Parasitoid Ratio Research Articles

Ecological and morphological characteristics of parasitoids in Phauda flammans (Lepidoptera, Zygaenidae).

Phauda flammans Walker (Lepidoptera, Zygaenidae) is one of the notorious defoliators on Ficus spp. trees. In order to avoid environmental pollution, potential biological control agents for P. flammans need to be investigated instead of chemical control. Four species of insect parasitoids were identified from P. flammans, including three hymenopteran species (i.e., Gotra octocinctus, Apanteles sp. and Eurytoma verticillata) and one dipteran species (i.e., Exorista yunnanica). Parasitoid ratios of G. octocinctus, Apanteles sp., Eu. verticillata and Ex. yunnanica were 7.2%, 4.2%, 1.6% and 0.9%. The four species were all larval endoparasitoids of P. flammans larvae. Time of cocoon (pupa) to adult, life span, major axis of cocoon and body length of females were all longer compared to males for G. octocinctus, Apanteles sp. and Ex. yunnanica. Based on the parasitoid ratios, the most abundant parasitoid species was G. octocinctus.

Standardisation of Host-Parasitoid Ratio of Plutella xylostella (Linnaeus) and Trichogrammatoidea bactrae Nagaraja

Host parasitoid ratio for Plutella xylostella and its egg parasitoid Trichogrammatoidea bactrae was worked out under invitro conditions, at 26+1oC and 65% RH. Host to parasitoid ratio of 35:1 was optimum with parasitism and adult emergence of >90%. The ratio was on par with ratio range from 21-30:1. Mass rearing of the parasitoid for would be more economical when reared at the optimum ratio. Effective dose for inundative releases of the parasitoid for suppression of Plutella xylostella could be determined based on the field evaluation of the optimum host – parasitoid ratio (35 host eggs:1 female parasitoid).

Toxicity of some insecticides used in maize crop on Trichogramma pretiosum (Hymenoptera, Trichogrammatidae) immature stages

Fall armyworm Spodoptera frugiperda (J.E. Smith, 1797) (Lepidoptera: Noctuidae) is an important pest of maize (Zea mays L.) crops in Brazil. The effects of beta-cypermethrin, chlorfenapyr, chlorpyrifos, spinosad, etofenprox, triflumuron, alpha-cypermethrin/teflubenzuron, and lambda-cyhalothrin/thiamethoxam on Trichogramma pretiosum Riley, 1879 (Hymenoptera: Trichogrammatidae) immature stages were evaluated. Eggs of Anagasta kuehniella (Zeller, 1879) (Lepidoptera: Pyralidae), containing immature stages of the parasitoid were dipped in water solution pesticides, to evaluate their effects on emergence and sex ratio of F1 parasitoids. For F2 parasitoids, emergence, parasitism capacity, and sex ratio were evaluated. Beta-cypermethrin, chlorfenapyr, chlorpyrifos, and spinosad affected the emergence success of F1 T. pretiosum. Insects exposed to etofenprox and alpha-cypermethrin/teflubenzuron during the egg-larval period and to lambda-cyhalothrin/thiamethoxam during the pupal stage also suffered reduction in the emergence. Beta-cypermethrin affected the sex ratio of F1 T. pretiosum from host eggs treated during the egg-larval period; spinosad affected it during the egg-larval period and the pupal stage, whereas chlorpyrifos did the same when applied during the pupal stage. Chlorpyrifos also affected the sex ratio of F2 parasitoids, but only when applied during the egg-larval period, whereas chlorfenapyr reduced this trait when applied during the pre-pupal phase. Chlorpyrifos and alpha-cypermethrin/teflubenzuron affected the parasitism capacity of F1 females from eggs treated during the egg-larval period. Considering the overall effects, only etofenprox and triflumuron were selective on T. pretiosum when applied on parasitized A. kuehniella eggs. Further studies need to be carried out to verify the toxicity of the other pesticides under semi-field and field conditions.

A First Record ofBlaesoxipha rufipes(Diptera: Sarcophagidae) ParasitizingPoekilocerus bufonius(Orthoptera: Pyrgomorphidae) in Saudi Arabia

The tropical grasshopper (Usherhopper), Poekilocerus bufonius (Orthoptera: Pyrgomorphidae) is found on several host plants such as Calotropis procera, Aizoon canarense, Zygophyllum simplex and Pulicaria crispa in Saudi Arabia (KSA). Many species of Sarcophagidae and Tachinidae parasitize P. bufonius. Here we present the first published record of Blaesoxipha rufipes parasitizing P. bufonius and the first record of its occurrence in Saudi Arabia. We collected 568 adults of the host from five regions in the Middle West of KSA. These were dissected in order to study the parasitoid distribution, parasitism ratio and sex ratio. The parasitoid occurred in all regions investigated but its incidence gradually decreased from East to West. We found that hopper females were significantly more infested (=32.3%) than males (=18.3%). Also, the number of maggots per infested host ranged from 2 to 11 and averaged 6.7 with a significant difference in the mean number of parasitoids for each infested adult male (=3.8) vs. adult female (=7.7). Parasitoid sex ratio overall was 40.1%:59.1% males to females. Occurrence of this parasitoid in KSA suggests further study to investigate its potential as a biological control agent for more damaging Orthoptera.

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.

Efforts to Support Sustainable Agriculture with The Understanding of Invasion and Colonization Egg Parasitoid of Yellow Rice Stemborer, Scirphopaga Incertulas Walker (Lepidoptera: Pyralidae) in Bali

The arrangement of sustainable agriculture in Bali which appropriate with Bali government’s mission: Bali Clean and Green 'Go to Organic'. The concept of modern agriculture looks like contradiction with the aspects of sustainable agriculture. The aspects of rice cultivation have been done by local agriculture community in Bali (call it SUBAK) for many years, but the attack of yellow rice stemborer still happen, which adverse farmer’s side, persist. The efforts control which has been done, still rely on insecticides because it can give quick effect, but it is not appropriate for sustainable agriculture. The other solution to solve that issue is with the integrated pest management (IPM), as the main component of which is the role of parasitoids. Therefore needed research to investigate the invasion and colonization of yellow rice stemborer parasitoids in Bali. The research was conducted in three districts centers of rice stemborer (Badung, Tabanan, Jembrana), since December 2013 to March 2014. This research using survey method with the rule is collecting the group of egg with purposive random sampling at 10 - 66 days after planting (dap), as many as 70 groups of eggs per week. The observed of variables include the percentage of infected eggs, diversity, dominance, similarity, abundance, attack level and ratio of female parasitoids. The result showed that invasion and colonization of the egg parasitoid of yellow rice stemborer in Bali vary in diversity, dominance, abundance, the percentage of infected eggs and attack level. Three types of parasitoids associated with rice plants, they are Trichogramma japonicum, Telenomus rowani and Tetrastichus schoenobii. The percentage of infected eggs, diversity, dominance of T. japonicum, T. rowani and T. schoenobii, similarity, abundance of T. japonicum, T. rowani and T. schoenobii, attack level of T. japonicum, T. rowani and T. schoenobii and ratio of female of T. japonicum, T. rowani and T. schoenobii found in Tabanan regency, were (90.14%; 0.32; 0.00; 0.06; 0.49; 100%; 96.16; 424.09; 1.193,54 tail; 1.30; 11.98; 85.13%; 77.36; 84.67; 79.51%), in Badung regency were found (83.68%; 0.42; 0.02; 0.12; 0.26; 100%; 199.94; 471.14; 708.83 tail; 5,22; 20,61; 64,25%; 76.48; 83.44; 77.63%) and at Jembrana regency were found (78.61%;0.39;0.02;0.35;0.07;100%;144,76;635,97; 293,15 tail; 4.79;39.43;50.20%;75.83;80.77; 75.30%). The above data’s as a basis for determining the measures to support sustainable agriculture.

Trissolcus semistriatus (HYMENOPTERA: SCELİONİDAE)'UN -20°C'DE DEPOLANMIŞ Dolycoris baccarum (HETEROPTERA: PENTATOMIDAE) YUMURTALARINDAKİ PERFORMANSI

A project was carried out between 2004 and 2008 in order to improve the mass production of an egg parasitoid Trissolcus semistriatus Nees (Hymenoptera: Scelionidae) of Sunn pest, which is important pest on wheat fields, in the laboratory conditions in Antalya Bati Akdeniz Agricultural Research Institute. Dolycoris baccarum L. (Heteroptera:Pentatomidae) which is the alternative host of T. semistriatus was reared in insectarium and the produced eggs were stored in eppendorph tubes for 12 months at -20°C. Monthly parasitism performance of T. semistriatus was evaluated. The parasitism ratio was 27.08-89.64 %; adult emergence ratio was 58.92-87.34 %; the sex ratio was 0.37-0.61; development period was 10.16-14.65 days for males and 11.67-15.38 days for females, the life span of males was 7.73-13.50, and 6.25-13.98 days for females. The longevity of males and females were 7.73-13.50 and 6.25-13.98 days respectively. According to the results, it was suggested that D. baccarum eggs stored up to 7 months at -20°C would be convenient for mass production of T. semistriatus due to the parasitism ratio was 51.63 % and hatching ratio of parasitoids was 72.47 % in these eggs.

Flowers for better pest control? Effects of apple orchard groundcover management on mites (Acari), leafminers (Lepidoptera, Scitellidae), and fruit pests

Flowering companion plants provide nectar, pollen, alternative prey, shelter, and overwintering habitat for arthropod natural enemies and thus might increase their abundance and efficacy in pest control in agricultural fields. We report the results of a 6-year study on the effects of annual and perennial flowering herbs sown in alleys of an apple orchard on phytophagous and predacious mites, leafminer moths and their parasitoids and on pests causing fruit injury. Plots with weed-free bare ground and with regularly mowed grass served as controls. The abundance and diversity of predatory phytoseiid mites increased in the presence of flowering ground cover plants. However, this positive effect on phytoseiids was confined only to spring and autumn and intraguild predation (Typhlodromus pyri gradually displaced Amblyseius andersoni in the presence of flowers) also constrained their enhancement. Spider mites’ (Tetranychidae) abundance was low in all years and did not increase with the alley herb coverage. Incidence of the leafminer Leucoptera malifoliella was similar among the treatments despite the higher parasitism rate and parasitoid diversity in the plot with flowering herbs. We demonstrated that in the presence of flowering ground cover plants, the sex ratio of eulophid parasitoids' (mainly Chrysocharis pentheus) reared from L. malifoliella larvae and pupae shifted towards a male bias. Ground cover management had no effect on fruit injury caused by codling moth (Cydia pomonella) and summer fruit tortrix moth (Adoxophyes orana) and on the percentage of apples without insect damage.

Interspecific larval competition between two egg parasitoids in refrigerated host eggs of Riptortus pedestris (Hemiptera: Alydidae)

In a previous study, we found that soybean fields could be supplemented with refrigerated eggs of Riptortus pedestris (Fabricius) (Hemiptera: Alydidae) to enhance parasitism. As a part of a study to evaluate the effect of host egg refrigeration on parasitism, host acceptance behavior and interspecific larval competition between Gryon japonicum (Ashmead) (Hymenoptera: Scelionidae) and Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) were studied in multiparasitized unrefrigerated and refrigerated eggs. O. nezarae showed complete host acceptance behavior when offered refrigerated host eggs that were preparasitized by G. japonicum. Adult emergence rate of O. nezarae was 43 and 74% when the interval between the first and second oviposition was 0 and 4 days, respectively, and was not different between refrigerated and unrefrigerated eggs. Refrigeration did not change host acceptance behavior of G. japonicum, but adult emergence declined from 80% in unrefrigerated eggs to 37% in refrigerated eggs that were pre-parasitized by O. nezarae on the same day. No negative effects of refrigeration on sex ratio, adult longevity, and adult size of the both parasitoids were found. Generally host egg refrigeration did not negatively affect host acceptance behavior of the both parasitoids on preparasitized eggs or larval competition between the two parasitoids in multiparasitized host eggs with exceptions in the development time and emergence rate of G. japonicum. Therefore, host egg refrigeration may not interrupt interactions between the parasitoid populations in the field.

Evidence for parasitoid‐induced premature mortality in the Argentine stem weevil

The Argentine stem weevil Listronotus bonariensis Kuschel (Coleoptera: Curculionidae) is an exotic pest of New Zealand ryegrass and the adult‐stage is parasitized by the introduced solitary endoparasitoid Microctonus hyperodae Loan (Hymenoptera: Braconidae: Euphorinae). This biological control agent is effective, although, under both laboratory and field conditions, an unexplained source of premature mortality in the weevils is observed after exposure to M. hyperodae. This premature mortality may be affected to varying degrees by the length of time of parasitoid exposure, the physiological conditions of the host, and the host to parasitoid ratios, although it occurs naturally without any physical interruption to the parasitoid ovipositional process. In the present study, the premature mortality reported in earlier studies is confirmed and it is conjectured to be the result of injection of parasitoid venom without an egg. Moreover, the lack of premature mortality resulting from longer exposure periods indicates that there might be a curative effect resulting from subsequent oviposition; the egg reverses the toxic effect induced by the injection of venom only. As discussed, this phenomenon may not be restricted to the L. bonariensis/M. hyperodae system and, accordingly, there are evolutionary, biosecurity and general pest management questions to be considered.

Biological characteristics and parasitism capacity of Trichogramma pretiosum Riley (Hymenoptera, Trichogrammatidae) on eggs of Spodoptera frugiperda (J. E. Smith) (Lepidoptera, Noctuidae)

This study aimed at evaluating the biological characteristics and the capacity of parasitism of a Trichogramma pretiosum Riley, 1869 (Hymenoptera, Trichogrammatidae) strain (T. pretiosum RV) collected in Rio Verde County, State of Goiás, Brazil. The study was carried out on eggs of Spodoptera frugiperda (J. E. Smith, 1797) (Lepidoptera, Noctuidae) and conducted under controlled environmental conditions at different constant temperatures. The biological parameters determined were: developmental time (egg-adult; days); emergence (%); sex ratio; number of progeny/egg; number of generation/year; thermal constant (K); temperature threshold (Tb); daily number of parasitized eggs; cumulative parasitism (%); total number of eggs parasitized by T. pretiosum; and female longevity. To study the T. pretiosum parasitism capacity, 20 S. frugiperda eggs (< 24 h old) were placed into 8.0 cm x 2.0 cm glass vials containing one female (< 24 h old) each. Trials were carried out in a completely randomized experimental design, with 20 replications at each temperature. The environmental chambers (BOD type) were set at 18ºC, 20ºC, 22ºC, 25ºC, 28ºC and 32ºC ± 1ºC, 70 ±10% relative humidity, and 14/10 h (L:D) photoperiod. The eggs of S. frugiperda were replaced daily until parasitoid death. Results have shown an inverse correlation between developmental time and temperature, with statistically significant differences among means, except at 25ºC and 28ºC (10 days). Parasitoid emergence (%) was also influenced by temperature. The lowest percent emergence was observed at 32ºC, and the highest ones at 18ºC and 20ºC temperatures. The temperature did not affect T. pretiosum sex ratio and number of parasitoids per egg, thus allowing changes in the temperature to control insect mass production in the laboratory to meet the needs for field releases.

Biology and Behavior ofSpathius agrili, a Parasitoid of the Emerald Ash Borer,Agrilus planipennis, in China

Spathius agrili Yang (Hymenoptera: Braconidae) is a gregarious larval ectoparasitoid of the emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) and is a recently described species. Both pest and parasitoid are native to China. In Tianjin City, China, S. agrili typically exhibited 3–4 generations per year, overwintering as a prepupa in a cocoon inside the host gallery. The multiple generations of S. agrili overlapped with its host, as did the emergence dates of the overwintering generation. From a single host, 1–18 S. agrili successfully developed to the adult stage (average 8.4), but in all cases the host was killed. The sex ratio (female: male) of the parasitoid adults emerging from field-collected cocoons was 2:1, whereas the sex ratio of parasitoids reared from field collected eggs and larvae was greater than 3:1. On average, adult females lived 29.1 d, and males lived 23.6 d when fed with 20% honey solution, significantly longer than without a nutritional supplement. Sexual reproduction is the normal mode of reproduction, but in the laboratory females did reproduce parthenogenetically, producing only males. The average fecundity was 23.3 eggs per female in the laboratory. S. agrili developed through five larval instars, and the larvae fed gregariously on the host hemolymph. The generation time from egg to adult wasp was 27–28 d at 22–26°C. Natural parasitism rates were as high as 60%, and in October they reached over 90% in some stands. This study showed that S. agrili is a promising agent for biocontrol of A. planipennis.

Evaluation of Irradiated Caribbean Fruit Fly (Diptera: Tephritidae) Larvae for Laboratory Rearing of Doryctobracon areolatus (Hymenoptera: Braconidae)

We report here that it is possible to rear D. areolatus on irradiated A. suspensa larvae without adversely affecting sex ratio and overall parasitoid emergence and with no adult A. suspense emergence. There was no difference in emergence of D. areolatus adults from irradiated versus non-irradiated hosts (72.4 ± 1.9% vs. 73.0 ± 1.9%), and no difference in sex ratio of parasitoids obtained from irradiated and non-irradiated hosts (50.0 ± 1.6 and 47.0 ± 1.4% female, respectively). The successful use of A. suspensa larval hosts can greatly ease the process of rearing, transporting, and releasing fruit fly parasitoids while eliminating the need to separate flies from parasitoids. Further improvements in the laboratory rearing process of D. areolatus, including irradiating late A. suspensa larvae at a lower dosage and irradiating A. suspensa as egg or early instars, are discussed.

Parasitism rate and sex ratio of Psyttalia (=Opius) concolor (Hymenoptera: Braconidae) reared on irradiated Ceratitis capitata larvae (Diptera: Tephritidae)

Tests were conducted to evaluate use of irradiated Mediterranean fruit fly (medfly), Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), larvae as factitious hosts for mass-rearing the parasitoid Psyttalia concolor (Szepligeti) (Hymenoptera: Braconidae). In order to prevent the release of the alternative host adults, eclosion from unparasitized larvae must be prevented. Exposure of medfly larvae to 40, 50 or 60 Gy of 60Co gamma radiation showed that 60 Gy was the most effective dose in inhibiting adult medfly eclosion. The most suitable host:parasitoid ratio was found to be three larvae per parasitoid regardless of exposure time. When three larvae per parasitoid were exposed for 3 h, there was no significant difference in parasitism rates using irradiated vs. unirradiated host larvae (16.4 vs. 18%, respectively). Irradiation of host larvae also had no significant effect on the sex ratio of resulting parasitoids. Implementation of this practice will improve the efficiency of mass production and release of this biocontrol agent.

Enhancing biological control of sugarcane shoot borer, Chilo infuscatellus (Lepidoptera: Pyralidae), through use of radiation to improve laboratory rearing and field augmentation of egg and larval parasitoids

Feasibility studies were conducted to evaluate the use of gamma radiation to improve the production and field performance of the egg parasitoid Trichogramma chilonis Ishii and to improve production of the gregarious larval endoparasitoid Cotesia flavipes Cameron for biological control of the sugarcane shoot borer, Chilo infuscatellus Snellen. Sitotroga cerealella (Olivier) eggs were used as hosts for T. chilonis and the suitability of non-irradiated host eggs decreased as the age of the eggs increased, with no success in parasitization of eggs older than 4 days of age. However, irradiation of host eggs using 20–25 Gray (Gy) decreased the age effect and significantly more 2-, 3-, 4- and 6-day-old irradiated eggs were successfully parasitized than non-irradiated eggs. Radiation doses of 20 and 25 Gy were most effective for economical production of T. chilonis. Irradiation of host eggs did not affect the hatch percentage up to a dose of 15 Gy. Hatchability was significantly reduced at higher doses, with negligible hatching at 50 Gy. Irradiation also skewed the sex ratio of S. cerealella in favor of males at higher doses. Radiation at 60–80 Gy improved the suitability of C. infuscatellus larvae for parasitism by C. flavipes, allowing normally unsuitable fourth and fifth instar larvae of C. infuscatellus to be successfully parasitized. The sex ratio of parasitoids reared on irradiated larvae was skewed in favor of females. Irradiation also slowed immature development of C. flavipes and the combination of irradiation and low temperature (10°C) proved effective for prolonged storage of the parasitoids. Pupae of C. flavipes irradiated at 20 Gy could be stored for 2 months at 10° C without apparent loss of quality and deferred emergence by 29–30 days. Provisioning with irradiated supplemental hosts in the field increased overall pest suppression. The infestation by C. infuscatellus was higher in the control sugarcane block, where it remained above the economic threshold level (10% infestation) from April to October. High temperatures and low relative humidity during May to July reduced increases of the parasitoid populations. These findings were used to facilitate the area-wide application of biocontrol agents in a 40,000 hectare area to suppress sugarcane borers to sub-economic levels (<10% infestation). Sugarcane borer damage was 5.9% in treated blocks vs. 19.2% in untreated control blocks.

Effects of host density, host age, temperature and gamma irradiation on the mass production of Nesolynx thymus (Hymenoptera: Eulophidae), an endoparasitoid of Uzi fly, Exorista sorbillans (Diptera: Tachinidae)

The Uzifly, Exorista sorbillans Weidemann, is an endoparasitoid of the the silkworm moth, Bombyx mori L., and can impact commercial sericulture. Effects of Uzifly age, density, temperature and gamma radiation (60Co) on the mass-production of the hyperparasitoid Nysolynx thymus (Girault) were investigated. There was a direct relationship between progeny production and an increase in number of host puparia presented, and a significant decline in the number of progeny with increased host-age. Maximum progeny production was obtained by maintaining a 1:5 to 1:8 parasitoid-to-host ratio for all the age groups. Two to 4-day-old host puparia were most suitable for obtaining the maximum progeny production of N. thymus for all the host-densities. The intrinsic rate of increase (r m day−1) increased with the increased host density for all the host-age groups. The values of net reproductive rate (R 0) and gross reproductive rate (GRR) increased for all the density levels and host age groups. On the other hand, the values for the doubling time (D) and finite capacity of increase (λ) gradually decreased with increased host density for all the host age groups. Host density and host-age significantly influenced the sex-ratio of progeny in N. thymus. Higher proportions of females were observed at higher host density levels and for younger host age groups. The progeny production and sex ratio of the parasitoid varied significantly with temperature. The maximum mean number of progeny was recorded at 25°C, while the minimum was at 30°C. The trend of progeny production at different temperatures was on the order 25 > 20 > 30°C. The highest values for the net reproductive rate (R 0) and GRR for the progeny production were recorded at 25°C compared to 20 and 30°C. Both the values for doubling time of capacity (D) and finite capacity (λ) increased with the trend of 25, 30 and 20°C. The highest value for the intrinsic rate of increase (r m day−1) of progeny production was recorded at 25°C, while the lowest value was at 20°C. The sex-ratios were always female-biased at all the temperatures. Temperature had a significant effect on the longevity of adult N. thymus. The longevity of the adults decreased with an increase of temperature for both sexes. The highest rate of parasitism was observed at 20°C followed by 25 and 30°C. More than 95% parasitism was observed at all temperatures. Gamma irradiation significantly increased the progeny production of N. thymus when reared either on early or late irradiated host puparia, particularly in the parental generation, but irradiated early host pupae were more suitable for mass production of N. thymus than the irradiated late pupae. The sex ratio of parasitoids developing from gamma irradiated host pupae varied significantly. Higher proportions of females were observed for all the dose and host-age groups.

Evaluating the use of nuclear techniques for colonization and production of Trichogramma chilonis in combination with releasing irradiated moths for control of cotton bollworm, Helicoverpa armigera

Gamma radiation was tested as a means of increasing production of the egg parasitoid Trichogramma chilonis Ishii by improving the suitability of host eggs and by stimulating reproduction of the parasitoid females. For manipulation of the host eggs’ suitability, radiation was used to either (a) produce developmentally-inactivated (DI) eggs incapable of hatching, or (b) to produce F1 sterile host eggs. For treatment of the parasitoid females with the intent of stimulating reproduction, parasitoid pupae were exposed to very low dose radiation (250 mGray). For tests on host suitability using radiation-induced DI host eggs, newly-laid (<8 h old) host eggs (Helicoverpa armigera Hubner) were exposed to 300 Gy of 60Co gamma radiation. For tests of F1 sterile host eggs, H. armigera moths were mated with individuals exposed to 250 Gy as pupae. Tests were performed with eggs resulting from all possibilities of normal (N) and sterile (S) ♀ × ♂ matings. Both types of DI host eggs (irradiated or sterile), along with untreated host eggs (controls), were exposed to T. chilonis females, using the following host egg-to-parasitoid ratios: 1:10, 1:30, 1:60 and 1:90. Developmentally-inactivated host eggs exposed to 300 Gy did not differ in suitability from normal host eggs at a 1:10 parasitoid–host ratio, but were significantly more suitable at the higher host–parasitoid ratios. F1 sterile eggs were not significantly different in suitability from normal eggs at a 1:10 host–parasitoid ratio but were marginally better at the higher host–parasitoid ratios. In tests performed using T. chilonis females exposed to low-dose radiation (250 mGy), no effects were observed when cohorts of 5 T. chilonis females were provided with only 50 host eggs, but when more hosts were provided (ratios of 1:30, 1:60 and 1:90), significantly higher rates of parasitization were noted for the parasitoids exposed to low-dose radiation. This effect prevailed using both normal host eggs and DI host eggs exposed to 300 Gy. The stimulatory effect also was noted when F1 sterile host eggs were provided to the irradiated T. chilonis females. These results suggest that release of T. chilonis irradiated with 250 mGy may complement release of irradiated H. armigera moths, which produce sterile F1 eggs that can serve as supplemental hosts in the field and thereby enhance the pest management system.

Models for integrated pest control and their biological implications

Successful integrated pest management (IPM) control programmes depend on many factors which include host–parasitoid ratios, starting densities, timings of parasitoid releases, dosages and timings of insecticide applications and levels of host-feeding and parasitism. Mathematical models can help us to clarify and predict the effects of such factors on the stability of host–parasitoid systems, which we illustrate here by extending the classical continuous and discrete host–parasitoid models to include an IPM control programme. The results indicate that one of three control methods can maintain the host level below the economic threshold (ET) in relation to different ET levels, initial densities of host and parasitoid populations and host–parasitoid ratios. The effects of host intrinsic growth rate and parasitoid searching efficiency on host mean outbreak period can be calculated numerically from the models presented. The instantaneous pest killing rate of an insecticide application is also estimated from the models. The results imply that the modelling methods described can help in the design of appropriate control strategies and assist management decision-making. The results also indicate that a high initial density of parasitoids (such as in inundative releases) and high parasitoid inter-generational survival rates will lead to more frequent host outbreaks and, therefore, greater economic damage. The biological implications of this counter intuitive result are discussed.

Progeny Fitness of the Mealybug Parasitoid Anagyrus sp. nov. nr. Sinope (Hymenoptera: Encyrtidae) as Affected by Brood Size, Sex Ratio, and Host Quality

Abstract Anagyrus sp. nov. nr. sinope Noyes & Menezes (Hymenoptera: Encyrtidae) is a gregarious, koinobiont parasitoid of the Madeira mealybug, Phenacoccus madeirensis Green (Hemiptera: Pseudococcidae). We investigated effects of larval competition on development, survival, and progeny body size of the parasitoid over a range of brood sizes and sex ratios. We recorded the brood size, sex ratio, and fitness parameters of parasitoids developing from second instars and adult P. madeirensis. Adult mealybugs as hosts produce larger brood and progeny body sizes and more female progeny. Second instar P. madeirensis continued to develop after parasitism, and mummies achieved a more advanced developmental stage yielding parasitoid cohorts of larger brood and body sizes, female-biased sex ratio, and longer developmental time than mummies formed from younger host instars. Overall, the sexual composition within a brood had little or no effect on the development, survival and body size of the parasitoid progeny develo...

The parasitoid of a fruit moth caterpillar utilizes fruit components as nutrient source to increase its longevity and fertility

Longevity and fecundity of female wasps are two decisive factors for the effectiveness of parasitoid species as biological control agents. Accessibility and suitability of nutrient sources determine parasitoid survival and reproduction. Host, nectar and honeydew feeding are frequent adult parasitoid behaviors to cover nutritional needs. Here we postulate that especially parasitoid species of endophytic herbivores might use plant tissue as a nutrient source that becomes accessible upon herbivory. We investigated the influence of plant consumption and host feeding on longevity and fecundity of Hyssopus pallidus, a gregarious ecto-parasitoid of caterpillars of the codling moth that feed inside apple fruits. Longevity of unmated and mated ovipositing female parasitoids was highest in treatments with fruit pulp. While longevity in this treatment was not significantly different from that with honey, it was significantly higher than in treatments without food, with water or with a host alone. Reproduction was significantly increased by these sugar-rich nutrient sources compared to the control with a host alone. In contrast, host feeding did not yield any significant contribution to longevity and fecundity in a series of bioassays with different host–parasitoid ratios and with differently aged and sized hosts, compared to controls without food. We conclude that in this synovigenic species host feeding does not contribute to longevity and fecundity, but females can increase survival and reproduction in the field relying solely on the plant tissue damaged by their host caterpillar.