Foraging Behavior and Patch Time Allocation by Fopius arisanus (Hymenoptera: Braconidae), an Egg-Larval Parasitoid of Tephritid Fruit Flies

This study quantitatively describes the host-searching behavior of Fopius arisanus (Sonan) (Hymenoptera: Braconidae), an important egg-larval parasitoid of tephritid fruit fly pests, on coffee berries infested with host eggs of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae). We also investigate the parasitoid's response to local variation in host patch quality. The temporal pattern of behavioral organisation was examined by constructing an ethogram. The parasitoid spent over 90% of its foraging time in detecting and locating hosts after arriving on a host-infested fruit, and displayed a relatively fixed behavioral pattern leading to oviposition. Patch residence time increased in the presence of host-associated cues, following successful ovipositions, and with increasing size of host clutches per fruit, but decreased with each successive visit to the same host patch and with increasing availability of alternative host patches. The parasitoid females discriminated against previously parasitized hosts and spent significantly less time and searching effort on patches previously exploited by herself or by conspecific females. The effective host-searching behavior, perfect host discrimination ability, and success-motivated searching strategy shown by F. arisanus ensured a thorough exploitation of host resources by this parasitoid.     

Patch Time Allocation by the Parasitoid Diadegma semiclausum (Hymenoptera: Ichneumonidae). I. Effect of Interpatch Distance

We observed the foraging behavior of Diadegma semiclausum (Hymenoptera:Ichneumonidae), a larval parasitoid of the diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae), in a wind tunnel to determine how interpatch distance affects patch time allocation. Individual female wasps were released onto an experimental patch infested with host larvae and were allowed freely to leave for an identically extrapatch placed upwind of the experimental patch with varying interpatch distances. The effects of interpatch distance and within-patch foraging experience on the patch-leaving tendency of the parasitoid were analyzed bymeans of the proportional hazards model. Increasing interpatch distance andunsuccessful host encounter as a result of host defense decreased the patch-leaving tendency, while successful oviposition and unsuccessful search time since last oviposition increased the patch-leaving tendency. Asa result, both patch residence time and number of ovipositions by D. semiclausum increased with increasing interpatch distance, which appears to agree with the general predictions of the marginal value theorem that a parasitoid should stay longer and parasitize more hosts with increasing interpatch distance.     

Comparison of Host-Searching and Ovipositional Behavior of Cardiochiles nigriceps Viereck (Hymenoptera: Braconidae), a Parasitoid of Heliothis virescens (Fabricius) (Lepidoptera: Noctuidae), in Tobacco and Cotton

To compare host-searching and ovipositional behavior of Cardiochiles nigriceps Viereck (CN) in tobacco and cotton, behavior of CN females was observed on Hellothis virescens (Febricius)-infested plants and recorded using a Psion Organizer II with Observer software. Hover, search, oviposit, preen, rest, walk, agony-search, drop-search, and miss-search were the nine behaviors observed for each plant species. Agony-search was a searching behavior exhibited when CN females were prevented from ovipositing in a host because they were unable to reach the host. Drop-search and miss-search were the searching behaviors that occurred by CN females after a host dropped from the plant and when CN females missed ovipositing in a host, respectively. Hovering, searching, oviposition, miss-search, resting, and walking were equally common for CN on tobacco and cotton. Agony-search was exhibited more on tobacco than cotton, while drop-search and preening occurred more on cotton than tobacco. Female CN spent more time hovering in tobacco than in cotton, indicating that these females preferred tobacco to cotton. Female parasitoids also spent more time in the main ovipositional sequence, hover–search–oviposit, in tobacco than in cotton, mainly because females hovered more in tobacco than in cotton. Frequency and time of behavioral sequences associated with experiencing frustration in ovipositing due to difficulty in reaching or finding a host and subsequent level of success in ovipositing in a new host were determined. Overall, the rate of successful oviposition by CN females was significantly higher in tobacco (87.7%) than in cotton (79.5%). For cotton and tobacco, the rate of successful oviposition by CN females was significantly reduced (ca. 40.0%) when they experienced frustration in ovipositing compared to the rate of ovipositional success (100%) for CN females when hosts were present and easily accessible. Encountering ovipositional frustration also increased the duration of time for successful oviposition in comparison to the time spent for problem-free oviposition in cotton and tobacco. Interestingly, with successful oviposition, the amount of time spent in a behavioral sequence was not significantly different for tobacco and cotton regardless of whether females experienced ovipositional frustration or not. However, female CN invested more time in tobacco than in cotton when they were unsuccessful in ovipositing due to the inaccessibility or disappearance of hosts. CN females' preference for tobacco over cotton probably gave them more motivation to continue searching for hosts, especially those not easily attained, on tobacco than on cotton. Nevertheless, CN females readily searched in cotton for HV even in the presence of host-infested tabacco. CN females possibly could be successful in maintaining levels of HV below an economic threshold when using a tobacco trap crop to protect cotton as the main crop.     

Within-patch foraging behaviour of the aphid parasitoidAphidius funebris: plant architecture, host behaviour, and individual variation

The influence of plant architecture, host colony size, and host colony structure on the foraging behaviour of the aphid parasitoidAphidius funebris Mackauer (Hymenoptera: Aphidiidae) was investigated using a factorial experimental design. The factorial design involved releasing individual parasitoid females in aphid colonies consisting of either 10 or 20 individuals ofUroleucon jaceae L. (Homoptera: Aphididae) of either only larval instar L3 or a mixture of host instars, both on unmanipulated plants and on plants that had all leaves adjacent to the colony removed. Interactions between the parasitoid and its host were recorded until the parasitoid had left the plant. The time females spent on the host plant and the number of eggs laid varied greatly among females. Host colony size significantly affected patch residence time and the number of contacts between parasitoids and aphids. Plant architecture influenced the time-budget of the parasitoids which used leaves adjacent to the aphid colony for attacking aphids. Female oviposition rate was higher on unmanipulated plants than on manipulated plants. No further significant treatment effects on patch residence time, the number of contacts, attacks or ovipositions were found. Oviposition success ofA. funebris was influenced by instar-specific host behaviour. Several rules-of-thumb proposed by foraging theory did not account for parasitoid patch-leaving behaviour.     

Comparison of learning in related generalist and specialist eucoilid parasitoids

Effects of learning in two microhabitat specialists, Leptopilina boulardia Barbotin et al. and L. fimbriata Kieffer were compared to previous and new results of learning in the microhabitat generalist L. heterotoma Thomson. Females were given one or more oviposition experiences on hosts in different types of substrate. In all species oviposition experience affected the choice for a substrate, although this effect of learning was considerably less in L. fimbriata compared to the other two species. Patch times, known to be highly determined by experience in the generalist L. heterotoma, were much less flexible in the specialists. L. boulardi and L. fimbriata have fixed patch times on their natural substrate and have variable patch times on other substrates only. In all three species one oviposition affected the choice for a substrate. Additional ovipositions showed no different effect. An accumulative effect of the number of ovipositions on patch times was found in L. heterotoma only. Retention of the learning effect was only studied in L. boulardi, and was shown to be similar to that reported for L. heterotoma, i.e. two to three days. Although learning was found in both the generalist and the specialist species studied, it seems to affect their foraging behaviour differently.     

Effects of pre-adult and adult experience on host acceptance in choice and non-choice tests in two strains ofTrichogramma

The effect of adult learning through an oviposition experience, and pre-adult learning through development inside a host was investigated in two strains of an Australian egg parasitoid,Trichogramma nrivelae (Hymenoptera: Trichogrammatidae). Host response was measured in two types of laboratory preference tests. In single host tests, females reared on three lepidopteran hosts (Heliothis punctigera (Noctuidae),Papilio aegeus (Papilionidae), andHypolimnas bolina (Nymphalinae)) were presented host eggs individually, and allowed two ovipositions. Pre-adult experience affected host preference in only one strain, while acceptance of a host was increased in both strains when they had previously oviposited in this host species. An oviposition experience had a stronger effect on host preference than pre-adult experience. In choice tests, pairwise combinations of hosts were arranged in an alternating grid. The ratio of host acceptances to host contacts was computed for the whole test and up to the first oviposition. These indicated that effects of rearing host were weak or absent, but the host chosen initially had a strong effect on host preference. Relative size of the hosts had a strong effect on choice of the first host. The implications of learning inTrichogramma are discussed in relation to host preference testing procedures and the selection of candidate strains for mass rearing and inundative release.     

Larvicidal activity of lectins onLucilia cuprina: mechanism of action

Foraging behaviour and host-instar preference of young and old females of the solitary aphid parasitoid,Lysiphlebus cardui Marshall (Hymenoptera: Aphidiidae), were studied in the laboratory. The analysis of interactions between parasitoids and different stages ofAphis fabae cirsiiacanthoidis Scop. (Homoptera: Aphididae) revealed that encounter rates between aphids and parasitoid females and defence reactions of the aphids influenced the degree to which a particular aphid age class is parasitized. Encounter rates between hosts and parasitoid females depended on the foraging pattern of the parasitoid, which varied with age. In mixed aphid colonies patch residence time increased with parasitoid age. Furthermore, younger parasitoids (≦1 day old) laid more eggs into second and third instars, while older parasitoids (≧4 days old) did not show distinct host instar preferences. It is suggested that the oviposition behaviour ofL. cardui is influenced by the physiological state, i.e. the age of the wasp.     

Influence of adult experience on host microhabitat location by the generalist parasitoid,Campoletis sonorensis (Hymenoptera: Ichneumonidae)

The effect of adult experience on microhabitat location behavior of the generalist parasitoid Campoletis sonorensis (Cameron)was examined in a wind tunnel bioassay. Responses were tested to the odors of two host plants (cotton and sesame) of Heliothis virescens (F.) or a nonhost plant (potato), either damaged and infested with host larvae and host products (host/plant complex) or intact, clean and uninfested. Parasitoid females remained naive or were allowed one oviposition experience on either of the plants, 1 min, 2 h, or 24 h prior their introduction into the wind tunnel. In a no-choice test, parasitoids experienced 1 min prior to bioassay completed significantly more flights to sesame and potato host/plant complexes than did naive parasitoids. However, 24 h after experience, only females experienced on potato completed more flights to the host/ plant complex than did naive females. Parasitoids experienced 1 min prior to flight to undamaged plants showed a slight increase in flight response (significant only for potato) but, after 24 h, completed only as many flights as naive parasitoids. In a dual-choice situation, parasitoids did not show a preference for either of the two host plants but did prefer a host to a nonhost plant. This innate plant preference was not changed by a single oviposition experience. The potential significance of these results to the microhabitat location behavior of C. sonorensisin the field is discussed.     

Patch Time Allocation by a Parasitoid: The Influence of Con-specifics,Host Abundance and Distance to the Patch

Patch residence time is at the core of models of decision making by foragers living in patchy environments. We studied patch residence time (PRT) of Ibalia leucospoides, a parasitoid of the woodwasp Sirex noctilio, as assigned to 4 treatments (recent feeding and/or oviposition experience) foraging in an array of host-infested pine logs. We tested the effects of distance from release point, host abundance, and the number of con-specifics at the time of arrival, on patch (pine log) residence time. PRT depended on a combination of patch quality (number of hosts in a log) and distance from the release point. Neither the presence of con-specifics on the patch, prior exposure to hosts, nor feeding prior to the experiment affected the time spent on a patch. We conclude that PRT in I. leucospoides meets Marginal Value Theorem predictions qualitatively, overruling the effects recent oviposition experience, access to food and contact with conspecifics. These findings are in line with the reported pro-ovigeny in I. leucospoides as well as the strong spatial aggregation of hosts in the field.     

Olfactory Associative Learning of the Pupal Parasitoid Pimpla luctuosa Smith (Hymenoptera: Ichneumonidae)

Laboratory experiments were conducted to determine the role of learning in olfactory host searching by the ichneumonid pupal parasitoid, Pimpla luctuosa Smith. Females learned to associate novel odors such as vanilla and strawberry with hosts when they oviposited in at least several hosts with the odors. Repeated experiences of hosts with an odor increased the response of the experienced odor, and females that had experienced host odor seven times responded to the experienced odors 90% of the time. Although the response by females to a learned odor gradually decreased with increasing host-deprivation time, 60% of the females that had experienced host odor 7 days earlier still responded to the experienced odor. Females also learned two separate odors associated with hosts at a time and responded to both odors without a preference for one odor over the other. When trained two separate odors with hosts, females learned the second odor more quickly than the first odor. After females experienced several stings in simulated hosts with the previously learned odor, they ceased to respond to the learned odor, suggesting that repeated unrewarding experiences cause females to cease to respond to the learned odors.     

The influence of prior experience on preference and performance of a cryptoparasitoid Scleroderma guani (Hymenoptera: Bethylidae) on beetle hosts

1. Numerous studies have reported the effects of learning or experience on parasitoid host preference and location. However, the integration of pre‐imaginal and adult experiences on the subsequent host preference and adult/offspring performance has been rarely tested in host–parasite interactions. 2. We present direct evidence that theses two kinds of experiences affect host preference and related fitness in the polyphagous parasitoid, Scleroderma guani. Two colonies of parasitoids were reared on Monochamus alternatus and Saperda populnea (Cerambycidae: Lamiinae). Individuals from the two colonies were given host‐switching experience for one generation (pre‐imaginal experience) while other individuals were given prior ovipositing experience on the two species, respectively (adult experience). 3. Scleroderma guani females demonstrated that their experiences determined adult behavioural responses and their subsequent performance to hosts. Females maximised both adult fitness (fecundity and longevity) and offspring fitness (survival and sex ratio) when they encountered hosts similar to their maternal hosts. Behavioural plasticity in host choice was affected by adult experience, resulting in improved adult feeding and ovipositing behaviour and further modifying adult fecundity and the offspring sex ratio. There was a positive correlation between oviposition preference and adult fecundity. 4. The results indicated that S. guani exhibited positive preference–performance correlations. This is most likely due to an adaptation to maternal hosts over multiple generations. However, foraging potential of adults to available cues from hosts may be driven quickly by an experience‐induced learning process rather than by natural selection processes shaped over many generations.     

Olfactory host location and learning in the granary weevil parasitoidLariophagus distinguendus (Hymenoptera: Pteromalidae)

The sources of volatiles that attract the parasitoid Lariophagus distinguendus(Först.) to its hosts, the larvae of the granary weevil Sitophilus granarius(L.) infesting grains of Triticum aestivumL., were investigated in bioassays. The influence of oviposition experience on the responsiveness of the parasitoids to the sources of volatiles was considered. The potential sources of attractants are the host larvae, their feces, and the grain infested by the host. Weevil larvae were not attractive. Feces were attractive to females without and females with oviposition experience. Infested grains from which the larvae and feces were removed were slightly attractive to inexperienced, but very attractive to experienced females. Healthy and artificially damaged grains were attractive to experienced parasitoids only. Refering to the “variable response model,” we discuss the effect of experience on the response of the parasitoids to the several stimuli. Stimuli from different trophic levels are used by the foraging parasitoids: feces of the host larvae is an important source of attractants, but also the grains, particularly after experience.     

Do foraging bumblebees scent-mark food sources and does it matter?

Summary The foraging of worker bees of Bombus terrestris visiting artificial feeders in a climatic test chamber was investigated. The behaviour of worker bees visiting rewarding and unrewarding feeders is completely different. Of all flower visits to rewarding feeders 94% are probing-visits, i.e. the bees land on the flower and probe for nectar. In contrast, only 0.3% of all visits to unrewarding feeders are probing-visits, whereas 47% are approach-visits, i.e., the bees approach the feeders without landing. Exchanging feeder discs proves that the signal used for discrimination must be associated with the plastic disc used as landing platform. Most probably it involves scent-marking of the rewarding feeders with components of high and low volatility. The mean foraging efficiency of bees in a scent-marked foraging arena is 5.7 mg sugar/min and drops to 2.8 mg sugar/min after the scent marked discs are replaced by clean ones. Three components generate this drop in foraging efficiency: (1) the between-flower flight time increases, i.e. the bees search for a longer time before landing on flowers, (2) the bees no longer discriminate between rewarding and unrewarding feeders, and (3) the bees probe empty feeders longer than necessary; obviously they expect to find nectar.     

Patch marking in the aphid hyperparasitoid,Dendrocerus carpenteri: the information contained in patch marks

The aim of this study was to test if females of the aphid hyperparasitoid Dendrocerus carpenteri (Curtis produce patch marks. We tested if these marks inform a foraging female of the identity of the producer of the mark (the female herself or a conspecific female) and on the producer's success or failure in finding hosts in the marked area. We also tested if the responses to patch marks differ depending on the size and/or egg load of the female. On average, females walked shorter paths and spent less time in previously explored areas in comparison to control areas only if the area had first been explored successfully (host found) by a conspecific female. If no host had been found or if the area had been explored by the same female previously, no differences between average values were recoreded. However, egg load also seemed to influence foraging decisions in those experiments where average values were not different between previously explored and control areas. Females with a low egg load tended to spend less time in previously explored areas than females with a high egg load. Average values therefore somehow obscured the individual responses to pathc marks. The results suggest that at least D. carpenteri females with a low egg load continuously apply a marking pheromone while walking. This pheromone seems to contain information on the identity of the producer. In addition, different pheromones seem to be applied depending on whether or not hosts are present in the area.     

Increased host acceptance in experienced females of the parasitoid Brachymeria intermedia: which types of oviposition behaviour contribute to experience?

Brachymeria intermedia (Nees) (Hymenoptera: Chalcididae) is a solitary endoparasitoid of the gypsy moth, Lymantria dispar (L.) (Lepidoptera: Lymantriidae). The probability that a wasp will parasitise this host is increased if she had a previous oviposition experience. We investigated which types of pre-oviposition and oviposition behaviour induced this change by comparing the acceptance behaviour of wasps with zero to five oviposition experiences as well as wasps with various partial host handling experiences (from no contact with a host to one complete oviposition sequence). The percentage of females accepting the host increased gradually with both the number of previous oviposition experiences and the amount of handling of a single host. Furthermore, the naive females were less likely (44%) to walk to the host than females with a variety of experiences (72–100%). A single antennal contact with the host was sufficient to increase the probability of walking to the host. Additional handling and additional oviposition experiences further elevated the propensity to oviposit. Thus, the modification of the acceptance behaviour through experience was essentially a gradual process in which antennal contact with a pupa was a major element. It is suggested that naive wasps learned the host odour when they first antennated a pupa. As a result, they were attracted to the host odour in subsequent encounters.     

Flexible patch time allocation by the leafminer parasitoid, Opius dimidiatus

Abstract.

• 1 The ability to use flexible decision rules can be an advantage to parasitoid females searching for patchily-distributed hosts. In a series of laboratory experiments the hypothesis that Opius dimidiatus, a solitary parasitoid of the chrysanthemum leafminer (Liriomyza trifolii), adjusts the time she allocates to searching for her larval hosts in response to both patch qualities and experiences with hosts was tested by varying such patch parameters as area, presence of host mines and density of host mines, and by allowing ovipositions and encounters with parasitized hosts.
• 2 Though leaf area was not a factor, the presence of host mines in a leaf did increase the time a female O.dimidiatus spent searching, over time spent on unmined leaves.
• 3 When host mine density was increased, females responded by increasing their search period in a density-dependent manner, suggesting a perception of patch quality.
• 4 Ovipositions in hosts caused females to reset their‘giving-up time’(GUT), or increase search intensity, by adding an amount of search time that increased with each successive oviposition. Conversely, encounters with parasitized (unsuitable) hosts incremented the GUT, but by an amount that decreased with each successive encounter.

     

Adult experience modifies attraction of the leafminer parasitoidOpius dissitus (Hymenoptera: Braconidae) to volatile semiochemicals

Oviposition-experienced females of Opius dissitus Muesebeck, a braconid parasitoid of Liriomyza sativaeBlanchard, preferentially landed on leafminer-infested rather than uninfested lima bean (Phaseolus lunatus L.) plants in a flight tunnel assay. Both naive and oviposition-experiencedparasitoids responded strongly to odors of infested lima bean plants in a four-arm olfactometer in comparison with odors of uninfested plants, suggesting that volatile semiochemicals are used in host location. Parasitoids with an oviposition experience on lima bean (lima-experienced) spent significantly more time in the infested odor than naive individuals, however, eggplant-experienced wasps did not spend significantly more time in the infested odor field than naive wasps. When parasitoids reared on leafminers in lima bean were provided a choice between the odor of infested lima bean and the odor of infested eggplant or cotton, naive and lima-experienced wasps preferred infested lima odor. An oviposition experience on the other plant species resulted in a dramatic shift in preference. It was concluded that the experience effect was due, at least in part, to associative learning, as has been reported for other parasitoids. The parasitoids may perceive unconditioned stimuli during host contact and oviposition on an infested leaf and may associate those stimuli with volatile semiochemicals emanating from the leaf or host. Subsequently, the volatiles associated with the presence of hosts are used in directing the search for hosts.     

Influence of Conspecific Presence, Experience, and Host Quality on Oviposition Behavior and Clutch Size Determination in Anastrepha ludens (Diptera: Tephritidae)

Females of some insect species adjust the number of ovipositions and clutch size adaptively depending on conspecific density and probably experience. In a series of three experiments, we examined the effect of the presence of conspecifics, host quality, and oviposition experience on oviposition behavior and clutch size determination by females of the polyphagous fruit fly Anastrepha ludens (Diptera: Tephritidae). In the first experiment, we determined that grouped (eight females per cage) A. ludens females tended to visit and oviposit in more hosts than did solitary females probably as a result of stimulation by the presence of conspecifics. We also determined that females with previous oviposition experience visited and oviposited in more hosts than inexperienced ones. Importantly, when females were grouped, we observed significantly more landings on unoccupied hosts (i.e., devoid of flies) than on occupied ones (i.e., with at least one fly on it). However, oviposition experience, and not female density, was the most important factor affecting clutch size. Naive females deposited larger egg clutches than experienced ones. In the second experiment, we found that oviposition experience and host quality (i.e., clean fruit or fruit covered with a host marking pheromone [HMP] extract), influenced clutch size and the decision of females to defend or not defend the host. Clutch size and number of fights were greater on clean than on HMP-marked hosts. In the third experiment, we observed that host quality (i.e., size) played a significant role with regard to the number of female fights, host marking behavior, and clutch size. Specifically, females fought and dragged their aculeus longer on small- and medium-sized hosts than on large ones. But this behavior varied according to whether females were kept alone or grouped. Clutch size was greatest in the largest hosts. Considering all the above, we believe that the observed increase in ovipositional activity by grouped A. ludens females can be attributed to competition through mutual interference and not social facilitation as has been reported in other tephritid species.     

Carry-over effects of bumblebee associative learning in changing plant communities leads to increased costs of foraging

Flower visitors learn to avoid food-deceptive plants and to prefer rewarding ones by associating floral cues to rewards. As co-occurring plant species have different phenologies, cue-reward associations vary over time. It is not known how these variations affect flower visitors’ foraging costs and learning. We trained bumblebees of two colonies to forage in a community of deceptive and rewarding artificial inflorescences whose flower colours were either similar or dissimilar. We then modified the community composition by turning the rewarding inflorescences into unrewarding and adding rewarding inflorescences of a novel flower colour. In the short term, bees trained to similar rather than dissimilar inflorescences experienced higher costs of foraging (decreased foraging speed and accuracy) in the novel community. The colonies differed in their speed-accuracy trade-off. In the longer term, bees adapted their foraging behaviour to the novel community composition by increasingly visiting the novel rewarding inflorescences.     

Can imperfect host discrimination explain partial patch exploitation in parasitoids?

1. Host discrimination by Aphidius rhopalosiphi (De Stefani Perez) (Hymenoptera: Braconidae) was first studied on the grain aphid Sitobion avenae (Fabricius) (Homoptera: Aphididae). Females tended to avoid oviposition in hosts parasitised 3 h earlier. No evidence of host discrimination ability on freshly parasitised hosts was suggested, however, and ovipositional experience had no effect on host discrimination. 2. The effects of host discrimination ability on the exploitation strategy of patches containing different proportions of unparasitised hosts and hosts parasitised for 3 h were studied. Females spent less time on patches with a higher proportion of parasitised hosts, reflecting the females' ability to perceive the potential profitability of the patch. This ability may be based on the nature of the hosts encountered (unparasitised or parasitised). 3. Incomplete exploitation of unparasitised hosts was also observed. It seems that this partial exploitation is related to the inability of A. rhopalosiphi to recognise freshly parasitised hosts. As a female may experience a risk of self‐superparasitism during patch depletion, this could promote early departure from incompletely exploited patches. 4. The effect of previous experience on the patch exploitation strategy was also assessed. Females were tested twice on two patches of the same quality. Results suggested that the experience acquired during a previous visit led the females to leave the patch sooner and to lay fewer eggs in parasitised hosts. 5. Patch exploitation strategy may therefore be the result of different factors such as host discrimination and experience. The evolutionary consequences of the results are discussed.