Noncrop flowering plants restore top‐down herbivore control in agricultural fields

Herbivore populations are regulated by bottom‐up control through food availability and quality and by top‐down control through natural enemies. Intensive agricultural monocultures provide abundant food to specialized herbivores and at the same time negatively impact natural enemies because monocultures are depauperate in carbohydrate food sources required by many natural enemies. As a consequence, herbivores are released from both types of control. Diversifying intensive cropping systems with flowering plants that provide nutritional resources to natural enemies may enhance top‐down control and contribute to natural herbivore regulation. We analyzed how noncrop flowering plants planted as “companion plants” inside cabbage (Brassica oleracea) fields and as margins along the fields affect the plant–herbivore–parasitoid–predator food web. We combined molecular analyses quantifying parasitism of herbivore eggs and larvae with molecular predator gut content analysis and a comprehensive predator community assessment. Planting cornflowers (Centaurea cynanus), which have been shown to attract and selectively benefit Microplitis mediator, a larval parasitoid of the cabbage moth Mamestra brassicae, between the cabbage heads shifted the balance between trophic levels. Companion plants significantly increased parasitism of herbivores by larval parasitoids and predation on herbivore eggs. They furthermore significantly affected predator species richness. These effects were present despite the different treatments being close relative to the parasitoids’ mobility. These findings demonstrate that habitat manipulation can restore top‐down herbivore control in intensive crops if the right resources are added. This is important because increased natural control reduces the need for pesticide input in intensive agricultural settings, with cascading positive effects on general biodiversity and the environment. Companion plants thus increase biodiversity both directly, by introducing new habitats and resources for other species, and indirectly by reducing mortality of nontarget species due to pesticides.     

Increasing vole numbers cause more lethal damage to saplings in tree monocultures than in mixed stands

Overall, mammalian herbivores are more harmful in mixed plantations than in monocultures, but the effect of herbivore abundance has not been experimentally tested in this context. It has been proposed that there is a critical threshold density where herbivore pressure spreads from preferred plants to everything edible, leading to non-linear density effects on low-quality plants. We experimentally investigated whether survival of an unpalatable plant is similarly related to herbivore density in both monocultures and mixed stands. This we did by establishing monocultures of unpalatable black alder (Alnus glutinosa) and mixed stands of black alder and five more palatable tree species in enclosures, where Microtus voles were introduced and their abundances monitored.The effect of stand diversity tended to depend on vole abundance. Vole damage of tree saplings did not differ between monocultures and mixed stands, but at higher vole abundances attacks had a stronger effect on sapling survival in the monocultures. Sapling survival showed a significant drop in the monocultures at peak abundance of approximately 300 voles ha^?1. In monocultures herbivores do not have alternatives and therefore are forced to become deadlier consumers.     

Potential risks of systemic imidacloprid to parasitoid natural enemies of a cerambycid attacking Eucalyptus

A community of insect herbivores has established on eucalyptus species in California following their introduction from Australia. A number of the species are under complete or partial biological control. A response to introduction of additional pest species into the complex has been the application of systemic insecticides to infested trees. Natural enemies that have been introduced to control the various pest species feed on the nectar of treated trees, and thus may be affected by these pesticides. In this study, Eucalyptus rudis trees were treated at label rates with the neonicotinoid systemic insecticide imidacloprid and nectar sampled at 5 months post-treatment during the spring bloom. The concentration of imidacloprid and its toxic metabolites in nectar was measured by ELISA at 660 ppb. Adults of the encyrtid egg parasitoid Avetianella longoi that were fed floral nectar collected from treated trees had significantly lower survival and reproductive fitness than adults fed nectar from untreated trees. In feeding bioassays, in which the adults were fed a range of concentrations of imidacloprid in sugar water, the LC₅₀ for A. longoi was 212 ppb imidacloprid. Bioassays were also conducted with the braconid larval parasitoid, Syngaster lepidus. The LC₅₀ for S. lepidus was 288 ppb imidacloprid. The insecticide appears to be concentrating in the nectar at higher levels than reported from other plant species and at concentrations exceeding the LC₅₀ for two important parasitoids. If tree treatments become widespread as a result of continual introductions of new eucalypt herbivores, established biological control programs could be at significant risk.     

Parasitoid and moth movement from refuge to crop

Refuges may provide habitat and resources which enhance population size of natural enemies of herbivorous pests and add to their colonisation into target crops, potentially increasing effectiveness of biological control. They may also allow for an increase in numbers of herbivorous pests. In addition, these refuges may be attractive so that natural enemies aggregate there, neglecting predation and parasitism of pests in the crop. We investigate the movements of marked Diadegma semiclausum (Hellén) a key larval parasitoid, and the adult stage of the host it attacks, diamondback moth, Plutella xylostella (L.), from an on-farm flowering refuge of Brassica vegetables to the Brassica crop. Our results showed that parasitoids and moths visit the flowering refuge, and that they move from the refuge into the crop before and after disturbing the refuge by ploughing. For D. semiclausum, the pattern of movement from the refuge into the crop was similar for males and females, but more males than females were captured. Ploughing the refuge resulted in increased dispersal by males but not females into the crop. Neither moths nor parasitoids preferentially aggregated around the flowering refuge, instead most often their spatial pattern was random throughout the field indicating that they are quite vagile, quickly moving to distances >100 m. This basic understanding of the movements of these insects has implications beyond this system and is relevant to any agricultural system implementing a refuge to enhance natural enemy effectiveness.     

cis-Jasmone indirect action on egg parasitoids (Hymenoptera: Scelionidae) and its application in biological control of soybean stink bugs (Hemiptera: Pentatomidae)

In many plants, the secondary metabolite cis-jasmone activates the metabolic pathway that produces volatile organic compounds attractive to natural enemies and, sometimes, repellent to herbivores. Previous studies indicate that the feeding damage caused by the herbivore Euschistus heros or the exogenous application of cis-jasmone in soybean plants induces the release of herbivore-induced plant volatiles (HIPVs) with a similar chemical profile and these compounds can attract the stink bug egg parasitoid Telenomus podisi (Scelionidae). Herein we tested in field conditions the effect of exogenous application of cis-jasmone in soybean plants on the parasitoid and stink bug community and on stink bug egg parasitism. In two areas, one within a soybean and another within a Crotalaria matrix, we randomly distributed 2 m² plots, with soybean plants induced (treatment, n = 5) or not induced by cis-jasmone (control, n = 5) in the field. We sampled the parasitoid community weekly with yellow sticky traps (n = 3/plot) and monitored parasitism with sentinel eggs of E. heros (n = 150/plot). We also monitored the population of stink bugs weekly, by sampling each plot with shake-cloth technique. The abundance of Scelionidae was highest overall and also in treated plots during the first four weeks in the area with a soybean matrix, but decreased thereafter. The richness of parasitoid families was similar between treatment and control plots in the area with a soybean matrix, but higher in control plots in the area with a Crotalaria matrix. Evenness was higher in control plots in the area with soybean matrix, whereas the reverse occurred in the area with a Crotalaria matrix. Results suggest that treatment with cis-jasmone effectively attracted and enhanced the population of scelionid parasitoids, but had no effect on the occurrence and intensity of parasitism and in the number of stink bugs.     

Proteomic interactions between the parasitoid Diachasmimorpha longicaudata and the oriental fruit fly,Bactrocera dorsalis during host parasitism

The oriental fruit fly, Bactrocera dorsalis, is an important agricultural pest and biological control is one of the most effective control methodologies. We conducted an investigation on the molecular response of the fruit fly to parasitism by the larval parasitoid, Diachasmimorpha longicaudata using two-dimensional gel electrophoresis and mass spectroscopy. We identified 285 differentially expressed protein spots (109 proteins) during parasitism. The molecular processes affected by parasitism varied at different time point during development. Transferrin and muscle specific protein 20 are the only two proteins differentially expressed that play a role in host immunity 24 h after parasitism. Developmental and metabolic proteins from parasitoids (transferrin and enolase) were up-regulated to ensure establishment and early development of parasitoids 48 h post parasitism. 72 h after parasitism, larval cuticle proteins, transferrin and CREG1 were overexpressed to support the survival of parasitoids while host metabolism proteins and parasitoid regulatory proteins were down-regulated. Host development slowed down while parasitoid development went up at 96 h after parasitism. All developmental, regulatory, structural, and metabolic proteins were expressed at their optimum at 120 h post parasitism. Host development was reduced, metabolism and regulatory proteins were strongly involved in the activities. The development deteriorated further at 144 h after parasitism. Enolase and CREG1 were indicators of parasitoid survival. Hexamerin and transferrin from the parasitoid was peaked at 168–216 h after parasitism, strongly indicating that parasitoid would survive. This study represents the first report that reveals the molecular players involved in the interaction between the host and parasitoid.     

Crop domestication relaxes both top-down and bottom-up effects on a specialist herbivore

Domestication of crop plants selects for numerous traits that often distinguish them dramatically from their wild progenitors. In some cases, these modifications lead to increased herbivory, by enhancing their attractiveness to herbivorous insects or reducing the efficiency of natural enemies, or both. This study investigated the effects of fruit enlargement on the olive (Olea europaea L.), the specialist olive fruit fly, Bactrocera oleae (Rossi), and its specialized larval parasitoids. Wild olive fruit are small (<2 mm pulp thickness) and the larval parasitoids associated with B. oleae have short ovipositors (<3 mm), while cultivated fruit are larger (4–8 mm pulp thickness). Female flies allocate more offspring to large than to small fruit within or across different-sized commercial cultivars, without reducing the fitness of their offspring. Fly larvae move deeper into the olive pulp with their increasing age and fruit size. In contrast, the specialist larval parasitoid, Psyttalia lounsburyi (Silvestri), more effectively parasitizes hosts in smaller than larger fruit. The inverse relationship between the performance of the fly and its co-evolved parasitoids on fruit of increasing sizes indicates that olive cultivation favors the success of the fly by providing a better food resource and more enemy-free space. These findings offer some explanation for the failure of the decades-old classical biological efforts to manage B. oleae using specialized larval parasitoids in the Mediterranean Basin and provide further evidence that crop domestication can alter host–parasitoid interactions.     

Tree species composition rather than diversity triggers associational resistance to the pine processionary moth

The reduction of insect herbivory is one of the services provided by tree diversity in forest ecosystems. While it is increasingly acknowledged that the compositional characteristics of tree species assemblages play a major role in triggering associational resistance to herbivores, underlying mechanisms are less well known. We addressed this question in the ORPHEE experiment by assessing pine processionary moth infestations (Thaumetopoea pityocampa) across a tree diversity gradient from pine monocultures to five species mixtures. We showed that tree species richness per se had no effect on the probability of attack by this pest. By contrast, the infestation rate was strongly dependent on plot composition. Mixtures of pines (Pinus pinaster) and birches (Betula pendula) were less prone to T. pityocampa infestations, whereas mixtures of pines and oaks (Quercus spp.) were more often attacked than pine monocultures. By taking into account the relative height of pines and associated broadleaved species, this effect could be explained by pine apparency. Pines were on average 343 ± 5 cm height. Birches, as fast growing trees, were slightly taller than pines (363 ± 6 cm), while oak trees were significantly smaller (74 ± 1 cm). Host trees of T. pityocampa were then partly hidden in mixtures of pines and birches but more apparent in mixtures with oaks. We suggest that reduced pine apparency disrupted visual cues used by female moths to select host trees prior to oviposition. This study highlights the need to take into account tree traits such as growth rate when selecting the tree species that have to be associated in order to improve forest resistance to pest insects.     

Biological attributes of Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) reared on refrigerated eggs of Riptortus pedestris (= clavatus) Fabricius (Hemiptera: Alydidae)

Storing host eggs at low temperatures has been used to mass rear parasitoids of stink bugs, including Riptortus pedestris Fabricius (Hemiptera: Alydidae), a major soybean pest in Korea and Japan. However, no information on the effect of cold storage on parasitization by Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae), one of the major parasitoids of R. pedestris, has been published. In this study, we examined biological attributes, including parasitism rate, development time, sex ratio, adult size, and longevity, of O. nezarae when the adult parasitoids were provided with host eggs refrigerated for 0, 15, 30, 60, and 120 days at 2.0 °C. None of the attributes of the first or second generation of O. nezarae was negatively affected by host egg refrigeration up to 30 days. In addition, O. nezarae could parasitize refrigerated host eggs successfully for the first four days of post-refrigeration period when they were kept at 26.3 °C and 78.7% RH conditions. Therefore, refrigeration of R. pedestris eggs can be a good method to mass rear O. nezarae.     

Quality assessment of Riptortus pedestris (Hemiptera: Alydidae) eggs cold-stored at different temperature and relative humidity regime

Supplementation of host resource can be more economical method for the biological control of insect pest compared to direct release of adult parasitoids. Periodical release of non-viable cold-stored eggs of Riptortus pedestris (Fabricius) (Hemiptera: Alydidae) has been found to enhance parasitism of this pest in soybean fields. To find the optimum environmental conditions for cold storage of these host eggs, we evaluated nine different combinations of temperature (2, 6, and 10 °C) and relative humidity (high 90–95%, medium 70–75%, and low 30–35%). After 30 d of cold-storage, eggs were weighed and held at 26.6 °C and 75% relative humidity for 8 d before testing. To test the eggs’ suitability as hosts following cold storage, females of Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) were released individually onto batches of eggs, and parasitization rates and the development, emergence, sex ratio, adult longevity, and size of parasitoid progeny were examined. Eggs stored at high relative humidity showed less weight loss than those stored at low relative humidity. The number of eggs parasitized was highest (5.9/15) on eggs stored at 6 °C and high relative humidity. Developmental times and adult emergence were optimal on host eggs stored at 2 °C and high relative humidity. A significantly lower proportion of eggs produced male parasitoids when eggs were stored at 2 or 6 °C. Adult longevity was not affected by egg storage conditions, but adult size of progeny decreased in eggs stored at 10 °C. In conclusion, eggs of R. pedestris stored below 6 °C and with a high relative humidity maintained the best quality for parasitization by O. nezarae.     

Control the egg hatchling process of Pomacea canaliculata (Lamarck) by water spraying and submersion

Pomacea canaliculata (Lamarck) is an invasive snail species that has become a serious pest of rice and other hydrophytes. Usually it is aquatic but likes to lay its eggs higher than the waterline. In order to seek a feasible and efficient way to control the egg hatchling of this pest, here we systematically studied the effects of water spraying and submersion on its egg hatchling rates and durations. Our results demonstrated that water spraying and submersion could dramatically decrease the hatchling rates to maximal 5.8% and increase the hatchling duration up to 26.4 days on P. canaliculata. Not only the beginning time of water treatment, but also the frequencies of the water spraying is critical to control the hatchling rate and duration of P. canaliculata. Water submersion that began in 12 h after the eggs laid and lasted at least 48 h will significantly decrease the snails’ hatchling rates and extend the hatchling time. In addition, compared to spraying, the water submersion could achieve more remarkable effects. The capsule of the snail’s egg is able to withstand the water treatment. Based on our water spraying and submersion results, it can be inferred that 0–6 h after egg being laid, egg capsule precipitates are beginning to form, and this process will complete after 12–24 h. This special breeding characteristic of P. canaliculata makes the physical control by water treatment become feasible.     

Performance of diapausing parasitoid wasps,Habrobracon hebetor,after cold storage

The ectoparasitoid Habrobracon hebetor (Say) (Hymenoptera: Braconidae) is an important potential biological control agent for lepidopterous pests of stored products. We investigated the effects of long-term cold storage of diapausing and nondiapausing H. hebetor on their performance after cold storage. Mortality during storage increased with increasing storage duration, and the mortality of diapausing females was lower than that of nondiapausing females after 8, 12, and 16 weeks of storage. Longevity, egg laying, number of progeny produced, and time to 50% egg laying were all reduced, as compared with the culture females when parasitoids were reared at conditions that do not induce diapause. But, for females reared at 20 °C at conditions that induce diapause, all of these quality parameters did not differ from those of culture insects when the storage duration was 8 weeks or less. The percentage of female F1 offspring was always lower for cold stored insects than for the culture insects. Presence of a male after cold storage did not impact any of the quality parameters measured. Thus, rearing parasitoids at 20 °C and 10L:14D and then storing them for up to 8 weeks at 5 °C would produce parasitoids that are similar to culture parasitoids, except that the percentage of females is lower than that in the cultures (36% vs. 52%).     

Multitrophic influences on egg distribution in a specialized leaf beetle at multiple spatial scales

Egg distribution in herbivorous beetles can be affected by bottom-up (host plant), and by top-down factors (parasitoids and predators), as well as by other habitat parameters. The importance of bottom-up and top-down effects may change with spatial scale.

In this study, we investigated the influence of host plant factors and habitat structure on egg distribution in the leaf beetle Cassida canaliculata Laich. (Coleoptera: Chrysomelidae), a monophagous herbivore on Salvia pratensis L. (Lamiales: Lamiaceae), on four spatial scales: individual host plant, microhabitat, macrohabitat, and landscape. At the individual host plant scale we studied the correlation between egg clutch incidence and plant size and quality. On all other scales we analyzed the relationship between the egg clutch incidence of C. canaliculata and host plant percentage cover, host plant density, and the surrounding vegetation structure. Vegetation structure was examined as herbivores might escape egg parasitism by depositing their eggs on sites with vegetation factors unfavorable for host searching parasitoids.

The probability that egg clutches of C. canaliculata were present increased with an increasing size, percentage cover, and density of the host plant on three of the four spatial scales: individual host plant, microhabitat, and macrohabitat. There was no correlation between vegetation structure and egg clutch occurrence or parasitism on any spatial scale. A high percentage of egg clutches (38–56%) was parasitized by Foersterella reptans Nees (Hymenoptera: Tetracampidae), the only egg parasitoid, but there was no relationship between egg parasitism and the spatial distribution of egg clutches of C. canaliculata on any of the spatial scales investigated. However, we also discuss results from a further study, which revealed top-down effects on the larval stage.     

The prospect of using sub-lethal imidacloprid or pirimicarb and a parasitoid wasp, Lysiphlebus fabarum, simultaneously,to control Aphis gossypii on cucumber plants

The broad-spectrum insecticides greatly influence the control of cotton aphids; however, due to frequent chemical control, Aphis gossypii (Hemiptera: Aphididae) has developed resistance against several classes of synthetic insecticides. In this study, we explored the sub-lethal effects of imidacloprid and pirimicarb, two commonly used insecticides for aphid control, on a parasitoid wasp, Lysiphlebus fabarum (Marshall) (Braconidae: Aphidiinae), when simultaneously used to control melon aphid on cucumber plants, as part of a comprehensive study for integrated pest management. Bioassays of imidacloprid and pirimicarb were performed to calculate LC₅₀ with third instars of A. gossypii. The LC₅₀ of these insecticides (110.55 and 250.89 μg/lit, respectively) were used to expose the wasp larvae, pupae, and adult parasitoids on a cucumber leaf. The percent mortality, percent adult emergence, and sex ratio were calculated during each exposure test. Moreover, the body size, egg load, and mature egg size of wasps surviving the insecticide treatments, as well as the sex ratio of the second generation was evaluated. Regardless of the host aphid mortality, none of the insecticides caused mortality of larval stage of the parasitoid. The insecticide application on pupal stage revealed that the percentage of mortality, sex ratio, body size, and egg load of surviving wasps, as well as the sex ratio of their offspring was adversely affected by imidacloprid, but not by pirimicarb. The present study suggests pirimicarb as a preferred insecticide, with less harmful effects on the fitness components of L. fabarum, for integrated pest management of cotton aphids.     

Habitat isolation affects plant–herbivore–enemy interactions on cherry trees

Understanding the interactions between herbivores and natural enemies in fragmented landscapes is essential for conservation biological control. Studies including multiple enemies affecting multiple herbivores, plant damage and growth are needed. Here, we separated independent effects of (1) isolation of cherry trees from woody habitat and (2) the amount of woody habitat in the surrounding landscape (500 m buffers) on interactions between different groups of herbivores with their natural enemies and resulting changes in the growth of young cherry trees. Most predatory arthropods declined with habitat isolation, except some aphid predators (ladybeetles and hoverflies). Herbivores either increased with isolation (herbivorous beetles) or showed no significant response (aphids). In contrast, the amount of woody habitat in the landscape was not relevant for herbivore–enemy interactions at the investigated scale. Plant growth was affected by bottom-up (nutrient availability) and top-down (aphid density) forces but did not change significantly with habitat amount or isolation. We conclude that herbivores can be released from natural enemies at isolated sites, in accordance with the hypothesis that habitat connectivity improves pest control. However, each herbivore group responded differently to the landscape context and had contrasting effects on the same host plant, demonstrating the difficulty to predict landscape effects on plant growth.     

Oviposition and reproductive performance of a generalist parasitoid (Trichogramma pretiosum) exposed to host species that differ in their physical characteristics

The response of generalist egg parasitoids to alternative natural hosts that are present simultaneously is not well known. We investigated the behavior of Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) in relation to two field hosts Helicoverpa armigera Hübner and Spodoptera litura Fabricius, in choice and no choice tests. We quantified the effects of natal host species and post-emergence adult age on the oviposition preference of the parasitoids. H. armigera eggs were consistently preferred over S. litura eggs, regardless of the natal host and adult age. When only S. litura eggs were available as hosts, they were parasitized at statistically similar rates to H. armigera eggs (average of 17 ± 2.7 vs. 13 ± 3.0, H. armigera to S. litura). The adult lifespan and lifetime fecundity of T. pretiosum were variable but were affected by natal host species and/or host species to which they were exposed. Mean lifespan and fecundity of parasitoids that had developed in H. armigera eggs and were exposed to H. armigera eggs for oviposition were 13.9 ± 1.8 days and 98.7 ± 11.0 adult offspring. By contrast, those that developed in S. litura eggs and were exposed to S. litura eggs for oviposition lived for 7 ± 0.9 days and produced 53.8 ± 8.0 adult offspring. The ovigeny index (OI) was significantly lower in the parasitoids exposed to H. armigera eggs than in those exposed to S. litura eggs, regardless of the natal host, indicating that H. armigera eggs sustain the adult parasitoids better than S. litura eggs. These results are used to predict parasitoid behavior in the field when both hosts are available.     

Habitat selection by endangered Himalayan musk deer (Moschus chrysogaster) and impacts of livestock grazing in Nepal Himalaya: Implications for conservation

Habitat management within and outside protected areas is a key to effective conservation of wildlife. This is particularly vital for declining wildlife populations within the boundary of conservation areas, while sharing their potential habitat range with foraging livestock. In an effort to understand the habitat selection by Himalayan musk deer (Moschus chrysogaster) and explore any potential impacts of livestock grazing, we conducted the present study in a conservation area of central Nepal Himalaya. We recorded data on musk deer and livestock presence and absence (based on signs of fecal pellet, footprint, and resting site) along the elevational transect with associated topographic features (elevation, slope, aspect, distance to water, and vantage point distance) and vegetation features (tree spp., shrub spp., herb spp., and canopy-cover). Using logistic regression model we found that elevation, aspect, canopy-cover, and tree spp. in the area significantly affect the likelihood of habitat selection by musk deer. In particular, they selected the southern aspect of the area with elevation ≥ 3529 m, canopy-cover ≥ 42%, and with stands of Pinus spp. and Abies spp. Slope and canopy-cover significantly affected the foraging area selection by livestock. They selected the gentler slopes in the northern aspect of the area with altitude < 3529 m and canopy-cover < 42%. Also, presence of one group of herbivore (i.e. musk deer and livestock) was not found to affect the likelihood of habitat selection by the other group. These independent habitat selections are possibly the responses to morphological and behavioral adaptations than to impacts and interactions between these two groups of herbivores. We suggest to avoid any disturbances and livestock grazing on the area that disrupt the resources and conditions likely selected and occupied by musk deer population.     

The Hohenheimer Box – A new way to rear and release Lariophagus distinguendus to control stored product pest insects

To improve the biological control of stored product pests, the present paper reports on the development of a rearing box for parasitoids of pest insects. The box contains breeding substrate and populations of hosts and parasitoids and is placed in storage sites, where parasitoids are released continuously over several months. The box was developed to rear Lariophagus distinguendus (Förster) (Hymenoptera: Pteromalidae) to control the granary weevil Sitophilus granarius (L.) (Coleoptera: Curculionidae). Due to sanitary reasons, the bean weevil Acanthoscelides obtectus Say (Coleoptera: Bruchidae) was chosen as an alternative host. Rearing experiments revealed that the cowpea Vigna unguiculata unguiculata (L.) Walp. is most suitable as host substrate. For the outlet of the rearing device, a wire gauze mesh size of 0.8–1.0 mm was found suitable to release wasps while holding back the bean weevils. The size of the starting populations of hosts and parasitoids was determined experimentally in a storage building. An amount of 5 ml weevils plus 21–60 adult parasitoids on 2 kg of cowpeas produced an average of 56 and 62 wasps per week respectively, from June to September. Wasps reared in the boxes had the same number of offspring on granary weevils as wasps from regular lab-cultures. This study demonstrates the feasibility of a rearing box for parasitoids of stored product pests that releases large numbers of wasps over several months. We consider our study as a guideline for the development of similar rearing boxes also for other parasitoid-pest systems in stored products protection throughout the world.     

Influence of plant phenostage and ploidy level on oviposition and feeding of two specialist herbivores of spotted knapweed,Centaurea stoebe

A caged field experiment was used to determine how Centaurea stoebe L. phenostage (rosette, single-stem, multiple-stem) and ploidy level (diploid = 2× and tetraploid = 4×) influence oviposition and feeding of two biological control agents, Agapeta zoegana (Lep.: Cochylidae) and Cyphocleonus achates (Col.: Curculionidae). Ploidy level did not influence oviposition patterns of A. zoegana but rosette and one-stem plants had significantly more eggs than multiple-stem (4×) plants. Differences in oviposition levels did not translate into differences in larval densities, but 2× plants (particularly large one-stem plants) had significantly more larvae than 4× plants. There was a significant positive correlation between numbers of larvae and root diameter. Ploidy level and phenostage both had a significant effect on C. achates feeding damage, with adults feeding more frequently on multiple-stem plants. No C. achates larvae were observed when the roots were dissected. Furthermore, the generalist herbivore Arion lusitanicus, naturally present in the garden plots, was predominantly associated with young rosette plants, a stage at which survival rate is acknowledged to be the most important determinant of knapweed density. These results indicate that the combined damage caused by A. zoegana and C. achates, superimposed on damage caused by generalist herbivores in the local community, could provide effective control for C. stoebe.     

Biology of Apanteles myeloenta (Hymenoptera: Braconidae), a larval parasitoid of carob moth Ectomyelais ceratoniae (Lepidoptera: Pyralidae)

The carob moth, Ectomyelois ceratoniae (Lepidoptera: Pyralidae), is the most important pest of pomegranate orchards (in terms of economic damage) within Iran, and hence, several control procedures, including biological methods of control, have been attempted as a means of controlling populations of this insect. This research was carried out in order to study the biology of Apanteles myeloenta (Hymenoptera: Braconidae), a larval parasitoid of the carob moth. Laboratory studies were conducted to determine larval developmental time, adult longevity, sex ratio, parasite progeny production, and host stage preference of A. myeloenta. At 25 ± 1 °C, immature developmental time (egg to pupa; mean ± SE) was 28.33 ± 0.85 days and 27.46 ± 0.37 days for male and females, respectively. Adult females survived on average 17.5 ± 0.14, 11.7 ± 0.22, 3.4 ± 0.18, and 2.8 ± 0.12 days at 25 C when provided with honey and water, honey only, water only or no food source, respectively. The sex ratio (females to males) of A. myeloenta was 1:3.5 from hosts parasitized in the first instar, 1:3 for second instars and 1:2 for third instar carob moth larvae. Female A. myeloenta typically preferred to parasitize second instar over third or first instar. The oviposition activity peaked on the 7th and 8th days following emergence, when provided with honey, and 10% sucrose solution, respectively.