Parasitoid Longevity Research Articles

Transgenic Cotton-Fed Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) Affects the Parasitoid Encarsia desantisi Viggiani (Hymenoptera: Aphelinidae) Development.

Cotton cultivars expressing Cry proteins are widely used to control lepidopteran pests. The effects of transgenic plants containing insecticidal Cry proteins on non-target species must be comprehended for a better and rational use of this technology for pest management. We investigated the influence of the Bt cotton cultivars NuOPAL and FM 975 on biological parameters of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), a non-target pest of Bt cotton cultivars and on its parasitoid Encarsia desantisi Viggiani (Hymenoptera: Aphelinidae). The experiments were conducted in a climatized room, and the non-transgenic near isolines were used for rearing whiteflies as control hosts. The effects of the Bt cotton cultivars on the period of embryonic and larval development and the percentage of adult emergence of B. tabaci were assessed. The period required for embryonic, larval, and pupal development and the percentage of emergence and longevity of E. desantisi females were determined using Bt cotton-fed and non-Bt cotton-fed B. tabaci as hosts. Both Bt cotton cultivars resulted in a decrease of approximately 20% of adult emergence of B. tabaci. Differently, an increase of approximately 10% of adult emergence of E. desantisi was observed for parasitoids that used hosts fed with both Bt cotton cultivars. However, female parasitoid longevity decreased when their hosts were fed on Bt cotton cultivars. Our data suggest that the use of Bt cotton cultivars in association with the biological control agent E. desantisi could be functional for the management of B. tabaci in Bt cotton crops.

Risk assessment of non-target effects of Closterocerus chamaeleon (Girault) parasitoid of the eucalypt gall maker Ophelimus maskelli (Ashmead) (Hymenoptera, Eulophidae)

The pre-release risk assessment, a recommended practice in biological control programmes, was carried out before introducing Closterocerus chamaeleon (Girault), a eulophid parasitoid of the eucalypt gall maker Ophelimus maskelli (Ashmead) (Hymenoptera, Eulophidae), in Sicily, Italy. We evaluated its host specificity in laboratory small arena no-choice tests on six non-target hosts, using O. maskelli as a control species. The non-target species fit with at least one of the following criteria: a) common geographical origin; b) ecological or behavioural affinities with the target host; c) concealed habit of the preimaginal stages; d) taxonomic affinity; e) taxonomic affinity with hosts of congeneric parasitoids of the candidate agent; and f) presence in Italy/Sicily. Closterocerus chamaeleon performed an oviposition sequence of 10 recognisable behaviours, always leading to parasitization when exposed to O. maskelli. The same behaviour sequence was carried out on the gall maker Leptocybe invasa Fisher et La Salle, the only non-target species living on Eucalyptus, but just until Step 6, i.e. until ovipositor extraction and insertion, and never until egg-laying. All of the other non-target hosts were ignored. Furthermore, the adult parasitoid longevity was assessed in three rearing conditions: 1) no food/no parasitisation permitted; 2) food/no parasitisation permitted; and 3) food provided after parasitisation. Adult wasp longevity was significantly higher in treatment 2 (21.1 days ± 4.1 SE) than in treatment 1 (3.6 days ± 0.5 SE) or 3 (3.8 days ± 0.6 SE). Laboratory tests carried out in this study on C. chamaeleon indicated high host selection ability, later confirmed by our post-release field data.

Sugar provisioning maximizes the biocontrol service of parasitoids

Summary There is increasing interest in the use of food supplements in agriculture to enhance the performance of parasitoids as part of conservation biological control. Nevertheless, there is limited evidence demonstrating the effectiveness of this approach, and this shortage of successful examples raises doubt regarding the validity of this approach. The use of sugar sources relies on tiered premises that: (i) parasitoids are sugar limited and (ii) this limitation is alleviated through the provision of sugar sources, thereby increasing both (iii) parasitoid fitness and (iv) the population density, which together lead to (v) an increase in parasitism. In the present study, we address these five premises through experiments examining the release of the parasitoid Aphytis melinus DeBach (Hymenoptera: Aphelinidae) into the citrus agroecosystem with and without sugars. The results demonstrated that A. melinus is sugar limited when honeydew producers are scarce in the field. The provision of sugars did not increase the sugar contents in A. melinus females but rather increased the realized fecundity in these parasitoids, suggesting that females use energy for foraging and oviposition. Sugar sources increased the parasitoid population density twofold, and this increase most likely reflects the enhanced parasitoid longevity. Higher population densities and the increased realized fecundity of A. melinus obtained from trees with sugars were reflected in a twofold increase of parasitized hosts. Synthesis and applications. This study provides the first evidence supporting the five premises underlying sugar provisioning for parasitoids and demonstrates the potential value of sugar provisioning to enhance natural pest control in agricultural systems.

The Effect of Buckwheat Flowers and Cahaba Vetch Extrafloral Nectaries on Fitness of the Vine Mealybug ParasitoidAnagyrus pseudococci(Hymenotpera: Encyrtidae)

The effect of access to buckwheat flowers (Fagopyrum esculentum Moench; Polygonales: Polygonaceae) or vetch extrafloral nectaries (Vicia sativa L. cv. ‘cahaba white’; Fabales: Fabaceae) on the fitness of Anagyrus pseudococci (Girault) (Hymenotpera: Encyrtidae) (a parasitoid of the vine mealybug, Planococcus ficus [Signoret]) (Hemiptera: Pseudococcidae) was determined in the laboratory. Female A. pseudococci provided with vetch survived 4 days longer compared with water only. Buckwheat had no effect on the average longevity of A. pseudococci. Anagyrus pseudococci offspring production increased by 132% and 152% when females were provided either vetch or buckwheat, respectively, when compared with water. There was no significant difference in parasitoid longevity or fecundity between plant species. Buckwheat increased the percentage of female A. pseudococci offspring by 15% and 19% when compared with water and vetch, respectively.

Biological studies on Bracon brevicornis (Hymenoptera: Braconidae) reared on different host larvae

The present work was carried out to study the biological aspect of B. brevicornis when reared on different hosts (Ephestia kuehniella, Galleria mellonella, Corcera cephalonica, Sesamia cretica, Spodoptera littoralis and Pectinophora gossypiella). Our Results assured that the type of host had great impact on the durations of the immature stages and longevity of the parasitoid. The highest & lowest incubation periods were when reared the parasitoids on Pectinophora gossypiella (45.75±1.4hours) and E. kuehniella (39.87±0.95 hours) respectively, the difference was insignificant at the other hosts. Duration of larval stages was significant shorter when parasitoid reared on S. cretica (1.86±0.079 days) than the rest hosts. The longer pupation period was recorded when parasitoid reared on Pectinophora gossypiella (7.6±0.13 days), but was insignificant on the other hosts. The highest duration period of immature stage was when reared B.brevicornis on P. gossypiella (12.75±0.74 days) but insignificant difference when reared on G.mellonella [ 9.16±0.22 days ] and S. cretica [ 9.91±0.14 days ]. The mean duration of male longevity of parasitoids was longer when reared on E. kuehniella (15.73±0.73 days) and shorter when reared on C.cephalonica (11.75±0.51 days). The mean duration of female parasitoids was highest when reared parasitoids on S. cretica (19.6±0.51 days). The total number of eggs laid per female of B.brevicornis during its life span was highest on Galleria mellonella (268.88±19.65 eggs), and lowest on C.cephalonica (78.1±10.63 eggs). A percentage of eggs hatchability was significantly lowest when reared on S. littoralis (0.09±0.02642 %) than when reared on the other hosts, while percentage of emergence was insignificantly different when reared on Sesamia cretica (87.36±3.92 %) and Pectinophora gossypiella (87.02±3.85 %).

Comparing existing weeds and commonly used insectary plants as floral resources for a parasitoid

The potential consequences of deploying weed and non-weed floral resources in a three trophic-level system were evaluated in the laboratory. Four flowering plants were used: the two common weeds shepherd’s purse Capsella bursa-pastoris (globally widespread) and white rocket Diplotaxis erucoides (a common weed in Europe) and two common flowering plants: buckwheat Fagopyrum esculentum and alyssum Lobularia maritima. Adults of the aphid parasitoid Diaeretiella rapae were exposed to flowering buckwheat and survived 4–5 times longer than those in the control (water only) and 2–3 times longer than when provided with flowering alyssum, or the other two species. All plant species significantly increased parasitoid longevity, egg load and achieved fecundity compared with the control, with buckwheat having the greatest effect. This work illustrates that the functional diversity of ‘weeds’, if appropriately managed, has potential to enhance biological control efficacy without the need for agronomic and other challenges which are involved in adding specific non-crop flowering plants such as buckwheat to agroecosystems. In the field, factors such as the plants’ phenology, agronomy and competitiveness with the crop will need to be evaluated before they can be truly ranked.

Infection of rice plants by rice black streaked dwarf virus improves an egg parasitoid, Anagrus nilaparvatae (Hymenoptera: Mymaridae), of rice planthoppers.

The effects of rice plants infected by rice black streaked dwarf virus (RBSDV) on the host preference, duration of immature stages, sex ratio, and adult longevity and parasitic capacity of an egg parasitoid, Anagrus nilaparvatae Pang et Wang, of rice brown planthopper, Nilaparvata lugens Stål, were evaluated. Tests of response to plant volatiles using an olfactometer showed that A. nilaparvatae preferred rice plants harboring rice brown planthopper eggs over plants free of rice brown planthopper eggs. However, both the response to plant volatiles and the host selectivity test showed no significant differences in host preference between RBSDV-infected plants and healthy plants when both contained rice brown planthopper eggs. The developmental duration at immature stage of the male A. nilaparvatae in rice brown planthopper eggs on RBSDV-infected rice plants was significantly prolonged, and the parasitic capacity of rice brown planthopper eggs was significantly increased in comparison with the A. nilaparvatae parasite in rice brown planthopper eggs on healthy rice plants. There were no significant differences between RBSDV-infected rice plants and healthy rice plants in other ecological fitness parameters, including the developmental duration of female adults, female percentage, and adult longevity of A. nilaparvatae.

Aphid honeydew quality as a food source for parasitoids is maintained in Bt cotton.

Bt-transgenic cotton has proven to be highly efficient in controlling key lepidopteran pests. One concern with the deployment of Bt cotton varieties is the potential proliferation of non-target pests. We previously showed that Bt cotton contained lower concentrations of insecticidal terpenoids as a result of reduced caterpillar damage, which benefited the aphid Aphis gossypii. It is thus important that non-target herbivores are under biological control in Bt cotton fields. The induction or lack of induction of terpenoids could also influence the quality of aphid honeydew, an important food source for beneficial insects. We therefore screened A. gossypii honeydew for cotton terpenoids, that are induced by caterpillars but not the aphids. We then tested the influence of induced insect-resistance of cotton on honeydew nutritional quality for the aphid parasitoid Lysiphlebus testaceipes and the whitefly parasitoid Eretmocerus eremicus. We detected the cotton terpenoids gossypol and hemigossypolone in A. gossypii honeydew. Although a feeding assay demonstrated that gossypol reduced the longevity of both parasitoid species in a non-linear, dose-dependent manner, the honeydew was capable of sustaining parasitoid longevity and reproduction. The level of caterpillar damage to Bt and non-Bt cotton had no impact on the quality of honeydew for the parasitoids.These results indicate that the nutritional quality of honeydew is maintained in Bt cotton and is not influenced by induced insect resistance.

Telenomus remus (Hymenoptera: Platygastridae) Parasitism on Eggs of Anticarsia gemmatalis (Lepidoptera: Eribidae) Compared With Its Natural Host Spodoptera frugiperda (Lepidoptera: Noctuidae)

Abstract The capacity of Telenomus remus to parasitize eggs of Anticarsia gemmatalis, compared with its natural host, Spodoptera frugiperda, was evaluated under different temperatures. The parasitoid T. remus was reared at 25 ± 1°C for a single generation on both hosts. After reaching the adult stage, they were allowed to parasitize both hosts to study parasitoid biology and parasitism capacity at temperatures between 19°C and 37 ± 1°C. Egg-to-adult developmental time was similar on both hosts. The number of A. gemmatalis eggs parasitized was lower than that of S. frugiperda eggs at all temperatures. Parental female longevity of parasitoids was greater on A. gemmatalis eggs. This indicated a smaller metabolic expense during parasitism, acommonfeature observed on nonpreferable hosts. In general, sex ratio was little affected by temperature or hosts. When parental T. remus were reared on A. gemmatalis before the experiment, base temperature (Tb) and the thermal constant (K) were 9.53°C and 209.57 DD on eggs of A. gemmatalis and 9.68°C and 197.79 DD on eggs of S. frugiperda, respectively. When parental T. remus were reared on S. frugiperda eggs, Tb and K were 10.12°C and 188.46 DD and 9.69°C and 190.24 DD for the evaluated host eggs of A. gemmatalis and S. frugiperda, respectively. Therefore, T. remus develops in eggs of A. gemmatalis. This can be beneficial for its use in field crops where outbreaks of both Spodoptera spp. and A. gemmatalis occur. However, A. gemmatalis is a less favorable host for the parasitoid development.

Life and Fertility Tables ofTrichospilus diatraeae(Hymenoptera: Eulophidae) withTenebrio molitor(Coleoptera: Tenebrionidae) Pupae

AbstractAlternative hosts may increase rearing and possibilities of using Trichospilus diatraeae (Cherian & Margabandhu) (Hymenoptera: Eulophidae) for biological control. The aim of this study was to evaluate T. diatraeae reproduction with the alternative host Tenebrio molitor L. (Coleoptera: Tenebrionidae) with life and fertility tables. Twenty-five 24-h-old T. diatraeae females were individualized per Te. molitor pupae of the same age, who were replaced daily until their death of this parasitoid. Survival of T. diatraeae immature in Te. molitor pupae was 92.65%. Longevity of female parasitoids was 8.28 d with an innate density increase of 0.15, net reproductive rate of 37.50, finite rate of increase of 1.16, mean generation time of 23.67, and population doubling time of 4.52 wk. Te. molitor pupae are suitable for development and rearing of T. diatraeae.

Alternating Temperatures Affect the Performance ofTrichogrammaSpecies

The environmental compatibility of a biological control agent is an important aspect of successful reduction of agricultural pests. Temperature fluctuations during the day have a strong influence on the performance of laboratory-reared parasitoids. In field conditions, Trichogramma (Hymenoptera: Trichogrammatidae) wasps are exposed to variable temperatures during their development, which has a significant impact on their ability to control pest species. A simulation-based study was undertaken to evaluate the impact of variations in daily temperature on the pest-control abilities of female Trichogramma and their immature progenies. Considering the temperature variability of different agricultural zones of India, five temperature levels ranging from 20°C to 40°C were selected for daily short-term heat shocks to the immature progenies and egglaying females of two major Trichogramma species. Intensity and frequency of thermal shocks showed inverse relationships with adult emergence, fecundity, and longevity of T. chilonis and T. poliae. Parasitoid pupae were found to be more tolerant to temperature variations than eggs and larvae. Fecundity and longevity of parasitoids were significantly reduced under high temperature shocks to egg-laying females. Sex ratio was significantly affected by high temperature shocks to the immature and adult stages. However, the effect was more severe in eggs. A female-biased sex ratio was apparent in both parasitoids throughout the experiment. Overall, daily short-term temperature shocks to different developmental stages of parasitoids showed radical effects on emergence, fecundity, longevity, and sex ratio of the progeny. Therefore, releases of parasitoids should be conducted when they are in their pupal stages during the morning and evening in order to achieve their highest effectiveness for pest management.

Natural Enemies of <I>Atta vollenweideri</I> (Hymenoptera: Formicidae) Leaf-Cutter Ants Negatively Affected by Synthetic Pesticides, Chlorpyrifos and Fipronil

In southern South America, Ada vollenweideri Forel (Hymenoptera: Formicidae) is a significant pest of several crops and forestry, also considered to reduce the carrying capacity of pastures. The most usual control method used in Latin America is the application of synthetic pesticides, mainly chlorpyrifos and fipronil. However, no studies have assessed the effects of these agrochemicals on natural enemies of ants. We aimed to evaluate the efficiency of these pesticides on leaf-cutter ants' control and to test their effect on phorid fly parasitoids. Chlorpyrifos failed to exert complete control over ant colonies in the field and was gravely detrimental to specific parasitoids, reducing their percentage of parasitism, pupal survivorship, and adult longevity. Fipronil, however, exerted complete control over the treated colonies. Laboratory tests using both pesticides, either on ants from foraging trails or on pupariae, showed that chlorpyrifos and fipronil decreased larval and pupal survivorship, as well as adult longevity of parasitoids, in comparison to controls. In conclusion, these pesticides will likely affect parasitoids with regard to their reproductive capacity, leading to the decreased levels of natural parasitism observed in the field after treatments. We discuss why neither pesticide should be taken into account for integrated pest management programs.

Alternating temperatures affect the performance of Trichogramma species.

The environmental compatibility of a biological control agent is an important aspect of successful reduction of agricultural pests. Temperature fluctuations during the day have a strong influence on the performance of laboratory-reared parasitoids. In field conditions, Trichogramma (Hymenoptera: Trichogrammatidae) wasps are exposed to variable temperatures during their development, which has a significant impact on their ability to control pest species. A simulation-based study was undertaken to evaluate the impact of variations in daily temperature on the pest-control abilities of female Trichogramma and their immature progenies. Considering the temperature variability of different agricultural zones of India, five temperature levels ranging from 20ºC to 40ºC were selected for daily short-term heat shocks to the immature progenies and egg-laying females of two major Trichogramma species. Intensity and frequency of thermal shocks showed inverse relationships with adult emergence, fecundity, and longevity of T. chilonis and T. poliae . Parasitoid pupae were found to be more tolerant to temperature variations than eggs and larvae. Fecundity and longevity of parasitoids were significantly reduced under high temperature shocks to egg-laying females. Sex ratio was significantly affected by high temperature shocks to the immature and adult stages. However, the effect was more severe in eggs. A female-biased sex ratio was apparent in both parasitoids throughout the experiment. Overall, daily short-term temperature shocks to different developmental stages of parasitoids showed radical effects on emergence, fecundity, longevity, and sex ratio of the progeny. Therefore, releases of parasitoids should be conducted when they are in their pupal stages during the morning and evening in order to achieve their highest effectiveness for pest management.

Biology and Ecology of Pleurotroppopsis podagrica (Waterston) (Hymenoptera: Eulophidae): A Potential Parasitoid of the Oil Palm Pest, Coelaenomenodera Elaeidis (Coleoptera: Chrysomelidae)

Coelaenomenodera elaeidis (Coleoptera: Chrysomelidae) is endemic in almost all oil palm growing areas of West Africa and regarded as the most devastating insect pest of the oil palm. For the purpose of a detailed knowledge of the rearing, life cycle and ecology of the natural enemy of C. elaeidis , field and laboratory studies were conducted in the main station of the Nigerian Institute for Oil Palm Research. Pruned, damaged and infested fronds from the field were cut open and studied for presence of different life stages of C. elaeidis , and their potential parasitoids. Parasitoid larval developmental period averaged 8 d while pupal developmental period had a mean of 7.2 ± 1.48 d. The total developmental period of the parasitoid from larva to adult averaged 23.2 ± 3.56 d. Average longevity of the adult parasitoid was 3.9 ± 3.56 d. Temperature was between 25 - 30oC and relative humidity ranged between 81-86%. The eulophid wasp, Pleurotroppopsis podagrica,/i> was found to parasitize C. elaeidis . Its larva is predominantly whitish, oval and translucent. The larva is averagely 3mm, oblong at the anterior and posterior sections tapering at both ends. The parasitoid emerged from the posterior region of C. elaeidis with the anterior region inside the host. This paper has shown that control of the C. elaeidis in its larval stage seems most promising and P. podagrica offers potential as bio-control agent for the C. elaeidis .

Flowers to selectively enhance the fitness of a host-feeding parasitoid: Adult feeding by Tuta absoluta and its parasitoid Necremnus artynes

Several parasitoids require both host and non-host resources, such as nectar, for maintenance, survival and egg maturation. However, the impact of sugar feeding has primarily been studied in parasitoid species that do not engage in host-feeding, and the importance of non-host resources for host-feeding parasitoids has so far received little attention. The Palaearctic parasitoid Necremnus artynes has been shown to attack the exotic invasive Tuta absoluta in the field, but its parasitism is generally low. Understanding the use of host and non-host resources by this parasitoid could reveal whether there is potential for enhancing the biocontrol of T. absoluta through provision of targeted food supplements. Cage experiments were conducted to investigate the influence of selected non-host resources on the longevity and fecundity of both the pest and its parasitoid. The parasitoid was also provided with the opportunity to feed on larvae of the pest. Sweet Alyssum, Lobularia maritima, had the most pronounced effect on the fecundity and longevity of T. absoluta, while buckwheat Fagopyrum esculentum had the strongest effect on parasitoid longevity. Fecundity of T. absoluta was shown to be a function of the age of the adults and food sources provided. Sugar resources did not influence the egg load of N. artynes, whilst host-feeding was relatively ineffective at enhancing parasitoid longevity. Host-feeding had a strong positive effect on egg load. The impact of non-host resources on host-parasitoid interactions and the potential for using selective food resources in conservation biological control of the exotic pest T. absoluta are explored.

Influence of cabbage resistance and colour upon the diamondback moth and its parasitoid Oomyzus sokolowskii

AbstractHost plant resistance and biological control are vital integrated pest management tools against the diamondback moth (DBM), Plutella xylostella (L.) (Lepidoptera: Plutellidae), but to date no study has investigated this system including the DBM parasitoid Oomyzus sokolowskii (Kurdjumov) (Hymenoptera: Eulophidae). We examined oviposition and development of P. xylostella exposed to two commercial cabbage cultivars (green ‘Chato de quintal’ and red ‘Roxo’) and possible effects upon O. sokolowskii. Under free‐choice tests, DBM females laid significantly more eggs on plants of the green cabbage, even though several population growth parameters showed that DBM developed better on the red cabbage. Furthermore, a laboratory free‐choice test with artificially green‐ and red‐painted kale leaf discs demonstrated a similar oviposition preference pattern, with green colour being preferred over red colour. The preference was apparently visually mediated; olfactometer tests showed similar attraction of moths to both green and red cultivars in choice and non‐choice tests. Host plant cultivar had no statistically significant effect on female parasitoid behaviour towards DBM larvae, nor on parasitoid numbers or longevity. Moreover, wasps parasitizing DBM larvae reared on the green cultivar developed more quickly and in larger numbers per parasitized larva. Thus, feeding on green cabbage rather than red does not hinder, and potentially even enhances, control of DBM by O. sokolowskii. On a practical level, these results suggest that intercalating green cabbage cultivars as a trap crop might help protect more profitable red cultivars in growing fields.

Telenomus remus Nixon Egg Parasitization of Three Species of Spodoptera Under Different Temperatures

Telenomus remus Nixon is a promising biocontrol agent as an egg parasitoid of Spodoptera spp., but the lack of information on the host-parasitoid interactions in this system precludes its applied use in agriculture. Therefore, we studied the parasitism capacity of T. remus on eggs of Spodoptera cosmioides (Walker), Spodoptera eridania (Cramer), and Spodoptera frugiperda (Smith) in a range of temperatures (19, 22, 25, 28, 31, and 34 ± 1°C) under controlled conditions (70 ± 10% RH and 12h photophase). Egg masses of Spodoptera spp. were offered to a single-mated T. remus female on a daily basis. More than 80% lifetime parasitism on eggs of S. cosmioides, S. frugiperda, and S. eridania was reached from 1 to 5, 1 to 7, and 1 to 9 days, respectively, at temperatures from 19 to 34°C. More than 80% parasitization was obtained at extreme temperatures for all hosts studied. Lifetime parasitization of S. frugiperda, S. cosmioides, and S. eridania was affected by temperature, with the lowest values for S. frugiperda (34°C) and S. cosmioides (19 and 34°C). Parasitization of S. eridania eggs was reduced around 18% at 28 and 31°C, but dropped more severely at 34°C. Parasitoid longevity was reduced as temperature increased. Thus, our data indicated that T. remus might be suitable as a biocontrol agent against S. eridania, S. cosmioides, and S. frugiperda in geographical areas that fit the temperature range studied here, even though T. remus parasitism was reduced at 34°C.

Elevated Temperature and Drought Interact to Reduce Parasitoid Effectiveness in Suppressing Hosts

Climate change affects the abundance, distribution and activity of natural enemies that are important for suppressing herbivore crop pests. Moreover, higher mean temperatures and increased frequency of climatic extremes are expected to induce different responses across trophic levels, potentially disrupting predator-prey interactions. Using field observations, we examined the response of an aphid host-parasitoid system to variation in temperature. Temperature was positively associated with attack rates by parasitoids, but also with a non-significant trend towards increased attack rates by higher-level hyperparasitoids. Elevated hyperparasitism could partly offset any benefit of climate warming to parasitoids, and would suggest that higher trophic levels may hamper predictions of predator-prey interactions. Additionally, the mechanisms affecting host-parasitoid dynamics were examined using controlled laboratory experiments that simulated both temperature increase and drought. Parasitoid fitness and longevity responded differently when exposed to each climatic variable in isolation, compared to the interaction of both variables at once. Although temperature increase or drought tended to positively affect the ability of parasitoids to control aphid populations, these effects were significantly reversed when the drivers were expressed in concert. Additionally, separate warming and drought treatments reduced parasitoid longevity, and although temperature increased parasitoid emergence success and drought increased offspring production, combined temperature and drought produced the lowest parasitoid emergence. The non-additive effects of different climate drivers, combined with differing responses across trophic levels, suggest that predicting future pest outbreaks will be more challenging than previously imagined.

Effect of temperature on immature development and longevity of two introduced opiine parasitoids on Bactrocera invadens

AbstractTemperature‐dependent development, parasitism and longevity of the braconid parasitoids, Fopius arisanus Sonan and Diachasmimorpha longicaudata Ashmed on Bactorcera invadens Drew Tsuruta & White, was evaluated across five constant temperatures (15, 20, 25, 30 and 35°C). Developmental rate decreased linearly with increasing temperature for both the parasitoid species. Linear and Brière‐2 nonlinear models were used to determine the lower temperature threshold at which the developmental rate (1/D) approached zero. For F. arisanus, lower thresholds to complete development estimated with the linear and nonlinear models were 10.1 and 6.9°C, respectively. The total degree‐days (DD) required to complete the development estimated by the linear model for F. arisanus was 360. In D. longicaudata, the linear and nonlinear models estimated lower thresholds of 10.4 and 7.3°C, respectively, and the total DD estimated was 282. In F. arisanus, percentage parasitism differed significantly across all temperatures tested and was highest at 25°C (71.1 ± 2.5) and lowest at 15°C (46.4 ± 1.4). Parasitoid progeny sex ratio was female biased at all temperatures except at 20°C. In D. longicaudata, percentage parasitism was highest at 20°C (52.2 ± 4.0) and lowest at 15°C (27.7 ± 2.5). Parasitoid progeny sex ratio was female biased and similar for all temperatures. Adult longevity of both parasitoids was shortest at 35°C and longest at 15°C, and females lived significantly longer than males at all temperatures tested. Our findings provide some guidance for future mass rearing and field releases of the two parasitoids for the management of B. invadens in Africa.

Effect of host plant on bionomic and life history parameters of Anagyrus pseudococci (Hymenoptera: Encyrtidae), a parasitoid of the mango mealybug Rastrococcus iceryoides (Homoptera: Pseudococcidae)

Anagyrus pseudococci Girault is a solitary koinobiont endoparasitoid of several mealybug species. The effect of five host plants (Mangifera indica L., Cucurbita moschata Duchesne, Parkinsonia aculeata L., Cajanus cajan L. and Ficus benjamina Roxb.) on host acceptability for oviposition and suitability for immature development of this parasitoid in the invasive mango mealybug Rastrococcus iceryoides Green were investigated. Effect of host plant on fitness traits (parasitoid size, egg load and longevity) and life table parameters were also assessed. Although A. pseudococci accepted the mealybug regardless of the host plant, the level of acceptability varied significantly. Percentage of parasitized nymphs was higher on C. moschata, followed by P. aculeata and M. indica, while it was lowest on F. benjamina. Host suitability was also strongly affected by the host plant and largely mirrored host acceptability for all the parameters evaluated. Female wasps reared on mealybugs maintained on C. moschata and P. aculeata were bigger and more fecund, while those reared from mealybugs maintained on F. benjamina were of inferior quality with regard to all fitness parameters evaluated. A. pseudococci achieved a greater intrinsic rate of natural increase (rm), net reproductive rate (Ro) and finite rate of increase (λ) on mealybugs maintained on C. moschata and P. aculeata. In addition, the wasp had a shorter mean generation time (G) and population doubling time (Td) on mealybugs maintained on C. moschata. The reverse was true for those maintained on F. benjamina. The findings are discussed in view of improvement of laboratory mass rearing, as well as field enhancement of the parasitoid performance.