25 25 25 25 30 30 30 35 35 35
18 18 25 18 25 18 25 30 35 25 30 25 35 25 30 30 25 35 35
No. of females examined
Total egg production (means ± SD)
12 15 10 10 9 11 10 10 11 9 8 9 9 10 13 11 13 11 10
13.9 ± 8.8d 30.7 ± 5.3bc 31.9 ± 6.1bc 26.4 ± 3.1bc 35.4 ± 8.5ab 33.3 ± 2.4bc 46.1 ± 3.6a 35.7 ± 4.1ab 34.2 ± 6.6ab 33.4 ± 6.4bc 31.5 ± 9.5bc 29.6 ± 8.3bc 28.2 ± 10.2bc 27.1 ± 6.4bc 29.8 ± 10.3bc 26.6 ± 3.6bc 28.1 ± 12.4bc 27.8 ± 8.2bc 23.9 ± 11.4cd
The means followed by different letters within the same column are significantly different (one-way ANOVA and Tukey HSD test; p b 0.05). Exp. Code: Three digits indicate temperatures (1; 18, 2; 25, 3; 30, 4; 35) at immature, mating and oviposition periods in order, respectively. Data for Exp. Codes 111, 222, 333 and 444 were collected from Nguyen and Amano (2009).
Egg production After the single mating, females were kept on leaflets with prey under four different temperature conditions. Due to the large number of combinations of experimental temperature, observations were generally concentrated on the mating temperature of 25 °C. In total, 19 different combinations (Exp. codes) were used in the analysis (see Table 2). Data analysis A one-way analysis of variance was used to determine the overall statistical significance of each variable (duration of copulation, Table 1 Effects of constant and a combination of different temperatures at immature and mating stages of N. californicus on mating duration and spermatophore diameter. Exp. Code Temperature (°C) at different stages Immature Mating 11 21 31 41 12 22 32 42 13 23 33 43 14 24 34 44
18 25 30 35 18 25 30 35 18 25 30 35 18 25 30 35
18 18 18 18 25 25 25 25 30 30 30 30 35 35 35 35
Mating duration Diameter of No. of spermatophore in minutes females (μm) (means ± SD) examined (means ± SD) 17 10 12 11 10 10 8 9 11 10 10 13 12 15 11 10
533.6 ± 45.7 520.8 ± 74.1 516.2 ± 58.1 511.8 ± 56.1 323.5 ± 38.1 315.3 ± 35.7 319.5 ± 95.1 301.9 ± 39.6 289.1 ± 38.4 240.7 ± 35.3 261.2 ± 34.1 241.2 ± 61.1 259.7 ± 45.8 271.2 ± 50.4 250.1 ± 53.5 253.6 ± 41.9
a a a a b b b b bc c c c c bc c c
44.7 ± 13.8 ns 37.2 ± 10.6 36.7 ± 12.9 32.3 ± 18.1 36.2 ± 10.3 37.7 ± 10.4 39.9 ± 9.5 44.1 ± 7.8 38.0 ± 9.4 41.1 ± 9.5 34.8 ± 16.7 30.0 ± 10.4 35.3 ± 12.6 34.2 ± 10.4 41.8 ± 8.7 35.0 ± 11.2
The means followed by different letters within the same column are significantly different (one-way ANOVA and Tukey HSD test; p b 0.05), and ns indicates not significant (one-way ANOVA; p N 0.05). Exp. Code: Two digits indicate temperatures (1; 18, 2; 25, 3; 30, 4; 35) at immature and mating periods in order, respectively. Data for Exp. Codes 11, 22, 33 and 44 were collected from Nguyen and Amano (2009).
diameter of female spermatophore, and total egg production). Tukey's honestly significant difference test (Landau and Everitt, 2004) was applied to test for pair-wise comparisons among individual means. Results Mating duration and estimated volume of transferred sperm Table 1 lists the durations of copulation for pairs that completed their immature development and mated at various temperatures. The table also lists the diameters of spermatophores in the female spermatheca. Statistical analyses clearly revealed that mating duration was determined by the temperature during mating, and that it was not influenced by the temperature at which the mites were raised. Males generally transferred only one spermatophore each into a single female spermatheca, and there were no cases in which more than two spermatophores were injected into a spermatheca. The results of sperm transfer at the various temperatures revealed no clear trend in spermatophore diameter (or appearance), because treatment means were not significant. Egg production Table 2 lists total female egg production under 19 temperature regimes. Unlike copulation duration, trends for total egg production were complicated. Mean total egg production differed among the four different mating temperature groups (df = 18 and 181, F = 7.126, p b 0.0001). Females that were raised, mated, and oviposited at 18 °C (Exp. code 111) produced the fewest eggs (13.9 eggs/female). Total egg production by females that mated at 18 °C, 30 °C, and 35 °C was also generally low. Total egg production was greatest (46.1 eggs/female) at a constant temperature of 25 °C (Exp. code 222). Three experimental conditions (Exp. codes 122, 223, and 224) did not differ significantly from this mean value; although these females spent their immature and oviposition stages at different temperatures, they all mated at 25 °C.
T.T.P. Nguyen, H. Amano / Journal of Asia-Pacific Entomology 13 (2010) 65–68
Fig. 1. Total egg production (A) and daily egg production (B) of N. californicus females mated at 25 °C with differing temperatures at the immature and oviposition stages. The various bar patterns shown in (A) indicate statistically separate groups as shown in Table 2; data for Exp. Code 222 were collected from Nguyen and Amano (2009).
Total egg production (see Table 2) and daily fecundity of females that mated at 25 °C are illustrated in Figs. 1A and B, respectively. To visually present the differences, 10 means are arranged by value (1A) and classified into three groups by statistical significances (1B). In general, if mites were raised at ≤25 °C and oviposited at ≥25 °C, total egg production was relatively high. Daily egg production curves show a variety of patterns but tend to suggest that two factors (possibly in combination) result in decreased total egg production: short oviposition period (Exp. codes 322, 323, 422, and 424) and low daily egg production (Exp. codes 221 and 121) (Fig. 1). Discussion Organisms always try to produce a healthy population of their progeny. We found that predaceous mites try to guarantee this by producing a maximum number of progeny as fast as possible. Females likely mate more than once in a natural setting, but examination of their reproductive behavior when they are mated once should provide useful information about their potential reproductive ability. Mating duration of N. californicus was strictly determined by ambient temperature at the time of mating, regardless of the tempe-
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ratures under which they were raised. Lower temperatures during mating resulted in longer copulation periods. We identified a negative relationship between ambient temperature and mating duration. At first glance, this result may be related to the male's initiative in mating termination after completion (or incompletion) of temperaturedependent sperm transfer activity, although more research is needed to verify this hypothesis because total egg production of females that were raised at 25 °C and mated at 18 °C (Exp. code 212) was not as high as those at a consistent temperature of 25 °C (Exp. code 222). With regard to the estimation of sperm volumes in this study, it is necessary to re-evaluate the effectiveness of this index as an indicator of sperm volume at the scale of the present experiment. The total egg production by females that mated at identical temperatures varied considerably with the temperature conditions of their (and/or their mates) immature and oviposition periods. We identified reduced total egg production when a pair was raised under conditions of high temperatures; Margolies and Wrensch (1996) demonstrated similar results for the two-spotted spider mite, T. urticae, a mite used as prey in this study. The reasons for this reduction are not clear, but daily egg production curves (Exp. codes 322, 323, 422, and 424) suggest a shortened oviposition period, possibly due to a lack of healthy sperm during the later period. Females exposed to the low temperature of 18 °C during the oviposition period also produced fewer total eggs, due to the lower daily egg production rate (Exp. codes 221 and 121). The reduced activities of mites under cool temperature conditions generally limited daily reproduction, and it is possible that either some sperm transferred by males did not remain viable long enough, or that females were unable to prolong the potential oviposition period. Low daily prey consumption and reproduction at low temperatures and a positive relationship between prey consumption rate and egg production have been reported for other phytoseiid mites such as Galendromus occidentalis (Nesbitt) and T. pyri, as well as N. californicus (Cuellar et al., 2001; MacRae and Croft, 1993). Certain experimental results (such as Exp. codes 122, 221, and 121) were particularly interesting. A cool environment of 18 °C certainly reduced daily egg production rate (Exp. codes 221 and 121); these results indicate that when mites are raised at 18 °C, the female's oviposition period is shorter. Females from Exp. code 221 should have had the same amount of sperm as those from Exp codes 222, 223, and 224 because they were raised under identical conditions during their immature stages, but they did not fully complete their reproductive potential. This may be a result of two factors: limited sperm lifespan and limited female oviposition period, as stated above. Both factors are equally able to explain the difference between the results from Exp. codes 122 and 121, and the results do not clearly indicate which factor had a stronger effect. At present, we can safely claim that multiple factors are involved in the observed differences of total egg production and additional observations such as effect of multiple mating are needed. As discussed above, females mated once at 25 °C produced fewer total eggs when they had been raised at higher temperatures and those produced eggs at lower temperatures also reduced egg production even though they had been raised and mated at 25 °C. Another interesting subject for future research will be the difference in thermal optimums between immature and adult stages. In a natural setting, immature mites may stay in relatively cooler areas such as under surfaces of leaves or crevices in tree trunks, while adult mites must move around to find prey. Furthermore, knowledge on differential thermal adaptation of immature and adult stages may provide useful information to related industry such as biological agent production. Optimal thermal condition for production and transportation of predacious mite population is one of the essential knowledge which business sector urgently needs. Further study of these relationships will be required to answer its adaptive significance and more efficient utilization of predators.
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Acknowledgments Our study was supported in part by Grants-in-Aid for Scientific Research (Nos. 14360026, 17380034 and 21580062) to HA from the Japan Society for the Promotion of Science and by the Support program by Tojo-GakujutsuShinkoukai, Chiba University, to TTPN. References Amano, H., Chant, D.A., 1978. Mating behaviour and reproductive mechanisms of two species of predacious mite, Phytoseiulus persimilis Athias-Henriot and Amblyseius andersoni (Chant) (Acarina: Phytoseiidae). Acarologia 20, 196–213. Canlas, L.J., Amano, H., Ochiai, N., Takeda, M., 2006. Biology and predation of the Japanese strain of Neoseiulus californicus (McGregor) (Acari: Phytoseiidae). Syst. Appl. Acarol. 11, 141–157. Chant, D.A., McMurtry, J.A., 2007. Illustrated keys and diagnoses for the genera and subgenera of the Phytoseiidae of the world. Mesostigmata). Indira Publishing House, MI, USA, Acari, p. 220. Cuellar, M.E., Calatayud, P.A., Melo, E.L., Smith, L., Bellotti, A.C., 2001. Consumption and oviposition rates of six phytoseiid species feeding on eggs of the cassava green mite Mononychellus tanajoa (Acari: Tetranychidae). Florida Entomologist 84, 602–607. Ferragut, F., Garcia-Marí, F., Costa-Comelles, J., Laborda, R., 1987. Influence of food and temperature on development and oviposition of Euseius stipulatus and Typhlodromus phialatus (Acari: Phytoseiidae). Exp. Appl. Acarol. 3, 317–329. Ferrero, M., Moraes, G...J. de, Kreiter, S., Tixier, M-S., Knapp, M., 2007. Life tables of the predatory mite Phytoseiulus longipes feeding on Tetranychus evansi at four temperatures (Acari: Phytoseiidae, Tetranychidae). Exp. Appl. Acarol. 41, 45–53. Gotoh, T., Yamaguchi, K., Mori, K., 2004. Effect of temperature on life history of the predatory mite Amblyseius (Neoseiulus) californicus (Acari: Phytoseiidae). Exp. Appl. Acarol. 32, 15–30.
Herbert, H.J., 1956. Laboratory studies on some factors in the life-history of the predacious mite Typhlodromus tiliae Oudms. (Acarina: Phytoseiidae). Can. Entomol. 88, 701–704. Landau, S., Everitt, B.S., 2004. A handbook of statistical analyses using SPSS. Chapman and Hall/CRC, p. 337. MacRae, I.V., Croft, B.A., 1993. Influence of temperature on interspecific predation and cannibalism by Metaseiulus occidentalis and Typhlodromus pyri (Acarina: Phytoseiidae). Environ. Entomol. 22, 770–775. Margolies, D.C., Wrensch, D.L., 1996. Temperature-induced changes in spider mite fitness: offsetting effects of development time, fecundity, and sex ratio. Entomol. Exp. Appl. 78, 111–118. McMurtry, J.A., Scriven, G.T., 1965. Life history studies of Amblyseius limonicus, with comparative observations on Amblyseius hibisci (Acarina: Phytoseiidae). Ann. Entomol. Soc. Amer. 58, 106–111. Momen, F.M., Abdel-Khalek, A., 2008. Effect of the tomato rust mite Aculops lycopersici (Acari: Eriophyidae) on the development and reproduction of three predatory phytoseiid mites. Int. J. Trop. Inst. Sci. 28, 53–57. Nguyen, T.P.T., Amano, H., 2009. Mating duration and egg production of the predaceous mite Neoseiulus californicus (Acari: Phytoseiidae) vary with temperature. J. Asia Pac. Entomol. 12, 297–299. Schulten, G.G.M., Van Arendonk, R.C.M., Russell, V.M., Roorda, F.A., 1978. Copulation, egg production and sex-ratio in Phytoseiulus persimilis and Amblyseius bibens (Acari: Phytoseiidae). Entomol. Exp. Appl. 24, 145–153. Vasconcelos, G.J.N. de, de Moraes, G.J., Júnior, Í.D., Knapp, M., 2008. Life history of the predatory mite Phytoseiulus fragariae on Tetranychus evansi and Tetranychus urticae (Acari: Phytoseiidae, Tetranychidae) at five temperatures. Exp. Appl. Acarol. 44, 27–36. Zaher, M.A., Shehata, K.K., 1971. Biological studies on the predator mite Typhlodromus pyri Sch. (Acarina Phytoseiidae) with the effect of prey and non prey substances. Z. Ang. Entomol. 67, 389–394. Zhang, Y.., Zhang, Z., Lin, J., Ji, J., 2000. Potential of Amblyseius cucumeris (Acari: Phytoseiidae) as a biocontrol agent against Schizotetranychus nanjingensis (Acari: Tetranychidae) in Fujian. China. Syst. Appl. Acarol. Special publications 4, 109–124.
Contents lists available at ScienceDirect
Journal of Asia-Pacific Entomology j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / j a p e
Temperature at immature and adult stages differentially affects mating duration and egg production of Neoseiulus californicus females mated once (Acari: Phytoseiidae) Thao T.P. Nguyen, Hiroshi Amano ⁎,1 Graduate School of Horticulture, Chiba University, Matsudo, Chiba 271-8510, Japan
a r t i c l e
i n f o
Article history: Received 11 September 2009 Revised 9 October 2009 Accepted 12 October 2009 Keywords: Developmental stages Temperature Mating duration Fecundity N. californicus
a b s t r a c t A series of experiments was conducted to investigate whether temperatures of 18 °C, 25 °C, 30 °C, and 35 °C and a photoperiod of 16L:8D at immature and adult stages would differentially affect the mating duration and egg production of Neoseiulus californicus females mated once. Mating duration was strictly determined by ambient temperature at the time of mating, regardless of the temperatures under which they were raised. Compared with a consistent 25 °C condition, total fecundity of females decreased when temperature conditions of 18 °C, 30 °C, and 35 °C were applied during any life stage (immature, mating, and oviposition periods) or a combination of different stages. In general, however, if mites were raised in conditions of ≤ 25 °C, and mated and oviposited at conditions of ≥ 25 °C, total egg production was relatively high. Based on these results, the adaptation of mites to thermal environments was discussed. © Korean Society of Applied Entomology, Taiwan Entomological Society and Malaysian Plant Protection Society, 2009 Published by Elsevier B.V. All rights reserved.
Introduction Our first paper revealed that the duration of copulation and total egg production of Neoseiulus californicus mated once were significantly affected by temperature, which was kept constant throughout the mite's life (Nguyen and Amano, 2009). Pairs copulated for the longest duration when they were maintained at 18 °C and for the shortest duration at 30 °C and 35 °C. However, females produced the fewest eggs at 18 °C; egg production peaked at 25 °C and dropped at 30 °C and 35 °C. We concluded that the optimum reproductive temperature for N. californicus females was 25 °C, while lower or higher temperatures reduced their reproductive ability. (Constant) temperature conditions are well-known to determine mating duration and egg production of phytoseiid mites. As temperatures rise, the duration of copulation becomes shorter; this negative relationship between temperature and mating duration has been demonstrated in many species of phytoseiid mites such as Typhlodromus tiliae Oudemans (Herbert, 1956), Typhlodromus pyri Scheuten (Zaher and Shehata, 1971), and N. californicus (Nguyen and Amano 2009). Temperature also significantly affects N. californicus egg production, and the reproductive ability of this species is reduced when it is maintained at low or high temperatures (Gotoh et al., 2004; Canlas et al., 2006). The same trend has been reported for other phyto-
⁎ Corresponding author. Tel.:/ fax: +81 75 753 6135. E-mail address: [email protected] (H. Amano). 1 Present address: Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan.
seiid species, such as Euseius stipulatus (Athias-Henriot), Typhlodromus phialatus Athias-Henriot (Ferragut et al., 1987), Amblydromalus limonicus (Garman and McGregor) (McMurtry and Scriven, 1965), Neoseiulus cucumeris (Zhang et al., 2000), Phytoseiulus longipes Evans (Ferrero et al., 2007), Phytoseiulus fragariae Denmark and Schicha (Vasconcelos et al., 2008), Typhlodromus swirskii Denmark, and Typhlodromus athiasae Porath and Swirski (Momen and Abdel-Khalek, 2008). However, little is known about the total effects of a combination of different temperatures during immature and adult stages on mating duration and egg production of phytoseiid females. Researchers are now interested in identifying which stage of the life cycle of N. californicus is sensitive to temperature and responsible for observed differences. We carried out a series of experiments on the mating and reproductive behavior of N. californicus mites that were subjected to various temperatures during immature, mating, and oviposition periods to investigate thermal effects and possible mechanisms underlying any temperature-related effects. Materials and methods The materials and basic observation methods of copulation and oviposition in this study were the same as those described in Nguyen and Amano (2009). The N. californicus population was collected at Ichihara, Chiba, Japan, in 1995 and was maintained at the Laboratory of Applied Entomology and Zoology, Chiba University, at a temperature of 25 °C and a photoperiod of 16L:8D. Prey for the mites was the greenform of the two-spotted spider mite Tetranychus urticae Koch reared on kidney bean plants Phaseolus vulgaris L. Predaceous mites were always kept in vials with abundant prey and during the experiments,
1226-8615/$ – see front matter © Korean Society of Applied Entomology, Taiwan Entomological Society and Malaysian Plant Protection Society, 2009 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.aspen.2009.10.002
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T.T.P. Nguyen, H. Amano / Journal of Asia-Pacific Entomology 13 (2010) 65–68
vials were transferred between chambers maintained at specific temperatures: 18 °C, 25 °C, 30 °C, and 35 °C. Mating duration was observed every 5 or 10 min and any subsequent egg production was checked daily. Experimental details are described below under separate headings. Throughout the text, we use the generic names proposed by Chant and McMurtry (2007). Mating duration and estimated transferred sperm volume Immature mites that developed at temperatures of 18 °C, 25 °C, 30 °C, and 35 °C were transferred to a chamber with identical or differing temperature conditions and kept there for one day. Each mite engaged in a single mating. Table 1 lists the combinations of temperature conditions during immature development and during mating, by experimental code. A total of 16 different combinations (Exp. codes) were used in the study. To estimate the volume of sperm ejaculated into the female spermatheca (female mites each have a pair of spermathecae inside their body cavity) immediately after copulation was completed, females were killed and mounted on Hoyer's medium. The size of the spermatophore (or the mass of sperm and seminal fluid) injected by each male was estimated by measuring the size of the inflated vesicle of the female spermatheca, using a micrometer attached to a phasecontrast microscope. Previous research has demonstrated a positive relationship between spermatophore size and the resultant total egg production (Amano and Chant, 1978; Schulten et al., 1978).
Table 2 Total egg production of N. californicus females under different temperature regimes. Exp. Code
111 211 212 121 122 221 222 223 224 322 323 422 424 232 233 333 242 244 444
Temperature (°C) at different stages Immature
Mating
Oviposition
18 25 25 18 18 25 25 25 25 30 30 35 35 25 25 30 25 25 35
18 18 18 25 25 25 25 25 25 25 25 25 25 30 30 30 35 35 35
18 18 25 18 25 18 25 30 35 25 30 25 35 25 30 30 25 35 35
No. of females examined
Total egg production (means ± SD)
12 15 10 10 9 11 10 10 11 9 8 9 9 10 13 11 13 11 10
13.9 ± 8.8d 30.7 ± 5.3bc 31.9 ± 6.1bc 26.4 ± 3.1bc 35.4 ± 8.5ab 33.3 ± 2.4bc 46.1 ± 3.6a 35.7 ± 4.1ab 34.2 ± 6.6ab 33.4 ± 6.4bc 31.5 ± 9.5bc 29.6 ± 8.3bc 28.2 ± 10.2bc 27.1 ± 6.4bc 29.8 ± 10.3bc 26.6 ± 3.6bc 28.1 ± 12.4bc 27.8 ± 8.2bc 23.9 ± 11.4cd
The means followed by different letters within the same column are significantly different (one-way ANOVA and Tukey HSD test; p b 0.05). Exp. Code: Three digits indicate temperatures (1; 18, 2; 25, 3; 30, 4; 35) at immature, mating and oviposition periods in order, respectively. Data for Exp. Codes 111, 222, 333 and 444 were collected from Nguyen and Amano (2009).
Egg production After the single mating, females were kept on leaflets with prey under four different temperature conditions. Due to the large number of combinations of experimental temperature, observations were generally concentrated on the mating temperature of 25 °C. In total, 19 different combinations (Exp. codes) were used in the analysis (see Table 2). Data analysis A one-way analysis of variance was used to determine the overall statistical significance of each variable (duration of copulation, Table 1 Effects of constant and a combination of different temperatures at immature and mating stages of N. californicus on mating duration and spermatophore diameter. Exp. Code Temperature (°C) at different stages Immature Mating 11 21 31 41 12 22 32 42 13 23 33 43 14 24 34 44
18 25 30 35 18 25 30 35 18 25 30 35 18 25 30 35
18 18 18 18 25 25 25 25 30 30 30 30 35 35 35 35
Mating duration Diameter of No. of spermatophore in minutes females (μm) (means ± SD) examined (means ± SD) 17 10 12 11 10 10 8 9 11 10 10 13 12 15 11 10
533.6 ± 45.7 520.8 ± 74.1 516.2 ± 58.1 511.8 ± 56.1 323.5 ± 38.1 315.3 ± 35.7 319.5 ± 95.1 301.9 ± 39.6 289.1 ± 38.4 240.7 ± 35.3 261.2 ± 34.1 241.2 ± 61.1 259.7 ± 45.8 271.2 ± 50.4 250.1 ± 53.5 253.6 ± 41.9
a a a a b b b b bc c c c c bc c c
44.7 ± 13.8 ns 37.2 ± 10.6 36.7 ± 12.9 32.3 ± 18.1 36.2 ± 10.3 37.7 ± 10.4 39.9 ± 9.5 44.1 ± 7.8 38.0 ± 9.4 41.1 ± 9.5 34.8 ± 16.7 30.0 ± 10.4 35.3 ± 12.6 34.2 ± 10.4 41.8 ± 8.7 35.0 ± 11.2
The means followed by different letters within the same column are significantly different (one-way ANOVA and Tukey HSD test; p b 0.05), and ns indicates not significant (one-way ANOVA; p N 0.05). Exp. Code: Two digits indicate temperatures (1; 18, 2; 25, 3; 30, 4; 35) at immature and mating periods in order, respectively. Data for Exp. Codes 11, 22, 33 and 44 were collected from Nguyen and Amano (2009).
diameter of female spermatophore, and total egg production). Tukey's honestly significant difference test (Landau and Everitt, 2004) was applied to test for pair-wise comparisons among individual means. Results Mating duration and estimated volume of transferred sperm Table 1 lists the durations of copulation for pairs that completed their immature development and mated at various temperatures. The table also lists the diameters of spermatophores in the female spermatheca. Statistical analyses clearly revealed that mating duration was determined by the temperature during mating, and that it was not influenced by the temperature at which the mites were raised. Males generally transferred only one spermatophore each into a single female spermatheca, and there were no cases in which more than two spermatophores were injected into a spermatheca. The results of sperm transfer at the various temperatures revealed no clear trend in spermatophore diameter (or appearance), because treatment means were not significant. Egg production Table 2 lists total female egg production under 19 temperature regimes. Unlike copulation duration, trends for total egg production were complicated. Mean total egg production differed among the four different mating temperature groups (df = 18 and 181, F = 7.126, p b 0.0001). Females that were raised, mated, and oviposited at 18 °C (Exp. code 111) produced the fewest eggs (13.9 eggs/female). Total egg production by females that mated at 18 °C, 30 °C, and 35 °C was also generally low. Total egg production was greatest (46.1 eggs/female) at a constant temperature of 25 °C (Exp. code 222). Three experimental conditions (Exp. codes 122, 223, and 224) did not differ significantly from this mean value; although these females spent their immature and oviposition stages at different temperatures, they all mated at 25 °C.
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Fig. 1. Total egg production (A) and daily egg production (B) of N. californicus females mated at 25 °C with differing temperatures at the immature and oviposition stages. The various bar patterns shown in (A) indicate statistically separate groups as shown in Table 2; data for Exp. Code 222 were collected from Nguyen and Amano (2009).
Total egg production (see Table 2) and daily fecundity of females that mated at 25 °C are illustrated in Figs. 1A and B, respectively. To visually present the differences, 10 means are arranged by value (1A) and classified into three groups by statistical significances (1B). In general, if mites were raised at ≤25 °C and oviposited at ≥25 °C, total egg production was relatively high. Daily egg production curves show a variety of patterns but tend to suggest that two factors (possibly in combination) result in decreased total egg production: short oviposition period (Exp. codes 322, 323, 422, and 424) and low daily egg production (Exp. codes 221 and 121) (Fig. 1). Discussion Organisms always try to produce a healthy population of their progeny. We found that predaceous mites try to guarantee this by producing a maximum number of progeny as fast as possible. Females likely mate more than once in a natural setting, but examination of their reproductive behavior when they are mated once should provide useful information about their potential reproductive ability. Mating duration of N. californicus was strictly determined by ambient temperature at the time of mating, regardless of the tempe-
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ratures under which they were raised. Lower temperatures during mating resulted in longer copulation periods. We identified a negative relationship between ambient temperature and mating duration. At first glance, this result may be related to the male's initiative in mating termination after completion (or incompletion) of temperaturedependent sperm transfer activity, although more research is needed to verify this hypothesis because total egg production of females that were raised at 25 °C and mated at 18 °C (Exp. code 212) was not as high as those at a consistent temperature of 25 °C (Exp. code 222). With regard to the estimation of sperm volumes in this study, it is necessary to re-evaluate the effectiveness of this index as an indicator of sperm volume at the scale of the present experiment. The total egg production by females that mated at identical temperatures varied considerably with the temperature conditions of their (and/or their mates) immature and oviposition periods. We identified reduced total egg production when a pair was raised under conditions of high temperatures; Margolies and Wrensch (1996) demonstrated similar results for the two-spotted spider mite, T. urticae, a mite used as prey in this study. The reasons for this reduction are not clear, but daily egg production curves (Exp. codes 322, 323, 422, and 424) suggest a shortened oviposition period, possibly due to a lack of healthy sperm during the later period. Females exposed to the low temperature of 18 °C during the oviposition period also produced fewer total eggs, due to the lower daily egg production rate (Exp. codes 221 and 121). The reduced activities of mites under cool temperature conditions generally limited daily reproduction, and it is possible that either some sperm transferred by males did not remain viable long enough, or that females were unable to prolong the potential oviposition period. Low daily prey consumption and reproduction at low temperatures and a positive relationship between prey consumption rate and egg production have been reported for other phytoseiid mites such as Galendromus occidentalis (Nesbitt) and T. pyri, as well as N. californicus (Cuellar et al., 2001; MacRae and Croft, 1993). Certain experimental results (such as Exp. codes 122, 221, and 121) were particularly interesting. A cool environment of 18 °C certainly reduced daily egg production rate (Exp. codes 221 and 121); these results indicate that when mites are raised at 18 °C, the female's oviposition period is shorter. Females from Exp. code 221 should have had the same amount of sperm as those from Exp codes 222, 223, and 224 because they were raised under identical conditions during their immature stages, but they did not fully complete their reproductive potential. This may be a result of two factors: limited sperm lifespan and limited female oviposition period, as stated above. Both factors are equally able to explain the difference between the results from Exp. codes 122 and 121, and the results do not clearly indicate which factor had a stronger effect. At present, we can safely claim that multiple factors are involved in the observed differences of total egg production and additional observations such as effect of multiple mating are needed. As discussed above, females mated once at 25 °C produced fewer total eggs when they had been raised at higher temperatures and those produced eggs at lower temperatures also reduced egg production even though they had been raised and mated at 25 °C. Another interesting subject for future research will be the difference in thermal optimums between immature and adult stages. In a natural setting, immature mites may stay in relatively cooler areas such as under surfaces of leaves or crevices in tree trunks, while adult mites must move around to find prey. Furthermore, knowledge on differential thermal adaptation of immature and adult stages may provide useful information to related industry such as biological agent production. Optimal thermal condition for production and transportation of predacious mite population is one of the essential knowledge which business sector urgently needs. Further study of these relationships will be required to answer its adaptive significance and more efficient utilization of predators.
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Acknowledgments Our study was supported in part by Grants-in-Aid for Scientific Research (Nos. 14360026, 17380034 and 21580062) to HA from the Japan Society for the Promotion of Science and by the Support program by Tojo-GakujutsuShinkoukai, Chiba University, to TTPN. References Amano, H., Chant, D.A., 1978. Mating behaviour and reproductive mechanisms of two species of predacious mite, Phytoseiulus persimilis Athias-Henriot and Amblyseius andersoni (Chant) (Acarina: Phytoseiidae). Acarologia 20, 196–213. Canlas, L.J., Amano, H., Ochiai, N., Takeda, M., 2006. Biology and predation of the Japanese strain of Neoseiulus californicus (McGregor) (Acari: Phytoseiidae). Syst. Appl. Acarol. 11, 141–157. Chant, D.A., McMurtry, J.A., 2007. Illustrated keys and diagnoses for the genera and subgenera of the Phytoseiidae of the world. Mesostigmata). Indira Publishing House, MI, USA, Acari, p. 220. Cuellar, M.E., Calatayud, P.A., Melo, E.L., Smith, L., Bellotti, A.C., 2001. Consumption and oviposition rates of six phytoseiid species feeding on eggs of the cassava green mite Mononychellus tanajoa (Acari: Tetranychidae). Florida Entomologist 84, 602–607. Ferragut, F., Garcia-Marí, F., Costa-Comelles, J., Laborda, R., 1987. Influence of food and temperature on development and oviposition of Euseius stipulatus and Typhlodromus phialatus (Acari: Phytoseiidae). Exp. Appl. Acarol. 3, 317–329. Ferrero, M., Moraes, G...J. de, Kreiter, S., Tixier, M-S., Knapp, M., 2007. Life tables of the predatory mite Phytoseiulus longipes feeding on Tetranychus evansi at four temperatures (Acari: Phytoseiidae, Tetranychidae). Exp. Appl. Acarol. 41, 45–53. Gotoh, T., Yamaguchi, K., Mori, K., 2004. Effect of temperature on life history of the predatory mite Amblyseius (Neoseiulus) californicus (Acari: Phytoseiidae). Exp. Appl. Acarol. 32, 15–30.
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