Development rate and lower temperature threshold in the eggs of Eurygaster integriceps (Heteroptera: Scutelleridae)

The sunn pest, Eurygaster integriceps Put. has a wide distribution in the Palearctic region. It is the most important pest problem of wheat in Turkey. The objective of this study was to attain better knowledge of the development of the sunn pest eggs. The lower temperature threshold and development rate of eggs were determined at 17, 20, 23, 26 and 32°C ± 1°C in the laboratory. A linear model was used to describe the developmental rate and temperature. The egg development required 90.9 degree‐days above the theoretical threshold of 11.7°C. The development time was 17.6 ± 0.1 days at 17°C, and 4.5 ± 0.01 days at 32°C. Incubation time was inversely related to temperature. The study showed that the eggs of E. integriceps needed shorter periods of time to complete their development than immature stages of their parasitoids Trissolcus spp.     

Field oviposition rates and egg load dynamics of pollen beetles (Meligethes aeneus Fab.) (Colepotera: Nitidulidae)

Abstract 1 Egg loads from field collected pollen beetles (Meligethes aeneus Fab., Coleoptera: Nitidulidae) were determined by dissecting beetles caught at the beginning and end of the putative daily oviposition period. Field collected beetles were offered Brassica napus (L.) plants in cages for 8 (morning and early afternoon), 16 (overnight), and 24 h to ascertain the number of eggs laid during these time periods. 2 Most eggs were laid in the morning and early afternoon. The proportion of gravid females was higher at the beginning of the oviposition period than at the end. Most females in the morning carried two eggs, whereas one egg was more common in the afternoon. 3 We hypothesized that the number of eggs laid during the oviposition period would be equivalent to the difference between egg loads at the beginning and end of oviposition. This was not the case; differences in egg loads were significantly lower than number of eggs laid. However, the number of eggs laid was equivalent to the egg load at the beginning of the oviposition period, suggesting that eggs available in the morning are laid during the following day. 4 Population estimates of daily oviposition rates, approximately 0.7 eggs per beetle and day, were close to estimates from laboratory studies when the proportion of gravid females was taken into consideration.     

Oviposition choice by the Onopordum capitulum weevil Larinus latus (Coleoptera: Curculionidae) and its effect on the survival of immature stages

Female Larinus latus lay eggs into the capitula of their Onopordum spp. host plants from the onset of capitulum development until the completion of flowering. This tight linkage between insect life-history and plant development optimised larval survival, apart from some initial asynchrony between the readiness of the females to oviposit and the suitability of the very small capitula to physically support eggs. Eggs were laid on bracts and stems of capitula or directly in the florets, when these became available. Both the location of the egg and time of oviposition influenced mortality factors such as egg and larval parasitism, egg desiccation and larval establishment. Overall, survival of eggs laid later in the season into florets was higher, although the adults that emerged were smaller. The change in choice of oviposition site that occurs at the onset of flowering, not only favours survival, but ensures more efficient resource use by the larvae. This occurs because sequential flowering of Onopordum spp. drives a sequential oviposition pattern and spreads the egg load more evenly over the available capitula, reversing a trend earlier in the season to clump eggs that were laid directly on the bracts. Other potential constraints, such as capitulum size, absolute egg density and previous egg-laying do not play a major role in determining the oviposition pattern of L. latus. Larval survival was positively correlated with capitulum size and not strongly influenced by egg density. Competition for resources only appeared to play a role in smaller capitula, and manifested itself in a reduction in the size of emerging adults rather than the death of immatures. In the absence of strong interspecific competition, the oviposition behavior of L. latus has become geared to maximising resource use for larvae (i.e. its own potential competitiveness) rather than minimising interactions with other members of the capitulum endophage guild.     

Field evaluation of (E)-2-hexenal efficacy for behavioral manipulation of egg parasitoids in soybean

We studied the influence of synthetic (E)-2-hexenal on the abundance of Telenominae aiming to attract parasitoids and enhance stink bug egg parasitism in treated areas. We conducted experiments in 2006, 2007 and 2008 soybean seasons with two short-term (one week) and one long-term (seven weeks) experiment, respectively. We evaluated the abundance of parasitoids with yellow sticky traps and estimated the incidence and intensity of parasitism with sentinel eggs of Euschistus heros Fabricius (Hemiptera: Pentatomidae) or with tulle bags, enclosing laboratory pregnant E. heros as an egg source. In short-term experiments, there was increased abundance of Trissolcus spp. (Hymenoptera: Platygastridae: Telenominae) in treated areas, associated with greater intensity of parasitism. In long-term experiments, treatment with (E)-2-hexenal did not influence the abundance of Telenominae or parasitism levels, but increased egg predation. Applications of (E)-2-hexenal can be used to increase recruitment of Trissolcus spp. in the early flowering stages of soybean and also to attract other natural enemies, but do not increase egg parasitism.     

Trichogramma egg parasitism ofHelicoverpa armigera on short-duration pigeonpea intercultured with sorghum

The levels of egg parasitism byTrichogramma spp. (Hymenoptera: Trichogrammatidae) on populations ofHelicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) were recorded on sorghum (Sorghum bicolor L.) and on two flushes of flowers on short-duration pigeonpea (Cajanus cajan L.).H. armigera oviposition was concentrated on the early flowering stage of sorghum and the flowering and early podding stages of both flushes of pigeonpea. Parasitism on sorghum increased rapidly as egg density increased and reached a peak of 74.6%. Parasitism on pigeonpea was concentrated onH. armigera eggs laid on the first flush of pigeonpea flowers with a maximum of 69.2%. These high levels of parasitism on pigeonpea coincided with the period of parasite activity on sorghum. The levels of parasitism then declined rapidly and only very low levels were detected on a second flush of flowers. This rapid decline resulted in the overall egg mortality caused byTrichogramma on pigeonpea to be low, with a maximum of 7.8% caused by parasitism, compared to 34.4% on sorghum. The pattern of parasitism suggests that a transfer of parasites occurred from sorghum to pigeonpea. The rapid decline of parasitism on the pigeonpea indicates that parasite populations cannot be sustained on pigeonpea once the influx from sorghum stops. The results are discussed in terms of a possible method of encouraging the transfer of parasites from sorghum to short-duration pigeonpea by producing a more continuous cropping environment.     

The introduction and recovery in the United States ofAnaphes diana [Hym.: Mymaridae], an egg parasite ofSitona weevils [Col.: Curculionidae]

Anaphes diana (Girault) (=Patasson lameerei Debauche), a mymarid egg parasite ofSitona spp., was introduced from Europe beginning in 1976 and is now tentatively established in the United States. Techniques are described for the separation of eggs ofSitona spp. from soil, using a series of fine-mesh sieves, water, and a saturated salt solution. Data from 9 years of sampling in an alfalfa field at Newark, Del. (>19,300 host eggs extracted), showed that the mean peak density of viable overwintering eggs ofSitona hispidulus (F.) was 14.6 per 100 cm³ of 1 cm deep surface soil. At the study site,Sitona egg densities consistently increased during the fall as a result of oviposition, peaked during January and February and decreased during the spring as a result of egg hatch. Although the incidence of parasitism byA. diana remained surprisingly low (0.29%), the fact that the species was recovered during 3 years and up to 7 years after the last release, indicates that it has colonized at the Delaware release site.      

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.     

椰子木蛾的产卵节律及其对寄主植物的产卵选择性

【背景】椰子木蛾是近年来新入侵我国棕榈科植物的害虫,研究其产卵习性可为监测和防治该虫提供参考。【方法】在室内条件下,观察、记录了椰子木蛾雌成虫的产卵节律及其对不同寄主植物的产卵选择性。【结果】椰子木蛾最高日产卵量可达34.4粒·头-1,且主要集中在羽化后4 d内产卵,占总产卵量的54.1%;产卵活动主要发生在夜间23:00到次日8:00;在椰子、蒲葵、大王棕、槟榔和散尾葵等寄主植物上的产卵量无显著差异,为89.3~147.7粒·头-1,但产卵位置存在差别。【结论与意义】椰子木蛾雌成虫具有较强的繁殖能力和产卵节律性,且在不同寄主植物上的产卵量一致。     

Host preference: parasitism, emergence and development of Trissolcus semistriatus (Hym., Scelonidae) in various host eggs

Abstract: Trissolcus semistriatus is an important egg parasitoid of the sunn bug, Eurygaster integriceps. Conservation and the supportive augmentation of populations of egg parasitoids appears to offer high potential for the biological control of sunn bug in an integrated pest management system. The present study was conducted to determine the host preference of T. semistriatus on various heteropteran host eggs. When each host species was examined separately, the eggs of E. integriceps, Dolycoris baccarum, Graphosoma lineatum, Carpocoris pudicus and Holcostethus vernalis, were parasitized at high levels, namely 88.0, 83.6, 94.8, 87.3 and 80.8%, respectively, whereas a smaller portion of Eurydema ornatum eggs were parasitized (24.0%). There was no parasitism in Nezara viridula eggs by T. semistriatus. Similar high rates were recorded for the percentage of adult emergence in each host species, with the exception of E. ornatum. The average development time was shorter for males than for females. The average development period for both male and female was significantly longer in eggs of E. ornatum than in those of the other host species. These results and observations recorded during the experiments showed that G. lineatum and D. baccarum were available, cheap hosts and it was demonstrated that these hosts could be used for the mass production of egg parasitoids.     

Effect of induced tolerance to Bt toxin on the egg size of Helicoverpa armigera and parasitism by Trichogramma pretiosum

Larvae of Helicoverpa armigera (Hübner) can develop a form of Bt tolerance after exposure to sub‐lethal doses of Bt‐toxin subclass Cry1Ac. Increasing levels of tolerance are produced over generations of larval exposure, which are not related to DNA sequence changes, and are largely maternally transmitted. The characteristic of maternal transmission, combined with the importance of egg parasitoids to cotton pest management, raises questions about the effects of Bt tolerance/exposure on the eggs of H. armigera and on some key metrics of egg parasitism. In the present study, the effect of inducible tolerance on eggs of H. armigera and parasitism by Trichogramma pretiosum (Riley) is investigated. First, the volumes of eggs laid by susceptible and tolerant H. armigera females are compared. In addition, the effect of inducible tolerance on egg parasitism is determined by comparing parasitism success, the number of adult wasps emerged per host egg, and the proportion of male and female offspring emerged per host egg. The results obtained suggest that Cry1Ac‐tolerance is associated with increased egg volume, even after just one generation of sub‐lethal exposure. When tolerant H. armigera are freed from ongoing sub‐lethal exposure, a corresponding decrease in egg volume is not detected. Although there is no difference in the percentage of eggs parasitized, there is an increase in the number of emergent parasitoids, especially males, from eggs laid by tolerant H. armigera. These results confirm that maternally‐transmitted Bt tolerance is reflected in the phenotype of the eggs of tolerant offspring, which affects egg parasitism.     

Determination of Homalodisca coagulata (Hemiptera: Cicadellidae) egg ages suitable for oviposition by Gonatocerus ashmeadi, Gonatocerus triguttatus, and Gonatocerus fasciatus (Hymenoptera: Mymaridae)

Homalodisca coagulata (Say) (Hemiptera: Cicadellidae) eggs 1–10 days of age were exposed to Gonatocerus ashmeadi Girault, Gonatocerus triguttatus Girault, and Gonatocerus fasciatus Girault (all Hymenoptera: Mymaridae) in no choice laboratory trials to investigate egg age utilization and to determine which egg ages are vulnerable to attack by these three parasitoids. The H. coagulata egg ages that were most suitable for oviposition by G. ashmeadi, G. triguttatus, and G. fasciatus were eggs 3, 4, and 2 days of age, respectively. Egg ages least suitable for parasitoid development were 6–10 days for G. ashmeadi (resulting in <50% parasitism), 1–2 and 7–10 days for G. triguttatus (resulting in <25% parasitism), and 3–10 days for G. fasciatus (resulting in <11% parasitism). Pooling parasitism data across all egg ages showed that parasitism by G. ashmeadi was 12.9 and 28.5% higher compared with G. triguttatus and G. fasciatus, respectively, and G. triguttatus resulted in 15.6% higher percentage parasitism compared with G. fasciatus. Egg age had a significant effect on the percentage of female G. ashmeadi offspring produced, but this was not significant for G. triguttatus, and low G. fasciatus parasitism prevented statistical analyses for comparisons. Results from tests where females were offered a choice for oviposition between eggs 1, 3, and 5 days of age demonstrated that G. ashmeadi and G. triguttatus showed no significant oviposition preference, while percentage parasitism by G. fasciatus was 29.4 and 7.4% higher when females were presented eggs 1 and 3 days of age, respectively, compared with eggs 5 days of age. Choice tests indicated that an overlap in egg age suitability for oviposition exists between G. ashmeadi, G. triguttatus, and G. fasciatus, and that interspecific competition for eggs 1, 2, and 3 days of age may occur in the field environment.     

Synchronization of laying by great spotted cuckoos and recognition ability of magpies

Brood parasites rely entirely on the parental care of host species to raise the parasitic nestlings until independence. The reproductive success of avian brood parasites depends on finding host nests at a suitable stage (i.e. during egg laying) for parasitism and weakly defensive (i.e. non‐ejector) hosts. Finding appropriate nests for parasitism may, however, vary depending on ecological conditions, including parasite abundance in the area, which also varies from one year to another and therefore may influence coevolutionary relationships between brood parasites and their hosts. In this scenario, we explored: 1) the degree of laying synchronization between great spotted cuckoos Clamator glandarius and magpies Pica pica during two breeding seasons, which varied in the level of selection pressure due to brood parasitism (i.e. parasitism rate); 2) magpie responses to natural parasitism in the pre‐laying period and successfulness of parasitic eggs laid at this stage; and 3) magpie responses to experimental parasitism performed at different breeding stages. We found that, during the year of higher parasitism rate, there was an increase in the percentage of parasitic eggs laid before magpies started laying. However, the synchronization of laying was poor both years regardless of the differences in the parasitism rate. The ejection rate was significantly higher during the pre‐egg‐laying and the post‐hatching stages than during the laying stage, and hatching success of parasitic eggs laid during the pre‐egg‐laying stage was zero. Thus, non‐synchronized parasitic eggs are wasted and therefore poor synchronization should be penalized by natural selection. We discuss four different hypotheses explaining poor synchronization.     

Responses of native egg parasitoids to the invasive seed bug Leptoglossus occidentalis

1. The Western conifer seed bug Leptoglossus occidentalis, a native insect of North America, was accidentally introduced in Europe in the late 1990s. Since then, it has spread rapidly. Biological control could provide an efficient management option but natural enemies of the pest have been poorly examined in Europe.
2. In this study, we exposed sentinel egg masses and collected naturally laid egg masses in southern France in 2016 and 2017, to identify the egg parasitoids of L. occidentalis and investigate their potentials.
3. Three egg parasitoids were detected: Anastatus bifasciatus, Ooencyrtus pityocampae and Ooencyrtus telenomicida. The overall parasitism was low compared to that observed in the native range with 6.4% of all eggs being parasitized, while 17.1% of egg masses carried at least one parasitized egg. The total number of parasitized egg masses was similar between parasitoid species, but the mean number of parasitized eggs per egg mass was highest for A. bifasciatus (5.57 vs. 1.25 for Ooencyrtus spp.).
4. Sentinel egg masses underestimated the parasitism compared to natural egg masses (respectively, 1.42% and 7.71%).
5. Our results suggested that the three generalist parasitoids detected can respond in a Leptoglossus egg density-dependent manner, but this requires further investigations.

     

Parasitism of frozen Halyomorpha halys eggs by Trissolcus japonicus: applications for rearing and experimentation

The brown marmorated stink bug, Halyomorpha halys (Stål), has become a well-known pest to growers and homeowners since its 1996 introduction to the United States. A classical biocontrol programme is under development using the egg parasitoid Trissolcus japonicus. Widespread implementation of biocontrol requires efficient mass rearing, which is constrained by the availability of fresh H. halys eggs. In this study, parasitism rate, developmental time, sex ratio and size were compared between wasps reared on fresh versus frozen, newly laid (<1 d old) versus variably aged (0–3 d old), and frozen egg masses stored ≤4 y. Frozen eggs yielded 56–65% fewer wasps, with parasitism rate decreasing 1–3% per month stored. Parasitism rate, sex ratio and developmental time were comparable between newly laid and variably aged eggs. Freezing eggs for any duration did not affect sex ratio or weight of emerged wasps, but delayed emergence 5–6 d. To simulate deployment of sentinel eggs in the field, we incubated frozen eggs at 20°C and 30°C for 1–9 d before exposing them to T. japonicus, then evaluated parasitism trends. Trissolcus japonicus parasitism rate decreased 5–8% per day incubated, unhatched wasps increased 9% per day incubated and sex ratio was not impacted. Variably aged, frozen and longer stored eggs can be used for T. japonicus rearing and experimentation without affecting emerged wasp sex ratio or size within one generation, but have lower parasitism and slower development. Frozen sentinel eggs are effective <3–5 d, especially in hot conditions.     

Reproductive properties of two sympatric dung beetles,Aphodius haroldianus andA. Elegans (Coleoptera: Scarabaeidae)

1. Reproductive properties of two sympatric dung beetles, Aphodius haroldianus and A. elegans, were studied at a pasture in the central Japan.
2. Overwintered adults of A. haroldianus came flying to dung pats from May to early August and bred from June to July. A. elegans overwintered as larvae, new adults came to dung pats from mid May to mid June. After aestivation, they reproduced from October to November.
3. A. haroldianus was a species with low fecundity and large food reserve for larvae. Female of this species had short duration of residence and laid fewer number of eggs in one dung pat. On the other hand, A. elegans was a species with high fecundity and small food reserve for larvae. Female of this species had long duration of residence and laid larger number of eggs in one dung pat.
4. The daily egg production in A. haroldianus reached a peak (0.40 eggs/female/day) at middle of oviposition period, but, that in A. elegans reached a peak (6.49 eggs/female/ day) at the beginning of oviposition period. The mortality of A. haroldianus female occurred after the daily egg production reached a peak and then rapidly increased, whereas that of A. elegans began soon after the beginning of oviposition and then gradually increased.

     

Seasonal history,plant interactions and egg parasitism of the variegated caper bug Stenozygum coloratum Klug (Heteroptera: Pentatomidae)

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<Emphasis Type="Italic">Fopius arisanus</Emphasis> oviposition in four <Emphasis Type="Italic">Anastrepha</Emphasis> fruit fly species of economic importance in Mexico

We studied the oviposition performance of Fopius arisanus (Sonan) (Hymenoptera: Braconidae) attacking eggs of four fruit flies of the genus Anastrepha Schiner (Diptera: Tephritidae) under laboratory conditions. The complete process of oviposition on an individual egg of Anastrepha ludens (Loew) lasts in average 85.4 ± 2.9 s, including a tremor (25.8 ± 1.03 s) observed in the middle of this process related to the egg’s descent. The average parasitism of A. ludens egg was 60.9 ± 7.5%, with only 1.2% of superparasitized eggs. During individual acts of oviposition, we noted that F. arisanus possesses a highly flexible ovipositor that curves easily as it searches for additional suitable eggs, which may be of particular benefit when a female finds large clutches of eggs. The individual oviposition of F. arisanus in host fruits attacked by Anastrepha spp. varies with the egg clutch size of each fruit fly species: A. serpentina laid the biggest egg clutches (21.3 ± 1.4), followed by A. ludens (14.2 ± 0.9), and A. striata (1.0 ± 0.0) (=A. obliqua). The time spent by F. arisanus in individual ovipositions was parallel to these findings, reinforcing the idea that F. arisanus attacks several eggs in each individual insertion of its ovipositor. Neither formal oviposition acts, nor adult emergences of F. arisanus were registered in A. obliqua. We discuss the potential of F. arisanus as natural enemy of fruit flies of the genus Anastrepha, and explore the eventual developing of its mass rearing. Handling Editor: Torsten Meiners.     

Oviposition in Triatoma protracta: Role of mating and relationship to egg growth

Yolk deposition begins in the terminal oocytes of virgins of Triatoma protracta a few days after adult eclosion, and while a few eggs may be matured before vitellogenesis ceases, none are laid. Mating at day four stimulates egg maturation and oviposition in fed and unfed females, egg-laying beginning as early as nine days after eclosion. If mating is delayed until day 16, by which time vitellogenesis normally has ceased, stored eggs are laid within two to four days and yolk deposition is resumed. Removal of the brain prevents oviposition, as does the severance of the ventral nerve cord. Thus, an intact central nervous system is required for egg-laying. Also, since neither operation inhibits egg maturation or ovulation, it appears that the latter reproductive responses to mating are independent of oviposition.     

Density dependence of Anaphes sordidatus (Hymenoptera: Mymaridae) parasitism on eggs of Listronotus oregonensis (Coleoptera: Curculionidae)

Listronotus oregonensis (LeConte) (Coleoptera: Curculionidae) oviposits in carrot leaves and the larvae feed in carrot roots. Its eggs are parasitized by Anaphes sordidatus (Girault) (Hymenoptera: Mymaridae) throughout its oviposition period. This parasitoid is the major biotic mortality factor for L. oregonensis. Parasitism by A. sordidatus was studied for three years in sequentially sown plots of carrots, Daucus carota var. sativa. Over the scason, significantly fewer L. oregonensis eggs were oviposited in later sown carrots than in earlier sown carrots because oviposition started later in late sown plots of carrots. A positive temporal density-dependent relationship was observed each year between parasitism rates and host densities. This positive density dependence occurred in early and mid-summer for earlysown carrots where host density reached 1–2 host eggs per plant but disappeared in late summer when host density decreased while parasitism remained high. Latesown carrots had low host egg density (0.2 host egg per plant) and contributed little to the total number of eggs. In these late sown plots, parasitism increased rapidly to over 80% but no density dependence was observed. Spatially, few statistically significant regressions were found but all indicated a positive spatial density-dependence. Most non-significant regressions occurred because the range of egg density was too small between plots for a given date.     

Biology and population development ofAblattaria arenaria [Coleoptera: Silphidae], a snail predator

The biology ofAblattaria arenaria (Kraatz) was studied in the laboratory by using a helicid snail,Xeropicta derbentina (Kyrnicki) as prey. Population development ofA. arenaria in the field was studied in 1985 and 1986. The eggs ofA. arenaria were laid in the soil in lots of 5–45 at various intervals, and the total number of eggs per female varied from 144 to 193 during the oviposition period of 24–88 days.A. arenaria passed through the egg, 3 larval, prepupal, and pupal stages before reaching the adult stage. The mean duration of these stages was 9.8, 3.9, 2.5, 5.9, 3.8 and 5.7 days, respectively, with a total of 31.4 days. A. arenaria overwintered as an adult and became active and laid eggs during the spring. The start of spring activity seemed to be highly influenced by relative humidity. High humidity resulted in early emergence from overwintering sites. There was 1 generation in 1985, but 2 population peaks occurred in 1986. Immature stages of the 2nd generation became adult before the beginning of aestivation. Activity of the beetles was stopped by the beginning of hot weather in June, which synchronized well with the beginning of snail aestivation.