Reproductive performance of Nesolynx thymus (Hymenoptera: Eulophidae), in relation to age of Musca domestica (Diptera: Muscidae)

An investigation was undertaken to record the influence of host age on the reproductive performance of Nesolynx thymus (Hymenoptera:Eulophidae). This is an indigenous, gregarious, ecto-pupal parasitoid of certain dipteran insects, including the tachinid fly, Exorista bombycis (Louis) which is a well-known endo-larval parasitoid of the silkworm, Bombyx mori. Each gravid N. thymus female was allowed to parasitise 1–4-day-old puparia of Musca domestica L. for 2 days at a parasitoid–host ratio of 1:20. The parasitised host puparia were observed for progeny recovery, sex ratio, female longevity and fitness (adult size). In addition, reproductive performance of the parasitoid progeny was assessed by allowing its females to parasitise for 2 days, 3-day-old puparia of E. bombycis at a parasitoid–host ratio of 1:4. There was a significant negative correlation between host age and parasitisation rate, parasitoid developmental duration, sex ratio and female longevity while the correlation was positive between host age and parasitoid recovery per host puparium. Similarly, negative correlation was observed between host age and morphometric parameters (body length, head width and wing span of male and female and length and width of female abdomen) of the progeny adults. Host age did not have any impact on the reproductive performance of progeny adults when allowed to parasitise puparia of E. bombycis.     

Reproductive attributes of the eulophid Oomyzus sokolowskii,a biological control agent of diamondback moth,Plutella xylostella (Lepidoptera: Plutellidae)

Oomyzus sokolowskii (Kurdjumov) is a gregarious larval-pupal parasitoid of the diamondback moth, Plutella xylostella L. Under laboratory conditions, we explored the reproductive attributes including the functional response of O. sokolowskii and the impact of mutual interference among female parasitoids on progeny production and progeny sex ratio. In the functional response experiment, groups of 1–50 late instar larvae were exposed to groups of five female parasitoids for 48 h. Both Holling's disc equation (type II response) and Williams and Martinez's model (type III response) fit significantly better than the null-model assuming density-independent parasitation efficiency. Williams and Martinez's model was only marginally better than Holling's disc equation which explained 82% of the variation in the number of parasitized hosts. According to Holling's disc equation, the estimated maximum number of hosts parasitised during 48 h was 17 per group of five parasitoids, the estimated attack efficiency of a single female parasitoid (a) was 0.0024 larvae per hour, and the estimated handling time of a single female (T _h) was 14.4 h per host. In the mutual interference experiment 50 host larvae were exposed to different numbers of female parasitoids (P=5, 10, 20, 30, 40 and 50) for 48 h. With increasing numbers of conspecifics, the proportion of male progeny increased and total number of progeny per parasitoid decreased, yielding an estimated mutual interference constant (m) (±SE) of 0.95±0.14. The total number of wasps emerging from individual host pupae increased with increasing number of conspecifics. The age-specific fecundity of O. sokolowskii was investigated by providing 10 host larvae daily to individual female parasitoids. After 3 days of oviposition, 90% of the females were still alive and had achieved 76.4% of their lifetime fecundity. The proportion of female progeny decreased with female age. No relationship was found between female longevity and lifetime fecundity. The results suggest that parasitoid and host densities influence the progeny production and sex allocation strategy of O. sokolowskii. The information obtained from this study would help to develop a mass-rearing protocol for O. sokolowskii.     

Incidence of superparasitism in the egg parasitoid,Ooencyrtus kuvanae Howard (Hymenoptera: Encyrtidae)

The encyrtid Ooencyrtus kuvanae is a solitary parasitoid of the gypsy moth, Lymantria dispar L. (Lepidoptera-Lymantridae) that is used in biological control programmes and whose mass rearing is influenced by superparasitism. The purpose of this study was to investigate the effect of the self-superparasitism of O. kuvanae at different host densities (5, 10, 15 and 20), female ages (3 and 5 days) and durations of exposure (1 and 5 days) under various laboratory conditions (25°C?±?1°C, RH 60?±?5% and a 16:8?h light:dark photoperiod) as well as in a new laboratory host, Philosamia ricini (Danovan) (Lepidoptera: Saturniidae) of O. kuvanae. In this study, we determined the rate of egg superparasitism and adult emergence and recorded development time, longevity and body weight. Superparasitism increased with female age and the duration of exposure to parasitoids when females had access to five host eggs. Superparasitism increased the number of parasitoid offspring, but it resulted in male-biased (56.90%) progeny. Furthermore, superparasitism caused deleterious effects to the fitness of the progeny by prolonging the developmental process, and decreasing longevity. For example, we found that when four adults can emerge from one superparasitised host egg, the body size of the parasitoid offspring decreases significantly. Hence, superparasitism should be avoided when mass rearing O. kuvanae.     

Bionomics of Opius bellus (Hymenoptera: Braconidae), an endoparasitoid of Anastrepha fraterculus (Diptera: Tephritidae) in fruit-growing areas of Northwestern Argentina

Opius bellus is a neotropical larval-prepupal parasitoid known to attack the pestiferous fruit fly, Anastrepha fraterculus. Due to interest in the use of native parasitoids in forthcoming fruit fly biocontrol programmes in Argentina, O. bellus was colonised for the first time using laboratory-reared A. fraterculus larvae. A series of experiments were conducted to (1) best achieve an efficient parasitoid rearing by determining optimal larval host age, host:parasitoid ratio and host exposure time and (2) assess their potential as biological control agents by determining reproductive parameters. The most productive exposure regimen was: 7–9 d-old (early and middle third-instars) A. fraterculus larvae for 4 h at a 4:1 host:parasitoid ratio; this array of factors was sufficient to achieve the highest average adult emergence (48%) and an offspring sex ratio at equitable proportion. Increasing both host:parasitoid ratio further than 4:1 and the host exposure time beyond 4 h did not significantly enhance parasitoid female offspring yield. Females produced eggs for 29.5 ± 1.4 days. At 32 days of age, 50% of the females were still alive. The majority of the progeny were produced by females between 20 and 24 d-old. At 26°C, gross fecundity rate, net reproductive rate, intrinsic rate of increase and mean generation time were 20.7 ± 4.2 offspring/female, 9.6 ± 2.5 females/newborn females, 0.06 ± 0.01 females/female/day and 8.4 ± 0.2 days, respectively. The long lifespan and reproductive parameters suggest that this parasitoid species has suitable attributes for mass-rearing.     

Recurrent warming to improve cold storage of Trichogrammatids (Hymenoptera: Trichogrammatidae)

Cold storage can be used to slow development, facilitate accumulation of the organisms and accommodate fluctuating demand for augmentative biological control agents. Previous research suggested the possibility of improving cold storage of Trichogrammatids by recurrent warming, so we subjected Trichogramma ostriniae juveniles within Ephestia kuehniella host eggs to either 2°C constant or to 2°C with twice-weekly recurrent warming for 3 h to 20°C. Parasitoid subsamples were allowed to mature for 1–9 days before placement in cold storage for up to 8 weeks. Parasitism by parentals, progeny emergence and fecundity and longevity of progeny were measured weekly for 8 weeks. Relative to constant 2°C, recurrent warming generally improved emergence, fecundity and longevity, and all the response variables were affected by the interaction of temperature regimen, parasitoid maturity class, and cold storage duration. This implies the utility of recurrent warming to improve egg parasitoid performance and for extending the duration of cold storage.     

Fumigant toxicity of essential oil from Tanacetum balsamita L. (Compositae) against adults and eggs of Callosobruchus maculatus F. (Coleoptera: Bruchidae)

The essential oil of Tanacetum balsamita L. was tested against Callosobruchus maculatus F. at the rates of 5.12, 7.23, 10.19, 14.36 and 20.24?μl/l?air for adults and 5.3, 8.5, 10.8, 13.7 and 17.4?μl/l?air for eggs. All experiments were conducted at 27?±?1?°C and 65?±?5% relative humidity. Mortality was counted after 24, 48 and 72?h of exposure and all adults (dead and alive) were taken out of the vials and the vials were left at the same conditions for further 35?days to assess progeny production. For mortality of eggs, unhatched eggs were counted after 7?days. The adults treated with oil were more susceptible than eggs. At highest dose (20.24?μl/l?air) mortality of adults after 72?h, received 75.2%, but this amount for egg at 17.4?μl/l?air after 72?h was 49.06%. The lowest LC₅₀ value on 72?h was observed in adults (1.96?μl/l?air). Also, the lowest LC₉₅ value on 72?h was observed in adults (42.86?μl/l?air). The percentage of reduced progeny on 72?h was 50.92% at 20.24?μl/l?air. Our results suggest that T. balsamita can be used as an alternative to synthetic insecticides but higher dose may be needed.     

The influence of humidity on emergence in Dacnusa sibirica Telenga (Hymenoptera: Braconidae)

The effects of four humidities (33, 55, 76 and 93% relative humidity) and four ages (0–1, 2–3, 4–5, 6–7 days) of parasitized Chromatomyia syngenesiae puparia on adult emergence in the leafminer parasitoid Dacnusa sibirica were examined in the laboratory. Parasitized puparia harvested at 0–1 days were susceptible to low humidities resulting in a significantly reduced parasitoid emergence. Aging of the puparia appeared to protect the developing parasitoid from low humidities. Increasing humidity produced a corresponding increase in the longevity of the adult parasitoid.     

Transgenic GNA Expressing Potato Plants Augment the Beneficial Biocontrol of Lacanobia Oleracea (Lepidoptera: Noctuidae) by the parasitoid Eulophus Pennicornis (Hymenoptera; Eulophidae)

The effect of expressing the gene encoding snowdrop lectin (Galanthus nivalis agglutinin, GNA) in transgenic potato plants, on parasitism of the phytophagous insect pest Lacanobia oleracea by the gregarious ectoparasitoid Eulophus pennicornis, was investigated in glasshouse trials. Expression of GNA (approx. 1.0% total soluble protein) by transgenic plants significantly reduced the level of pest damage, thus confirming previous studies. Furthermore, the presence of the parasitoid significantly reduced the levels of damage incurred either by the transgenic or control plants when compared to those plants grown in the absence of the parasitoid. For the GNA expressing plants the presence of the parasitoid resulted in further reductions (ca. 21%) in the level of damage caused by the pest species. The ability of the wasp to parasitise and subsequently develop on the pest larvae was not altered by the presence of GNA in the diet of the host. E. pennicornis progeny that developed on L. oleracea reared on GNA expressing plants showed no significant alteration in fecundity when compared with wasps that had developed on hosts fed on control potato plants, although mean size and longevity of female parasitoids was significantly reduced. The number of F ₂ progeny produced by parasitoids derived from hosts fed on GNA-expressing plants was not significantly different to those produced by parasitoids from hosts fed control plants. Results from the present study demonstrate that the use of transgenic plants expressing insecticidal proteins can be compatible with the deployment of beneficial insects and that the two factors may interact in a positive manner.     

Functional response of <Emphasis Type="Italic">Pteromalus cerealellae</Emphasis> (Hymenoptera: Pteromalidae) on the cowpea weevil, <Emphasis Type="Italic">Callosbruchus maculatus</Emphasis> (Coleoptera: Bruchidae), and interaction between parasitism and cowpea varietal susceptibility

Laboratory studies were carried out to determine the functional response of the parasitoid, Pteromalus cerealellae (Boucek) to cowpea weevil, Callosobruchus maculatus (F.) hosts, and the relationship between parasitism and cowpea variety susceptibility to the weevil. The attack response of P. cerealella to weevil larvae was best described by a type III functional response using an egg limitation model. The mean attack rate (a) of the parasitoid was estimated as 1.7 and the upper limit of the response was 24 weevil larvae per individual parasitoid within a 48-h period. The results also showed that cowpea varieties resistant to weevil infestation supported fewer weevil progeny and facilitated a greater suppression of the weevil by the parasitoid. The parasitoid progeny index, a measure that compares the number of the parasitoid progeny to the number of the beetle progeny was higher in cowpea weevil resistant varieties than in susceptible varieties. Additionally, the presence of P. cerealellae resulted in reduced weight losses of cowpea caused by the weevil infestation in both susceptible and resistant varieties.     

Mediterranean flour moth Ephestia kuehniella eggs and larvae exposed to a static magnetic field and preference by Trichogramma embryophagum

This study investigated the effect of strong magnetic fields as insecticidal activity on Ephestia kuehniella (Zeller) (Lepidoptera: Pyralidae) larvae and eggs at different stages of development and their preference by the egg parasitoid, Trichogramma embryophagum Hartig (Hymenoptera: Trichogrammatidae). Eggs ranging in age from 24-h to 48-h and 72-h-old and larvae (1 to 2 days) were exposed to 1.4 Tesla (T) magnetic fields from a DC power supply at 50 Hz for different time periods (3, 6, 12, 24, 48 and 72 h). Twelve hours of exposure at 1.4 T was toxic to 24-h-old eggs of E. kuehniella. The 72-h-old host eggs treated with 1.4 T for 6–72 h were not significantly preferred by T. embryophagum. The magnetic field was toxic to 24-h-old eggs of E. kuehniella exposed to 1.4 T for 12. The treatment of magnetic fields on the 72-h-old host egg with 1.4 T at 6–72 h was not significantly preferred by T. embryophagum. Magnetization of 24-h-old eggs of E. kuehniella for 3 h could be effectively used with T. embryophagum as sterilised host eggs. These eggs were markedly preferred by T. embryophagum. The LT₅₀ and LT₉₉ values of magnetic fields at different egg stages of E. kuehniella, and larvae were measured. A level of 1.4 T at 72 h completely prevented the development of the larvae. There was no significant effect on larval survival at 1.4 T at 48 and 72 h. Increasing magnetic fields exposure times for eggs that were 24-h, 48-h and 72-h-old prevented larval emergence and increased their mortality rate. Consequently, magnetic fields could be used in controlling stored-product pest eggs and larvae of E. kuehniella.     

Nesting ecology of the wasp Sceliphron destillatorium (Illiger, 1807) (Hymenoptera,Sphecidae) in the Crimea

The nests of Sceliphron destillatorium in the Crimea were mainly built in attic spaces of houses and in various uninhabited buildings, and consisted of 3–39 (on average 16.5) cells. Twelve species of spiders from 11 genera of 4 families with predomination of Araneidae and Oxyopidae were recorded as prey. One nest cell contained 4–13 (on average 7.9) spiders, mostly adult ones. Successful development of S. destillatorium progeny was recorded in 48.6% of the cells; 26.5% of the progeny died from parasites: Amobia pelopei (16.0%), Chrysis taczanovskyi (4.3%), and Melittobia acasta (6.2%); 24.9% of the progeny died for unknown causes at the egg (13.0%) or prepupal (11.9%) stage. Nests of 17 other wasp and bee species from the families Pompilidae (2 species), Vespidae (4), Colletidae (1), and Megachilidae (10 species) were found in abandoned nest cells of S. destillatorium. The abundance of S. destillatorium has noticeably decreased in the last ten years, possibly due to immigration of a congener, S. curvatum, which has more diverse trophic links and a significantly higher rate of nesting success.     

Effects of host age and host availability on developmental period,adult size,sex ratio,longevity and fecundity inLariophagus distinguendus Förster (Hymenoptera: Pteromalidae)

The effects of host age on parasitoid reproductive capacity are studied using the pteromalid parasitoid Lariophagus distinguendusFörster and its bruchid hosts, Callosobruchus chinensis (L.) and C. maculatus (F.). A series of experiments were performed to investigate relationships between age and size of host parasitized and the developmental period of pre-imaginal progeny, sex ratio, female size, longevity, fecundity and oviposition rate. There was no effect of host size on preimaginal parasitoid developmental period. Sex ratio varied from less than 5% females from young (small) hosts to 60% females from mature (large) hosts. Adult size, female longevity, fecundity, and oviposition rate were also positively related to host age. Females provided mature hosts lived longer than those provided either young hosts or no hosts, possibly because of an increased ability to host-feed from the larger hosts. The implications of these findings to parasitoid population reproductive capacity and host-parasitoid synchrony are discussed.     

Biology of Cotesia ( = Apanteles) telengai (Hymenoptera: Braconidae) on its natural host Agrotis segetum (Lepidoptera: Noctuidae)

The host suitability of Agrotis segetum Denis & Schiff., A. ipsilon Hufn., Spodoptera littoralis Boisd, S. exigua Hub., Mythimna loreyi Duponchel and Mamestra oleracea L. for the gregarious braconid Cotesia ( = Apanteles) telengai Tobias was determined under laboratory conditions. The parasitoid only completed its development in larvae of A. segetum. The percentage of successfully parasitized larvae and the mean duration of C. telengai egg‐larval period were inversely related to the age of the host or host instar at parasitization. The mean number of parasitoids which emerged per parasitized larva was positively correlated with the larval age. The sex ratio was consistently high (ca. eight males to one female), independent of the host instar parasitized, as compared to 1:1 as observed frequently in field populations of this wasp. The females of C. telengai were active and produced offspring at temperatures of 15, 20, 25 and 30° C. However, the mean percentage of parasitized larvae increased from 13.1 to 72% and the mean progeny per parasitoid female increased from 14.7 to 129.4 parasitoids, both significant, when the experimental temperature was raised from 15 to 30°C, while their mean development time decreased from 75.5 to 19.2 days. At 25°C, the virgin and mated females continued oviposition until days 16 and 17, with a lifetime total of progeny of 397.6 (SD ±224.7) and 611.1 (SD± 128.8) parasitoids respectively, reaching a maximum of 64.3 and 99.2 on day 2 respectively.     

Developmental time,longevity, reproductive capacity and sex ratio of the mealybug parasitoid Anagyrus sp. nr. pseudococci (Girault) (Hymenoptera: Encyrtidae)

Key biological parameters of Anagyrus sp. nr. pseudococci reared on the citrus mealybug Planococcus citri (Risso) were determined. The mean longevity of female wasps was 21.1 days, the median lethal time (LT₅₀) was 22 days, the mean number of offspring per female was 30.2 wasps and the sex ratio of the progeny was slightly male biased (1.1 males per female). Wasps fed with water showed a significantly lower longevity compared to that recorded for wasps fed with syrup for bee nutrition mixed with water. The longevity of female wasps was significantly higher compared to males when the syrup-water solution was provided as food. Longevity was significantly higher for female wasps fed with syrup and water in comparison with those exposed to host mealybugs. The mean development time of female and male wasps was 14.7±0.1 and 14.5±0.1 days, respectively.     

Mating and prey stage affecting life history,reproduction and life table of the predacious mite Phytoseiulus macropilis (Banks) (Acari: Phytoseiidae)

Abstract

Two factors were examined to determine their effect on the life history, reproduction and life table parameters in the predacious mite Phytoseiulus macropilis (Banks) in the laboratory. The factors studied included multiple mating and various prey stages of Tetranychus urticae Koch. When females fed on mixed actives (protonymphs and deutonymphs) of T. urticae, the fecundity of females mated more than once was 1.7 times higher than in females mated only once, also oviposition period and adult longevity was longer. The adult longevity and life span of P. macropilis were similar when fed on mixed actives, eggs (0 – 24-h-old) and (0 – 48-h-old) of T. urticae, while both periods were increased and reproduction was higher when fed on older eggs (72 – 96-h-old) of T. urticae. The total number of eggs deposited by females was significantly higher on eggs of (various ages) than on mixed actives of T. urticae. Life table parameters showed that a diet of (72 – 96-h-old) eggs of T. urticae provided the longest generation time (11.066 days) and female longevity (33.54 days) as well as the highest intrinsic rate of natural increase (rm = 0.36755) and greatest total fecundity which resulted in the highest net reproductive rate (Ro = 58.4136) value. The adult female consumed daily an average of 6.8 mixed actives of T. urticae during its life cycle, while it was increased to 13.6 during the oviposition period. The daily (72 – 96-h-old) eggs of T. urticae consumed by female P. macropilis during its life cycle and adult longevity was significantly higher than that recorded on either (0 – 24-h-old) or (0 – 48-h-old) eggs of T. urticae.     

Acceptance and suitability of different host stages of Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) and seven other tephritid fruit fly species to Tetrastichus giffardii Silvestri (Hymenoptera: Eulophidae)

Tetrastichus giffardii Silvestri is a gregarious eulophid endoparasitoid of several tephritid fruit fly species. Host stage suitability was studied using nine age groups of Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), namely, eggs less than 24 h and between 24 and 48 h old, and 1- to 7-day-old larvae. Life table studies for T. giffardii using C. capitata as host were done at 26 ± 5 °C and 55–60% RH. Egg load in relation to age of the female parasitoid was also assessed as was the effect of host deprivation on adult longevity. Host acceptance and suitability were examined with respect to eight species of tephritids. Potential hosts so tested were five Ceratitis species, the Medfly, C. capitata, the mango fruit fly, Ceratitis cosyra (Walker), the Natal fruit fly, Ceratitis rosa Karsch, Ceratitis fasciventris (Bezzi), and Ceratitis anonae Graham; two Bactrocera species, the melon fruit fly, Bactrocera cucurbitae (Coquillett) and the newly invasive Bactrocera invadens Drew, Tsuruta, and White; and one Dacus species, the lesser pumpkin fly, Dacus ciliatus Loew. No parasitoids were obtained from eggs while all larval stages were suitable though at varying degrees. Parasitism and number of progeny was related to host age in a curvilinear manner with maxima at 4- to 5-day-old larvae. By contrast, development time decreased with age of host larvae while sex ratio was not affected. The intrinsic rate of increase was 0.17 ± 0.01; gross and net reproductive rates were 64.9 ± 4.3 and 44.9 ± 3.8, respectively. Non-ovipositing females lived significantly longer than ovipositing ones. The females accepted all host species tested, but only C. capitata, D. ciliatus and, to a much lesser extent, C. cosyra were suitable. In the remaining host species, most eggs were encapsulated. In C. capitata and D. ciliatus, percent parasitism was similar, but number of progeny was lower and the sex ratio, as the proportion of females, was higher when the parasitoid was reared on D. ciliatus. Progeny per puparium were also similar for the two hosts. In the light of these results it can be concluded that T. giffardii has a narrow host range, but it attacks and successfully develops in larvae representing a wide range of ages.     

Sublethal effects of NeemAzal- T/S botanical insecticide on Dutch and Serbian populations of Encarsia formosa (Hymenoptera: Aphelinidae)

Sublethal effects of an azadirachtin-based botanical insecticide (commercial product NeemAzal-T/S) on behaviour, life history traits and population growth of one commercial (Dutch strain, D) and two Serbian populations (Bujanovac, B; Negotin, N) of Encarsia formosa Gahan were evaluated in laboratory bioassays. In a two-choice test, parasitoids from all tested populations preferred to parasitise the untreated whitefly nymphs over those treated with 50, 25, 12.5, 6.25 and 3.12?mg/l of azadirachtin. All concentrations caused significant deterrent effects after 24?h, and the following deterrence indices were calculated: 9.7–60.9% (B), 5.5–57.5% (N) and 12.9–63.5% (D). The longevity of adults exposed for 48?h to residues of the botanical insecticide (applied at LC₅₀) was shorter (1.5–1.7 days) than that of control wasps. Both daily and total parasitism were significantly reduced (by 41.7, 48.3 and 60.1% for N, D and B, respectively) compared to control, as well as adult emergence in the F₁ generation. The instantaneous rate of increase (r_i) of surviving adults was also significantly reduced (by 13.2, 19. 3 and 20.5%, for populations N, B, and D, respectively). Adults from all tested populations, emerged from pupae treated with the botanical insecticide applied at LC₅₀, showed reduced parasitism, adult emergence, and r_i levels, but the reduction was significant only for adult emergence of B and r_i of B and N. Juvenile development of the parasitoid in treated pupae was significantly extended, compared to control. The implications of these results on integrated control of the greenhouse whitefly are discussed.     

Interaction between MbMNPV and the braconid parasitoid Habrobracon hebetor (Hym., Braconidae) on larvae of beet armyworm,Spodoptera exigua (Lep., Noctuidae)

The survival of a braconid parasitoid Habrobracon hebetor was investigated on nucleopolyhedrovirus (NPV)-infected Spodoptera exigua larvae. The second-instar larvae were exposed to 30, 51.4 and 180 PIB/mm² of Mamestra brassicae NPV (MbMNPV) as under-LD₅₀, LD₅₀ and over-LD₅₀ values, respectively. They were accessible to be parasitized by H. hebetor after 24, 48 and 72 h post-treatment. Infection of the larvae with MbNPV was deleterious to the survival and parasitism of H. hebetor. The survival of H. hebetor in MbNPV-infected S. exigua larvae was dependent on the interval between viral infection and parasitization, as well as on the treatment dose of MbMNPV; very few adults of parasitoid emerged from infected hosts when host larvae were exposed to 180 PIB/mm² of MbNPV on 72-h interval treatment. The inoculation dose of MbNPV and the timing of parasitoid release had significant effect on the development of H. hebetor on virus-infected hosts. Field applications of virus for biocontrol of S. exigua may lead to substantial mortality of immature parasitoids.     

Effect of mating combinations on the host parasitisation and sex allocation in solitary endoparasitoid,Aenasius arizonensis (Hymenoptera: Encyrtidae)

Aenasius arizonensis (Girault) is an important solitary endoparasitoid of Phenacoccus solenopsis Tinsley. To optimise the mass production of high-quality females, it is important to assess the influence of mating regimes on the progeny fitness and sex allocation. We, therefore, hypothesise that mating combinations in A. arizonensis adults emerged from different host instars may influence parasitism and sex allocation in the subsequent generation. Therefore, we compared three nymphal instars (1st, 2nd and 3rd) and adults host stages of P. solenopsis for parasitism and sex allocation by A. arizonensis. Further, F₁ female progeny of the parasitoid emerged from different host instars was henceforth evaluated for its fitness in six mating combinations. A. arizonensis females parasitised all the host stages except the 1st instar nymphs. The parasitised 2nd instar nymphs yielded only males, while the sex ratio in the later host instars was strongly female-biased. The parasitoid females preferred 3rd instar nymphs with respect to higher parasitism (74.0–84.0%) and produced more females in the F₁ progeny as compared to other host stages. F₁ females that emerged from 3rd instar nymphs produced significantly higher parasitism (74.0–79.0%). These mating combinations also yielded more female progeny in the F₂ generation. However, parasitism by F₁ females was significantly lower (9.0–12.0%) when mated with males that emerged from 2nd instar P. solenopsis nymphs. Moreover, latter combinations yielded only male progeny in F₂ generation. These findings can be used in laboratory mass rearing of this parasitoid vis-à-vis biological control of P. solenopsis.     

Interactions among the entomopathogenic fungus, Beauveria bassiana (Ascomycota: Hypocreales), the parasitoid, Aphidius matricariae (Hymenoptera: Braconidae), and its host, Myzus persicae (Homoptera: Aphididae)

The effect of the entomopathogenic fungus Beauveria bassiana on the biological characteristics and life table of Aphidius matricariae, a parasitoid of the green peach aphid, Myzus persicae, was studied under laboratory conditions. Aphids were first infected with twice the LC₉₅ of B. bassiana for third-instar M. persicae (2 × 10⁸ conidia/ml). Subsequently, at different intervals they were exposed to 1-day-old mated parasitoid females for 24 h. The number of mummies produced per female and the percentage emergence of the F1 generation differed significantly as a function of the time interval between application of the fungus and exposure to the parasitoid. The interference of B. bassiana on parasitoid development was also studied by first exposing the aphid hosts to the parasitoid for 24 h and subsequently applying B. bassiana. The number of mummies produced by a female A. matricariae varied from 11.8 to 24.8 and was significantly different when the aphids were first exposed to the parasitoids and then treated with B. bassiana 24, 48, 72, and 96 h after exposure. There were no significantly different effects of B. bassiana on net reproductive rate (R₀), mean generation time (T), intrinsic rate (r_m) and the finite rate of increase (λ) of A. matricariae as a result of development in hosts exposed to low or high conidial concentrations (1 × 10², 2 × 10⁸ conidia/ml). The parasitoids developed in infected hosts had lower r_m, λ, T and DT (doubling time) values compared with those that developed in uninfected hosts but no differences were observed in R₀ values. With proper timing, A. matricariae and B. bassiana can be used in combination in the successful biological control of M. persicae.