Female Development Time Research Articles

Fitness gain in a koinobiont parasitoid Diaeretiella rapae (Hymenoptera: Aphidiidae) by parasitising hosts of different ages

Host age-dependent fitness of Diaeretiella rapae was studied on cabbage aphid Brevicoryne brassicae. When given a choice of nymphs of four different ages (1, 3, 5 and 7 days), females showed a strong preference for oviposition in older nymphs, which were also the largest in the body size, and left the majority of younger nymphs unparasitised. More than 70% of offspring emerged from 5-day and 7-day old parasitised nymphs. Parasitoids develop faster in older hosts than in younger hosts. Development time of males was shorter than females in older hosts, but the development time of males and females was similar in younger hosts. The body size of adult D. rapae was positively correlated with the age of the hosts in which they developed. The sex ratio of offspring was found to be female-biased. A higher proportion of females emerged from older hosts. D. rapae females emerged from older hosts lived significantly longer. The potential fecundity of the females emerged from older (larger in body size) hosts was significantly greater than of those emerged from younger hosts with smaller bodies. Results suggest that D. rapae preferred older hosts to maximise the reproductive fitness gain. The oviposition strategy of D. rapae is discussed in the context of efficiency of this parasitoid in biological control programmes.

Effect of Temperature and Insecticide Stress on Life-History Traits of Culex restuans and Aedes albopictus (Diptera: Culicidae)

The chronic effects of exposure of Culex restuans (Theobald) and Aedes albopictus (Skuse) (Diptera: Culicidae) to low concentrations of malathion were examined by exposing larvae of the two species to four malathion doses at 20, 25, and 30 degrees C and maintaining the resulting adults at 25 degrees C. For both species, a significant temperature by malathion interaction on survival was found. Greater temperatures at the highest malathion dosage had significantly lower survivorship than in other treatments, but this effect was not observed at 20 degrees C. These results suggest that low temperature may buffer against some of the negative effects of malathion. For both species, temperature but not malathion had significant effects on female developmental time to adulthood and adult longevity. Temperature also affected adult female size for Ae. albopictus but not Cx. restuans. Ae. albopictus females developed faster as temperature increased, lived longer when larvae were maintained at 30 degrees C than at 20 degrees C, and were larger when larvae were maintained at 25 degrees C than at 20 or 30 degrees C. Cx. restuans females developed faster at 25 and 30 degrees C than at 20 degrees C and lived longer at 25 degrees C than at 20 or 30 degrees C. The estimated finite rate of increase (lambda') for Cx. restuans was significantly lower at 20 degrees C than at 25 and 30 degrees C, whereas that of Ae. albopictus was significantly influenced by an interaction between temperature and malathion with significantly lower lambda' at 20 degrees C than at 25 and 30 degrees C for all malathion treatments except 0.014 mg liter(-1). Understanding how pesticides interact with abiotic environmental conditions will contribute to management decisions about vector control practices.

Spatial Variation in Foliar Chemicals Within Radish (Raphanus sativus) Plants and Their Effects on Performance of Spodoptera litura

Foliar chemicals are variable within a plant and this may affect herbivore feeding preference. This study was carried out to quantify concentrations of primary (nitrogen, water, and total nonstructural carbohydrates) and secondary substances (sinigrin) in young and old leaves of Raphanus sativus L. and to evaluate performance and survival of a generalist herbivore Spodoptera litura F. feeding on them. Forty to 50-d-old R. sativus plants were used in both foliar chemical analysis and insect performance bioassays. Leaves located on the third to the sixth node from the base of the plant were defined as old leaves and the remaining leaves (from seventh node to the plant apex) of the plant were referred as young leaves in this study. All foliar chemicals except water differed significantly between young and old leaves. Moreover, young leaves were more nutritious but much more defended, based on sinigrin content, against S. litura than old leaves. Performance and survival of S. litura were reduced on young leaves as compared with old leaves. Male and female larval duration only differed significantly on young leaves. Female larval development time was longer than male development time on young leaves, but not on older leaves. Therefore, this study revealed that defenses in young leaves have differential effects upon male and female S. litura.

Differences in Development, Glycogen, and Lipid Content Associated With Cytochrome P450-Mediated Permethrin Resistance inCulex pipiens quinquefasciatus(Diptera: Culicidae)

Insecticide resistance in populations of mosquitoes is an escalating problem that can directly affect disease prevalence. Determining the fitness associated with an insecticide resistance mechanism (allele) will provide for greater understanding of the evolution of resistance, and help inform effective vector management programs. Previously, a population cage experiment in which the alleles of two highly related strains of Culex pipiens quinquefasciatus (Say) SLAB (susceptible) and ISOP450 (permethrin resistant because of cytochrome P450-mediated detoxification) were placed in direct competition in the absence of insecticide revealed that the P450 resistance allele frequency decreased over time. In the current study, SLAB and ISOP450 development, mortality and energetic resources derived from glycogen, other sugars and lipids were measured to identify biological parameters that might explain the previously observed fitness cost. SLAB exhibited shorter egg-to-adult female development time and larger body size when reared in groups when compared with ISOP450. ISOP450 female adults provided 20% sugar water lived longer than 20% sugar water fed females of the SLAB strain. No significant differences in larval development time, larval mortality, pupal stage duration time, pupal mortality, longevity of male and female adults provided with distilled water and males provided sugar water were found between the strains. The caloric content from glycogen and lipids were significantly higher in SLAB relative to ISOP450 in adults. The slower female emergence time and smaller body size when reared in groups combined with lower energy reserves (glycogen and lipids) associated with the resistance allele (in ISOP450) are likely fitness costs associated with the resistance allele of P450-mediated detoxification.

Differences in Development, Glycogen, and Lipid Content Associated With Cytochrome P450-Mediated Permethrin Resistance in <I>Culex pipiens quinquefasciatus</I> (Diptera: Culicidae)

Insecticide resistance in populations of mosquitoes is an escalating problem that can directly affect disease prevalence. Determining the fitness associated with an insecticide resistance mechanism (allele) will provide for greater understanding of the evolution of resistance, and help inform effective vector management programs. Previously, a population cage experiment in which the alleles of two highly related strains of Culex pipiens quinquefasciatus (Say) SLAB (susceptible) and ISOP450 (permethrin resistant because of cytochrome P450-mediated detoxification) were placed in direct competition in the absence of insecticide revealed that the P450 resistance allele frequency decreased over time. In the current study, SLAB and ISOP450 development, mortality and energetic resources derived from glycogen, other sugars and lipids were measured to identify biological parameters that might explain the previously observed fitness cost. SLAB exhibited shorter egg-to-adult female development time and larger body size when reared in groups when compared with ISOP450. ISOP450 female adults provided 20% sugar water lived longer than 20% sugar water fed females of the SLAB strain. No significant differences in larval development time, larval mortality, pupal stage duration time, pupal mortality, longevity of male and female adults provided with distilled water and males provided sugar water were found between the strains. The caloric content from glycogen and lipids were significantly higher in SLAB relative to ISOP450 in adults. The slower female emergence time and smaller body size when reared in groups combined with lower energy reserves (glycogen and lipids) associated with the resistance allele (in ISOP450) are likely fitness costs associated with the resistance allele of P450-mediated detoxification.

Preimaginal Development Response to Constant Temperatures inHypera postica(Coleoptera: Curculionidae): Picking the Best Model

Immature survival and development of alfalfa weevil, Hypera postica (Gyllenhal) (Coleoptera: Curculionidae), were examined at 15 constant temperatures ranging from 9 to 37 degrees C. At 9 and 37 degrees C, eggs did not develop. Embryos developed to adulthood between 11.5 and 36 degrees C, although survival was low at both ends of the temperature range. Distribution of development times for all stages of alfalfa weevil were skewed toward longer times mainly at moderate temperatures. Constant proportion of time spent in egg, larva, and pupa indicated rate isomorphy within the range 14-31.5 degrees C. No significant difference was shown between development time of males and females at any of the temperatures tested. Two linear and 23 nonlinear models were fitted to describe development rate of immature stages of H. postica as a function of temperature, as well as estimating the thermal constant and critical temperatures (i.e., T(min), T(opt), and T(max)). There was no statistical difference between the estimated parameters, using Ikemoto and ordinary linear methods. Of the nonlinear models fitted, the Logan-6/Lactin-2, Analytis-3/Briere-2, and Analytis-3/Briere-2 models were found to be the best for modeling development rate of egg, larva, and entire immature stages of H. postica, respectively. Our findings will be incorporated in more efficient phenological models of this pest and its population dynamics.

Determination of biotypes of Dactylopius tomentosus (Hemiptera: Dactylopiidae) and insights into the taxonomic relationships of their hosts, Cylindropuntia spp.

Host specialization to form biotypes is common among phytophagous insects, and it has been hypothesised that biotypes of Dactylopius tomentosus L. (Hemiptera: Dactylopiidae) occur. D. tomentosus is an important biological control agent for Cylindropuntia cacti when they occur as weeds. Additionally, there is uncertainty surrounding the taxonomic status of some species of Cylindropuntia. This study aimed to confirm the existence of D. tomentosus biotypes and to assess whether host specialization can help to resolve this systematic uncertainty. For this study, the host specificity and performance of ten provenances of D. tomentosus collected from C. cholla, C. fulgida var. fulgida, C. imbricata, C. f. var. mamillata, C. rosea and C. tunicata and reared on C. cholla, C. fulgida var. fulgida, C. imbricata and C. rosea were investigated. Five life-history parameters were measured including: crawler development time and survival, female development time, and the weight and number of eggs produced by females. Results revealed significant variation in host specificity with provenances either thriving, surviving or dying on the different hosts, thus demonstrating the existence of biotypes. Also, host specificity was related to host species and not to the geographic locality from which either the host or provenance was sourced. These findings suggest that the characteristics of Cylindropuntia species may differ sufficiently, there by presenting different selection pressures that induce and sustain distinct biotypes of D. tomentosus. The observed host use patterns of the biotypes separated the plant species into two groups that accorded with known phylogenetic relationships among Cylindropuntia species, suggesting that biotypes can be used to elucidate their taxonomic relatedness. Besides advancing our knowledge of the ecology and evolution of D. tomentosus, these novel findings have important implications for the biological control of Cylindropuntia species.

Temperature-Dependent Development of the Cycad Aulacaspis Scale, Aulacaspis yasumatsui (Hemiptera: Diaspididae)

ABSTRACT Egg duration period, immature development time, and pre-oviposition period of the cycad aulacaspis scale, Aulacaspis yasumatsui Takagi, were measured at 9 constant temperatures in the laboratory. Egg duration period ranged from 15 d at 20°C to 7 d at 30°C. First instar development time was 30 d at 18°C but only 4 d at 35°C. No first instars completed development below 18°C or above 35°C. Development time of second instar females ranged from 19 d at 18 and 20°C to 9 d at 30°C. Development time of male second instar + pupa ranged from 15 d at 20°C to 9–10 d at 25–32°C. Pre-oviposition period averaged 14 d at 20°C to 8 d at 25– 32°C; no females laid eggs at 18 and 35°C. The lowest temperature threshold for all stages ranged from 8 to 12°C and 538 degree-days were required for female immature development in a linear model. Development rates of the scale are compared to those of 3 of its natural enemies, Cybocephalus nipponicus Endrody-Younga, Rhyzobius lophanthae (Blaisdell), and Coccobius fulvus (Co...

Effect of Temperature and Food on Development and Growth of Daphnia similoides (Cladocera: Daphniidae) from Lake Donghu

ABSTRACT Growth, reproduction, and life history parameters of Daphnia similoides from a subtropical eutrophic Chinese lake (Lake Donghu) were measured at four temperatures (10, 15, 25 and 35°C) and two food concentrations (0.2 and 2 mg carbon L−1 of a green alga) in the laboratory. D. similoides had five juvenile instars and up to 28 adult instars. The number of adult instars was greater at the low food level than at the high food level. The number of adult instars with maximal number of offspring, the cumulative number of offspring per female, development time, and body lengths of females and offspring were higher or longer at the low temperatures than at the high temperatures. Body length of females was significantly correlated with offspring number per adult instar at all combinations of temperature and food. Innate capacities of increase (0.13–1.01) linearly increased with temperature.

Extreme cost of male riding behaviour for juvenile females of the Zeus bug

Precopulatory male mate guarding is predicted to occur close to the female's fertile period. However, in many species mate guarding commences when females are juveniles and may be several moults from sexual maturity. Such behaviour is inconsistent with the above prediction. In the Zeus bug, Phoreticovelia disparata, sexual size dimorphism is very pronounced and adult males commence riding on the backs of juvenile fourth-instar females. Males derive direct benefits from this association but the fitness consequences of precopulatory male riding behaviour for females are unknown. We investigated the effect of male presence during juvenile development for female Zeus bugs. We found a dramatic cost of male riding for females allocated a mate from the fourth instar: they were less likely to survive to adulthood and had substantially reduced adult longevity. These costs were significantly reduced for females allocated a mate during their fifth instar or as adults. We found no evidence that male presence affected female development time, adult size, body shape or the number of melanized dorsal scars present on their abdomen. Our study indicates that adult females and older juvenile females (fifth instar) are adapted to bear the costs imposed by riding males but that sexual conflict is likely to be intense between males and fourth-instar females. We suggest that the Zeus bug mating system originates from both sexes striving to make the best of a bad job: males ride immature females in the absence of unguarded adult females and females permit riding males as a form of convenience polyandry.

Distinguishing suitable biotypes ofDactylopius tomentosus(Hemiptera: Dactylopiidae) for biological control ofCylindropuntia fulgidavar.fulgida(Caryophyllales: Cactaceae) in South Africa

Cylindropuntia fulgida (Engelmann) F.M. Knuth var. fulgida (Engelmann) F.M. Knuth (Cff) (Caryophyllales: Cactaceae) is native to Mexico and Arizona and was introduced into South Africa for ornamental purposes. It subsequently became highly invasive, necessitating control. The cochineal insect, Dactylopius tomentosus (Lamarck) (Hemiptera: Dactylopiidae), was selected as a potential biological control agent based on its restricted host range among Cylindropuntia species and previous success in controlling C. imbricata (DC.) F. Knuth (Ci). Eight D. tomentosus provenances (Cholla, Cholla E, Fulgida, Mamillata, Imbricata, Tunicata U, Tunicata V and Rosea) from Cylindropuntia species in their native ranges were reared on Cff, whilst Cholla and Imbricata were also reared on Ci. Large differences were found in the development and survival of crawlers, and in the reproductive capacity of females. Three subjective categories of provenance interaction with host plants were identified based on a fitness index (FI) calculated from data relating to crawler survival, female development time and fecundity: (i) thriving (FI > or = 1) - insects had shorter developmental times, high crawler survival and highly fecund females (Cholla); (ii) surviving (FI<1 but >0) - insects had extended development times, low crawler survival and low fecundity (Imbricata, Fulgida and Mamillata); and (iii) dying (FI = 0) - insects died before or at the second instar (Rosea, Tunicata U and Tunicata V). Cholla, therefore, is highly suitable for biological control of Cff in South Africa. In addition, Cholla thrived on Cff but only survived on Ci whilst, in contrast, Imbricata thrived on Ci but only survived on Cff. This differential ability of provenances to thrive or survive on different host plants demonstrated that host adapted biotypes of D. tomentosus exist; therefore, biotypes should be taken into account when considering this species as a biological control agent of cactus weeds.

Behavior and Development of &lt;I&gt;Pseudacteon curvatus&lt;/I&gt; (Diptera: Phoridae) Varies According to the Social Form of Its Host &lt;I&gt;Solenopsis invicta&lt;/I&gt; (Hymenoptera: Formicidae) in Its Native Range

We assessed the performance of Pseudacteon curvatus Borgmeier with respect to the social form of Solenopsis invicta Buren in Argentina In the field, we studied the effect the parasitoid on size and proportion of ant foragers. In the laboratory, we evaluated P. curvatus oviposition preferences; host size elected; developmental periods; and sexual size dimorphism, sex ratio, and parasitoid survivorship. P. curvatus affected the average size of foraging workers on both social forms diminishing the proportion of big and increasing the proportion of minor workers. P. curvatus required a shorter orientation time and exhibited a greater number of attacks when ovipositing on monogynes workers. In the laboratory, host sizes elected by P. curvatus were similar between social forms. However, attacks on polygyne colonies were more variable, increasing the number of unviable offspring. Developmental times of females and males of P. curvatus were similar for both social forms, but total developmental periods were shorter for males from monogyne colonies. We did not find differences between sexes in emerging adults' size by social form and the female: male sex ratio was 1:1 for both social forms. P. curvatus pupae survival and adult emergence per trial from monogyne colonies were greater than from polygyne colonies. The rarity of polygyne S. invicta in its native range may prevent this phorid from adjusting its life history to that social form. Consequences of applying this phorid in biological control are discussed.

Potential constraints on evolution: sexual dimorphism and the problem of protandry in the butterfly Bicyclus anynana

The earlier mean adult emergence between males and females, protandry, has been well studied mathematically and in comparative studies. However, quantitative and evolutionary genetic research on protandry is scarce. The butterfly, Bicyclus anynana exhibits protandry and here we selected for each of the different combinations of male and female development time in this species, thus including direct selection on protandry (i.e., FAST, fast males and fast females; SLOW, slow males and slow females; FMSF, fast males and slow females; and SMFF, slow males and fast females). After eight generations of selection there was no significant response for increased or decreased protandry, whereas selection for increased or decreased development time in both sexes (FAST or SLOW) was successful. Continued selection (> 30 generations) for decreased or increased protandry showed a significant difference between the FMSFC and SMFFC lines (subscript c for continued selection), which was of the same magnitude as the nonsignificant difference observed between the FMSF and SMFF lines at generation eight. This indicated that the initial selection was successful, but that the difference between the lines did not increase with continued selection. Our results also indicate that the genetic covariance across sexes for development time is near unity. Interestingly, lines selected for decreased protandry (SMFF) had lower egg-to-adult survival, and broods from these lines had lower rates of egg hatching. This suggests that interactions with fertility might constrain certain directions of change in patterns of protandry. Moreover, selection yielded a change in the ratio of male to female development time for slow lines, suggesting that some amount of sex-specific genetic variance for development time is still present in this population. The FMSFC line showed the largest effect of selection on protandry, mainly through an effect on female developmental time. Lastly, our results show that temperature has an effect on the amount of protandry in the selected lines. These results are discussed in relation to the ecology of this species and the evolution of protandry.

Amblyseius Filcae Denmark and Villanueva, N. Sp. (Acari: Phytoseiidae) Found on Viburnum in Florida: Description, Life Cycle and Feeding Studies

Amblyseius filcae Denmark and Villanueva, n. sp. was found on Viburnum odoratissimum Ker Gawl. var. awabuki (K. Koch) Zabel (Caprifoliaceae) in Florida. The adult female can be identified by its rosy coloration, and, on permanent slides, by its tubular-fundibular spermathecal calyx 15 μm long and nodular atrium. Developmental times on pollen of crocea iceplant (Malephora crocea Jacquin) (Alzoaceae) were 60.6 ± 1.3, 32.2 ± 1.3, 41.3 ± 1.0, 29.6 ± 1.6, 54.7 ± 1.4, 218.7 ± 3.3 h for eggs, larvae, protonymphs, deutonymphs, preoviposition time and total female developmental time (up to first oviposition), respectively. Amblyseius filcae showed a weak or no predatory performance on Phyllocoptruta oleivora (Ashmead) and adult female Brevipalpus phoenicis (Geijkes) during predator-prey laboratory bioassays, but B. phoenicis egg predation was observed.

Enemy‐free space? Host preference and larval performance of a willow leaf beetle

AbstractTo examine whether enemy‐free space is an important factor determining the host utilization pattern of a leaf beetle Plagiodera versicolora, we investigated the relationship between adult preference and offspring performance on three co‐occurring willow species, Salix sachalinensis, S. miyabeana and S. integra. Salix sachalinensis was by far the most preferred host plant of feeding adults, while both S. miyabeana and S. integra were rarely fed upon. The fact that most oviposition was observed on S. sachalinensis also suggested that P. versicolora preferred S. sachalinensis to other willows for oviposition. This adult preference did not correspond well to patterns of larval performance on the three willow species in the absence of enemies. Higher survivorship, shorter developmental time and larger adult size were achieved on S. sachalinensis and S. miyabeana than on S. integra. Performance as indicated by female adult size and development time on S. miyabeana were higher than on S. sachalinensis. In the presence of enemies, however, the survivorship of first‐instar larvae on S. miyabeana was much lower than on other willows. Adults of P. versicolora apparently avoided S. miyabeana as an oviposition and feeding host and preferred S. sachalinensis as an enemy‐free space. This was not because larvae had poorer performance on S. miyabeana, but because predation pressure on eggs and early instar larvae was more severe on S. miyabeana.

Nesting biology of the trap-nesting Neotropical wasp Trypoxylo n(Trypargilum) aurifrons Shuckard (Hymenoptera, Crabronidae)

The present study was carried out in three localities of the state of São Paulo, Brazil: Araras (Dec/03-Dec/06), São Carlos (Nov/04-Nov/06) and Rifaina (Jul/04-Dec/06). Trap-nests were distributed among sites in the sampling areas and were collected every 35 days. Data from 295 nests indicate that T. aurifrons is a multivoltine species, with higher rates of nest building and cell production in the warm, rainy season. The trap-nests used by the females ranged from 117 to 467 mm in length and 3.1 to 16.6 mm in diameter. All nests showed deep plugs and a vestibular cell was found in 37% of the complete nests. The number of cells per nest ranged from one to 12. Females were larger than males, emerged from longer cells and their cocoons were significantly larger. A secondary 1:1 sex ratio was found in Araras and Rifaina. No correlation was observed between the diameter of the trap-nest and sex ratio. Males were usually oviposited in the first brood cells. Male and female developmental time from egg to adult was longer in the cold, dry season. Trypoxylon aurifrons provisioned their nests mainly with orb-spiders from the family Araneidae. The most important mortality factor was the death of immature forms, probably due to development failure. The most important parasitoid was Melittobia sp.

Tabela de vida de fertilidade de Aphidius colemani Viereck (Hymenoptera: Braconidae, Aphidiinae) em Aphis gossypii Glover (Hemiptera: Aphididae)

The intrinsic rate of increase of a parasitoid related to its hosts play an important role in biological control programs. In this work, fertility of the parasitoid Aphidius colemani Viereck was evaluated on Aphis gossypii Glover by means of a fertility life table. To determine the immature mortality, the development time and the sex ratio, 12 mated females of A. colemani (24h old), and 240 nymphs of A. gossypii (3 days old) were used. To evaluate fertility 15 mated females (24h old) were used. For each parasitoid female, 300 nymphs were offered in the 1st day, 250 nymphs in the 2nd day, 200 nymphs in the 3rd day, 150 nymphs in the 4th day, 100 nymphs in the 5th day and 50 nymphs in the other days. Immature mortality of A. colemani was 22.1%, development time of males and females were 12.0 and 11.8 days, respectively, and sex ratio was 0.6. The females of A. colemani laid 420 eggs and had longevity of 5.9 days. The net reproduction rate (R(o)) was 194.81 females and the intrinsic rate of increase (r(m)) was 0.384 females/females/day. The finite rate of increase (lambda) was 1.48 females/day, the mean length of a generation (T) was 13.74 days and the time to duplication the population (TD) was 12.60 days. The parasitoid A. colemani had a great potential of population growth on A. gossypii as a host and could be an effective biological control agent of this aphid.

Effects of larval energetic resources on life history and adult allocation patterns in a caddisfly (Trichoptera: Phryganeidae)

Abstract 1. How populations respond to environmental change depends, in part, on the connection between environmental variance during early life stages and its effect on subsequent life‐history traits. For example, environmental variation during the larval stage can influence the life histories of organisms with complex life cycles by altering the amount of time spent in each stage of the life cycle as well as by altering allocation to life‐history traits during metamorphosis.2. The effects of larval energetic resources on developmental timing, adult mass, fecundity, mating success, and allocation to adult body structures (thorax, abdomen, wings) were examined in an aquatic caddisfly (Agrypnia deflata Milne, Trichoptera: Phryganeidae). Larval energetic reserves were manipulated by removing larval cases just prior to pupation. In the first experiment, cases of all individuals were removed just prior to pupation; experimental individuals were required to build a new case whereas control individuals were allowed to re‐enter their case without building. In the second experiment, energy differences were maximised between the two treatments by supplementing the larval diet of the control group and removing cases and not supplementing the diet of the experimental group.3. Male and female development time, adult mass, and female fecundity were not influenced by case removal or diet supplementation. In contrast, allocation to adult body parts indicated a trade‐off between abdominal and thoracic mass among case‐removal females, suggesting that, under larval resource stress, females adjust resource allocation during metamorphosis to alleviate potential negative impacts on clutch size. In addition, latency to copulation increased when cases were removed, indicating larval resource stress could influence male mating success.4. This study suggests that, under larval energetic stress, the negative impacts on female reproduction might be mitigated by re‐allocating resources during metamorphosis, whereas male allocation strategies might not be as flexible as female strategies.

Response ofTetranychus cinnabarinus feeding on NaCl-stressed strawberry plants

The development and reproductive rates ofTetranychus cinnabarinus Boisduval (Acari: Tetranychidae), the carmine spider mite, were studied on two strawberry cultivars (Fragaria ×ananassa Duch.; ‘Camarosa’ and ‘Sweet Charlie’) at three NaCl concentrations, 1760, 2400 and 3040 mgl −1, and control. The effects of NaCl application on the contents of plant nutrients, chlorophyll, proline, peroxidase activity (POX) and proteins were assessed. On Camarosa,T. cinnabarinus had a faster development rate with applications of NaCl than without, except for female development at the highest salinity level. The total development time of females increased with the NaCl concentration, whereas total development time of males decreased. The oviposition period and female longevity on Camarosa was significantly longer in the control than with NaCl, whereas daily and total fecundity were significantly higher at all NaCl concentrations than in the control, except for total fecundity at the lowest salinity level. The total development time, oviposition period, female longevity, daily and total fecundity on Sweet Charlie did not differ significantly between NaCl salinity levels and the control. The intrinsic rate of natural increase (r m ) on Camarosa and Sweet Charlie were significantly higher with NaCl than in the control. However, the contents of Na, Cl, P, chlorophyll, proline, POX and protein in the two strawberry cultivars changed depending on NaCl concentration. On the other hand, the K and N contents were not affected significantly by NaCl salinity.

Comparison of the suitability of three pest leafminers (Diptera: Agromyzidae) as hosts for the parasitoid Dacnusa sibirica (Hymenoptera: Braconidae)

The suitability of Liriomyza sativae Blanchard, L. trifolii (Burgess) and L. bryoniae (Kaltenbach) as hosts of the solitary larval-pupal parasitoid Dacnusa sibirica Telenga was studied. This parasitoid is used as a biological control agent against L. trifolii and L. bryoniae. The parasitoid laid eggs in L. sativae, but no adult parasitoids emerged from the puparia. In contrast, D. sibirica adults emerged from the puparia of L. trifolii and L. bryoniae, and there was no significant difference in emergence rate, female developmental time, or sex ratio when parasitizing these two host species. The parasitoid adults that emerged from the L. bryoniae puparia were significantly larger than those from L. trifolii puparia. In conclusion, D. sibirica, a useful biological control agent of L. trifolii and L. bryoniae, cannot control L. sativae.