Influence of Landscape Diversity and Composition on the Parasitism of Cotton Bollworm Eggs in Maize

We deployed >50,000 Helicoverpa armigera eggs in maize fields to assess the rate of parasitism by Trichogramma chilonis across 33 sites during a three-year span (2012–2014) in northern China. Subsequently, we used a partial least squares (PLS) regression approach to assess the relationship of landscape diversity with composition and parasitism potential. The parasitism rate of H. armigera eggs by T. chilonis ranged from 0–25.8%, with a mean value of 5.6%. Landscape diversity greatly enhanced parasitism at all four different spatial scales (0.5, 1.0, 1.5 and 2.0 km radius). Both the proportion of arable area and the total planting area of two major crops (cotton and maize) had a negative correlation to the parasitism rate at each scale, whereas parasitism was positively correlated to the proportion of host crops of H. armigera other than cotton and maize at the 0.5 to 2.0 km radius scales as well as to that of non-crop habitat at the 0.5 and 1.0 km radius scales. The study indicated that maintaining landscape diversity provided an important biocontrol service by limiting H. armigera through the egg parasitoid T. chilonis, whereas rapid agricultural intensification would greatly reduce the presence and parasitism of T. chilonis in China.     

Evaluation of an endosulfan tolerant strain of <Emphasis Type="Italic">Trichogramma chilonis</Emphasis> on cotton

The performance of an endosulfan tolerant strain of Trichogramma chilonis Ishii was evaluated against Helicoverpa armigera (Hübner) eggs on cotton plants in a net house. Under pesticide pressure, the tolerant strain could provide significantly higher parasitism in comparison to the susceptible strain. The parasitoid adult emergence was also significantly higher in the treatment with the tolerant strain in comparison to the susceptible strain, when parasitoids were released within 3 days of endosulfan spraying. Release of the tolerant strain of T. chilonis in conjunction with endosulfan spray application resulted in significantly higher pest mortality in comparison to the endosulfan treatment or release of T. chilonis alone. It could be inferred from the results that T. chilonis should be released only 3 days after endosulfan spray application as during the first 3 days after the spraying, endosulfan provided the required protection and adversely affected the performance of the parasitoid.     

Effects of host-egg ages on host selection and suitability of four Chinese Trichogramma species,egg parasitoids of the rice striped stem borer,Chilo suppressalis

The striped stem borer, Chilo suppressalis (Walker), is one of the most economically important rice pests worldwide. However, biological control of this pest using natural-enemy insects has been rarely documented to date. With the objective of screening suitable candidate species for controlling the striped stem borer, we investigated the effect of the age of host eggs on the host selection and suitability by four indigenous Trichogramma species on their native host, C. suppressalis. The results indicated that the differently aged eggs of C. suppressalis were all accepted by T. japonicum, T. dendrolimi and T. chilonis, and there was a clear tendency to parasitize older eggs less under no-choice and choice conditions. The number of parasitized host eggs by T. ostriniae also decreased with the increasing host age in the no-choice test, but more 2-day-old host eggs were parasitized in the choice test. When 0-, 2-day-old eggs were offered, T. dendrolimi, T. japonicum and T. chilonis exhibited similar parasitism ability, whereas T. ostriniae appeared to have a stronger ability to attack the older host eggs (4-day-old). Trichogramma japonicum developed and emerged on parasitized C. suppressalis eggs of all ages tested, while showing a better adaptation to younger host eggs with significantly faster developmental time, higher survival and more female progeny on 0-day-old eggs. No adults for each of the other three Trichogramma species emerged from parasitized 4-day-old host eggs, and they had similar developmental time, survival and female progeny on parasitized 0-, 2-day-old host eggs with an exception of female progeny for T. chilonis. On 0-day-old host eggs, T. japonicum developed faster and T. ostriniae had lower progeny survival than the other three Trichogramma species evaluated, respectively. The current study provides useful information to select suitable Trichogramma species for controlling the striped stem borer, C. suppressalis.     

The Effectiveness of Trichogramma chilonis,Trichogramma pretiosum and Trichogramma brasiliense (Hymenoptera: Trichogrammatidae) as Parasitoids of Helicoverpa armigera (Lepidoptera: Noctuidae) on Sunflower (Helianthus annuus) and Redgram (Cajanus cajan)

The performance of three species of trichogrammatids on the pest, Helicoverpa armigera was evaluated in the laboratory and screenhouse conditions in Karnataka, India during 1996-97. Laboratory studies indicated that Trichogramma chilonis and Trichogramma pretiosum were more effective parasitoids of H. armigera than Trichogramma brasiliense. In screenhouse conditions, T. chilonis was the most effective parasitoid of H. armigera eggs on sunflower plants in comparison to the other two trichogrammatid species. When releasing 50?000 per ha on sunflower and redgram, T. chilonis parasitised 50.1 and 11.4% H. armigera eggs, respectively. The position of H. armigera eggs on different plant parts of sunflower had no effect on parasitism by T. chilonis. However, parasitism by the same trichogrammatid among different plant parts of redgram varied significantly. It parasitized 43.4 and 18.7% H. armigera eggs on leaves and flowers, respectively, and significantly fewer, 3.9%, on pods (P&lt;0.05). The growth stage of redgram plants also had an effect on parasitism by T. chilonis, parasitism being extremely low on plants with pods.     

Functional response of Trichogramma chilonis to Galleria mellonella and Chilo sacchariphagus eggs

A biological control programme using inundative releases of Trichogramma chilonis Ischii (Hymenoptera: Trichogrammatidae) reared on Galleria mellonella L. (Lepidoptera: Pyralidae) is currently underway to reduce infestations of Chilo sacchariphagus Bojer (Lepidoptera: Crambidae) in sugarcane, Saccharum spp., on Réunion Island. To assess the potential of the parasitoid as an inundative biocontrol agent, the functional response of three T. chilonis strains was tested with G. mellonella and one strain with C. sacchariphagus host eggs in glass tubes in the laboratory. The shape of the functional response (type II or III) was determined using logistic regression, and attack coefficients and handling times (T_h) were determined using non‐linear least‐square regression. The behaviour of all three strains with G. mellonella host eggs corresponded to a type III response. The St Benoît T. chilonis strain had a significantly shorter estimate of T_h than the St Pierre strain (P<0.05) and may, therefore, be more appropriate as a biocontrol agent. The functional response with C. sacchariphagus host eggs was a type II with the St Benoît T. chilonis strain. More T. chilonis wasps developed per host egg from the larger C. sacchariphagus host eggs (2.9) relative to G. mellonella (1.1). Superparasitism at low host egg densities was, therefore, likely to have been less frequent with C. sacchariphagus. Black eggs were chosen as an estimate of number of eggs parasitized, although they represent the number of eggs where parasitism led to complete pupal development. The low rate of detected parasitism at low host densities with G. mellonella eggs may be due to incomplete pupal development due to superparasitism rather than lack of parasitism, thus explaining the type III functional response.     

Comparative assessments of Gonatocerus ashmeadi and the ‘new association’ parasitoid Gonatocerus tuberculifemur (Hymenoptera: Mymaridae) as biological control agents of Homalodisca vitripennis (Hemiptera: Cicadellidae)

Egg age preference, competitive ability, and behavior of Gonatocerus tuberculifemur (‘new association’ parasitoid) and Gonatocerus ashmeadi (‘old association’ parasitoid) were investigated in the laboratory to determine if one species exhibited competitive superiority. When searching concurrently for Homalodisca vitripennis egg masses, G. ashmeadi consistently outperformed G. tuberculifemur by parasitizing 25–53% more eggs under three different experimental systems in the laboratory with varying host densities, egg ages, and exposure times. G. ashmeadi parasitism in control vials containing one parasitoid ranged from 81–97% across all egg ages. G. tuberculifemur in control vials parasitized 60–66% of eggs 1 and 3 days old, and just 18% of eggs 5 days old. G. ashmeadi produced 5–16% more female offspring than G. tuberculifemur for all experimental conditions. In comparison to G. ashmeadi, G. tuberculifemur was observed off leaves with host eggs 20% more frequently and it oviposited 15% less frequently. G. ashmeadi and G. tuberculifemur when confined together allocated ∼1% of behaviors to antennating or aggressively chasing competitors off egg masses, and up to 2% of behaviors to antennating host egg masses and/or ovipositing into eggs from the opposite side of the leaf. These latter behaviors did not occur when parasitoids were confined alone with host eggs.     

Importance of host oviposition pattern and plant size for the selection of Trichogramma strains to control the diamondback moth

The aim of this work was to select a candidate strain of Trichogrammatidae (Hymenoptera: Chalcidoidea) to control the diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae), an important pest of cabbage in Europe. The parasitic efficiency of Trichogramma chilonis Ishii from Japan and Réunion Island, Trichogramma evanescens Westwood from Egypt, Trichogramma ostriniae Pang & Chen from Japan, and Trichogramma semblidis (Aurivillius) from France was studied with sentinel eggs in greenhouse‐grown cauliflower. The percentage of parasitized eggs was measured 1 m from the release point and 3 days after release. Two factors were studied: host‐egg density (three eggs per stem vs. 50 eggs per stem) and plant size (50–100 cm high plants vs. 100–150 cm high plants). Trichogramma evanescens from Egypt achieved the best parasitism. Parasitism efficiency of T. ostriniae from Japan and T. chilonis from Réunion Island was not influenced by egg density. In contrast, parasitism efficiencies of the three other strains were higher at the lower egg density than at the higher egg density. Parasitism efficiency was lower when the plants were bigger, with the exception of T. chilonis from Réunion Island, for which the level of parasitism was not affected by plant size. Thus, T. chilonis from Réunion Island appeared to be the most suitable Trichogramma strain for use in controlling P. xylostella, regardless of the growth stage of the crop. However, T. ostriniae from Japan may also be more suitable for use on cauliflower crops at the early stage of crop development. If potential problems related to the introduction of exotic species are taken into consideration, it is possible to consider the native T. evanescens.     

Impact of Plant Phenolics as Semiochemicals on the Performance of <Emphasis Type="Italic">Trichogramma chilonis</Emphasis> Ishii

Phenolic compounds play a major role in the plant defense mechanisms and often offer protection from the feeding herbivore. They also constitute a major chemical component of many agriculturally important crops. We examined the effects of 23 common phenolic acids on the orientation and ovipositional behavior of the egg parasitoid, Trichogramma chilonis Ishii (Hymenoptera: Trichogrammatidae). The study was conducted in order to investigate the function of these compounds in the plant indirect defense. Parasitoids attractions towards the phenolics that are volatile in nature were observed by using culture tube bioassays. In addition in the Y- tube olfactometer experiments, T. chilonis were shown to be attracted towards the treatments of syringic, pyrocatechol, coumaric and quercetin at minimum dose of 10 μg and genistein, chlorogenic, vanillic, chlorobenzoic, sinapic, ellagic, protocatechuic, keampferol, tannic, caffeic, and luteolin at 30 μg and ferulic, epicatechin and gallic acid at 50 μg doses. Further experiments to examine the effect of phenolic compounds on parasitization by T. chilonis females were carried out using petri dish and artificial plant models. Among the tested compounds, syringic acid and quercetin recorded the highest percentage parasitization followed by coumaric acid and pyrocatechol. These results might imply that parasitoid attractant phenolic compounds when induced in engineered plants can further be used as cues by the egg parasitoids with potential application in biocontrol strategies.     

Parasitoids of the corn borerOstrinia furnacalis [Lep.: Pyralidae] in the Mariana Islands

A survey of the parasitoids of the Asian corn borer,Ostrinia furnacalis (Guenee), in the Mariana Islands showed that few of the borers were parasitized. Parasitoids were reared from only 30 pupae out of more than 4 500 sampled. Three species of pupal parasitoids were found:Xanthopimpla punctata (F.),Brachymeria albotibialis (Ashmead) andTetrastichus? inferens Yoshimoto. No parasitoids were reared from mature larvae. The only egg parasitoid observed wasTrichogramma chilonis Ishii. During the month prior to the sweet corn harvest, which was the peak period of moth oviposition, about 40% of the egg masses had at least one egg parasitized. An average of about 35% of the eggs within a mass were parasitized.     

Does the Polyphagous Egg Parasitoid <Emphasis Type="Italic">Trichogramma platneri</Emphasis> Nagarkatti (Hymenoptera: Trichogrammatidae) Display Behavioral Plasticity When Parasitizing Different Hosts?

Trichogramma platneri oviposition behavior on Amorbia cuneana egg masses was investigated under laboratory conditions. No relationship was detected between host surface area, number of edge turning on host eggs, and parasitoid clutch size. It was also observed that females parasitized the egg mass randomly by drilling into the egg mass and parasitizing individual eggs without using stereotypical behaviors to assess individual hosts (i.e. drumming and turning). However, clutch size did change due to ovipositional experience as naïve wasps with little or no ovipositional experience (<6 eggs parasitized), allocated significantly more progeny per host than wasps with longer ovipositional experience (24-h oviposition experience on a single egg mass). Moreover, naïve wasps parasitized significantly more eggs on the outer edge of the egg mass than experienced wasps. We contend that the physical characteristics of A. cuneana eggs and egg masses preclude T. platneri from completely discriminating between individual eggs. However, because T. platneri may be using kairomones from the egg mass, this described oviposition strategy remains effective.     

In vitro rearing ofOoencyrtus pityocampae [Hym., Encyrtidae], an egg parasitoid ofThaumetopoea pityocampa [Lep., Thaumetopoeidae]

Ooencyrtus pityocampae (Mercet) is a polyphagous egg parasitoid, known mainly as an egg parasitoid of the Pine Processionary Caterpillar,Thaumetopoea pityocampa (Denis &; Schiffermüller), a pest of pines in Southern Europe and in the Mediterranean region. Rearing on artificial medium was recently undertaken, and after a large screening of both materials and techniques available for this aim, a PVC film and a medium devoid of insect material were found as suitable for the complete development ofO. pityocampae. The artificial eggs allowed the parasitoid to oviposit and to develop up to the adult stage. Five adults (2 males and 3 females) were obtained. Development was slower than that observed in natural hosts. Two out of three females laid viable eggs in both natural and artificial eggs.     

甘肃陇南地区银杏大蚕蛾卵寄生蜂种类调查

银杏大蚕蛾Caligula japonica（Moore）作为危害核桃、板栗、银杏等坚果类果树的重要害虫之一,已经引起国内外广泛关注。明确银杏大蚕蛾卵期寄生蜂的种类、分布和自然寄生状况,可为银杏大蚕蛾天敌的保护利用提供科学依据。本文于2018-2019年在甘肃省陇南市银杏大蚕蛾核桃危害区采集该害虫的越冬卵并带回实验室培养,收集羽化的寄生蜂并记录其种类和数量,最后通过计算寄生率确定优势天敌物种。本研究共采集银杏大蚕蛾卵块1 114个约8万粒卵,平均单株核桃树木卵块数与卵粒数分别最高可达7.5块和533.5粒;共收集到膜翅目3科5属9种银杏大蚕蛾卵期寄生蜂,其中6种为首次报道;具体为旋小蜂科7种,包括平腹小蜂属4种：麻纹蝽平腹小蜂Anastatus fulloi、甘肃平腹小蜂A. gansuensis、日本平腹小蜂A. japonicus和梅岭平腹小蜂A. meilingensis;短角平腹小蜂属2种：白跗短角平腹小蜂Mesocomys albitarsis和枯叶蛾短角平腹小蜂M. trabalae;旋小蜂属1种：Eupelmus sp.;赤眼蜂科赤眼蜂属1种：螟黄赤眼蜂Trichogramma chilonis;姬小蜂科长尾啮小蜂属1种：短梗长尾啮小蜂Aprostocetus brevipedicellus。结果表明,旋小蜂科两种短角平腹小蜂数量最多,分布最广,物种优势度指数达86以上,为陇南地区野外寄生银杏大蚕蛾卵的优势性天敌,且卵块寄生率和卵粒寄生率分别最高可达55.91%和6.77%。本研究拓宽了银杏大蚕蛾自然天敌种类并为今后开发利用寄生蜂防治该害虫提供了理论依据。     

Isolation of microbes associated with field-collected populations of the egg parasitoid,Trichogramma chilonis capable of enhancing biotic fitness

Four bacterial and one yeast species, cultured and identified as Stenotrophomonas maltophilia, Acinetobacter sp., Pseudomonas sp. and Ochrobactrum sp. and the yeast as Metschnikowia reukaufii, were isolated from the internal organs of four collections of field-sourced egg parasitoid, Trichogramma chilonis, obtained as parasitised Helicoverpa armigera eggs. Bacteria were identified through 16 rRNA amplification and sequencing. The single species of yeast was identified through internal transcribed spacer sequences. A single bacterial species could be isolated from each of the four T. chilonis collections; however, all four T. chilonis collections yielded the yeast, M. reukaufii. In order to study the influence of the association of each of the bacterial species and the yeast, microbe-free laboratory-bred populations of T. chilonis were fed with the individual cultures and fitness parameters as parasitisation vigour and female bias were studied in T. chilonis over 10 generations. T. chilonis fed with either S. maltophilia or Acinetobacter sp. and Pseudomonas sp. showed a mean percent increase in female ratio of 26.2%, 30% and 30.3% and mean percent parasitisation of H. armigera eggs significantly increased by 38%, 32.2% and 31.3%, respectively. However, T. chilonis fed with Acinetobacter sp. did not positively influence the two T. chilonis fitness factors. The ubiquitous yeast, M. reukaufii, which could be isolated from all four collections of T. chilonis, could significantly increase both female count and percent parasitism ratio by 22% and 65%, respectively. This study has opened the possibility of modulating the parasitisation fitness of laboratory-bred T. chilonis, prior to field release, using microbes associated with them in the wild.     

Biological control of insect pests in litchi orchards in China

This paper describes the current state of the biological control of insect pests in litchi orchards in China. Litchi is growing in importance as a fruit in China and the control of litchi stink bug, Tessaratoma papillosa (Drury) (Hemiptera: Pentatomidae) by the solitary egg endoparasitoid Anastatus japonicus (Ashmead) (Hymenoptera: Eulophidae) is an example of successful classical biological control. This review will cover the current economic status of litchi production in China, the challenges faced in litchi pest management, and possible solutions. The review will also focus on research activities and experiences drawn from many years of experimentation and field work by researchers in an attempt to promote biological control and reduce insecticide use to produce healthier food and a safer environment. Studies on the biology and ecology of T. papillosa and its egg parasitoid A. japonicas will be summarized. The adult longevity and long oviposition period, in combination with the short life cycle, high fecundity, and resistance to harsh environmental conditions make this parasitoid ideal for biological control. The straightforwardness of mass-rearing and easy access to high quality factitious host eggs have made it possible to control T. papillosa with this parasitoid in litchi orchards over large areas in China. Both pest and parasitoid have been thoroughly studied, and A. japonicus has been used in the field for control since late 1960s. The introduction of techniques for mass-rearing of A. japonicus and the parasitoid’s efficacy in controlling T. papillosa once released will be discussed. Finally, we will address the problems currently facing litchi pest management and the importance of conservation biological control in the development and implementation of integrated pest management (IPM).     

Sentinel eggs underestimate rates of parasitism of the exotic brown marmorated stink bug,Halyomorpha halys

Native to eastern Asia, the brown marmorated stink bug (BMSB), Halyomorpha halys (Stål), has become a serious invasive pest in North America. Consequently, accurate assessment of parasitism rates under field conditions is critical for determining baseline parasitism rates of native egg parasitoids on BMSB, and for future evaluations of native or exotic parasitoid biological control release strategies and impacts. BMSB sentinel (laboratory-laid) egg masses have typically been used for this purpose, even though they could be providing misleading estimates of parasitoid activity. Accordingly, we compared the use of BMSB sentinel (laboratory-laid) and wild (naturally field-laid) egg masses in 2012 and 2013 to examine rates of parasitism and the parasitoid community composition of indigenous egg parasitoids in outdoor ornamental nurseries. Wild egg masses consistently had higher rates of parasitism than sentinel egg masses. In 2012, wild egg masses had a mean percent parasitism of 28.4% compared to 4.6% in sentinel egg masses, while in 2013 the difference between the two methods increased even further with a mean percent parasitism of 55.3% in wild egg masses compared to 0.8% in sentinel eggs. Furthermore, we found greater total numbers of parasitoids (889, 42) and greater species richness (seven, five), when using wild egg masses compared to sentinel egg masses, respectively. While sentinel egg masses provide a rapid and convenient way to assess the presence of natural enemies, our findings indicate that using sentinel egg masses could dramatically underestimate actual rates of parasitism and provide inaccurate estimates of parasitoid community composition. Future studies should address potential mechanisms underlying these patterns such as lack of certain host cues required by parasitoids in sentinel compared to wild egg masses.     

Effects of storage at low-temperature of various heteropteran host eggs on the egg parasitoid, <Emphasis Type="Italic">Trissolcus semistriatus</Emphasis>

Various heteropteran host eggs stored under two low-temperatures were tested in the laboratory for their usability in the production of sunn pest egg parasitoid, Trissolcus semistriatus. Parasitism, adult emergence rate and development time were assesed on stored and fresh eggs of Eurygaster integriceps, Dolycoris baccarum, Graphosoma lineatum and Eurydema ornatum. Masses of fresh host eggs in microcentrifuge tubes were maintained at +6 °C and −20 °C. Every 30 days, 50 eggs of host species were exposed to parasitism by T. semistriatus. The host eggs stored at 6 °C remained viable to parasitism by T. semistriatus up to 2 months, while those of stored at −20 °C were parasitized at high rates up to 4 months, alhough succesful parasitism rates decrease with time. However, it was indicated that both fresh or stored E. ornatum eggs were not preferred to parasitism by the parasitoid. A longer development time from egg to adult was observed in stored eggs under two tested storage techniques when compared with fresh eggs.     

Age-specific fecundity and life table of Trissolcus semistriatus, an egg parasitoid of the sunn pest Eurygaster integriceps

The effects of temperature on age‐specific fecundity and life table parameters of the egg parasitoid Trissolcus semistriatus (Nees, 1834) (Hymenoptera: Scelionidae) were examined under four constant temperature conditions (17, 20, 26 and 32°C), using eggs of the sunn pest Eurygaster integriceps Puton, 1881 (Hemiptera: Scutelleridae), an important pest of wheat, as hosts. The intrinsic rate of increase increased linearly, while the mean generation time and the doubling time decreased with increases in temperature. The net reproductive rate, however, varied without clear correlation with temperature. Fecundity tended to be higher at higher temperatures. The total number of eggs per female was estimated as 52.0 and 116.4 eggs, respectively, at 17°C and 32°C, with the highest fecundity rate during the first day of oviposition. The oviposition rate fluctuated from 4.4 to 14.3 eggs per day. Oviposition and postoviposition periods and longevity decreased when temperature increased. Maximum longevity for females was 21.6 days at 20°C, and female parasitoids lived longer than males at all temperatures. The development period ranged from 7.1 days (32°C) to 35.6 days (17°C) for males and from 8.4 days (32°C) to 37.2 days (17°C) for females. The development of female T. semistriatus required 166.7 degree‐days (DD) above a theoretical threshold of 11.8°C and the development of males required 142.9 DD above 13.1°C. The numbers of generations per year for female and male T. semistriatus, given the temperature in Tekirdag, Turkey, were estimated to be 9.0 and 8.8, respectively. The potential of the egg parasitoid for the control of E. integriceps is discussed.     

Host performance of Trichogramma species on Opisina arenosella,and evaluation of their biological control efficacy

Five candidate species for biocontrol of Opisina arenosella Walker, a destructive pest of palm trees, were evaluated. To compare host performance, 5 Trichogramma species were allowed to parasitize O. arenosella eggs of different ages and egg densities. The parasitization capacity of two species, T. embryophagum and T. japonicum, were evaluated with respect to adult age. Treatments consisted of field with releases of T. embryophagum or T. japonicum set up in Danzhou, Hainan, and the pest densities was recorded periodically. The results showed that T. embryophagum, T. chilonis, and T. dendrolimi had a strong parasitic ability on 0-day-old O. arenosella eggs. In species comparisons, the parasitism rates of T. embryophagum on 1-day-old and 4-day-old eggs, and T. japonicum on 2-day-old, 3-day-old, and 5-day-old eggs of O. arenosella were significantly higher than those of other Trichogramma species. At densities of 40 and 35 eggs/tube (84.8 cm³), the numbers of eggs parasitized by T. embryophagum and T. japonicum were the highest, at 29.9 and 24.6, respectively. During the first 24-h, the numbers of eggs parasitized by T. embryophagum and T. japonicum were 110.6 and 82.2, accounting for 84.7% and 59.5%, respectively, of the total parasitized eggs. After 2 months releases, the larvae and pupa density of O. arenosella under T. embryophagum and T. japonicun treatment were 0.95 and 0.94 individuals/leaflet, respectively, were significantly lower than untreated control (1.6 individuals/leaflet). These findings encouraged that T. embryophagum and T. japonicun are able to be used for biological control for O. arenosella.     

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 6–7 days, 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.