Sentinel Egg Research Articles

Intraguild interactions between two egg parasitoids of a true bug in semi-field and field conditions.

Research on interspecific competitive interactions among insect parasitoids has often been characterized by laboratory studies in which host insects are exposed to female parasitoids of different species in various sequences and combinations. In the last years, an increasing number of studies have investigated interspecific interactions under field and semi-field conditions although just a few number of works focused on egg parasitoids. In this work, we undertook a two-year study to investigate interspecific interactions between Trissolcus basalis (Wollaston) (Hymenoptera: Platygastridae) and Ooencyrtus telenomicida (Vassiliev) (Hymenoptera: Encyrtidae), two egg parasitoids of the pest Nezara viridula (L.) (Heteroptera: Pentatomidae) that co-occur in cultivated crops. Under semi-field (in out-door mesh cages) and field conditions, we investigated: 1) the seasonal occurrence of competing parasitoid species on sentinel egg masses; 2) the impact achieved by competing species on the shared host on naturally laid egg masses; 3) the outcome of intraguild interactions under controlled conditions. Results from sentinel egg masses showed that T. basalis occurs in May and successfully parasitizes hosts until the end of September/beginning of October, whereas O. telenomicida is mainly occurring in July-August. In both years, it was found that T. basalis is predominant. From naturally laid egg masses, results indicated that T. basalis achieves higher impact on the hosts, even in those egg masses which are parasitized by more than one female of different species ( = multiparasitism). Results from manipulating intraguild interactions showed that T. basalis achieves higher impact on N. viridula when released alone, but it suffers from competition with O. telenomicida. The ecological factors that play a role in intraguild interactions in the context of biological control perspective are discussed.

Biodiversity loss following the introduction of exotic competitors: does intraguild predation explain the decline of native lady beetles?

Exotic species are widely accepted as a leading cause of biodiversity decline. Lady beetles (Coccinellidae) provide an important model to study how competitor introductions impact native communities since several native coccinellids have experienced declines that coincide with the establishment and spread of exotic coccinellids. This study tested the central hypothesis that intraguild predation by exotic species has caused these declines. Using sentinel egg experiments, we quantified the extent of predation on previously-common (Hippodamia convergens) and common (Coleomegilla maculata) native coccinellid eggs versus exotic coccinellid (Harmonia axyridis) eggs in three habitats: semi-natural grassland, alfalfa, and soybean. Following the experiments quantifying egg predation, we used video surveillance to determine the composition of the predator community attacking the eggs. The extent of predation varied across habitats, and egg species. Native coccinellids often sustained greater egg predation than H. axyridis. We found no evidence that exotic coccinellids consumed coccinellid eggs in the field. Harvestmen and slugs were responsible for the greatest proportion of attacks. This research challenges the widely-accepted hypothesis that intraguild predation by exotic competitors explains the loss of native coccinellids. Although exotic coccinellids may not be a direct competitor, reduced egg predation could indirectly confer a competitive advantage to these species. A lower proportion of H. axyridis eggs removed by predators may have aided its expansion and population increase and could indirectly affect native species via exploitative or apparent competition. These results do not support the intraguild predation hypothesis for native coccinellid decline, but do bring to light the existence of complex interactions between coccinellids and the guild of generalist predators in coccinellid foraging habitats.

Susceptibility of Nezara viridula (L.) (Hemiptera: Pentatomidae) Egg Masses of Different Sizes to Parasitism by Trissolcus basalis (Woll.) (Hymenoptera: Platygastridae) in the Field.

Egg masses of Nezara viridula (L.) are commonly parasitized by Trissolcus basalis (Woll.), and we investigated the role of size of egg masses on parasitization by T. basalis. Sentinel egg masses were exposed to parasitism in the field for 6-7days, when they were collected for evaluation of parasitoid emergence. We recorded the number of eggs per egg mass, the number of emerged hosts, and the number of empty and parasitized eggs. We calculated the proportion of attacked host egg masses (DE), the proportion of parasitized eggs per attacked egg mass (PE), and total parasitism (PI). The total number of egg masses exposed to parasitism was 330. The minimum, mean, and maximum egg mass sizes were 25, 75.2, and 111, respectively. DE and PE varied widely between different fields, and they were independent of egg mass size. In 14.2% of all parasitized egg masses, we found simultaneous emergence of T. basalis and N. viridula independently of host egg mass size. PE exhibited low variability compared with PI and DE, which were linearly related. PI and DE values from other field studies are consistent with the linear relationship, suggesting that PI is mostly related to the proportion of the DE. This also suggests that total parasitism is independent of egg mass size, of possible differences in plant species, and T. basalis density and strains.

Mortality factors affecting Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae) eggs in the native and invaded ranges

An absence of diverse and coevolved natural enemies may explain the high levels of oak mortality caused by an invasive wood boring beetle, Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae), in California (CA). A field study was conducted to test the enemy release hypothesis for a single guild of natural enemies by comparing mortality factors affecting A. auroguttatus sentinel eggs deployed in both native (southern Arizona [AZ]) and introduced ranges (southern CA). The percentage of eggs attacked by natural enemies did not differ between sites, which does not support the enemy release hypothesis for this life stage. Although the predominant cause of mortality to sentinel eggs deployed in CA and AZ was due to factors other than natural enemy activity, chewed, missing, and parasitized eggs contributed to as much as 16% and 24% of sentinel egg mortality in CA and AZ, respectively. In addition, the first known egg parasitoid of A. auroguttatus was collected during this study from a single egg deployed in AZ, and was identified as Trichogramma sp. using molecular techniques. This parasitoid is a generalist, and therefore not suitable for use in a classical biological control program against A. auroguttatus in CA. A continuation of this study is needed across a larger number of field sites and over a longer period of time to optimize the potential detection of host specific egg parasitoids for potential introduction into CA as part of a future classical biological control program, and to better quantify natural enemy impacts on A. auroguttatus eggs.

Vacant land conversion to community gardens: influences on generalist arthropod predators and biocontrol services in urban greenspaces

Due to economic decline and the recent rise in home foreclosure, many U.S. cities are faced with managing large acreages of vacant land. Interest in local food production on this land has the potential to dramatically reshape the composition of greenspace found within urban landscapes. This study examined how the conversion of vacant land to urban gardens and farms influenced arthropod generalist predator populations and their ability to support biocontrol services. We found that the abundance of Coccinellidae and Syrphidae, and the activity density of Carabidae, Formicidae, and Lycosidae were equivalent among vacant lot and urban garden sites. Dolichopodidae abundance and the activity density of Linyphiidae and Opiliones were reduced in urban gardens whereas Anthocoridae abundance and the activity density of Staphylinidae were greater within urban gardens relative to vacant lots. The biocontrol service supplied by generalist predators was measured using sentinel eggs (Helicoverpa zea (Noctuiidae)) and pupae (Sarcophaga bullata (Sarcophagidae) and Musca domestica (Muscidae)). We found no difference in the biocontrol of H. zea eggs or M. domestica pupae among the focal greenspaces. We found no difference in the removal of S. bullata pupae by predators in June 2010, whereas in August 2010 a greater proportion of pupae were removed in urban garden sites relative to vacant lots. Based on these findings, we discuss the potential of the urban landscape to support generalist predators and sustainable urban gardening and farming.

Egg Parasitoids of the Corn Leafhopper,Dalbulus Maidis, in the Southernmost Area of its Distribution Range

Egg parasitoids of the corn leafhopper, Dalbulus maidis (DeLong and Wolcott) (Hemiptera: Cicadellidae), were surveyed exposing sentinel eggs of the leafhopper along a latitudinal transect of 600 km in Argentina, the southernmost area of its distribution range. Four parasitoid species were obtained: the mymarids Anagrus breviphragma Soyka (Hymenoptera: Mymaridae), Anagrus flaveolus Waterhouse, and Polynema sp., and the trichogrammatid Pseudoligosita longifrangiata (Viggiani) (Hymenoptera: Trichogrammatidae). The low parasitism rate, low species richness, and high proportion of generalist egg parasitoids were quite clear in the southern distribution limit of the vector, in contrast to regions where corn crops are available all year round and there are continuous and overlapping generations of the pest. Further studies need to be done in order to determine the native host of the above egg parasitoids, the seasonal abundance, and the possible occurrence of other species affecting D. maidis populations in the studied area.

Crop-specific mortality of southern green stink bug eggs in Bt- and non-Bt cotton, soybean and peanut

Increasing insecticide use against stink bugs erodes benefits accrued to cotton production in the southeastern USA by eradication of the boll weevil and widespread use of Bt-transgenic cotton. Biological control programs designed to mitigate the impact of these pests would be beneficial; therefore, we sought to identify and assess naturally occurring biological control agents of stink bug eggs in cotton, peanut and soybeans, three important crops and stink bug hosts in the region. Two studies were conducted utilising digital imaging of sentinel egg masses to capture enemies present and sequential imaging over time to characterise the type and amount of damage inflicted on the egg masses. The first study utilised plots of soybean, Bt cotton, non-Bt cotton and peanut. The second study focused on ant predation in cotton by excluding fire ants from half of the plots. Sentinel egg masses of the southern green stink bug were placed in all plots at weekly intervals and were photographed at placement and at intervals over 72 h. Surviving egg masses were collected and held in the laboratory to assess parasitism in the first study. Predation of eggs was high in peanut (74–86%) and soybean (39–65%), and lower in Bt (26–34%) and non-Bt (4–21%) cotton over the two years. Parasitism was low overall (0.17–19.0%). Most egg predation in cotton and peanut was attributable to fire ants, whereas long-horned grasshoppers dominated in soybean. Exclusion of fire ants in cotton significantly reduced egg mortality, indicating their predominance as mortality agents in cotton.

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 2m2 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.

Spatial scale of benefits from adjacent woody vegetation on natural enemies within vineyards

Abundance of predators in crops can be increased by augmenting the adjacent non-crop vegetation, with associated environmental benefits from reduced chemical inputs and landscape conservation. Fine-scale spatial analysis is required to assess the extent to which non-crop benefits extend into farmed areas. We used explicit spatial mapping to investigate benefits of woody vegetation in two vineyards. The abundance of canopy-dwelling predators and predation/parasitism rates was measured at two vineyards with woody vegetation on one margin. Grids were sampled monthly across two summer growing seasons and stability of spatial patterns determined for consecutive months for each season and between seasons. At these two locations small parasitoids and several species of ladybird beetles from the vine canopy exhibited spatial patterning, with regions of high and low abundance and activity, aggregated in rows near to woody vegetation. Aggregations varied in temporal stability, with some persisting throughout the season. When predation and parasitism of sentinel eggs of a moth pest were non-randomly distributed, levels were higher in vine rows closer to the woody vegetation and significantly associated with a known egg parasitoid and ladybird beetles. This study demonstrated predators and parasitoids had non random and stable distributions at two vineyards. Increased abundance of both Coccinellidae and parasitoids was seen over similar distances: extending approximately 40m from the vegetated edge. Increase in parasitism and predation extended a similar distance in from the vegetation. These results suggest management of vineyards where non-crop vegetation can be used to increase numbers and impact of beneficials, with recommendations for planting woody vegetation a minimum of 50m from vineyard edges.

Dispersal of Trichogramma ostriniae in field corn

Trichogramma ostriniae has shown success as a biological control agent for European corn borer (Ostrinia nubilalis) in sweet corn and the species offers potential for suppression of lepidopteran pests of field corn. Field corn is typically planted at higher densities, is taller, and has greater leaf area than sweet corn, presenting a possible restriction on T. ostriniae dispersal and efficacy. Therefore, parasitoid dispersal in field corn from the centre of a 6.25 ha square grid was determined using sticky cards to capture adult T. ostriniae and sentinel eggs of O. nubilalis to monitor parasitism after releases of ~1 million of T. ostriniae each into four fields of corn. Dispersal was rapid and extensive, achieving distances of ~175 m within 4–7 days after release. The pattern of movement fit well with a diffusion model of dispersal, with the greatest level of dispersal occurring from 7 to 10 days post-release. Parasitism of O. nubilalis sentinel egg masses declined linearly with distance from the release foci, and was also greatest 7–10 days post-release. However, measurement of association showed no significant differences between the spatial distributions of sticky trap captures and percentage parasitism of O. nubilalis egg masses. The distances from the release point that encompassed 98% of re-captured T. ostriniae increased over time and were estimated to range from a low of 100 m at 4 days post-release to 365 m at 14 days post-release. The results of this research suggest that T. ostriniae relies initially on random movement to locate host patches, and that a single release locus per hectare would be sufficient in field corn.

Diversity of Egg Parasitoids AttackingDalbulus maidis(Hemiptera: Cicadellidae) Populations at Low and High Elevation Sites in Mexico and Argentina

ABSTRACT The corn leafhopper, Dalbulus maidis (DeLong & Wolcott), is one of the most important pests of maize in Latin America because of its efficiency as a vector of 3 species of plant pathogens. In spite of its significance, however, little is known about its egg parasitoids. In this study, we present new data on D. maidis egg parasitoids in Mexico and Argentina. We surveyed the egg parasitoids in 2 locations: Mexico and Argentina, representing the farthest expansion of the D. maidis populations from Mexico. Using maize plants with sentinel eggs, parasitoids were surveyed in central Mexico and northwestern Argentina, at both low ( 1,000) elevation sites, during 2 maize-growing wet seasons. Parasitoids of the families Mymaridae and Trichogrammatidae were found in both countries. Argentinean sites showed the highest richness, with 10 species, whereas in Mexico we found 6 species. Also, the Shannon diversity index was 1.6 times greater in Argentina than in Mexico. Higher percentages of p...

Maize-Dwelling insects omnivory in Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) egg masses

This work reports the first record of omnivory behavior of Diabrotica speciosa (Coleoptera, Chrysomelidae), Leptoglossus zonatus (Hemiptera, Coreidae), Monocrepidius aff. posticus and Monocrepidius fuscofasciatus (Coleoptera, Elateridae) on fall armyworm Spodoptera frugiperda (Lepidoptera, Noctuidae) egg masses in maize fields. Macrophotography was used to record the activity of these insects on fall armyworm sentinel egg masses during 2009 and 2010 maize growing seasons. The presence of omnivorous insects changes the species population dynamics within the ecosystem. Therefore, the implications of these interactions should be understood and taken into consideration for integrated pest management enhancement.

Predation of codling moth eggs is affected by pest management practices at orchard and landscape levels

The low sustainability of pesticides calls for alternative pest control practices. Among these, the conservation of pest natural enemies is governed both by the local farming practices and by the presence of resources in the surrounding landscape. We investigated the effect of landscape composition on predation of sentinel eggs of the codling moth (Cydia pomonella), a key pest in apple orchards. Thirty egg cards of approximately 15 eggs were exposed twice in each of 12 orchards. Orchards were characterized by their area, their crop protection practices, the abundance of their codling moth population and the abundance of predatory earwigs. The landscape was characterized by the area and management of orchards host to the pest and by the characteristics of the hedgerow network in 50m and 100m wide buffers. On average, 12.4% and 48.3% of the egg cards were attacked by predators in June and August, respectively. Predation depended mostly on the toxicity of the crop protection programs. Predation rates were also lower in orchards surrounded by large areas of conventional orchards. No other landscape variable was significant. This indicates that the spatial distribution of pesticides around orchards impacted the within orchards natural enemies.

Dispersal and field progeny production of Trichogramma species released in an olive orchard in Egypt

Dispersal ability and field progeny production of augmentative released biological control agents depend on ecological adaptations of the particular species or strains used. Four species of the egg parasitoid genus Trichogramma were compared aiming to select suitable candidates for control of lepidopteran olive pests. Three of them (T. bourarachae Pintureau and Babault, T. cordubensis Vargas and Cabello, T. euproctidis Girault) had been previously collected from olive groves, whereas the commercially available strain used (T. evanescens Westwood) was originally isolated from sugarcane fields. During five consecutive field releases in an olive orchard near Cairo, dispersal and/or progeny production of these species was monitored using sentinel eggs placed at different heights in the release tree canopies as well as in neighboring trees (“distance effect”). The cardinal direction of dispersal was random for T. euproctidis and T. evanescens. Significant higher parasitism occurred on sentinel eggs placed on the middle part of tree canopy and highest parasitism was observed in trees where wasps had been released. Field progeny production was highest for T. bourarachae, followed by T. euproctidis and T. cordubensis. T. evanescens propagated less under field conditions. Inter-tree dispersal of all species except T. bourarachae was limited and, for biological control, releasing material should therefore be distributed on each olive tree, preferably also at different levels of the canopy.

Intraguild Predation and Native Lady Beetle Decline

Coccinellid communities across North America have experienced significant changes in recent decades, with declines in several native species reported. One potential mechanism for these declines is interference competition via intraguild predation; specifically, increased predation of native coccinellid eggs and larvae following the introduction of exotic coccinellids. Our previous studies have shown that agricultural fields in Michigan support a higher diversity and abundance of exotic coccinellids than similar fields in Iowa, and that the landscape surrounding agricultural fields across the north central U.S. influences the abundance and activity of coccinellid species. The goal of this study was to quantify the amount of egg predation experienced by a native coccinellid within Michigan and Iowa soybean fields and explore the influence of local and large-scale landscape structure. Using the native lady beetle Coleomegilla maculata as a model, we found that sentinel egg masses were subject to intense predation within both Michigan and Iowa soybean fields, with 60.7% of egg masses attacked and 43.0% of available eggs consumed within 48 h. In Michigan, the exotic coccinellids Coccinella septempunctata and Harmonia axyridis were the most abundant predators found in soybean fields whereas in Iowa, native species including C. maculata, Hippodamia parenthesis and the soft-winged flower beetle Collops nigriceps dominated the predator community. Predator abundance was greater in soybean fields within diverse landscapes, yet variation in predator numbers did not influence the intensity of egg predation observed. In contrast, the strongest predictor of native coccinellid egg predation was the composition of edge habitats bordering specific fields. Field sites surrounded by semi-natural habitats including forests, restored prairies, old fields, and pasturelands experienced greater egg predation than fields surrounded by other croplands. This study shows that intraguild predation by both native and exotic predators may contribute to native coccinellid decline, and that landscape structure interacts with local predator communities to shape the specific outcomes of predator-predator interactions.

Biology and host specificity of Gonatocerus deleoni (Hymenoptera: Mymaridae), a potential biocontrol agent of Homalodisca vitripennis (Hemiptera: Cicadellidae) in California, USA

The host-specificity and biological traits of Gonatocerus deleoni Triapitsyn, Logarzo & Virla (Hymenoptera: Mymaridae), a potential candidate for biological control of the glassy-winged sharpshooter (GWSS), Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae), were determined under laboratory conditions. G. deleoni is a solitary egg parasitoid native to Argentina, originally reared from sentinel eggs of Tapajosa rubromarginata (Signoret) (Cicadellidae). With GWSS as a fictitious host, G. deleoni’s average development time from oviposition to adult emergence was 18.8 ± 1.4 days, with males developing faster than females (18.0 ± 1.3 days, males; 19.0 ± 1.3 days, females). The average parasitism rate on 1–8-day-old eggs was 45.7% but this was significantly affected by the age of the egg, ranging from 1.4% to 69.9% (egg ages 8 and 3, respectively). The average sex ratio was 0.34 (percent males) and sex ratio was not significantly affected by egg age. G. deleoni was able to develop in eggs of GWSS and Homalodisca liturata Ball (both in the tribe Proconiini), but was unable to develop on eggs of Graphocephala atropunctata (Signoret) (different tribe, same subfamily) or Erythroneura elegantula Osborn (different subfamily).

Two new Encarsia species (Hymenoptera: Aphelinidae) reared from eggs of Cicadellidae (Hemiptera: Auchenorrhyncha) in Argentina: an unusual new host association

Males of two undescribed Encarsia species were reared from eggs of two cicadellid species during a study of egg parasitoids of corn leafhopper, Dalbulus maidis (DeLong and Wolcott) in northwestern Argentina. Samples were collected during the summer of 2004–2007 using sentinel eggs, and several males of a new species of Encarsia (Hymenoptera: Chalcidoidea: Aphelinidae) were obtained. A single male of a closely related Encarsia species, also previously undescribed, was reared from an egg of another cicadellid on maize, Plesiommata mollicella (Fowler). These are the first records of any Encarsia species reared from eggs of Cicadellidae. The two new species are described as Encarsia dalbulae Polaszek and Luft Albarracin sp. nov., and Encarsia mollicellae Polaszek and Luft Albarracin sp. nov.

Development of methods for the field evaluation of Oobius agrili (Hymenoptera: Encyrtidae) in North America, a newly introduced egg parasitoid of the emerald ash borer (Coleoptera: Buprestidae)

A field study was conducted in forested plots near Lansing, Michigan in 2008 and 2009 to evaluate the newly introduced egg parasitoid Oobius agrili Zhang and Huang (Hymenoptera: Encyrtidae) for control of the invasive emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae). To measure parasitism by O. agrili, laboratory-reared “sentinel EAB eggs” were deployed under bark flaps on trunks of selected ash trees in both parasitoid-release and non-release control plots. In addition, naturally occurring EAB eggs were collected in both parasitoid-release and control plots to measure parasitism. While no parasitism was detected with either sentinel or naturally occurring EAB eggs in control plots in either 2008 or 2009, a low level of parasitism by O. agrili was detected in the parasitoid-release plots in both artificially deployed sentinel eggs (⩽1%) and field-collected, naturally occurring eggs (1.1–4.2%) in both years. In addition to losses due to parasitism by O. agrili, a large proportion (37–52%) of the field-deployed sentinel eggs disappeared, possibly due to predators such as ants, in both parasitoid-release and control plots. While no statistical differences in parasitism by O. agrili were detected between parasitoid release and control plots, other sources of egg mortality such as disappearance due to predation on eggs, varied significantly across study sites in both 2008 and 2009. The relevance of these findings to future release and evaluation strategies for O. agrili for biological control of the invasive emerald ash borer in the US is discussed.

Parasitism and Predation of Stink Bug (Heteroptera: Pentatomidae) Eggs in Georgia Corn Fields

Nezara viridula L. and Euschistus servus (Say) are the predominant species of phytophagous stink bugs on corn, Zea mays L., in Georgia. Oebalus pugnax pugnax (F.) occurs in relatively low numbers, and the predatory stink bug Podisus maculiventris (Say) is commonly found. Limited information is available on natural biological control of these four stink bug species in Georgia corn fields; therefore, a 6-yr study of parasitism and predation of their eggs was initiated in 2003. Naturally occurring stink bug eggs were parasitized by six scelionid species, Trissolcus basalis (Wollaston), T. thyantae Ashmead, T. brochymenae (Ashmead), T. euschisti (Ashmead), Telenomus podisi Ashmead, Telenomus calvus Johnson, and one encyrtid species, Ooencyrtus sp. T. basalis was the most prevalent parasitoid of N. viridula, parasitizing E. servus and P. maculiventris eggs at low levels. T. podisi, the predominant parasitoid species emerging from eggs of E. servus and P. maculiventris, also parasitized O. p. pugnax eggs exclusively and parasitized N. viridula eggs at low levels. T. euschisti and T. thyantae parasitized E. servus egg masses. T. brochymenae parasitized eggs of both E. servus and P. maculiventris. T. calvus parasitized only P. maculiventris eggs. The same species of egg parasitoids that parasitized naturally occurring eggs of N. viridula and E. servus parasitized sentinel eggs of these bugs, except that no T. calvus and Ooencyrtus sp. were obtained from sentinel eggs, and T. thyantae and T. brochymenae emerged from sentinel eggs of N. viridula. Generally, parasitization of an egg mass was either greater than or equal to predation of sentinel eggs of N. viridula and E. servus. However, on some dates in late June and July, predation of sentinel egg masses was numerically approximately twice as high as parasitism. Results indicate stink bug egg parasitoids and predators are significant factors in the natural biological control of stink bugs in corn fields.

Effects of Native Grass Cover Crops on Beneficial and Pest Invertebrates in Australian Vineyards

Indigenous cover crops have the potential to promote an increase in natural enemies providing fortuitous control of pest species and other ecosystem services. We test this idea in a vineyard in south eastern Australia, where reduced water availability because of drought coupled with increased temperatures has generated interest in sustainable alternatives to the exotic perennial cover crops commonly planted. Three endemic perennial cover crops, comprising the grasses Austrodanthonia richardsonii and Chloris truncata and a mix of two saltbushes (Atriplex semibaccata and Atriplex suberecta) were established as cover crops and compared with introduced oats (Avena sativa). Abundance of a range of predators and parasitoids was higher in vines with native cover crops compared with the oat control. In addition, predation levels of sentinel eggs of a common vineyard pest, light brown apple moth (Epiphyas postvittana), were increased in the native cover crops. However, the native cover crops also increased the abundance of some potential pest species. Native plants therefore have potential to increase abundance of beneficial invertebrates that assist in pest control, but need to be used carefully to ensure that they do not increase local pest problems.