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Aphidius colemaniViereck is an important parasitoid of green peach aphid [Myzus persicae (Sulzer)], a serious pest of greenhouse crops. Augmentation of natural enemies is the most used approach to biological control of greenhouse pests. Yet, the optimal release time, rate, and age of natural enemies are often unclear. Here we tested the influence of population density of both A. colemani and M. persicae, as well as parasitoid age, on parasitism and sex allocation. We aim is to provide information for cost-effective aphid biological control programs. We show that 1) parasitoid females increased parasitism and produced more female-biased offspring with an increase of aphid density, 2) a moderate increase of parasitoid release rate elevated parasitism and daughter production when aphid density was high, 3) parasitism rate declined with an increase of aphid density but the moderate increase of parasitoid release rate eased the decline rate, and 4) 3-d-old parasitoids parasitized more aphids than younger ones but parasitoid age had no effect on daughter production. These findings suggest that A. colemani females can adjust their ability to regulate the aphid population in response to aphid population dynamics. In augmentative programs, a moderate increase of parasitoid release when aphid density is high could achieve effective control and a release of 3-d-old parasitoids could lead to a better control outcome.

Telenomus remus (Nixon) is an egg parasitoid of several Spodoptera spp. insects, especially the destructive agricultural pest Spodoptera frugiperda (J. E. Smith). Studies showed that this parasitoid can be efficiently reared on Spodoptera litura (Fabricius) eggs. Understanding the relationship among parasitoid age, host egg age, and parasitism efficiency is an important part of mass-rearing biological control agents. To this end, we measured the impacts of female T. remus age (1-, 2-, 3-, and 4-day-old), S. litura egg age (1-, 2-, and 3-day-old), and their interactions on parasitism capacity, developmental time, offspring fitness, and oviposition behavior. The results indicated that the 3-day-old and 4-day-old parasitoids had higher parasitism performance on all age eggs than 1-day-old and 2-day-old parasitoids, especially on 3-day-old eggs. The number of parasitized eggs decreased as egg age increased, and the developmental time of the progeny increased. The emergence rate and percentage of females were hardly affected. For oviposition behavior, 4-day-old parasitoids showed the same drumming and oviposition time on different age eggs, while for others the drumming, drilling, oviposition, and total time increased with increasing S. litura egg age. In summary, the optimal combinations were 3-day-old or 4-day-old female parasitoids and 1-day-old or 2-day-old S. litura eggs. The findings presented in this study can be employed to enhance T. remus mass-rearing efficiency and availability.

Trichogramma (Hymenoptera: Trichogrammatidae) are species used worldwide for the biological control of Lepidopteran pests, notably through inundative releases on millions of hectares. The optimal use of Trichogramma parasitoids in crop protection requires an accurate knowledge of their biology. More specifically, the importance of age factor in parasitoids during the time they forage in crops for host eggs (after initial release) and how the aging of host eggs could impact parasitoid biological traits may be important for overall efficiency in terms of crop protection. In this context, the importance of parasitoid female and host egg ages on parasitism rate and the development of offspring was studied in laboratory conditions on Trichogramma cacoeciae Marchal (Hymenoptera: Trichogrammatidae) and the eggs of the pest Lobesia botrana Denis and Schiffermüller (Lepidoptera: Tortricidae). Host eggs tested were 1–2- and 3–4-day-old, while the ages of T. cacoeciae adult females varied from 1-day-old to 4-day-old post-emergence. When L.   botrana eggs were 3–4-day-old, they were less parasitized by T. cacoeciae than 1–2-day-old eggs, and this was not linked to the age of T. cacoeciae females. The age of parasitoid females has an effect on parasitism, as 1-day-old females produced fewer parasitized eggs than 2, 3, and 4-day-old females. For the total number of L. botrana eggs killed by T. cacoeciae , the two factors did not show significant effects. When L. botrana eggs were 1–2-day-old, parasitoid emergence increased according to the age of parasitoid females with the highest success observed for 3-day-old females. The lowest emergence rates were obtained with T. cacoeciae females 1-day-old. The development time was also longer with the young 1-day-old parasitoid females. This study demonstrated that both the aging of parasitoids and host eggs play a role in the subsequent development of parasitoid offspring. The importance of these results in the context of biological control programs involving Trichogramma parasitoids is discussed.

We studied the parasitism capacity of Spalangia endius as a pupal parasite of Bactocera dorsalis after switching hosts. We used pupae of B. dorsalis and M. domestica as the hosts and studied parasitism by S. endius in the laboratory. The parasitism capacities were compared at different host densities and different parasitoid ages. The two functional responses of S. endius fitted a Holling Type II equation. More M. domestica were parasitized than B. dorsalis at all the densities. The ability of S. endius to control M. domestica was α/Th (parasitism capacity) = 32.1950, which was much stronger than that of control B. dorsalis, which was α/Th = 4.7380. The parasitism rate of wasps that had parasitized B. dorsalis had decreased by the emergence time of parasitoids. These results suggest that the parasitoid-pest ratio should be 1:25 to maintain a relatively stable parasitism rate for control of B. dorsalis. The S. endius colony reared on M. domestica successfully controlled a low-density population of B. dorsalis in the lab. We provide evidence suggesting that the parasitism capacity of S. endius needs to be improved.

In order to maximize the lifetime reproductive success of parasitoids, they should be induced to dynamically accept individual hosts that have different suitability for oviposition. Parasitoids tend to exhibit higher host-selective behavior when their egg load is limited, and are less selective if they are facing time constraints. Here, we evaluated the effects of parasitoid age on egg load, fecundity and host instar preference of a honey-fed aphid parasitoid, Aphelinus asychis Walker (Hymenoptera: Aphelinidae). Host selective experiment was conducted to measure host-preference of honey-fed A. asychis females at different ages, using the second and fourth instars of the green peach aphid Myzus persicae as their hosts. The results showed that the choice of host-instar for oviposition was significantly influenced by the parasitoid age. Honey-fed parasitoids in the age groups of 1, 5, 10 and 20 days tended to parasitize predominantly second-instar aphids, whereas 15-days old parasitoids showed no significant preference of host instars. On the other hand, host-feeding preference was not affected by parasitoid age. Parasitoid females of all ages preferred younger aphids to older aphids. This result could help evaluate the effectiveness of A. asychis for biological control of M. persicae when they encountered mixed-instar aphids in the field. In addition, the results might be helpful in assessing the host killing effects of other host-feeding parasitoids.

The effect of parasitoid age on the fecundity and sex ratio of Aenasius bambawalei Hayat (Hymenoptera: Encyrtidae) was determined on different life stages of the host Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae) by keeping both at 272°C and 655% relative humidity during parasitization. Fecundity of the female parasitoid did not change significantly during the first 5 days of its life span but afterwards it decreased significantly under laboratory conditions. While offspring sex ratio of 1 day old female wasp was found to be female biased on both 3rd and adult host stages but afterwards it changed to male biased sex ratio of 5 and 10 days old parasitoid female. The male emergence was more by 5 days old parasitoid female than 1 day old at 3rd instar host stage while at adult host stage it was more by 1 day old female than the 5 and 10 days old female wasp. Emergence of total progeny of the wasp (adult female and male) was significantly higher on adult host stage than 3rd instar host stage. The interaction of parasitoid age and host stage has significant effect on the emergence of male than on the female wasp. The fecundity and the parasitic potential of the female parasitoid reared on adult host stages were higher than those reared on 3rd instar host stages.

Little is known about the life cycle of Rhembobius parasitoids (Hymenoptera: Ichneumonidae). Known host records are mainly from saprophagous species of hoverflies of the tribe Eristalini (Diptera: Syrphidae), whose larvae develop in a wide range of aquatic and semi-aquatic breeding sites that are rich in microbial decay. We present an account of the biology and important details of the life cycle of the pupal parasitoid R. quadrispinus in both natural and controlled conditions. Host suitability, the influence of host pupal age and age of the female parasitoid on her production of progeny was evaluated in laboratory tests. Our results showed that the percentage of pupae of E. tenax that were parasitized by R. quadrispinus decreased as pupae matured, and the optimal age for successful parasitism ranged from 1 to 3 days. This biological information could be useful in the biological control of anthropophilic saprophagous eristalines that can act as potential mechanical vectors of pathogens on farms.

Parasitism of Diaprepes abbreviatus (L.) eggs by Ceratogramma etiennei Delvare as influenced by host age, age of the female parasitoid, and host plant preference was evaluated under laboratory or greenhouse tests. Percent parasitism of D. abbreviatus eggs by C. etiennei decreased as eggs matured. The optimal age of C. etiennei for successful parasitism ranged from 1-2-d old. Host plant leaf thickness, leaf pubescence, and plant strata probably played a role on the parasitism by C. etiennei. This parasitoid is diurnal and spent approximately 5 min searching for eggs laid in cryptic locations, 46 min parasitizing an egg mass and 24 min resting. This biological information is relevant in evaluating the potential of C. etiennei in the classical biological control of D. abbreviatus.

The parasitism rate and host-feeding rate of Tamarixia radiata (Hymenoptera: Eulophidae), an ectoparasitoid of Diaphorina citri (Hemiptera: Liviidae), were evaluated at 20, 27.5, 30, and 35°C, at 70 ± 5% RH, and 14 h of photo-period. The biological control efficacy of T. radiata was evaluated by linking the age-stage predation rate with the two-sex life table. The net host-feeding rate (C0) by T. radiata was 32.05, 54.40, 17.25, and 1.92 nymphs per female parasitoid at 20, 27.5, 30, and 35°C, respectively. The total net nymphs killing rate (Z0) was 103.02, 223.82, 72.95, and 6.60 nymphs per female parasitoid at 20, 27.5, 30, and 35°C, respectively. Noneffective parasitism rate was observed at 35°C because of high mortality at this temperature. Our results indicated that temperature had meaningful effects on parasitism and host-feeding rate parameters in the laboratory, and may affect biological control efficiency of the parasitoid in the field. The highest host-feeding rate and total biological control efficiency of T. radiata were recorded at 27.5°C. Most importantly, we found that host-feeding activity of the parasitoid is temperature-dependent, and changed across temperature regimes: the host-feeding rate increased as the temperature increased up to 30°C, started to decrease after this temperature and declined to its minimum level at 35°C. This information is valuable for developing biological control and integrated pest management techniques for Asian citrus psyllid management.

The evolutionary processes that shape host‐parasitoid coexistence in a changing environment are poorly understood. We examined the large‐scale distribution of highly specialised polysphinctine Darwin wasps associated with spiders along an elevational gradient and tested the hypothesis that distribution and parasitism rates depend on elevation, habitat type and the species and age composition of the host community. Further, on the basis of a large‐scale dataset, we examined the hypothesis that three‐dimensional webs in spiders may be an evolutionary adaptation against polysphinctine parasitoids. We found significant variation in parasitoid distribution and parasitism rates along a 1500 m elevational gradient in central Europe. The optimal model showed a humped shape for the parasitism rate on an elevational gradient. Overall, we found relatively low parasitism rates (4%) on spiders, with the highest parasitism rates in non‐forested riparian vegetation and the lowest in agroecosystems. Rates of parasitism varied significantly among spiders forming different types of webs (foraging guilds). Spiders spinning 3D webs were dominant in the spider community, but parasitism on them was lower compared to spiders spinning 2D webs, probably because of the defensive function of the 3D web architecture. The bottom‐up approach, in which the entire spider host community is analysed for parasitism rate, supports the hypothesis that 3D webs are evolutionarily novel and could have arisen as a result of the need for defence against enemies such as parasitoids. We examined the large‐scale distribution of highly specialised parasitoids associated with spiders along an elevational gradient and tested the hypothesis that distribution and parasitism rates depend on elevation, habitat type and the species and age composition of the host community. Further, on the basis of a large‐scale dataset, we examined the hypothesis that three‐dimensional webs in spiders may be an evolutionary adaptation against polysphinctine parasitoids.