Contact Kairomones Mediating the Foraging Behavior of the Aphid Hyperparasitoid Alloxysta victrix (Westwood) (Hymenoptera: Charipidae)

A variety of host-related substances was assessed in relation to their ability to induce arrestment and antennal examination behavior in adult females of the aphid hyperparasitoid Alloxysta victrix (Westwood). In laboratory bioassays, whole-body homogenates of both unparasitized host aphids [Myzus persicae (Sulzer)] and those parasitized by the primary parasitoid Aphidius colemani Viereck failed to elicit a response. However, significant kairomonal activity was associated with aphid cornicle secretions, aphid honeydew, and solvent extracts of parasitized aphids. Solvent extracts of unparasitized aphids (in either hexane or butan-1-ol) failed to elicit arrestment or antennal examination behavior in hyperparsitoid females. The response to aphid honeydew was significantly lower in experienced females than in naive individuals, suggesting that even relatively strong innate responses can be modified by learning.     

Physical and chemical cues influencing the oviposition behaviour of Aphidius ervi

The oviposition behaviour of the aphid parasitoid Aphidius ervi Haliday is influenced by both chemical and physical cues. Oviposition attack responses were elicited by paint pigments sealed into the tip of a glass capillary tube. Parasitoids reacted to yellow pigments with repeated oviposition attack responses, but they did not react to green pigments. The spectrum of reflected light from the yellow pigments was very similar to that from the `green' natural host Acyrthosiphon pisum (Harris), with a high proportion of the total radiation energy being emitted in the yellow-orange wavebands (580–660 nm). Pea aphid cornicle secretion also elicited oviposition attack responses, which were not exclusively induced by its pale yellow-green colour. In fact, the oviposition attack response to capillary tips coated with cornicle secretion remained evident under red light conditions, which, in contrast, nearly completely suppressed the response to yellow pigments. Chemical compounds from cornicle secretion do not appear to be involved in parasitoid orientation, even though they stimulate intense oviposition attack responses. Olfactometer experiments showed that the putative kairomone involved acts only at very short range or on contact. Host exuviae, which also elicited strong and persistent oviposition reactions from A. ervi females, appear to be a good alternative source of ovipositional kairomone(s). This work confirms the existence of an aphid cuticular kairomone.     

Oviposition vs. offspring fitness in Aphidius colemani parasitizing different aphid species

We measured the acceptance and suitability of four aphid species [Aphis gossypii Glover, Myzus persicae (Sulzer), Rhopalosiphum padi (L.), and Schizaphis graminum (Rondani)] (Homoptera: Aphididae) for the parasitoid Aphidius colemani Viereck (Hymenoptera: Braconidae). Female parasitoids parasitized fewer R. padi than the other three aphid species, and fewer offspring successfully completed development in R. padi than in the other three host species. Sex ratios of emerging adults were more male‐biased from R. padi than from the other three aphid species, suggesting that R. padi is a poor quality host for this population of A. colemani. Ovipositing A. colemani encountered R. padi at a slower rate, spent more time handling R. padi, and parasitoid offspring died at a higher rate in R. padi compared to A. gossypii. Our results show that oviposition behavior and offspring performance are correlated. In each experiment, we tested the effect of the host species in which the parasitoids developed (parental host) on the number of hosts attacked, the proportion of each host species accepted for oviposition and the survival of progeny. Parental host affected maternal body size and, through its effect on body size, the rate of encounter with hosts. Other than this, parental host species did not affect parasitism.     

Optimal foraging by an aphid parasitoid affects the outcome of apparent competition

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Can polyphagous predators control the bird cherry-oat aphid (Rhopalosiphum padi) in spring cereals?: A simulation study

Predation by two carabid species,Bembidion lampros (Herbst.) andPterostichus cupreus L., on the cereal aphid,Rhopalsiphum padi L., was described using a discrete event simulation model. The results were incorporated into an aphid population growth model. The aphid model was run using actual temperatures,R. padi emigration rates, field densities and distributions from three years with distinctly different aphid population levels. Predation was incorporated at different time periods. Predation during the arrival of emigrants and establishment of aphid populations had approximately the same effect as predation over the entire aphid period, whereas predation during the 20 days prior to peak had very little effect on resulting peak populations. We conclude that a) yearly levels ofR. padi infestation are mainly determined by the volume and intensity of emigrants; b) peak levels are sensitive to changes in predator density; and c) in some cases an outbreak ofR. padi may be prevented by the action of spring active polyphagous predators alone.     

The role of physical cues in the regulation of host recognition and acceptance behavior ofAphidius ervi Haliday (Hymenoptera: Braconidae)

The role of color and shape in the host recognition and acceptance behavior ofAphidius ervi Haliday was studied. A quantitative analysis of the oviposition behavior ofA. ervi was carried out with a computer-aided analysis of 150 video-recorded oviposition sequences on its natural host,Acyrthosiphon pisum (Harris). The importance of visual stimuli was assessed in a choice condition bioassay, observing the behavioral reaction of female parasitoids to various test materials flame-sealed into glass capillaries. Glass beads 2 and 6 mm in diameter and a flat arena were coated with cornicle secretion ofA. pisum, and their acceptance rates by both naive and experienced female parasitoids were assessed under no-choice conditions. In most cases,A. ervi females switched from random searching to attack position when the host was within a range of 1 cm, suggesting that host recognition is regulated in part by cues acting before physical contact. The glass capillary bioassay indicated that visual cues are important factors in the host recognition and acceptance phases. Pea aphid color alone can elicit the oviposition response of naiveA. ervi females, and this response is enhanced when color is combined with aphid shape. The cornicle secretion ofA. pisum stimulated an oviposition response which was stronger in naive females ofA. ervi than in experienced ones and was not significantly affected by the glass bead size or flat surface. These results, along with those from previous studies, suggest that manipulation of the oviposition behavior ofA. ervi is feasible under laboratory conditions.     

Influence of cornicle droplet secretions of the cabbage aphid,Brevicoryne brassicae,on parasitism behavior of na＇fve and experienced Diaeretiella rapae

Insects have evolved amazing methods of defense to ward off enemies. Many aphids release cornicle secretions when attacked by predators and parasitoids. These se cretions contain an alarm pheromone that alerts other colony members of danger, thereby providing indirect fitness benefits to the releaser. In addition, contact with cornicle se cretions could also threaten an attacker and could provide direct fitness to the releaser. However, cornicle secretions may also be recruited as a kairomonal cue by aphid natural enemies. In this study, we investigated the effect of the cornicle droplet volatiles of the cabbage aphid, Brevicoryne brassicae （L.）, on the hostsearching behavior of naive and experienced female Diaeretiella rapae （M＇Intosh） parasitoids in olfactometer studies. In addition, we evaluated the role ofB. brassicae cornicle droplets on the oviposition prefer ence of the parasitoid in a twochoice bioassay. Naive females did not exhibit any preference between volatiles from aphids secreting cornicle droplets over nonsecreting aphids, while experienced parasitoids exploited the secretions in their host location. Experienced females were also able to choose volatiles from both secreting and nonsecreting aphids over clean air, while this ability was not observed in naive females. Although secretion of cornicle droplets did not influence the percentage of first attack in either naive or experienced females, the success of attack （i.e. resulting in a larva） was significantly different between secreting and nonsecreting aphids in the case of experienced parasitoids.     

The price of protection:a defensive endosymbiont impairs nymph growth in the bird cherry-oat aphid,Rhopalosiphum padi

Bacterial endosymbionts have enabled aphids to adapt to a range of stressors,but their effects in many aphid species remain to be established.The bird cherry-oat aphid,Rhopalosiphum padi(Linnaeus),is an important pest of cereals worldwide and has been reported to form symbiotic associations with Serratia symbiotica and Sitobion miscanthi L-type symbiont endobacteria,although the resulting aphid phenotype has not been described.This study presents the first report of R.padi infection with the facultative bacterial endosymbiont Hamiltonella defensa.Individuals of R.padi were sampled from populations in Eastern Scotland,UK,and shown to represent seven R.padi genotypes based on the size of polymorphic microsatellite markers;two of these genotypes harbored H.defensa.In parasitism assays,survival of H.defensa-infected nymphs following attack by the parasitoid wasp Aphidius colemani(Viereck)was 5 fold higher than for uninfected nymphs.Aphid genotype was a major determinant of aphid performance on two Hordeum species,a modern cultivar of barley H.vulgare and a wild relative H.spontaneum,although aphids infected with H.defensa showed 16%lower nymph mass gain on the partially resistant wild relative compared with uninfected individuals.These findings suggest that deploying resistance traits in barley will favor the fittest R.padi genotypes,but symbiontinfected individuals will be favored when parasitoids are abundant,although these aphids will not achieve optimal performance on a poor quality host plant.     

Quality of different aphids as hosts of the parasitoid Lysiphlebus testaceipes (Cresson) (Hymenoptera: Braconidae, Aphidiinae)

Lysiphlebus testaceipes (Cresson) has a broad aphid host range; however the quality of these preys may interfere in its biological feature. This study aimed to evaluate the quality of three Macrosiphini, Brevicoryne brassicae (L.), Lipaphis erysimi (Kaltenbach) and Myzus persicae (Sulzer), and three Aphidini Schizaphis graminum (Rondani) Rhopalosiphum maidis (Fitch) and Aphis gossypii Glover as hosts to L. testaceipes and to determine the relation possible of host preference, of size and quality of the host. The tests were carried out in climatic chamber at 25 +/- 1 degrees C, RH 70 +/- 10% and 12h photophase. The parasitoid did not oviposite in B. brassicae and L. erysimi, while the other species were nutritionally suitable to the parasitoid. L. testaceipes showed preference for aphids from tribe Aphidini and these hosts presented better quality to the parasitoid when compared to Macrosiphini. Interactions among size, preference and quality between the Aphidini were found. L testaceipes showed preference (parasitism rate 76.7%) for R. maidis, the bigger host (hind tibia with 0.281 mm). This host provided bigger size (hind tibia with 0.49 mm) and higher emergence rate (95.6%) to the parasitoid when compared to A. gossypii (parasitism rate of 55.7%). Also the smaller host A. gossypii (0.266 mm) provided smaller size hind tibia (0.45 mm) and higher mortality of the parasitoid (emergence rate 72.1%). However, the development time was shorter and the longevity was higher in A. gossypii (6.3 and 5.4 days, respectively) when compared to the host R. maidis (6.7 and 3.8 days, respectively), and not been related to host size.     

In vitro enzymatic chlorophyll catabolism in wheat elicited by cereal aphid feeding

Chlorophyll degradation is a complex phenomenon that often accompanies insect feeding damage to plants. Loss of chlorophyll can be initiated by several reactions, including oxidative bleaching, chlorophyllase activity, and Mg-dechelatase activity. Extracts from the Russian wheat aphid [Diuraphis noxia (Mordvilko)], the bird cherry-oat aphid [Rhopalosiphum padi (L.)], and aphid-infested and uninfested wheat plants were assayed in vitro for activities involved in chlorophyll degradation. Although the initial infestation was the same (10 apterous adults) for both aphid species, D. noxia weight was significantly higher than R. padi after feeding for 12 days. Consequently, D. noxia feeding caused greater fresh leaf weight reduction than R. padi feeding. Chlorophyll degradation assays showed no activity from either D. noxia or R. padi extracts. Plant extract assays showed a significant difference in Mg-dechelatase activity, while no difference was detected in either the chlorophyllase or oxidative bleaching pathways among the aphid-infested or uninfested plant extracts. Diuraphis noxia-infested leaf extracts showed a greater increase of Mg-dechelatase activity than either R. padi-infested or the uninfested plants. The findings suggest that leaf chlorosis elicited by D. noxia feeding is different from the chlorophyll degradation that occurs in natural plant senescence. Aphid-elicited chlorosis might be the result of a Mg-dechelatase-driven catabolism of chlorophyll in challenged wheat seedlings, however, the factor(s) from D. noxia that elicited the increase of Mg-dechelatase activity still remain to be determined.     

Winter host exploitation influences fitness traits in a parasitoid

Organisms can either evade winter's unfavourable conditions by migrating or diapausing, or endure them and maintain their activities. When it comes to foraging during winter, a period of scarce resources, there is strong selective pressure on resource exploitation strategy. Generalist parasitoids are particularly affected by this environmental constraint, as their fitness is deeply linked to the profitability of the available hosts. In this study, we considered a cereal aphid–parasitoid system and investigated (1) the host–parasitoid community structure, host availability, and parasitism rate in winter, (2) the influence of host quality in terms of species and instars on the fitness of the aphid parasitoid Aphidius rhopalosiphi De Stefani‐Perez (Hymenoptera: Braconidae: Aphidiinae), and (3) whether there is a detectable impact of host fidelity on parasitism success of this parasitoid species. Host density was low during winter and the aphid community consisted of the species Rhopalosiphum padi L. and Sitobion avenae Fabricius (both Hemiptera: Aphididae), both parasitized by A. rhopalosiphi at non‐negligible rates. Aphidius rhopalosiphi produced more offspring when parasitizing R. padi compared with S. avenae, whereas bigger offspring were produced when parasitizing S. avenae. Although aphid adults and old larvae were significantly larger hosts than young larvae, the latter resulted in higher emergence rates and larger parasitoids. No impact of host fidelity on emergence rates or offspring size was detected. This study provides some evidence that winter A. rhopalosiphi populations are able to take advantage of an array of host types that vary in profitability, indicating that host selectivity may drop under winter's unfavourable conditions.     

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.     

The effect of banker plant species on the fitness of Aphidius colemani Viereck and its aphid host (Rhopalosiphum padi L.)

Banker plants, a type of open-rearing unit, are increasingly used in greenhouse crops to sustain natural enemy populations at times of low pest abundance. The most common banker plant system is a non-crop, cereal plant which supports Rhopalosiphum padi L. as an alternative host for Aphidius colemani Viereck. Although bottom-up effects of plants are known to affect natural enemies, this aspect has generally been ignored in previous investigations of banker plant efficacy. Here, we tested four cereal plant species with three varieties each to investigate host plant effects on R. padi and A. colemani. Though limited differences were observed in laboratory experiments spanning one aphid or parasitoid generation, longer greenhouse experiments spanning several generations revealed significant plant effects on both insects. R. padi performed poorly on oats (Avena sativa L.), resulting in wasps with the longest female development time, lowest emergence rates, and the lowest number of wasps produced per unit. Rye (Secale cereal L.) – intermediate in terms of aphid performance – produced a significantly male-biased wasp population with the smallest males. Conversely, R. padi placed onto either wheat (Triticum aestivum L.) or barley (Hordeum vulgare L.) performed consistently well in terms of aphid and parasitoid fitness and abundance, though neither species was obviously superior over the other. Overall, cultivars within each plant species did not significantly affect outcomes. As each plant species tested had different positive effects on aphid and parasitoid phenotypes, the potential benefits of mixing of cereal species is an area for future investigation.     

Host plant and natural enemy impact on cereal aphid competition in a seasonal environment

Competition between phytophagous insects could be mediated by differential impact of natural enemies or by induced changes in host plant quality. The interaction between the aphids Sipha flava and Rhopalosiphum maidis on the shared host plant, Sorghum halepense , was evaluated during the fall and spring seasons in the presence or absence of natural enemies in a garden experiment. During the fall, S. flava was negatively affected by R. maidis in all treatments. However, during the spring season, S. flava was not affected by R. maidis when natural enemies were excluded, and positively affected by R. maidis with natural enemies present. Rhopalosiphum maidis was negatively affected by S. flava during the fall and spring seasons under all treatments. Laboratory experiments demonstrated that changes in host plant quality induced by S. flava attack and the presence of the parasitoid Lysiphlebus testaceipes negatively affected R. maidis , but not S. flava . Under abiotic conditions simulating fall and spring (lower temperature and daylength in the fall than in the spring), S. flava showed lower performance than R. maidis under "fall" conditions, and both aphid species showed similar life history traits under "spring" conditions. For S. flava , the time to the first reproduction and longevity were longer, and the nymphal production was lower, under "fall" conditions than under "spring" conditions. Our results showed that S. flava is benefited when R. maidis and the parasitoid L. testaceipes are present but the abiotic conditions are not adverse.     

Host range limitation caused by incomplete host regulation in an aphid parasitoid

Defining host ranges in parasitoid insects is important both from a theoretical and an applied point of view. Based on the literature, some species seem able to use a wide range of hosts, while field studies indicate possible local host specialization. In koinobiont endoparasitoid species, such specialization could involve physiological processes. We tested the ability of two strains of the cosmopolitan and polyphagous parasitoid Diaeretiella rapae, to develop in three of its recorded aphid host species. Both strains produced high parasitism rates on the cabbage aphid Brevicoryne brassicae and the green peach aphid Myzus persicae but almost no progeny on the cherry-oat aphid Rhopalosiphum padi. This last species was less attacked by female parasitoids. Moreover, parasitoid eggs and larvae were smaller than in the two other host aphid species and their development was delayed. This abnormal development appeared to be due to an incomplete host regulation process, probably related to the low number and the size of teratocytes produced by D. rapae in R. padi individuals. Such a failure as far as gaining control of the host's metabolism is concerned could play an important role in shaping the host range of parasitoid insects, leading to local variation of the host spectrum in populations from various geographical areas.     

Interactions between ants attendingAphis fabae ssp.cirsiiacanthoidis on thistles and foraging parasitoid wasps

We describe the behavioral interactions between honeydew-collecting workers of the ants Lasius nigerand Myrmica ruginodisand females of three species of aphidiid wasps (Lysiphlebus cardui, Lysiphlebus testaceipes, Trioxys angelicae)foraging for their aphid host, Aphis fabaessp. cirsiiacanthoidis,on thistles. Using field and laboratory experiments, we show that the ant-parasitoid interactions are species specific. Workers of both ant species generally attacked and killed females of T. angelicae,but they ignored those of L. cardui.This pattern was not altered when we anesthetized the wasps slightly with carbon dioxide to reduce their mobility. Prior contacts between L. carduiand either conspecific L. nigerfrom a different nest or workers of a different ant species (M. ruginodis)did not influence L. niger'snonaggressive behavior. The number of aphids parasitized by L. testaceipeswas significantly reduced in aphid colonies attended by L. niger,although this parasitoid was rarely attacked by ants. In encounters between these species of ants and wasps, ant aggression is consistent with differences in wasp behavior. We suggest that, in addition, chemical cues located in the cuticula may enable L. carduito avoid detection by honeydew-collecting ants.     

Foraging for solitarily and gregariously feeding caterpillars: A comparison of two related parasitoid species (Hymenoptera: Braconidae)

In the present study we apply a comparative approach, in combination with experimentation, to study behavior of two parasitoid species that attack caterpillar hosts with different feeding strategies (gregarious or solitary). In a semifield setup, consisting of clean cabbage plants and plants infested with one of two host species, the foraging behavior of the specialistCotesia rubecula, on obligate parasitoid of solitarily feedingPieris rapae larvae, was compared to that of the generalistCotesia glomerata, a polyphagous parasitoid of several Pieridae species (mainly the gregariously feedingPieris brassicae).Cotesia glomerata displayed equal propensity to search for and parasitize larvae of both host species. AlthoughC. glomerata exhibited a relatively plastic foraging behavior in that it searched differently under different host distribution conditions, its behavior seems more adapted to search for gregariously feeding hosts. Females exhibited a clear area-restricted search pattern and were more successful in finding the gregariously feeding caterpillars.Cotesia rubecula showed a higher propensity to search forP. rapae than forP. brassicae, i.e., females left the foraging setup significantly earlier when their natural hostP. rapae was not present.C. rubecula showed a more fixed foraging behavior, which seems adapted to foraging for solitarily feeding host larvae. In a setup with onlyP. rapae larvae, the foraging strategies of the two parasitoid species were quite similar. In a choice situationC. glomerata did not show a preference for one of the host species, whileCotesia rubecula showed a clear preference for its natural host species. The latter was shown by several behavioral parameters such as the number of first landings, allocation of search time, and percentage parasitization.     

Prevalences of fungal pathogens and othernatural enemies of cereal aphids (Homoptera:Aphididae) in wheat under dryland and irrigatedconditions in South Africa

Surveys were conducted in the summer andwinter rainfall wheat producing regions of SouthAfrica in a first attempt to investigate theidentity and impact of entomopathogenic fungi withinthe cereal aphid complex. Wheat produced underdryland and irrigated conditions was surveyed duringthe 1996 and 1997 seasons. Six cereal aphid specieswere recorded of which the Russian wheat aphid, Diuraphis noxia, was the most abundantunder dryland conditions in the summer rainfallregion as opposed to the oat aphid, Rhopalosiphum padi, in the winter rainfallregion. Rose grain aphid, Metopolophiumdirhodum, was most prevalent underirrigated conditions in the summer rainfall region.Five species of entomopathogenic fungi were recordedincluding four entomophthorales and the hyphomycete,Beauveria bassiana. TheEntomophthorales included Pandora neoaphidis, Conidiobolus obscurus, C.thromboides, and Entomophthoraplanchoniana. Pandora neoaphidis wasthe most important etiological agent recorded fromD. noxia, with up to 50% mycosis recordedunder dryland conditions in the Bethlehem summerrainfall region. Similarly, P. neoaphidis wasthe most prevalent species within populations ofM. dirhodum. under irrigated conditions in theBergville/Winterton summer rainfall region (up to77% mycosis). However, mycoses of R. padi didnot exceed 1.7% in samples from these areas,suggesting that R. padi may be lesssusceptible to P. neoaphidis than M.dirhodum. Epizootics in populations of D.noxia under dryland conditions in both the winterand summer rainfall regions indicated a high levelof susceptibility to P. neoaphidis.Occurrences of hymenopterous parasitoids andpredators in populations of D. noxia were low,although a parasitism level of 25% was recorded inone small sample of R. padi collected from anirrigated field in the summer rainfall region.     

Body size affects host defensive behavior and progeny fitness in a parasitoid wasp,Lysiphlebus fabarum

This study tested effects of maternal body size on foraging behavior and progeny development in a thelytokous population of Lysiphlebus fabarum (Marshall) (Hymenoptera: Braconidae). Small and large wasps were reared from first and second instar hosts [black bean aphid, Aphis fabae Scopoli (Hemiptera: Aphididae)], respectively, and each was provided with a patch (bean leaf disk) containing either 15 small (second instar) or 15 large (fourth instar) hosts for a 30‐min foraging period. Neither body size nor host size affected time allocation to various behaviors within a patch, but second instar aphids produced significantly more mummies than fourth instars. The preferred attack orientation was from the side of the aphid, suggesting wasps were sensitive to the risk of smearing with cornicle secretions. Few wasps developed in fourth instar hosts, suggesting later host instars were somewhat resistant to parasitism. Second instar hosts, the most suitable stage for L. fabarum development, relied more on defensive behavior, specifically kicking and secreting cornicle droplets. Large wasps were more likely to elicit a double cornicle secretion, indicating that aphids graded their response to the size of the attacker. Larger wasps were also more likely to be smeared with cornicle secretion, suggesting they were more vulnerable than small wasps. Although small wasps had smaller eggs than large wasps, there was no effect of maternal egg size on the size of progeny. However, daughters of small females emerged with larger egg loads than daughters of large mothers, and their eggs tended to be slightly smaller, although not significantly. Regression analysis revealed a positive correlation between maternal egg size and progeny developmental time for small and large wasps, and between maternal egg size and progeny egg load for small wasps. These results confirm maternal effects of body size in an aphid parasitoid, and reveal that vulnerability to host behavioral defenses is also body size dependent.     

Effects of leaf epicuticular wax on the movement, foraging behavior, and attack efficacy of Diaeretiella rapae

Plant morphological characters can affect the foraging abilities of natural enemies. Heavy wax blooms have been shown to impede predators searching for herbivores on various species in the genus Brassica (Brassicaceae). This study determined whether epicuticular wax affected the foraging behavior of the braconid wasp Diaeratiella rapae (M’Intosh) (Hymenoptera: Braconidae) as it searched for its aphid host Brevicoryne brassicae L. (Homoptera: Aphididae) on the leaves of cauliflower varieties with heavy or light wax blooms. Wasps on the variety with a heavier wax bloom foraged more slowly, groomed more often and for longer periods of time, fell from the leaves more often, took longer to find colonies of aphids, and attacked them at a lower rate than wasps foraging on the variety with a lighter wax bloom. When epicuticular wax was removed from the leaves, the wasp's foraging efficiency and efficacy improved significantly on the cauliflower variety with a heavy wax bloom. The amount of epicuticular wax present on a leaf was shown to impede the ability of a parasitoid to forage, locate, and attack its host.