Host Discrimination Behavior Research Articles

Common cuckoos do not mimic the size and shape of host eggs

AbstractOften considered a textbook example of coevolution, common cuckoo (Cuculus canorus) eggs are among the best-studied eggs in the world. Female cuckoos belong to genetically distinct host-races, each laying a specific egg type. When host species evolved to reject cuckoo eggs from their nests, cuckoos evolved better egg color and pattern mimicry. In this study, we asked: have cuckoos also evolved eggs that are well matched to host eggs in size and shape, and is the match better for highly discriminating hosts? We used digital image analysis to quantify the sizes and shapes of ~1230 eggs laid by ten European host species and their respective cuckoo host-races. We found that there is some variation in egg size and shape among host species. By contrast, different cuckoo host-races lay eggs that are—on average—similar in size and shape. This generic “one size and shape fits all” cuckoo egg morph is a poor match to most host egg sizes but a good match to most host egg shapes. Overall, we showed that host discrimination behavior was not correlated with the degree of egg size or shape similarity. We concluded that cuckoo females have not evolved egg size or shape mimicry. Alternative explanations for egg shape similarity include biophysical constraints associated with egg formation and selection for incubation efficiency. Finally, to place our results in a broader context, we compared the egg shapes of the common cuckoo and its hosts to those of three Australian parasitic cuckoo species and their hosts.

Effects of Insecticides on Oviposition and Host Discrimination Behavior in Trichogramma chilonis (Hymenoptera: Trichogrammatidae).

Trichogramma chilonis Ishii is an important natural enemy of many lepidopterous pests on various crops. Effects of two conventional insecticides on oviposition and host discrimination behavior in T. chilonis were evaluated in the laboratory through video tracking. During the oviposition period, when the number of host eggs was limited (only one host egg), females exposed to beta-cypermethrin LC1 or LC20 exhibited significantly higher feeding and re-drilling rate and significantly longer post-oviposition duration than control females. Spinosad LC20 treatment not only decreased the wasp oviposition rate but also significantly extended the oviposition duration. When the number of host eggs was six, similarly, females exposed to spinosad LC20 exhibited a significantly lower oviposition rate (79.2%) than control ones (100%). In the host discrimination experiment, females exposed to LC20 of both tested insecticides (beta-cypermethrin and spinosad) spent significantly more time on the extra-patch area. The females that survived spinosad LC20 could not discriminate between unparasitized and parasitized host eggs. Our study suggests that even the LC1 and LC20 of the tested insecticides had negative effects on the oviposition and host discrimination behavior of T. chilonis Thus, the use of these two insecticides should be carefully evaluated.

Mate choice and host discrimination behavior of the parasitoid Trichogramma chilonis.

Trichogramma chilonis Ishii (Hymenoptera: Trichogrammatidae) is an important natural enemy of many species of lepidopterous pests and a widely used biological control agent. Detailed knowledge about its mate choice and host discrimination behavior is lacking. In this study, we studied the mate choice and host discrimination behavior of T. chilonis in experimental arenas through video tracking. Males' mate recognition capacity was realized by perceiving the sex pheromone of females. When offered two females of different species, male could distinguish the conspecific female from Trichogrammatoidea bactrae Nagaraja (Hymenoptera: Trichogrammatidae), a species that has overlapping hosts with T. chilonis. When placed with two females of different mating status, male preferred mating with the virgin female to the mated female. T. chilonis females could distinguish unparasitized host eggs from parasitized ones (parasitized by conspecific females or heterospecific females). They preferred to stay on and lay eggs in unparasitized host eggs. When T. chilonis females were only provided with parasitized host eggs (parasitized by T. chilonis and T. bactrae females), conspecific superparasitism occurred more often than heterospecific superparasitism. Furthermore, the host egg discrimination ability of T. chilonis females was mainly achieved through antennal perception.

アブラムシの高次寄生蜂<i>Dendrocerus carpenteri</i>（ハチ目：オオモンクロバチ科）の既寄生寄主識別：行動過程とマーカーの化学的特性

Dendrocerus carpenteri（Curtis）and Asaphes suspensus（Nees）are common aphid hyperparasitoids that attack braconid parasitoids in mummified aphids. In this study, we investigated the host discrimination behavior of D. carpenteri in hosts parasitized by each of these hyperparasitoid species, and compared the behavioral process and chemical characteristics of host marks involved in host discrimination. Females of D. carpenteri significantly avoided host mummies parasitized by D. carpenteri and A. suspensus. The avoidance behavior was observed soon after antennal drumming（tapping on the mummy surface）in cases of host mummies parasitized either by D. carpenteri or A. suspensus. This demonstrates that chemical markers deposited on the mummy surface are important cues for host discrimination, regardless of the hyperparasitoid species. Methanol extracts of mummy cases separated from hosts previously oviposited by D. carpenteri induced oviposition avoidance behavior, while methanol and hexane extracts for markers deposited by A. suspensus were active. The adaptive role of the markers in mediating host discrimination by the two hyperparasitoid species and implications for possible use of the semiochemicals involved in future biological control programs are discussed.

Host discrimination by the endoparasitoid Psyllaephagus pistaciae (Hymenoptera: Encyrtidae): A case of time-dependent ability

Host-discrimination behavior by the koinobiont parasitoid, Psyllaephagus pistaciae Ferrière (Hymenoptera: Encyrtidae), the major biocontrol agent of the common pistachio psylla, Agonoscena pistaciae Burckhardt & Lauterer (Hemiptera: Psyllidae), in Iran, was investigated in the laboratory. The results demonstrated that P. pistaciae quickly detected and avoided freshly parasitized hosts, either after antennating or by probing with their ovipositor. However, this discriminatory ability declined with time, probably influenced by both external and internal markers left by the previous ovipositing female. The results also confirmed that female P. pistaciae responded to changes in host quality associated with the parasitoid's larval development 4 days after the initial parasitization, clearly indicating that the second female could detect the presence of the larvae and adjust her host-selection decision. In addition, psyllid nymphs treated topically with a solution of Dufour's gland were rejected by the parasitoid, showing that Dufour's gland secretion had a significant effect as a host marking chemical. The current study also showed that superparasitism increased the host-mortality and that the rate of encapsulation decreased, suggesting that, when two eggs are laid in the same psyllid nymph, only one parasitoid develops to an adult.

Intraspecific Variations in Host Discrimination Behavior in the Pupal Parasitoid <I>Pachycrepoideus vindemmiae</I> Rondani (Hymenoptera: Pteromalidae)

In solitary parasitoid species, superparasitism incurs a high cost because only one individual can emerge per host. While avoiding already-parasitized hosts seems advantageous, it requires an ability to discriminate between parasitized and unparasitized hosts. The ability to discriminate can be based on physical or chemical cues or signal associated either internally or externally with a given host. The type of stimuli used to recognize parasitized hosts generally depends on the features of these hosts but also on costs and benefits associated with reusing them. Some local factors such as mortality rate of females, host availability, and competition level can influence this trade-off. In species that occupy a large geographic range, local conditions may favor either external or internal mechanisms of host discrimination. We describe the behaviors associated with host discrimination in Pachycrepoideus vindemmiae Rondani (Hymenoptera: Pteromalidae), a solitary pupal parasitoid of cyclorraphous dipteran species. To detect potential intraspecific variability in their host discrimination behavior, we compared two P. vindemmiae populations originating from different geographical areas in France. Our results revealed different host discrimination strategies in both populations and indicated a potential trade-off between the speed and the accuracy of host discrimination. One population discriminated hosts externally (faster but less accurately), whereas the other discriminated internally (more slowly but more accurately). In our experimental conditions, these two strategies resulted in differences in the fitness gains of both populations. The ecological conditions that could have selected for such differences in the host discrimination and oviposition strategies of the two populations remain to be investigated.

Host location and host discrimination behavior of Telenomus isis, an egg parasitoid of the African cereal stem borer Sesamia calamistis.

In the Republic of Benin, the scelionid egg parasitoid Telenomus isis (Polaszek) is one of the most important control factors of the noctuid maize stem borer Sesamia calamistis. In the present study, the role of various sources of contact kairomones (male or virgin or mated female moths) and of the moth's oviposition substrate (leaf sheath versus filter paper: host plant species) in host location and oviposition behavior of T. isis was investigated in Munger cells, open arenas, and/or Petri dish assays. Furthermore, its ability to distinguish between unparasitized eggs and eggs parasitized by a conspecific female or by the trichogrammatid Lathromeris ovicida was studied. In the Munger cell experiment, T. isis spent more time in moths' odor fields than in the control. There was no difference between virgin and mated females. In the open arena assay, traces left by both the male and female moths acted as contact cues, which elicited an arrestment response in the parasitoid. The residence and patch retention time in the arena with virgin or mated females of S. calamistis was about 4.8 times as long as that with males. The presence of maize leaf sheaths stimulated the oviposition behavior of T. isis when compared to eggs offered on filter paper. During the first 6 hr, more eggs were parasitized on maize leaves, although there was no difference in the final number of offspring between the two substrates. In addition, if eggs of S. calamistis were offered together with different host plant species or alone, maize and sorghum were both more attractive than millet or the egg alone and equally attractive between themselves, indicating that the plant tissue influences host finding of T. isis. Both T. isis and L. ovicida recognized markings of conspecific females, and intraspecific superparasitism was therefore low. Interspecific superparasitism was more than three times higher for L. ovicida than for T. isis, indicating that only T. isis was able to recognize the marking of the other species and tried to avoid superparasitism. Emergence of parasitoids from multiparasitized eggs generally was in favor of L. ovicida regardless of species order.

Learning affects host discrimination behavior in a parasitoid wasp

Learning is generally predicted not to be important in host discrimination by parasitoids, because the stimuli involved are less variable than those used in habitat location. However, Anaphes victus (Hymenoptera: Mymaridae), an egg parasitoid of Listronotus oregonensis (Coleoptera: Curculionidae) apparently learns to associate external pheromones with the presence of a conspecific in a host. In this species, females can reject a parasitized host either after antennal drumming (antennal rejection) or after the insertion of their ovipositor (sting rejection). When they encountered a series of parasitized hosts, females A. victus learned to associate the presence of the external pheromone with the presence of the internal one. Learning lasted less than 4 h and occurred earlier in a series when the female marking the egg and the one detecting that mark were close relatives. This behavior could be adaptive because antennal rejection is faster than sting rejection.

Genetic Differentiation between Unionicola formosa and U. foili (Acari: Unionicolidae): Cryptic Species of Molluscan Symbionts

Genetic Differentiation between Unionicola formosa and U. foili (Acari: Unionicolidae): Cryptic Species of Molluscan Symbionts

Competition for hosts between two hyperparasitoids of aphids,Dendrocerus laticeps andDendrocerus carpenteri (Hymenoptera: Megaspilidae): The benefit of interspecific host discrimination

The two hyperparasitoids of aphids, Dendrocerus carpenteri(Curtis) and Dendrocerus laticeps(Hedicke), differ in their interspecific host discrimination behavior: D. carpenterireadily accepts hosts for oviposition previously parasitized by D. laticeps,whereas D. laticepsoften refrains from ovipositing on hosts previously parasitized by D. carpenteri.The two species also differ in their competitive abilities: D. carpenteriis competitively superior to D. laticepswhen the time between ovipositions is 1 h. D. carpenteri's superiority probably arises from (a) the action of the venom produced by the female to paralyze the host, as evidenced by the comparison of emergence patterns from naturally vs artificially parasitized hosts, and (b) its more rapid egg development. Because of its competitive abilities, D. carpenterigains only limited benefit from discriminating interspecifically, at least when encountering a host parasitized by a competitively inferior species, such as D. laticeps.In contrast, D. laticepsgains considerable benefit from recognizing hosts previously parasitized by D. carpenteri,as the probability to produce offspring from such hosts is greatly reduced.

INTERPOPULATION DIFFERENCES IN HOST PREFERENCE AND THE EVOLUTION OF LEARNING IN THE BUTTERFLY, BATTUS PHILENOR.

The host-discrimination behavior of the adult female pipevine swallowtail butterfly (Battus philenor) was investigated for two populations, an east Texas population that uses two host species with different leaf shapes and a Virginia montane population that uses one host species with a single leaf shape. While Texas and Virginia females exhibited similar chemotactile responses after landing on various host species, butterflies from each population landed more frequently on certain host species used by that particular population. Despite this difference in searching behavior, Texas and Virginia populations were equally capable of learning to search for the leaf shape of a particular host species in artificial enclosure arrays. In addition, learning of leaf-shape preference was confounded equally when each population was introduced into arrays containing all the host species found in both populations. The lack of differentiation in learning of leaf-shape preference between populations that differ in host breadth and host preference argues against the specific hypothesis that learning of leaf-shape preference represents a local adaptation that permits foraging butterflies in the east Texas population to respond to seasonal changes in the relative quality or abundance of host species that differ in leaf shape. Three hypotheses are proposed to explain the apparent absence of interpopulation genetic variation in learning traits. One hypothesis supposes that learning of leaf-shape discrimination is mediated by the same physiological mechanisms that permit females to learn to discriminate among suitable and unsuitable conspecific plants. Selection for restriction of learning of leaf-shape preference in the Virginia montane population may therefore be constrained by selection for learning of other types of discrimination behavior.