Female egg dumping and the effect of sex ratio on male egg carrying in a coreid bug

Phyllomorpha laciniata Vill (Heteroptera, Coreidae) is uniqueamong terrestrial insects in that females glue eggs on the backsof other conspecifics. Egg carrying byP. laciniatamales haspreviously been considered as paternal care. We explored femaleoviposition with respect to previous mating experience of femalesand tested whether sex ratio affects male egg-carrying. Thehypothesis that male egg-carrying is a form of paternal carepredicts that a male should always accept eggs after matingwith a female. However, if male egg-carrying is a form of postcopulatorymate guarding rather than paternal care, egg carrying shouldincrease in the presence of other males. When two couples wereplaced together, females laid eggs on the backs of all individualsenclosed, including the backs of other females. However, whena female was accompanied by 2 males, 22 out of 26 females ovipositedon their mating partner. Thus, sexual competition rather thanpaternity alone, affects a male's eagerness to carry eggs. However,even if males sometimes carry their own eggs, females lay eggson the backs of all conspecifics they can easily acquire. Thus,egg carrying in P. laciniata is partially voluntary and partiallythe result of female egg dumping     

Paternity analysis in the golden egg bug using AFLPs: do the males preferentially accept their true genetic offspring?

Abstract.  1. The evolution of parental care and intraspecific parasitism involve conflicts of interest between mothers and other potential care givers who contribute to enhance offspring survival. In the golden egg bug, Phyllomorpha laciniata Villers (Heteroptera: Coreidae), females lay eggs on conspecifics and on plants. The adaptive significance of egg carrying in this species has been the subject of some controversy, which can only be resolved by determining the genetic relationship between the eggs and the adult who carries them. This study examined whether male acceptance of true genetic offspring occurs with a higher frequency than that expected from random oviposition on conspecifics.
2. Paternity analysis, using Amplified Fragment Length Polymorphism (AFLP) markers, was conducted on eggs carried by males housed with field-mated females.
3. Out of the total number of eggs sired by males in the experimental groups, the proportion of eggs carried by males that were their true genetic offspring was 30.8%.
4. Monte Carlo methods show that the probability of a male accepting an egg that is his true genetic offspring is higher than expected if females dumped eggs on males at random.
5. These results suggest that paternal care plays an important role in the maintenance of male egg carrying in this species. In addition, the methodology developed may become useful in determining true genetic parents in other species in which neither the father nor the mother can be determined by observational methods.     

Flexible oviposition behavior in the golden egg bug (Phyllomorpha laciniata) and its implications for offspring survival

Female golden egg bugs show unique flexibility in their oviposition behavior. Females can lay eggs on plants, where they are leftunattended, or on the back of conspecifics, where they remainuntil hatching. In this article we show that eggs have greatersurvival rates when carried by an adult than when laid on plants.The main causes of egg mortality are predators and a parasitoidwasp. Our results suggest that, although predation pressureis similar, fewer eggs are attacked by parasitoid wasps whencarried by an adult than when laid on plants. In addition,we show that, when given a choice, females prefer to lay eggson the backs of conspecifics than on plants. Thus, female ovipositionchoice is adaptive and minimizes individual offspring mortality.The factors that may maintain such behavioral variation in current populations are discussed.     

Conflict of interest between sexes over cooperation: a supergame on egg carrying and mating in a coreid bug

In the golden egg bug (Phyllomorpha laciniata Vill. Heteroptera: Coreidae) females lay eggs on the backs of conspecifics, oftenon courting males. Although the bugs do not provide care tothe eggs, this decreases the risk of egg predation. As an effectmales carry many eggs which are not their own. The male andfemale interests are in conflict; females need to find an ovipositionsite, and male fitness depends on the obtained number of matings. By using a very rare modeling approach, a supergame where theindividuals actions change payoffs over time, we show thatcombinations of reciprocating strategies where males obtaina mating in return for a carried egg can be stable. The valueof the mating, to males, is more important than the relatednessto the eggs in gaining their cooperation in carrying eggs. Females may also take advantage of the males without reciprocating.This is especially likely if the probability of future meetingis high and the value of a mating is high for the male. Werelate our results to our own data from empirical studies andexperiments on the species. In the light of the results we discuss the behavior of the bugs in relation to nuptial gifts. We alsodiscuss the general applicability of the supergame approach.     

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.

     

Sperm competition mechanisms,confidence of paternity,and the evolution of paternal care in the golden egg bug (Phyllomorpha laciniata)

Theoretical models predict how paternal effort should vary depending on confidence of paternity and on the trade-offs between present and future reproduction. In this study we examine patterns of sperm precedence in Phyllomorpha laciniata and how confidence of paternity influences the willingness of males to carry eggs. Female golden egg bugs show a flexible pattern of oviposition behavior, which results in some eggs being carried by adults (mainly males) and some being laid on plants, where mortality rates are very high. Adults are more vulnerable to predators when carrying eggs; thus, it has been suggested that males should only accept eggs if there are chances that at least some of the eggs will be their true genetic offspring. We determined the confidence of paternity for naturally occurring individuals and its variation with the time. Paternity of eggs fertilized by the last males to mate with females previously mated in the field has been determined using amplified fragment length polymorphisms (AFLPs). The exclusion probability was 98%, showing that AFLP markers are suitable for paternity assignment. Sperm mixing seems the most likely mechanism of sperm competition, because the last male to copulate with field females sires an average of 43% of the eggs laid during the next five days. More importantly, the proportion of eggs sired does not change significantly during that period. We argue that intermediate levels of paternity can select for paternal care in this system because: (1) benefits of care in terms of offspring survival are very high; (2) males have nothing to gain from decreasing their parental effort in a given reproductive event because sperm mixing makes it difficult for males to reach high paternity levels and males are left with no cues to assess paternity; (3) males cannot chose to care for their offspring exclusively because they can neither discriminate their own eggs, nor can they predict when their own eggs will be produced; and (4) males suffer no loss of further matings with other females when they carry eggs. Thus, our findings do not support the traditional view that paternal investment is expected to arise only in species where confidence of paternity is high. The results suggest that females maximize the chances that several males will accept eggs at different times by promoting a mechanism of sperm mixing that ensures that all males that have copulated with a female have some chance of fathering offspring, that this probability remains constant with time, and that males have no cues as to when their own offspring will be produced.     

Adjustment of copula duration and ejaculate size according to the risk of sperm competition in the golden egg bug (Phyllomorpha laciniata)

Several hypotheses have been proposed to explain the adaptivesignificance of prolonged copulations in insects, which includemate guarding and sperm loading functions. We have exploredthe adaptive significance of the prolonged copulations in thegolden egg bug (copulations up to 50 h) and the effect of anincreased risk of sperm competition on ejaculate investment.Our data support predictions derived from sperm competitiontheory, which posits that males are expected to increase ejaculateexpenditure in response to an increased risk of sperm competition.Results show a combined response by males that has not beenpreviously described: males in the presence of rivals increasecopulation duration and the rate of sperm transfer. No relationshipwas found between male or female size and copulation durationor ejaculate size. Golden egg bug males transfer sperm slowlyand gradually throughout copulation; thus an increase in theamount of sperm transferred and the corresponding increase inthe male's numerical representation in the female's storageorgans could be particularly important in a system in whichso few sperm are transferred and in which so few sperm are storedby females. In addition, copulation duration may not only serveto increase the total amount of sperm transferred, but it mayalso increase the chances that the female will lay an egg soonafter copulation has ended. This could explain why males tendto accept eggs after copulation, since they could be maximizingthe chances that such eggs are fathered by them, and in thisway they would substantially increase the survival rates oftheir offspring because eggs laid on plants suffer high mortalityrates.     

Ant predation on red oak borer confirmed by field observation and molecular gut-content analysis

1 Populations of an indigenous longhorn beetle, the red oak borer Enaphalodes rufulus (Haldeman) (Coleoptera: Cerambycidae), recently reached epidemic levels in the Ozark National Forests of Arkansas and Missouri, resulting in extensive tree mortality.
2 The factors regulating E. rufulus populations are largely unknown. Ants appear to be the most abundant potential predators in the Ozarks and have been shown to play a role in regulating populations of other forest insects.
3 The main objective of the present study was to determine whether ants are predators of early E. rufulus life stages by direct observation of E. rufulus eggs artificially placed on tree trunks and by development of molecular tools to detect E. rufulus DNA within ant gut contents.
4 Three hundred and eighty E. rufulus eggs were applied to ten northern red oaks. Ants ate or carried away 72% of the eggs within 1 h. Camponotus pennsylvanicus (De Geer) and Aphaenogaster tennesseensis (Mayr) were identified as the two primary ant species observed in the study.
5 A portion of the mitochondrial 16S rRNA gene of E. rufulus was sequenced and polymerase chain reaction primers were developed to detect E. rufulus DNA in the guts of C. pennsylvanicus . Enaphalodes rufulus DNA persisted in ant gut contents for at least 24 h after ingestion under laboratory conditions, and E. rufulus DNA was detected in field-collected ant populations, suggesting the natural occurrence of ant predation on this insect.     

Diel variation in habitat use by planktivores in field enclosure experiments: the effect of submerged macrophytes and predation

The importance of submerged macrophytes and predation risk for habitat use by 0+ perch ( Perca fluviatilis ) and 0+ roach ( Rutilus rutilus ) was investigated in triplicate 78-m² field enclosures with and without macrophytes in the middle. During three experimental runs, habitat use by fish were monitored every 6 h with Breder traps. Each period included 2 days of fish monitoring before stocking with piscivorous perch, and 2 days after. Predation risk significantly changed habitat use by 0+ perch in the morning, midday and evening, but not at night. By comparing with the unvegetated controls, we found a refuging effect of macrophytes in the morning. Under predation risk there was significant diel variation in habitat use by 0+ perch, suggesting a migration from the open water habitat at night into the macrophytes in the morning. Roach continued to use open water even after predators were stocked, but responded like perch by reducing overall activity.     

Testing the differential predation hypothesis for the invasion of rusty crayfish in a stream community: laboratory and field experiments

1. We tested the hypothesis that the non‐native rusty crayfish (Orconectes rusticus) is less vulnerable to predators than two native species (O. propinquus and O. obscurus) it is replacing in streams of the upper Susquehanna River catchment (New York, U.S.A.). 2. We used laboratory experiments to compare species‐specific predation rates by smallmouth bass (Micropterus dolomieu) on crayfish of equal size and field tethering experiments to compare relative predation rates between native O. propinquus and non‐native O. rusticus by the suite of crayfish predators in our system. We predicted that crayfish size would affect predation rate but that predation rates would be equal among species when size was controlled. 3. We also tested for two potential artefacts of tethering. We tethered crayfish in cages to test whether the ability to escape from tethers is size specific, and we tested whether tethering alters differential predation among crayfish species by the smallmouth bass. 4. In the laboratory, smallmouth bass predation on rusty crayfish was lower than on either of the native species. In the field, predation risk for tethered crayfish was inversely related to size but did not differ among species when size was taken into account. Because rusty crayfish in the field experiment were slightly larger than the native species, as in nature, mortality was overall lower for the rusty crayfish. 5. In cages, smaller crayfish were more probably to escape from tethers than larger ones, an artefact that may partially confound results from our tethering experiments. Unexpectedly, tethering nearly eliminated predation by smallmouth bass. This artefact prevented us from testing for an interaction of tethering with differential predation and means that the results of field tethering experiments do not include any contribution from smallmouth bass predation. 6. Our experiments highlight the importance of explicitly considering potential artefacts that could confound results. 7. Our results indicate that differential predation contributes to the rusty crayfish's invasion of a stream community. In our study system, predation rates on rusty crayfish are lower than for native species mostly because of selection by predators for smaller crayfish; species‐specific characteristics such as behaviour that further reduce predation may also contribute, especially where smallmouth bass predation is important.     

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

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Hazardous duty pay and the foraging cost of predation

We review the concepts and research associated with measuring fear and its consequences for foraging. When foraging, animals should and do demand hazardous duty pay. They assess a foraging cost of predation to compensate for the risk of predation or the risk of catastrophic injury. Similarly, in weighing foraging options, animals tradeoff food and safety. The foraging cost of predation can be modelled, and it can be quantitatively and qualitatively measured using risk titrations. Giving‐up densities (GUDs) in depletable food patches and the distribution of foragers across safe and risky feeding opportunities are two frequent experimental tools for titrating food and safety. A growing body of literature shows that: (i) the cost of predation can be big and comprise the forager's largest foraging cost, (ii) seemingly small changes in habitat or microhabitat characteristics can lead to large changes in the cost of predation, and (iii) a forager's cost of predation rises with risk of mortality, the forager's energy state and a decrease in its marginal value of energy. In titrating for the cost of predation, researchers have investigated spatial and temporal variation in risk, scale‐dependent variation in risk, and the role of predation risk in a forager's ecology. A risk titration from a feeding animal often provides a more accurate behavioural indicator of predation risk than direct observations of predator‐inflicted mortality. Titrating for fear responses in foragers has some well‐established applications and holds promise for novel methodologies, concepts and applications. Future directions for expanding conceptual and empirical tools include: what are the consequences of foraging costs arising from interference behaviours and other sources of catastrophic loss? Are there alternative routes by which organisms can respond to tradeoffs of food and safety? What does an animal's landscape of fear look like as a spatially explicit map, and how do various environmental factors affect it? Behavioural titrations will help to illuminate these issues and more.     

Predator-induced life history changes in amphibians: egg predation induces hatching

The timing of transitions between life history stages should be affected by factors that influence survival and growth of organisms in adjacent life history stages. In a series of laboratory experiments, we examined the influence of predation risk as a cue to trigger a life history switch in amphibians. In the Oregon Cascade Mountains, some populations of Pacific treefrogs ( Hyla regilla ) and Cascades frogs ( Rana cascadae ) are under intense egg predation by predatory leeches (families Glossiphonidae and Erpobdellidae). We document that both treefrogs and Cascades frogs show plasticity in hatching characteristics in response to the threat of egg predation. Pacific treefrogs hatch sooner and at an earlier developmental stage when either predatory leeches or non-predatory earthworms are allowed direct contact with the developing egg mass. The same response is elicited even without direct contact. Chemical cues of predatory leeches and chemicals released from injured eggs appear to elicit the same early hatching response in treefrogs. For Cascades frogs, cues of leeches, but not those of injured eggs, elicit an early hatching response. Hatching early in response to egg predators may reduce predation. Plasticity of hatching characteristics has rarely been examined. However, we suspect that it may be common, particularly in populations or species that experience high variability in predation pressure between years.     

Cooperation under predation risk: experiments on costs and benefits

Two fish that cooperatively inspect a predator may have negotiated the share of the risk that each takes. A test of both the costs of predator inspection dependent on the distance from which the predator is approached and the potential benefits of cooperation was carried out strictly experimentally. We made either singletons or pairs of dead sticklebacks, Gasterosteus aculeatus, approach hungry pike, Esox lucius, by remote control according to an algorithm that mimicked natural inspection. The predation risk of both single inspectors and parallel inspecting pairs increased with closer inspection distances. A member of an inspecting pair had only about half the risk of that of a single inspector. In pairs, a companion diluted the lead fish''s risk of being caught, depending on its distance behind the leader. The absolute risk difference between leader and follower was greatest for close inspection distances and decreased further away from the predator. The leader''s relative risk increased with its distance ahead of the laggard. However, for a given distance between leader and laggard, the relative risks of the two fish remained similar with distance from the predator. The cost side of the inequalities that define a ''Prisoner''s Dilemma'' has thus been measured for this system. In a second experiment the ''attack deterrence hypothesis'' of predator inspection (i.e. inspection decreases attack probability) was tested. The pike was offered a choice between two sticklebacks, one of which had carried out a predator inspection visit. There was no indication of attack deterrence through predator inspection.     

Parasitism and predation of stink bug (Heteroptera: Pentatomidae) eggs in Georgia corn fields

Nezara viridula L. and Euschistus servus (Say) are the predominant species of phytophagous stink bugs on corn, Zea mays L., in Georgia. Oebalus pugnax pugnax (F.) occurs in relatively low numbers, and the predatory stink bug Podisus maculiventris (Say) is commonly found. Limited information is available on natural biological control of these four stink bug species in Georgia corn fields; therefore, a 6-yr study of parasitism and predation of their eggs was initiated in 2003. Naturally occurring stink bug eggs were parasitized by six scelionid species, Trissolcus basalis (Wollaston), T. thyantae Ashmead, T. brochymenae (Ashmead), T. euschisti (Ashmead), Telenomus podisi Ashmead, Telenomus calvus Johnson, and one encyrtid species, Ooencyrtus sp. T. basalis was the most prevalent parasitoid of N. viridula, parasitizing E. servus and P. maculiventris eggs at low levels. T. podisi, the predominant parasitoid species emerging from eggs of E. servus and P. maculiventris, also parasitized O. p. pugnax eggs exclusively and parasitized N. viridula eggs at low levels. T. euschisti and T. thyantae parasitized E. servus egg masses. T. brochymenae parasitized eggs of both E. servus and P. maculiventris. T. calvus parasitized only P. maculiventris eggs. The same species of egg parasitoids that parasitized naturally occurring eggs of N. viridula and E. servus parasitized sentinel eggs of these bugs, except that no T. calvus and Ooencyrtus sp. were obtained from sentinel eggs, and T. thyantae and T. brochymenae emerged from sentinel eggs of N. viridula. Generally, parasitization of an egg mass was either greater than or equal to predation of sentinel eggs of N. viridula and E. servus. However, on some dates in late June and July, predation of sentinel egg masses was numerically approximately twice as high as parasitism. Results indicate stink bug egg parasitoids and predators are significant factors in the natural biological control of stink bugs in corn fields.     

Tables for the analysis of selective predation experiments

This paper discusses the analysis of selective predation experiments with two types of prey when the prey are not replaced after they have been removed by the predators. In an earlier paper (Manly et al., 1972) consideration was given to situations where the replication of experiments allows the estimation of standard errors from the experimental results; in the present paper a table of standard errors is given for a large range of experiments and replication is therefore no longer necessary. The standard errors were calculated on an electronic computer by solving the exact equations given in the earlier paper. The suggested method of analysis is illustrated using some data where the prey were red and yellow artificial ‘maggots’ and the predators were garden birds.