Caddisfly egg mass morphology mediates egg predation: potential costs to individuals and populations

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Brochosome influence on parasitisation efficiency of Homalodisca coagulata (Say) (Hemiptera: Cicadellidae) egg masses by Gonatocerus ashmeadi Girault (Hymenoptera: Mymaridae)

Abstract. 1. Many cicadellid females in the tribe Proconiini (Hemiptera: Cicadellidae) cover their egg masses with specialised, usually rod‐shaped, brochosomes as the eggs are being laid. The brochosomes are produced in Golgi complexes in the Malpighian tubules of Cicadellidae. In contrast to the gravid females, adult males, pre‐reproductive adult females, and nymphal males and females produce specialised, usually spherically shaped brochosomes. Brochosomes are also used to cover the external surfaces of nymphs and newly moulted adult males and females. 2. The function of the brochosome covering the egg masses is unknown but various hypotheses have been suggested, including protecting the eggs against pathogens, predators, and parasitoids. Based on preliminary observations of Gonatocerus ashmeadi Girault (Hymenoptera: Mymaridae) parasitising the eggs of the cicadellid, Homalodisca coagulata (Say), it is speculated here that brochosomes covering an egg mass hinder parasitisation of eggs by G. ashmeadi. This hypothesis was tested by observing G. ashmeadi females foraging on leaves with H. coagulata egg masses heavily covered with rod‐shaped brochosomes vs. those lacking brochosomes. 3. Cox's proportional hazards model was used to evaluate the probability, per unit time, that a female G. ashmeadi displayed the sequence of behaviours that ended in successful oviposition as influenced by five variables: (a) presence or absence of brochosomes on an egg mass, (b) the leaf surface, upper or lower, being searched by the parasitoid (the egg masses are laid in the parenchyma on the lower leaf surface), (c) the parasitoid's previous ovipositional experience, (d) egg mass size, and (e) the parasitoid's age. 4. Brochosomes significantly decreased oviposition efficacy of G. ashmeadi females. Scanning electron microscopy showed that females exposed to brochosome‐covered egg masses had brochosomes adhering to their tarsi, legs, antennae, and eyes, all of which prompted extensive bouts of grooming.     

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.

     

Effects of predation on clutch size and egg dispersion in the codling moth Laspeyresia pomonella

ABSTRACT.

• 1 The effects of predation on clutch size and egg dispersion in the codling moth Laspeyresia pomonella (L.) were experimentally studied in an orchard by recording survival of eggs glued onto different substrates.
• 2 Egg mortality due to sucking insects was readily distinguishable from that due to chewing insects.
• 3 In both the field and laboratory, females preferred to deposit eggs singly on the uppersides of leaves.
• 4 Eggs on the uppersides of leaves and on fruit survived significantly better than did those on the undersides of leaves or on twigs.
• 5 Egg losses were highest during the early part of the flight season.
• 6 The smallest (one egg) and largest (nine eggs) clutches, associated with one egg-bearing leaf per twig, both suffered the lowest rates of predation. Factors selecting against oviposition on fruits and production of large clutch sizes are presented and discussed.

     

Experimental field studies on predation and egg parasitism of rice brown planthopper in Indonesia

• 1 Egg parasitism and general predation are known to be important mortality factors in the population dynamics of rice brown planthopper (BPH) Nilaparvata lugens in tropical Asia, but previous studies have not attempted to quantify and compare them.
• 2 Field experiments in Java, Indonesia, are reported for 1993 and 1994. Plants previously infested with BPH eggs were put out in field cage‐enclosures, which, by means of different size mesh gauze covering, allowed either: (1) free access to all natural enemies, (2) access only to egg parasitoids, or (3) no access to any natural enemies.
• 3 After one BPH generation (30 days), numbers of adults and gravid females were counted for each treatment. In addition, plants were dissected to determine the numbers of eggs laid.
• 4 An additional treatment in which all natural enemies were excluded, but lycosid spiders were added, was used in 1994 experiments in an attempt to assess the effects of predators in the absence of egg parasitoids.
• 5 Numbers of BPH adults and eggs laid were highest when natural enemies were excluded and lowest when they had free access. Mortality due to egg parasitoids in the absence of predators was intermediate and significantly different to the two other treatments.
• 6 The effects of added predators in the absence of egg parasitoids gave variable results, but again clearly demonstrated the significance of egg parasitism in overall BPH mortality.
• 7 The conservation of BPH egg parasitoids should form an important element of any rice pest management programme in tropical Asia.

     

Effects of grapevine bunch exposure to sunlight on berry surface temperature and Lobesia botrana (Lepidoptera: Tortricidae) egg laying,hatching and larval settlement

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Parasitization by Edovum puttleri (Hymenoptera: Eulophidae) in relation to host density in the field

Abstract.

• 1 The relationship between parasitization by Edovum puttleri Grissell and density of eggs of the Colorado potato beetle, Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae), was studied on two spatial scales (eggs mass and 6 m² cage).
• 2 For both scales, rates of parasitism were generally inversely related to host density for periods ranging from 2 to 8 days after parasitoid release. Thereafter, parasitism became independent of host density.
• 3 The initial inverse-density relationship and subsequent shift to density independence may result from several factors: (1) ambient temperatures, (2) the parasitoid's limited egg production, (3) differential times of exposure of egg masses to parasitoids, and/or (4) the parasitoid's patterns of host feeding and oviposition.
• 4 Although overall levels of parasitism were relatively low, total mortality of L.decemlineata eggs (including nonviable and cannibalized eggs, and those killed by parasitoid feeding) in parasitized egg masses was consistently high (?70–90%).

     

Aggregative oviposition varies with density in processionary moths—Implications for insect outbreak propensity

1. In gregarious insects, groups commonly originate from females laying eggs in masses and feeding groups are established as soon as larvae hatch. Some group-living insect species may aggregate beyond the individual parent level, such that offspring from two or more egg masses develop within a common resource.
2. Here we show that aggregative oviposition can vary with population density at oviposition and possibly be an important factor in outbreak dynamics of phytophagous insects.
3. We analysed density data with respect to egg mass aggregation for two species of pine processionary moths, Thaumetopoea pinivora (in Sweden 2005–2019) and T. pityocampa (in Spain 1973–1991). Both species lay their eggs in egg masses and feed in groups. During the study periods, insect population density for both species varied by at least an order of magnitude.
4. The two species showed strikingly similar patterns of egg mass aggregation. Egg masses were overdispersed at high population density, with few trees showing a high load of egg masses.
5. Our data suggest that aggregative oviposition can be important in explaining the previously documented higher propensity for outbreaks in insects laying eggs in clusters, compared with those laying individual eggs.

     

A test of the preference–performance hypothesis with stream insects: selective oviposition affects the hatching success of caddisfly eggs

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Protective function of maternal care against egg predators in the shield bug Sastragala esakii (Hemiptera: Acanthosomatidae)

Females of many acanthosomatid shield bugs attend eggs and young nymphs by covering them with their bodies. Although such form of maternal care has been suggested to have evolved independently in four genera, Elasmucha, Sastragala, Acanthosoma and Sinopla, previous studies exploring its adaptive function have solely focused on species of Elasmucha. This study pioneered an experimental examination of maternal care in the Japanese species Sastragala esakii. Field experiments demonstrated that unattended egg masses suffered intense predation, whereas egg masses attended by their mothers were rarely preyed upon. The ant Crematogaster sp. was the most common egg predator, while two other insect species were also observed to prey on eggs. The exclusion of ant workers and other walking predators from accessing egg masses through the utilization of a sticky trap resulted in a remarkably improved egg survival rate in orphaned egg masses, suggesting that, at least in our study site, maternal care of S. esakii primarily functions to protect eggs from walking predators. Laboratory observations revealed that egg protection against predators was achieved through at least two distinctive defensive behaviors shown by egg-tending females: (i) tilting their bodies when approached by predators; and (ii) fanning their wings when in contact with predators. However, females displayed a limited response to predators approaching from the posterior direction, suggesting that visual cues play a significant role in predator recognition. These results indicate a similarity in the maternal care functions between Elasmucha and Sastragala, and suggest the parallel evolution of female defensive behaviors.     

Patch-exploitation patterns in an egg parasite of elm leaf beetle

Eggs of elm beetle,Pyrrhalta luteola (Muller), normally occur in masses which can be viewed as discrete host patches in space and time. Analysis of>800 egg masses from 3 field sites in northern California revealed that the number of eggs/mass varied from 2 to>40 and that the imported egg parasiteTetrastichus gallerucae (Fonsc.) exploited a relatively large proported of the egg masses at certain times. The spatial relationship between parasitization and number of eggs/egg mass was assessed in 2 ways-i.e., for exploited masses only and for all masses combined (exploited+nonexploited). Percent parasitization was density independent in most cases for both data sets. It is suggested that both methods of analysis can provide patterns which are relevant to biological control of insect pests.      

Larger clutches of chemically defended butterflies reduce egg mortality: evidence from Battus philenor

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The effects of egg position, egg mass size, substrate and biofouling on embryo mortality in the squid Sepioteuthis australis

Using a combination of laboratory and field investigations, this study examined embryo mortality in the southern calamary Sepioteuthis australis as a function of egg mass size, the substrate upon which the mass is attached, the position of the embryo within the mass, and the degree of biofouling. Egg mass size ranged from 2 to 1,241 egg strands, however most masses consisted of 200–299 strands. Small egg masses (<300 strands) were generally attached to soft-sediment vegetation (Amphibolis antarctica, Heterozostera tasmanica, Caulerpa sp.), whereas larger masses (>300 strands) were either securely attached to robust macroalgae holdfasts (Ecklonia sp., Marcocystis pyrifera, Sargassum sp.) or unattached. Rates of embryo mortality were highly variable ranging from 2 to 25%. Both laboratory and field results indicated a positive relationship between egg mass size and embryo mortality. Larger, unattached egg masses contained twice as many dead embryos than those securely attached to a substrate. Mortality rates were significantly affected by the embryos’ relative position within the mass and were highest in embryos located near the attachment point of the egg strand, within the interior of the mass, and in close contact with the substrate. This was attributed to the inability of the embryos to respire adequately and eliminate metabolic wastes. Biofouling did not strongly influence embryo mortality, but colonisation occurred in areas conducive to growth, photosynthesis, and respiration indicating ‘healthy’ regions within the mass.     

Oviposition‐induced plant cues: do they arrest Trichogramma wasps during host location?

Plants can defend themselves against herbivorous insects before the larvae hatch from eggs and start feeding. One of these preventive defence strategies is to produce plant volatiles, in response to egg deposition, which attract egg parasitoids that subsequently kill the herbivore eggs. Here, we studied whether egg deposition by Pieris brassicae L. (Lepidoptera: Pieridae) induces Brussels sprouts plants to produce cues that attract or arrest Trichogramma brassicae Bezdeko (Hymenoptera: Trichogrammatidae). Olfactometer bioassays revealed that odours from plants with eggs did not attract or arrest parasitoids. However, contact bioassays showed that T. brassicae females were arrested on egg‐free leaf squares excised from leaves with 72 h‐old egg masses, which are highly suitable for parasitisation. We tested the hypothesis that this arresting activity is due to scales and chemicals deposited by the butterflies during oviposition and which are thus present on the leaf surface in the vicinity of the eggs. Indeed, leaf squares excised from egg‐free leaves, but contaminated with butterfly deposits, arrested the wasps when the squares were tested 1 day after contamination. However, squares from egg‐free leaves with 72 h‐old butterfly deposits had no arresting activity. Thus, we exclude that the arresting activity of the leaf area near 72 h‐old egg masses was elicited by cues from scales and other butterfly deposits. We suggest that egg deposition of P. brassicae induces a change in the leaf surface chemicals in leaves with egg masses. A systemic induction extending to an egg‐free leaf neighbouring an egg‐carrying leaf could not be detected. Our data suggest that a local, oviposition‐induced change of leaf surface chemicals arrests T. brassicae in the vicinity of host eggs.     

Life history of a dipteran predator (Scathophagidae: Acanthocnema) of insect egg masses in a northern California stream

1. Little is known about the predators of insect eggs in fresh waters. This study describes aspects of the life history of a scathophagid fly (Acanthocnema sp.), whose larvae are predators of aquatic insect eggs. 2. Because the Acanthocnema predator oviposits its eggs on the surface of aquatic insect egg masses, all insect egg masses were collected regularly within a 200‐m reach of Redwood Creek (California, U.S.A.) between September 2003 and June 2007. Acanthocnema predators were found predominantly within egg masses of the caddifly Neophylax rickeri (Trichoptera: Uenoidae). 3. There was a mean of 0.25 Acanthocnema individuals per N. rickeri egg mass (n = 2367 egg masses). In general, N. rickeri egg masses were more commonly found clustered in aggregations (93.7%) than singly (6.3%), and Acanthonema were found more often within the aggregations of N. rickeri (98.7%) compared to singly laid egg masses (1.3%). 4. The duration of the Acanthocnema predator life stages was: egg 2.9 ± 0.8 (mean ± SD) days, larva 15.6 ± 10.2 days, pupa 80.3 ± 24.9 days and adult 7.2 ± 4.8 days. The short duration of the Acanthocnema egg stage (1–7 days) compared to that of its prey N. rickeri (2–4 weeks) raises the probability that the undeveloped eggs of N. rickeri would be available to the young predators upon hatching. Egg consumption of N. rickeri eggs by Acanthocnema averaged 262.6 eggs per larval period. 5. Acanthocnema had a bivoltine life cycle in which the first generation fed exclusively on N. rickeri egg masses in the winter and the second generation fed on the egg masses of several species, including other Trichoptera (Brachycentridae) and Diptera (Ceratopogonidae, Chironomidae) in the spring. These findings suggest differing feeding strategies by the first and second generations of Acanthocnema in response to the seasonal availability of prey species. This type of autecological information is important for understanding mechanisms of community interactions.     

Host handling behavior of the egg parasitoid Telenomus triptus to the egg mass of the stink bug Piezodorus hybneri

Host handling behavior of Telenomus triptus Nixon (Hymenoptera: Scelionidae) to an egg mass of Piezodorus hybneri Gmelin (Heteroptera: Pentatomidae) was studied in the laboratory. Five distinct behavioral events could be distinguished in the host handling behavior: drumming, ovipositor-insertion, marking, walking, and resting. Female wasps showed two types of behavioral sequence in an ovipositional bout. One consisted of drumming, ovipositor-insertion, and marking, and the other drumming, ovipositor-insertion, walking, and resting. Females did not seem to lay an egg when ovipositor-insertion was not followed by marking. This was observed frequently in the early oviposition bout, on average 2.9 times per female. Females finally succeeded in parasitizing all the eggs in a host egg mass in most cases. The durations of drumming, ovipositor-insertion, and marking on an egg mass were nearly constant, while the total time spent by a female on and beside a host egg mass varied considerably as a result of variable durations of walking and resting. Self-superparasitism occurred when almost all the eggs in a host egg mass were parasitized. Females laid the first male egg within the first four eggs; this could be an adaptation to small egg masses or single egg.     

Preliminary life table of the spotted tortoise beetle,Aspidomorpha miliaris (Coleoptera: Chrysomelidae) in Sumatra

From December, 1981 to February, 1982, a population study of the spotted tortoise beetle, Aspidomorpha miliaris, feeding on a shrub-like morning glory, Ipomea carnea, was conducted in Padang, Sumatra with the construction of a life table.

1. Dissection of oothecae collected from the field after hatching clarified that the average egg mass size was 43.4 and hatching rate was 25.0%. Causes for egg mortality included: parasitism by a wasp, Tetrastichus sp. A(Europhidae) (49.8% of eggs laid), predation (12.8%), disappearance of egg masses (5.3%) and hatching failure (7.1%). An ant, Dolichoderus bituberculatus, visiting the extrafloral nectaries of the host plnts was responsible for predation and disappearance of the egg masses. The ants again attacked the larvae and pupae.
2. Larvae showed a gregarious habit for almost the entire larval period. Survival rates between two successive instars were low and constant, ranging from 70 to 90%, but only 1.3% of final (5th) instars become pupae (six individuals). Since the growth of host plants was extremely rapid, shortage of food was rare in larval stages. The sudden drop in numbers after 5th instar may be due to predation and/or dispersal of matured larvae from the host plants for pupation.
3. Pupae were attacked by three species of parasitic wasps:Tetrastichus sp. C, Pediobius elasmi (Eulophidae) and Cassidocida aspidomorphae (Tetracampidae). Among the six pupae, two were parasitized, one died of disease and two disappeared. Out of 4078 eggs laid, only one emerged to adult.

     

Distribution of second generation European corn borer,Ostrinia nubilalis, egg masses in field corn and relationship to subsequent tunneling damage

The relationship between second generation European corn borer (Ostrinia nubilalis Hübner) egg mass numbers and subsequent field corn damage, as measured by stalk cavity numbers, was studied in 79 fields in northeastern North Carolina over three years. A mean of 0.028 egg masses per plant (645 egg masses/23400 plants) was found over the course of the study. Significant differences in oviposition rate were detected between fields and years. Ca. 85% of egg masses were deposited in a five leaf zone surrounding the primary ear; of these, 89% were found on the lower four leaves in this zone. Egg masses appeared to be distributed randomly within fields but at low rates of incidence, and oviposition was relatively uniform between sampling areas within individual fields. Under moderate to high oviposition pressure (mean number of egg masses per plant over the duration of the oviposition period >ca. 0.02), eggs laid during the early phases of the oviposition period account for more subsequent stalk damage than eggs laid during the later phases of the oviposition period. Variations in second generation egg mass numbers accounted for ca. 70% of variation in stalk cavity numbers.     

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

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