Host Preferences of Telenomus podisi (Hymenoptera: Scelionidae): Parasitism on Eggs of Dichelops melacanthus, Euschistus heros, and Podisus nigrispinus (Hemiptera: Pentatomidae)

The multispecies stinkbug iflavirus Halyomorpha halys virus detected in the multispecies stinkbug egg parasitoid microwasp, Telenomus podisi (Ashmead) (Hymenoptera: Platygastridae)

Wasps are important parasitoids of stinkbugs and frequently exposed to various types of microorganisms through environmental contact and fecal-oral transmission route. Many parasitize stinkbug eggs and are commercially used in the field to control insect population. The parasitoid T. podisi is known for its high parasitism capacity and ability to target multiple species of stinkbugs. In this study we asked whether T. podisi exposed to eggs infected by a multispecies asymptomatic stinkbug virus, the Halyomorpha halys virus (HhV) would get infected. HhV is a geographically distributed multispecies iflavirus previously found to infect four stinkbug hosts, including three Brazilian species, Chinavia ubica, Euschistus heros and Diceraeus melacanthus, and T. posidi can parasitize all of them. As results, RT-PCR screening revealed positive samples for the HhV genome in two out of four tested pools of T. podisi, whereas the antigenome, indicative of replicative activity, was not detected. The wasps were raised in E. heros eggs that presented both the genome and the antigenome forms of the HhV genome. Subsequent RNA-deep sequencing of HhV positive T. podisi RNA pools yielded a complete genome of HhV with high coverage. Phylogenetic analysis positioned the isolate HhV-Tp (isolate Telenomus podisi) alongside with the stinkbug HhV. Analysis of transcriptomes from several hymenopteran species revealed HhV-Tp reads in four species. However, the transmission mechanism and the ecological significance of HhV remain elusive, warranting further studies to illuminate both the transmission process and its capacity for environmental propagation using T. podisi as a potential vector.

Ecological zoning of Euschistus heros in Brazil based on the net reproductive rate at different temperatures and relative-humidity levels

The Neotropical brown stink bug, Euschistus heros (Fabricius, 1798) (Hemiptera: Pentatomidae), is one of the major insect pests in soybean crops, causing severe damage; however, some aspects of its biology that are essential for management remain unknown. To aid in the management of E. heros, the present study investigated the fertility life table of this species at 7 temperatures (18, 20, 22, 25, 28, 30, and 32 ± 1 °C) and 4 relative-humidity levels (30, 50, 70, and 90 ± 10%). Based on the net reproductive rate, R0, we developed an ecological zoning for this pest in Brazil, to identify climatically favorable areas for population growth. Our results indicated that the most favorable range is between 25 and 28 °C and above 70% RH. The ecological zoning indicated that farmers should be more concerned in the northern and Midwest regions, which include the state of Mato Grosso, the largest soybean and corn producer in Brazil. These results provide valuable information, indicating the hotspots most likely to be attacked by the Neotropical brown stink bug.

Emergence Response of Telenomus podisi (Hymenoptera: Scelionidae) to Field Temperature Originated from Colonies Reared at Different Temperature Regimes

We studied the impact of field temperature on the emergence of Telenomus podisi Ashmead (Hymenoptera: Scelionidae) after being released as either protected (encapsulated) or unprotected pupae close to adult emergence. Two independent bioassays (protected pupae vs. unprotected pupae) were carried out in a randomized block experimental design in a 2 (parasitoid rearing temperature regimes) ×4 (release positions within plant canopy) factorial scheme. One of the T. podisi colonies was reared at a constant temperature (25 °C) and 12:12 h L:D (Light: Dark) photoperiod. The second T. podisi colony was reared at fluctuating temperatures (20 °C during 12 h D and 30 °C during 12 h of L). Each bioassay had five replicates. Each replicate contained 40 pupae from each rearing temperature and release position within plant canopy. Parasitoid pupae were released in the bottom third, middle third, or upper third of the plant's canopy, as well as between planting lines. Each bioassay was repeated six times (in different plant developmental stages: R₁, R₂, R_3, R₄, R₅ and R₆). There was no difference in emergence of parasitoids between colonies reared at different temperatures after exposure to field conditions. Emergence of T. podisi was reduced after pupae exposure to temperatures above 35 °C in the field, regardless of the rearing temperature. Telenomus podisi tolerates temperature fluctuations for emergence as long as they fit the optimal range (20 to 30 °C).

Optimizing Mass Rearing of the Egg Parasitoid, Telenomus podisi, for Control of the Brown Stink Bug, Euschistus heros

The parasitoid Telenomus podisi Ashmead, 1893 is used in biological control programs in Brazil against eggs of Euschistus heros (Fabricius, 1798), a key pest of soybean, Glycine max (L.) Merr. To optimize the mass production of parasitoids, artificial diets and storage of host eggs at low temperatures have been developed; however, direct comparisons of the effects of these conditions have not occurred. We assessed a double factorial arrangement composed of six treatments (fresh or cryopreserved E. heros eggs from adults fed on natural or two artificial diets). We evaluated the biological characteristics and parasitism capacity of T. podisi produced from these treatments across seven temperatures. The thermal range between 21 and 30 °C resulted in satisfactory daily parasitism in all treatments tested, with an inverse relationship between temperature and female survival. The best parasitoid biological parameters were found between 21 and 27 °C, where all tested diets supported T. podisi development, with the best results from artificial diets. Fresh eggs and those frozen in liquid nitrogen and stored at -196 °C until use supported parasitoid development. These results suggest that the best method to mass rear T. podisi is to use artificial diets to rear E. heros and store eggs until needed, and then rear parasitoids at 24 °C.

Release strategies of Telenomus podisi for control of Euschistus heros: a computational modeling approach

BACKGROUND

The egg-parasitoid wasp Telenomus podisi has received attention as a biological-control agent for one of the most important soybean pests in Brazil, the stink bug Euschistus heros. As yet, no studies have conclusively established strategies for the release of T. podisi. We developed a computational model using cellular automata in the C programming language to investigate release strategies for T. podisi in soybean crops, in order to optimize the use of these wasps in managing E. heros, assuming a two-dimensional grid of cells corresponding to a soybean field.

RESULTS

The release strategies capable of maintaining an E. heros population below the Economic Threshold level involved releasing a total of at least 15 000 female parasitoids per hectare, in three or four releases of 5000 or more (equivalent to approximately 7142 or more male and female parasitoids per hectare, assuming a sex ratio of 0.70). A 25-m spacing between release points or strips was indicated. The model is very sensitive to the variation in the number of parasitoids per release and in the number of releases, but little sensitive to the release mode and spacing values.

CONCLUSION

The theoretical results produced by the computational model are expected to guide future field studies to improve T. podisi release plans for managing E. heros in soybeans. Therefore, we recommend the release strategy of three to four releases of 5000 or more female parasitoids per hectare, at points or strips spaced 25 m apart, to be tested in field experiments for proper implementation by producers. © 2022 Society of Chemical Industry.

Biology of Glyphepomis dubia Campos & Souza, 2016 (Hemiptera: Pentatomidae) and the parasitoids Telenomus podisi Ashmead, 1893 and Trissolcus basalis (Wollaston, 1858) (Hymenoptera: Platygastridae) on rice

The life cycle of stink bug, Glyphepomis dubia and the development of two egg parasitoids (Telenomus podisi and Trissolcus basalis) were studied at the Federal University of Maranhão, at 26 ± 2oC, relative humidity (RH) of 60 ± 10% and 12h photophase. Individuals used in the study were collected from seven rice fields located around the municipality of Arari, Maranhão, Brazil, and maintained in greenhouse and laboratory for the life cycle studies. From egg to adult, G. dubia took 35.2 days to complete the life cycle. The oviposition period was 37 days, with egg masses of about 12 eggs each and viability of 93.1%. Longevity was 53 and 65 days for females and males, respectively. The egg parasitoids Te. podisi and Tr. basalis parasitized and developed in G. dubia eggs; however, the biological characteristics of Tr. basalis were affected. Emergence of the parasitoids was higher for Te. podisi (83.5%) compared to the records for Tr. basalis (50.4%). Therefore, G. dubia may potentially achieve a pest status and Te. podisi is a promising biological control agent for G. dubia management in Brazil due to its higher longevity and better reproductive parameters.

Preempting the Arrival of the Brown Marmorated Stink Bug, Halyomorpha halys: Biological Control Options for Australia

The brown marmorated stink bug Halyomorphahalys (Stål) (Hemiptera: Pentatomidae) is native to Northeast Asia, but has become a serious invasive species in North America and Europe, causing major damage to crops. While it has not established itself in Australia, it has been intercepted at the border several times, indicating that future incursions and establishment are a case of when, not if. Biological control is one of the few control options for this species and will be important for managing H.halys should it become established in Australia. Prioritizing species that could be used as biological control agents would ensure Australia is prepared. This study summarizes the literature on natural enemies of H. halys in its native and invaded ranges and prioritizes potential biological control agents of H.halys that could be used in Australia. Two egg parasitoid species were identified: Trissolcusjaponicus (Ashmead) and Trissolcusmitsukurii (Ashmead) (Hymenoptera: Scelionidae). Future efforts to develop biological control should focus on T. mitsukurii, as it is already present in Australia. However, little is known about this species and further work is required to: (1) assess its potential effectiveness in parasitizing H. halys, (2) determine its current distribution and (3) host range in Australia.

Intrinsic Interspecific Competition Between Telenomus podisi and Trissolcus teretis (Hymenoptera: Scelionidae)

The competition between Telenomus podisi Ashmead and Trissolcus teretis (Johnson) parasitizing eggs of Diceraeus melacanthus (Dallas) and Euschistus heros (Fabricius) was studied in three different laboratory bioassays to gather knowledge in order to improve stink bug management and to strengthen the preservation of naturally occurring parasitoid species. The impact of parasitoid sequence and time intervals (4 to 192 h) between parasitoid species was evaluated. Competition of Te. podisi and Tr. teretis for the same host favored the parasitoid encountering the egg host first, as it usually outcompetes the second parasitoid. We conclude that it is unwarranted in a short-term goal to release both species together in augmentative biological control programs since the repeated release of Te. podisi led to higher parasitism than any other studied variation of parasitoid sequence. However, simultaneous release of multiple species could be important to help the preservation of the diversity of scelionids in the agroecosystem, a hypothesis that needs to be further investigated in future research.

Biological characteristics of Trissolcus urichi (Crawford) (Hymenoptera: Scelionidae) on Euschistus heros (Fabricius) and Dichelops melacanthus (Dallas) (Hemiptera: Pentatomidae) Eggs

Species of the genus Trissolcus are effective as egg parasitoids of Euschistus heros and can potentially be used in a multispecies pest management approach. However, in order to successfully use those biocontrol agents in the field, previous detailed knowledge about their life history are necessary. Therefore, we evaluate some biological characteristics of Trissolcus urichi on Euschistus heros and Dichelops melacanthus eggs. Three independent experiments were performed: (1) T. urichi host preference between E. heros and D. melacanthus eggs. (2) T. urichi eggs-adult period (days), number of parasitized eggs in 24 h, emergence rate (%) and sex ratio of the parasitoid in E. heros and D. melacanthus eggs. (3) Morphometric characteristics of T. urichi grown on E. heros and D. melacanthus eggs. Trissolcus urichi preferred to parasitize E. heros eggs, exhibiting a higher number of parasitized eggs, higher rate of emergence (%) and faster development, as well as producing progeny of larger size than the parasitoids emerged from eggs of D. melacanthus in relation to body length, wing length and width. Thus, it can be concluded that T. urichi had better performance on E. heros eggs, although the parasitoid had also acceptable parasitism capacity and development in D. melacanthus eggs.

Susceptibility of Euschistus heros and Dichelops furcatus (Hemiptera: Pentatomidae) to Selected Insecticides in Brazil

Euschistus heros (Fabricius, 1798) and Dichelops furcatus (Fabricius, 1775) are key pests of agricultural crops in Brazil. Chemical insecticides are the main control tactic used against these species. Here, we investigated the susceptibility of E. heros and D. furcatus from distinct regions to the mains insecticides used to stink bugs control in Brazil. Field populations of these species were collected throughout the 2017-2019 crop seasons and insects were exposed to insecticides in dip-test bioassays using fresh green bean pods. Populations of E. heros exhibited low variation in the susceptibility to acephate (LC50 = 172.2 to 1,008 µg a.i. per ml), and thiamethoxam (LC50 = 28.8 to 433.9 µg a.i. per ml); resistance ratios were less than 5.9- and 15.1-fold, respectively. In contrast, these populations had higher variation in the susceptibility to bifenthrin (LC50 = 26.7 to 636.1 µg a.i. per ml) and lambda-cyhalothrin (LC50 = 10.0 to 636.1 µg a.i. per ml); resistance ratios reaching 23.8- and 63.6-fold, respectively. Susceptibility monitoring data indicated a higher susceptibility of E. heros to the manufacturers field-recommended rates of acephate, lambda-cyhalothrin + thiamethoxam, and bifenthrin + acetamiprid than lambda-cyhalothrin. Populations of D. furcatus exhibited low variation in the susceptibility to acephate (LC50 = 219.2 to 614.1 µg a.i. per ml), bifenthrin (LC50 = 62.8 to 197.4 µg a.i. per ml), and lambda-cyhalothrin (LC50 = 189.5 to 2,538 µg a.i. per ml); resistance ratios were less than 13.4-fold. In summary, populations of E. heros are less susceptible to pyrethroids, while populations of D. furcatus have similar susceptibility to the insecticides evaluated.

Effect of the Ages of Parasitoid and Host Eggs on Telenomus podisi (Hymenoptera: Platygastridae) Parasitism

This study investigates the influence of parasitoid age and egg age of the hosts Euschistus heros (Fabricius) and Dichelops melacanthus (Dallas) on parasitism of Telenomus podisi Ashmead. Six separate bioassays were conducted: parasitism on eggs of E. heros (bioassay 1) and D. melacanthus (bioassay 2) by T. podisi females of different age (1, 5, and 10 days old); parasitism by T. podisi on eggs of different age (1, 2, 3, 4, and 5 days of embryonic development) of the hosts E. heros (bioassay 3) and D. melacanthus (bioassay 4); preference of T. podisi females for eggs at different embryonic developmental stages (eggs of 1, 2, 3, 4, and 5 days) of the hosts E. heros (bioassay 5) and D. melacanthus (bioassay 6). The age of T. podisi females and their hosts affected parasitism on both E. heros and D. melacanthus eggs. Overall, the parasitism rate was higher in older than younger parasitoids, independent of the tested host species, and host eggs between 1 and 3 days old were similarly parasitized. Thus, in T. podisi mass rearing facilities, it is recommended to use older adults (5 to 10 days old) as mother wasps to increase parasitism on the offered eggs. In addition, when hosts are completely absent in the field, or climatic conditions are unfavorable for release, mass-reared adults can be kept in the laboratory (25°C) for up to 10 days for later release in the field without any impairment of their subsequent parasitism performance.

Performance of Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) on eggs of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae)

Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) is a polyphagous pest with a wide geographic distribution. This pest first arrived in Brazil in 2013, and since then studies on possible control methods for it have been necessary. A possible method for the control of H. armigera is using the egg parasitoid Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae). Therefore, the objective of this study was to evaluate the performance of T. pretiosum on H. armigera eggs, which are known to represent suitable hosts for the development of this parasitoid species in the laboratory. Parasitism and emergence rates and the duration of the egg-to-adult period of T. pretiosum were investigated following 24- and 48-h exposures of this parasitoid to H. armigera and Corcyra cephalonica (Stainton) (Lepidoptera: Pyralidae) eggs. The longevity of offspring after the 24-h exposure was studied, as well as the frequency of parasitism and emergence, host preference, and the emergence of offspring from eggs of different ages or oviposited by lepidopterans on different days. Parasitism was 14.4 and 34.9% more frequent on C. cephalonica than on H. armigera after 24 and 48 h of exposure, respectively. In C. cephalonica, parasitism was 27.2% higher after 48 h. Parasitism was more frequent on C. cephalonica eggs collected on the second day of oviposition (76.2%), and on H. armigera on the third day of oviposition (71.1%). Parasitism frequency was lower on 2-day-old C. cephalonica eggs (63.3%) and on 3-day-old H. armigera eggs (41.3%). When tested with a chance of choice between hosts, T. pretiosum preferred H. armigera, while in the test with no chance of choice there was no difference in preference. Thus, T. pretiosum may be considered a tool for the Integrated Pest Management (IPM) of H. armigera.