Incidence of Anagrus obscurus (Hymenoptera: Mymaridae) egg parasitism on Calopteryx haemorrhoidalis and Platycnemis pennipes (Odonata: Calopterygidae: Platycnemididae) in Italy

Very little is known about the incidence of egg parasitoids in odonates, perhaps because Odonata eggs are well protected by stems or leaves, sometimes below water. In Central Italy (Pontecorvo, Frosinone Province) two damselflies, Calopteryx haemorrhoidalis and Platycnemis pennipes, occur in high densities. In August 2007 we collected 30 stems of the aquatic plant Potamogeton sp. used as substrate for oviposition and incubated eggs in the laboratory. Most stems (24 for C. haemorrhoidalis and 23 for P. pennipes) contained Odonata eggs. Parasitoids emerged from 12 stems, with a mean parasitism of 2% for C. haemorrhoidalis and 6% for P. pennipes, and a maximum of 14% and 50%, respectively. Furthermore, we observed egg‐laying of 19 females of C. haemorrhoidalis and 11 of P. pennipes, and marked the stems where oviposition was observed. Clutches remained in the river for five days and were then collected and incubated. Parasitoids emerged from 11 of 30 stems, with an average parasitism of 8% for C. haemorrhoidalis and 3% for P. pennipes (maximums of 50% and 29%, respectively). All parasitoids belonged to the family Mymaridae, and were identified as Anagrus (Anagrus) obscurus Förster, 1861, sensu Soyka, 1955 . This is the first time that this species is described as an egg parasitoid of odonates, and that the egg parasitoid of C. haemorrhoidalis and P. pennipes is identified. Our data suggest that egg parasitism might be a significant selective factor for both odonates in the studied locality, affecting female oviposition behavior.     

Nezara viridula parasitism by the tachinid fly Trichopoda pennipes ten years after its accidental introduction into Italy from the New World

Percent parasitism of Nezara viridula (L.) (Heteroptera:Pentatomidae) by Trichopoda pennipes F.(Diptera: Tachinidae) ten years after itsfortuitous introduction was evaluated in someareas of Italy. The parasitoid is acclimatisedin central Italy with a parasitism in 1998 of21.3% in the west coast area (Lazio) and of24.8% in the inland area (Umbria). Host adultsof both sexes were attacked with the same ratein 1998, whereas this was higher in males thanfemales in 1991 and 1992. Parasitism of nymphswas lower in all three years. In 1998parasitized bugs showed 1 (54.1%) to a maximumof 15 (0.4%) macrotype eggs per individual,distributed preferentially on the thorax ascompared with other body parts. None of theother pentatomid species collected in the sameareas were parasitized by T. pennipes,indicating that there have not been indirecteffects of this fortuitous introduction tillnow.     

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.     

Behavioral response of the egg parasitoid <Emphasis Type="Italic">Ooencyrtus telenomicida</Emphasis> to host-related chemical cues in a tritrophic perspective

The response of the generalist egg parasitoid Ooencyrtus telenomicida (Vassiliev) (Hymenoptera: Encyrtidae) to host-related chemical cues from tomato plants, Solanum lycopersicum L., and adults of Nezara viridula (L.) (Heteroptera: Pentatomidae) was investigated in laboratory-based no-choice and paired-choice tests. In Y-tube olfactometer experiments, when female wasps were exposed to volatiles from plants in different conditions, they were attracted only to volatiles produced by N. viridula adult-infested tomato plants. When female wasps were exposed to adults of N. viridula, they were attracted to volatiles from virgin males, and, at a lower level, to volatiles from mated females in preoviposition state. Finally, studies in open arena showed that chemical footprints left by adults of N. viridula did not induce arrestment responses in wasp females. These results are discussed in terms of extrinsic competition with other beneficial egg parasitoids that in field can compete for the same egg mass, since intraguild interactions may affect the success of a biological control program.     

Male-mediated aggregation of male, female and 5th-instar southern green stink bugs and concomitant attraction of a tachinid parasite,Trichopoda pennipes

In 124 days of field tests, 88.7% of male, 87.3% of female, and 90.2% of 5th-instarNezara viridula were caught on cages containing maleN. viridula rather than on female or control cages. Likewise, 92% of the female and 86% of the male parasite,Trichopoda pennipes (F.), were caught on cages containing maleN. viridula. Attraction ofN. viridula occurs throughout the daylight hours, but is strongest in a 5-min period immediately prior to complete darkness. The data suggest the presence of a male-emitted aggregation pheromone inN. viridula, acting concomitantly as a kairomone forT. pennipes females.

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Zusammenfassung Es wurden im Sommer und Herbst Käfige auf Feldern verschiedener Kulturpflanzen aufgestellt. In jeden Käfig wurdenNezara viridula (Hemiptera: Pentatomidae)-Imagines eingesetzt, die geschlechtsweise so sortiert waren, dass jeder Käfig ausschliesslich Weibchen, ausschliesslich Männchen, oder gleiche Mengen beider Geschlechter enthielt. FreilebendeN. viridula wurden von den eingesperrten Insekten angelockt. Jeweils über 87% der Männchen, Weibchen und der Altlarven, die angezogen wurden, kamen an die Käfige die Männchen enthielten. Die SchmarotzerfliegeTrichopoda pennipes (Diptera: Tachinidae) wurde auch angelockt — hier fanden sich 92% der weiblichen und 86% der männlichen Fliegen auf den Käfigen, die männliche Wanzen enthielten. Die Anlockung der Hemipteren dauerte den ganzen Tag an, mit einer vorübergehenden, aber sehr starken Zunahme direkt vor dem Einbruch der Dunkelheit. Wir nehmen an, dassN. viridula-Männchen ein Pheromon abgeben, das nicht nur Weibchen, sondern auch andere Männchen, Larven und auch Schmarotzerfliegen anzieht. Das Verhalten der Insekten blieb immer gleich in den beiden Jahreszeiten, und auch die verschiedenen Pflanzenarten hatten keinen Einfluss darauf.

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Nezara viridula (L.) (Hemiptera: Pentatomidae)

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Diptera: Tachinidae     

Aspects of the ecology and energetics of the egg sac parasites of the wolf spider Pardosa lugubris (Walckenaer)

Summary The egg sacs of the wolf spider Pardosa lugubris are parasitised by two ichneumonid wasps, namely Gelis micrurus and Hidryta sordidus. The parasites are bivoltine, the first generation parasitising the summer egg sac of P. lugubris and the second generation parasitising, and overwintering in, the autumn egg sac. Parasitised egg sacs have a characteristic appearance.The degree of egg sac parasitism was 9.8% and 6.9% for the two egg sac batches in 1965 and 2.9% and 34.8% for those of 1966. The degree of parasitism varies from area to area as does the percentage parasitism attributable to the two species.The gross growth efficiency for Hidryta from the first egg sac is 31.2% and from the second 16.2%. 3.0% in 1965 and 4.3% in 1966, of the annual yield from P. lugubris to predators and parasites, goes to the egg sac parasites. This represents reductions in recruitment of 9.1% in 1965 and 10.9% in 1966.     

Distribution of Empoasca devastans and its egg parasites in the Indian Union

The cotton jassid Empoasca devastans Distant has been reported as a major pest from all the cotton growing areas of the Indian Union. Its outbreaks have always been a difficult problem for the growers of cotton in the Punjab, and it has often resulted in the complete failure of this crop (Lal, 1941). This jassid also attacks other crops and ornamental plants (Sohi, 1964). A systematic survey of various stages of this jassid was undertaken in the Indian Union by collecting the natural parasites and predators during the period May 1964 to September 1966. We have restricted the survey to the following crops: okra (Abelmoschus esculentus), castor (Ricinus communis), eggplant (Solanum melongena), cotton (Gossypium spp.) and cowpea (Vigna catjang). Five mymarid and one trichogrammatid parasites and four predators were found and recorded (Subba Rao et al., 1965; Subba Rao, 1966), and a new species of egg parasite was described. The material collected from different areas of the survey (Fig. 1) was kept in the laboratory in 15 × 20 cm jars. Any parasites hatching from the material were preserved in 70% alcohol. In addition an assessment of the % parasitism of the eggs of this jassid at Delhi was made for one year from August 1965 to July 1966 on the two seasonal crops, okra and eggplant, and on castor which is available throughout the year. Leaves gathered on the fields of the Institute were dissected in search of the jassid eggs. The visibly parasitised eggs were sorted out and counted.     

Factors influencing egg parasitism in sub‐social insects: insights from the treehopper Alchisme grossa (Hemiptera,Auchenorrhyncha, Membracidae)

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An algal cyclostat with computer-controlled dynamic light regime

Platycnemis pennipes deposits eggs into plant tissue at or just below the water surface. On a number of different plant species egg deposition rate was found to be similar, while oviposition duration varied. Eggs were not always to be found in the substrate after a female had probed the substrate with her ovipositor. Actual oviposition took place only during longer stays.     

Release density,efficiency and disappearance ofTrichogramma nubilale for control of European corn borer

We evaluated how manyTrichogramma nubilale should be released at a single location to controlOstrinia nubilalis in sweet corn. Six 8.6×16 m plots received 18.4 to 2 090 ΦΦT. nubilale/SAI when plants were in the mid to late whorl stage, where SAI, surface area index, is the plant surface area/m². To evaluate the potential control by our releases, we exposed laboratory-rearedO. nubilalis egg masses to the released parasitoids at 4 times after the release. When an egg mass was parasitized byT. nubilale, 75.7% of the eggs in the egg mass were parasitized. We developed an equation to estimate the percent of egg masses that a single female was expected to parasitize in a day (efficiency of parasitism) and female disappearance (death and dispersal) rates, if both were constant during our experiment. The exponential disappearance rate was −0.52±0.03 day⁻¹, which implied that 40% of the remaining ΦΦ disappeared per day. The efficiency of parasitism was 0.050% parasitism/Φ/SAI/day, which implied that at least 351,000 ΦΦ/ha would be needed to achieve 90% parasitism. Clearly, forT. nubilale to be a successful biological control agent, efficiency of parasitism must be increased and disappearance rates must be reduced.      

Adult population parameters and life tables of an epilachnine beetle (Coleoptera: Coccinellidae) feeding on bitter cucumber in Sumatra

The population dynamics of an epilachnine beetle, which is closely related to Epilachna sparsaDieke (henceforth called “sp. C”) and feeds on bitter cucumber Momordica charantia, was studied by mark-recapture of adults and the construction of life tables. The study was repeated three times, i.e., March–May, July–September and October–December in 1982, in Padang, Sumatra, Indonesia. After the establishment of the host plants, adults of “sp. C” soon colonized, and each study period ended in the death of the plants due to defoliation by the larvae and adults. The estimated mean length of residence of adults ranged from 6–11 days, but this was probably much shorter than the actual longevity, because the adults were so active that they flew away, or dropped off the plants, when they were approached or slightly disturbed. Life tables indicated that egg mortality ranged from 17.8–53.9%, and a parasitic wasp Tetrastichus sp. B made up 41.1–64.2% of egg mortality. Two wasps, Tetrastichus sp. C and Pediobius foveolatus killed 1.2–19.4% (7.6–100%)^* of 4th instars and only the latter species attacked the pupae, killing 24.6–59.1% (45.1–72.4%). Parasitism and starvation by overcrowding contributed most to the total mortality from egg to adult emergence, which ranged from 89.4–99.5%. “Sp. C” had a higher diversity and level of parasitism than the Japanese species, E. vigintioctopunctata. The high dispersal power of “sp. C”, coupled with the prolonged l_x−m_x schedules shown under laboratory conditions, was advantageous for exploiting the food plant which was available throughout the year, but was rather patchily distributed in space.     

Density dependence and regulation in the systemNezara viridula (L.) (Hemiptera: Pentatomidae), host andTrichopoda giacomellii (Blanchard) (Diptera: Tachinidae), parasitoid

Summary The system formed byN. viridula and its almost specific parasitoidT. giacomellii has been studied in the Buenos Aires province, Argentina for 26 generations of the former and 20 generations of the latter. An intensive study over 9 host generations and key factor analysis made possible the identification and quantification of different mortality factors. The main factors determining the fluctuations in total generation mortality were: egg mortality due mainly to parasitism byT. basalis; nymphal predation on 1^st, 2^nd and 3^rd instar nymphs and migration; and adult mortality and reduction on potential natality due to parasitism byT. giacomellii. Adult mortality and reduction of potential natality, due to parasitism byT. giacomellii, was density dependent. This factor is capable of maintaining the simulations generated by a simple model based on key factor analysis, within the range of observed densities. These results suggest that parasitism byT. giacomellii can regulate the population, even in a small area of 450 m².     

Habitat selection in the larvae of two species of Zygoptera (Odonata): biotic interactions and abiotic limitation

Field and laboratory experiments were set up to obtain data on the reasons for different habitat selection of Enallagma cyathigerum and Platycnemis pennipes. (1) Rearing of larvae in two different ponds showed that while P. pennipes was not able to survive conditions of low oxygen content, 50% of the E. cyathigerum larvae survived. (2) In field predation experiments with sticklebacks and dragonflies as predators, we found that E. cyathigerum suffered highest predation by the fish. In P. pennipes, mortality was highest with Anax imperator. (3) Experiments regarding larval behaviour showed that E. cyathigerum was generally more active and had higher foraging success than P. pennipes. Both species reduced activity in the presence of fish, but E. cyathigerum did so to a minor extent. In contrast to P. pennipes, E. cyathigerum showed escaping behaviour. (4) In the laboratory, the growth of E. cyathigerum was faster than that of P. pennipes.     

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.     

Osservazioni sulla biologica dellaProspaltella perniciosi Tow. nella valle Padana

Summary Investigations have been carried out in the Po' Valley (Italy) during 1964 to establish the number of generations of the San José scale and its parasiteProspaltella perniciosi Tow. It was found that the San José scale has three generations per year, while its parasite has six. The percent of parasitism attained in one year after parasite release was 60.Prospaltella hibernates as an egg in the first larval instar of its host.      

Fecundity and Longevity of Green Vegetable Bug,Nezara viridula, Following Parasitism byTrichopoda giacomellii

The effects of parasitism by the ArgentinianTrichopoda giacomellii(Blanchard) on reproduction and longevity of its host,Nezara viridula(L.) are reported. Parasitoid larvae suppress egg maturation, reducing by 70% the fecundity of mature female hosts during the period of larval development. Egg viability was not affected, but mating frequency was reduced by approximately 50%. When parasitized as newly eclosed adults, 84% of females fail to reproduce. In male hosts, fertility and mating frequency were not affected during the period of larval parasitoid development. In male and reproductively immature female hosts, death was coincident with, or occurred shortly after parasitoid emergence (2–4 days); in mature females, death occurred on average 2 weeks after larval parasitoid emergence. Host mortality occurred as a consequence of tissue damage incurred as the parasitoid larvae emerged from the host. Some individuals survived parasitism though no further reproductive activity (mating or oviposition) occurred. The effectiveness ofT. giacomelliias a biological control agent is discussed in relation to its impact on reproduction and survival of its host and contrasted with the action of otherTrichopodaspecies.     

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.     

Tritrophic interactions and trade-offs in herbivore fecundity on hybridising host plants

Abstract. 1. Interspecific plant hybridisation can have important evolutionary consequences for hybridising plants and for the organisms that they interact with on multiple trophic levels. In this study the effects of plant hybridisation on the abundance of herbivores and on the levels of herbivore parasitism were investigated. 2. Borrichia frutescens, B. arborescens, and their hybrid (B. × cubana) were censused for Asphondylia borrichiae galls and Pissonotus quadripustulatus plant hoppers in the Florida Keys. Levels of egg parasitism were determined by dissecting parental and hybrid stems and galls for herbivore and parasite eggs and larvae. Stem toughness and gall size are plant‐mediated modes of protection from parasitism and these were also measured. For gall midges, fly size was measured as an estimate of fecundity. 3. Field censuses indicated that herbivore abundances varied on hybrid hosts relative to parent plant species and that the different herbivore species exhibited different patterns of abundance. Asphondylia borrichiae gall numbers followed the additive pattern of abundance while P. quadripustulatus numbers most closely resembled the dominance pattern. 4. Parasitism of P. quadripustulatus eggs was high on B. frutescens and the hybrids, and low on B. arborescens, which also had significantly tougher stems. Asphondylia borrichiae suffered the highest levels of parasitism on B. frutescens, the host plant which produced the smallest galls. On B. arborescens, which produced the largest galls, levels of A. borrichiae parasitism were lowest. Both parasitism and gall size were intermediate on the hybrid plants. Galls on B. arborescens and hybrid plants produced significantly smaller flies then those from B. frutescens suggesting that, when selecting hosts from among parent species and hybrids, gall flies may face a trade‐off between escape from natural enemies and maximising fecundity.     

The effect of grassy field margins and fertilizer on soil water,plant nutrient levels,stem borer attacks and yield of maize in the humid forest zone of Cameroon

Two field experiments, planted in a split plot design, were conducted during 2002 in the forest zone of Cameroon, to investigate the effect of border rows with Pennisetum purpureum (Poaceae) or with Panicum maximum (Poaceae) on soil water, plant nitrogen (N), phosphorus (P) and potassium (K), borer infestations, parasitism and maize yield. The grassy boundaries were the main plots and fertilizer treatment the sub plots. Soil humidity was significantly higher under the grass borders than in maize plots. Nitrogen uptake by maize tended to be highest in plots surrounded by P. purpureum but the differences were significant during the second season only. Busseola fusca (Fuller) (Lepidoptera: Noctuidae) was the predominant borer species followed by Eldana saccharina (Walker) (Lepidoptera: Pyralidae). The predominant parasitoid species was the scelionid egg parasitoid Telenomus busseolae Gahan (Hymenoptera: Scelionidae). During both seasons, plant nitrogen, B. fusca infestation, plant damage and yield were significantly higher in maize sub-plots that received fertilizer The interaction between the grassy margin effect and the fertilization was significant only for B. fusca infestations, during the second season with maize + P. purpureum having a significantly lower number of borers in the fertilized than the unfertilized sub-plots. The grassy borders had no effect on B. fusca egg parasitism variables except in the first season, when maize with P. purpureum had a significantly higher percentage of egg batches parasitized. During both seasons, there were some significant differences in yield variables between main plots but the trends were not clear. Multiple regression showed that B. fusca infestation, plant damage, egg parasitism, plant N, P and K affected yield, with plant nutrients explaining most of the variability. The implication of the findings for the feasibilty of this habitat management technology to farmers in southern Cameroon is discussed.