Nectar exploitation by herbivores and their parasitoids is a function of flower species and relative humidity

In conservation biological control, diversification of the agro ecosystem with flowering vegetation is seen as an important tool to support the broad range of predators and parasitoids that require nectar and pollen sources to survive and reproduce. In order to identify flowering plants that provide suitable food sources for natural enemies without supporting the pest species, we analyzed the exploitation of 19 flowering plants by two important lepidopteran cabbage pests, Pieris rapae and Plutella xylostella, and their hymenopteran parasitoids, Cotesia glomerata and Diadegma semiclausum. The experiments were conducted at 90% r.h., while Pieris rapae was tested both at 45% r.h. and at 90% r.h. At 45 ± 5% r.h., corresponding with field conditions at which P. rapae is predominantly active, the butterfly was unable to feed on a number of exposed floral nectar sources whose nectar was successfully exploited at 90% r.h. The broader nectar exploitation by P. rapae at the high humidity is presumably explained by the resulting decrease in nectar viscosity. When comparing D. semiclausum and its herbivorous host P. xylostella, the herbivore exploited a broader range of plants. However, those plants that benefited both the parasitoid and the herbivore had a much stronger effect on the longevity of the parasitoid. The results from the accessibility bioassay suggest that flowers where nectar is not accessible can have a negative impact on insect survival presumably by stimulating foraging without providing accessible nectar. Our results underline the importance of considering species-specific environmental conditions when fine-tuning the choice of nectar sources to be used in conservation biological control programs.     

Nectar‐providing plants enhance the energetic state of herbivores as well as their parasitoids under field conditions

Abstract 1. The use of flowering vegetation has been widely advocated as a strategy for providing parasitoids and predators with nectar and pollen. However, their herbivorous hosts and prey may exploit floral food sources as well. 2. Previous laboratory studies have shown that not all flower species are equally suitable in providing accessible nectar. Relatively little is known about actual nectar exploitation under field conditions. 3. The present study investigates nectar exploitation by the pest, Plutella xylostella, and its parasitoid, Diadegma semiclausum, under field conditions and examines whether floral nectar exploitation in the field can be predicted based on controlled laboratory studies. 4. Insects were collected from fields bordered by flowering margins containing Fagopyrum esculentum, Lobularia maritima, Anethum graveolens, Centaurea jacea or the grass Lolium perenne (control). Whole insect bodies were individually assayed by HPLC to establish their sugar profile as a measure of the level of energy reserves and the degree of food source use. 5. The average overall sugar content of P. xylostella and D. semiclausum collected in fields bordered by flowering margins was significantly higher than those of individuals collected from grass‐bordered control plots. To the authors’ knowledge, this represents the first demonstration that nectar‐providing plants enhance the energetic state of herbivores under field conditions. 6. In contrast to earlier laboratory studies, the present study did not find elevated sugar contents in P. xylostella and D. semiclausum individuals collected from fields bordered by buckwheat (F. esculentum). 7. The present study shows widespread sugar feeding by both the herbivore and its parasitoid. It also shows that laboratory studies establishing nectar exploitation under controlled conditions can not always be extrapolated to actual exploitation under field conditions. This emphasises the importance of studying field‐collected insects with regard to food source use and nutritional status.     

Role of Diadegma semiclausum (Hymenoptera: Ichneumonidae) in controlling Plutella xylostella (Lepidoptera: Plutellidae): Cage exclusion experiments and direct observation

We evaluated the role of the larval parasitoid, Diadegma semiclausum Hellén (Hymenoptera: Ichneumonidae), in controlling Plutella xylostella (L.) (Lepidoptera: Plutellidae) by cage exclusion experiments and direct field observation during the winter season in southern Queensland, Australia. The cage exclusion experiment involved uncaged, open cage and closed cage treatments. A higher percentage (54–83%) of P. xylostella larvae on sentinel plants were lost in the uncaged treatment than the closed (4–9%) or open cage treatments (11–29%). Of the larvae that remained in the uncaged treatment, 72–94% were parasitized by D. semiclausum, much higher than that in the open cage treatment (8–37% in first trial, and 38–63% in second trial). Direct observations showed a significant aggregation response of the field D. semiclausum populations to high host density plants in an experimental plot and to high host density plots that were artificially set-up near to the parasitoid source fields. The degree of aggregation varied in response to habitat quality of the parasitoid source field and scales of the manipulated host patches. As a result, density-dependence in the pattern of parasitism may depend on the relative degree of aggregation of the parasitoid population at a particular scale. A high degree of aggregation seems to be necessary to generate density-dependent parasitism by D. semiclausum. Integration of the cage exclusion experiment and direct observation demonstrated the active and dominant role of this parasitoid in controlling P. xylostella in the winter season. A biologically based IPM strategy, which incorporates the use of D. semiclausum with Bt, is suggested for the management of P. xylostella in seasons or regions with a mild temperature.     

Influence of crucifer cropping system on the parasitism ofPlutella xylostella (Lep., Yponomeutidae) byCotesia plutellae (Hym., Braconidae) andDiadegma semiclausum (Hym., Ichneumonidae)

Field experiments were conducted to study the influence of cabbage monoculture and mixed cropping on the parasitism of diamondback moth,Plutella xylostella (L.), a destructive pest of all crucifers, by 2 larval parasites,Diadegma semiclausum Hellén andCotesia plutellae Kurdjumov. There was no significant difference in parasitism by either species whether cabbage was planted in insecticide-free monoculture or in mixed cropping with 8 noncrucifers which were sprayed twice a week with chemical insecticides mevinphos, methamidophos and permethrin. Population ofP. xylostella increased as the cabbage plants grew older. Parasitism byC. plutellae was higher soon after cabbage transplanting but decreased as the plants grew older. Parasitism byD. semiclausum was very low soon after cabbage planting but increased as the plants grew older. A significant negative correlation was found betwen parasitism byC. plutellae andD. semiclausum. In a caged field study where only one parasite species was used in an individual cage, parasitism ofP. xylostella by both species decreased as theP. xylostella population increased. This is believed to be due to the absence of competition between the two parasites inside the cage. There was no relationship between host-plant age and parasitism ofP. xylostella larvae by either parasite species.     

Australian native flowering plants enhance the longevity of three parasitoids of brassica pests

Floral resources from native plants that are adapted to the local environment could be more advantageous than the use of nonnative plants. In Australia, there is a dearth of information on the benefits of native plants to natural enemies and their selectivity against pests. Accordingly, we examined the longevity of the parasitoids Diaeretiella rapae (McIntosh) and Cotesia glomerata (L.) (both Hymenoptera: Braconidae), and Diadegma semiclausum (Hellen) (Hymenoptera: Ichneumonidae) exposed to flowering shoots from Australian native plants which was compared with the nonnative buckwheat (Fagopyrum esculentum), often used in conservation biological control. Longevity of parasitoids was significantly enhanced by the Australian natives Westringia fruticosa, Mentha satureioides, Callistemon citrinus, Leptospermum cv. ‘Rudolph’, Grevillea cv. ‘Bronze Rambler’, Myoporum parvifolium, Lotus australis, and nonnative F. esculentum. The highest mean survival by native plant species was 3.4× higher for D. rapae with Leptospermum sp. and 4.3× higher for D. semiclausum with M. parvifolium. For C. glomerata, Grevillea sp. increased longevity by 6.9× compared with water only. Longevity of Plutella xylostella (L.) (Lepidoptera: Plutellidae), a major crop pest, was enhanced by all plants against which it was screened except Acacia baileyana, a species that had no effect on parasitoid longevity. Several Australian native plant species that benefit parasitoids were identified. None of the plant species provided a selective benefit to the parasitoid D. semiclausum compared with its host P. xylostella; however, the benefit of M. parvifolium and Grevillea sp. on the longevity of D. semiclausum was relatively higher compared with the pest. These results suggest the need for field studies to determine whether native Australian plants increase P. xylostella impact in nearby brassica crops.     

Effects of mixed cropping on population densities and parasitism rates of the diamondback moth, <Emphasis Type="Italic">Plutella xylostella</Emphasis> (Lepidoptera: Plutellidae)

Effects of mixed cropping and barrier crops on the population density and parasitism of the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), were evaluated in field plots of cabbage grown in Bali, Indonesia. The densities of P. xylostella at larval and pupal stages, as well as the overall density at larval plus pupal stages, were significantly lower in cabbage/coriander mixed cropping subplots than in cabbage monoculture subplots. Parasitism of P. xylostella by the larval parasitoid Diadegma semiclausum (Hellen) (Hymenoptera: Ichneumonidae) was not significantly different between the mixed and monocultural cropping systems. These results do not support the so-called enemies hypothesis, but suggest that disruption of the host searching behavior of female moths by neighboring non-host plants is the mechanism behind the associational resistance observed in the coriander mixed cropping system. The inclusion of a Napier grass barrier between mixed crop and monoculture subplots did not affect the influence of mixed cropping on larval and pupal densities. Therefore, Napier grass, which is used locally as a fence for preventing livestock invasion of fields, would not obstruct the pest-reducing effect of coriander/cabbage mixed cropping.     

Parasitoid and moth movement from refuge to crop

Refuges may provide habitat and resources which enhance population size of natural enemies of herbivorous pests and add to their colonisation into target crops, potentially increasing effectiveness of biological control. They may also allow for an increase in numbers of herbivorous pests. In addition, these refuges may be attractive so that natural enemies aggregate there, neglecting predation and parasitism of pests in the crop. We investigate the movements of marked Diadegma semiclausum (Hellén) a key larval parasitoid, and the adult stage of the host it attacks, diamondback moth, Plutella xylostella (L.), from an on-farm flowering refuge of Brassica vegetables to the Brassica crop. Our results showed that parasitoids and moths visit the flowering refuge, and that they move from the refuge into the crop before and after disturbing the refuge by ploughing. For D. semiclausum, the pattern of movement from the refuge into the crop was similar for males and females, but more males than females were captured. Ploughing the refuge resulted in increased dispersal by males but not females into the crop. Neither moths nor parasitoids preferentially aggregated around the flowering refuge, instead most often their spatial pattern was random throughout the field indicating that they are quite vagile, quickly moving to distances >100 m. This basic understanding of the movements of these insects has implications beyond this system and is relevant to any agricultural system implementing a refuge to enhance natural enemy effectiveness.     

Increasing floral diversity for selective enhancement of biological control agents: A double-edged sward?

Floral resource subsidies can have differential effects on insect herbivores compared with the herbivores’ natural enemies. While the nectar of many plant species enhances parasitoid fitness, it may also increase damage by herbivores. This may occur as a result of enhanced herbivore fitness or by enhancing fourth-trophic-level processes, possibly disrupting a trophic cascade as a result. The responses of different arthropod guilds to different floral resource subsidies were compared using Plutella xylostella (Hyponomeutidae), its parasitoid Diadegma semiclausum (Ichneumonidae) and data from two other published herbivore–parasitoid systems. These were Dolichogenidea tasmanica (Braconidae) and its host Epiphyas postvittana, and Copidosoma koehleri (Encyrtidae) and its host Phthorimaea operculella. The parasitoids and hosts in the three systems exhibited differential responses to the nectar sources. The differential response was not explained by morphology, demonstrating that physical access to nectaries alone does not determine the potential of flowers as a food source. For some flowering plants, enhancement of herbivore and parasitoid fitness occurred. Other flowering plants, such as buckwheat and phacelia, conferred a selective enhancement on parasitoids by increasing only their fitness. More effective conservation biocontrol may be achieved by the provision of selective floral resources. Attempts to ‘engineer’ agroecosystems to enhance biological control require an extensive knowledge of the ecology of the herbivore, its enemies and their interactions with potential resource subsidies.     

Sowing of margin strips rich in floral resources improves herbivore control in adjacent crop fields

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Can cruciferous agroecosystems grown under variable conditions influence biological control of Plutella xylostella (Lepidoptera: Plutellidae)?

Determining the most efficacious method for the release of parasitoids is challenging, depending on the crop area to be covered and the environmental conditions created by the agroecosystem. Release of the parasitoid Oomyzus sokolowskii (Kurdjumov) and the effect of crucifers cropping systems were investigated in relation to diamondback moth (DBM), Plutella xylostella (L.) control. First, we investigated the dispersal ability of O. sokolowskii. Kale plants were infested with 20, 25, 30 and 35 DBM larvae each, at distances of 0, 8, 16, and 24 m, from a central release point in the field. Second, the effect of a multiple host plant system composed of cabbage, broccoli and Napa cabbage on the parasitism capacity of O. sokolowskii was investigated. Lastly, the parasitism capacity of O. sokolowskii and the colonization rate of DBM were investigated comparing cropping systems composed of either a monoculture of cabbage, or three different intercropping systems: cabbage and green onion, cabbage and cilantro, and cabbage, green onion and cilantro. For all experiments, selected plants were infested with sentinel DBM larvae and caged with mesh that allowed parasitoids to search inside the cages while reducing the impact of opportunists on DBM larvae. Results showed that parasitoids were able to disperse and parasitize P. xylostella at similar rates throughout a field of kale up to 24 m from the release point. Intercropping of cabbages with other crop plants did not negatively affect parasitism rates of O. sokolowskii, which makes it promising for DBM biological control; however it did not interfere with cabbage colonization by DBM.     

Influence of crop background on aphids and other phytophagous insects on Brussels sprouts

More Brevicoryne brassicae and other alate aphids were caught in yellow water-traps in a weed-free crop of Brussels sprouts than in a crop with a weedy background. More B. brassicae colonized Brussels sprout plants in bare soil than in weeds; very few alatae were attracted to cruciferous weeds in the crop. Results in 1 yr suggest that initially larger populations on the weed-free sprouts became smaller than populations on the weedy sprouts because the larger aphid population attracted more natural enemies. Aleyrodes brassicae and certain Lepidoptera were also more abundant on sprout plants in bare soil than on sprouts surrounded by weeds; more adult A. brassicae were caught in water traps over the bare soil. More A. brassicae were present on sprout plants surrounded by a green than by a brown cloth background but the differences were not significant (P < 0–05). Numbers of B. brassicae on sprout plants with green and brown backgrounds varied greatly and did not differ significantly. In field cages, B. brassicae alatae were more attracted to potted sprout plants surrounded by bare soil than to ones surrounded by rings of living or cut grass or by artificial green rings. This effect was greater with small than with large sprout plants surrounded by grass rings. The maintenance of a limited weed cover is considered potentially useful in integrated control of some brassica pests.     

The influence of understory nectar resources on parasitism of the spruce budworm Choristoneura fumiferana in the field

1 Nectar provided by flowering plants has been suggested as an important factor enhancing parasitism rates of herbivorous insects. Artificial nectar has been shown to increase parasitoid longevity and fecundity in laboratory studies. 2 We studied the influence of understory nectar on parasitism of the spruce budworm Choristoneura fumiferana in a field experiment in which we either removed understory flowering herbs or sprayed a sucrose solution on the understory vegetation in 0.25 ha quadrats. 3 Cohorts of laboratory-reared second instars were transferred the field to evaluate parasitism in the quadrats. The larvae were harvested as fifth instars and reared for parasitoids. 4 Parasitoids of early instars caused greater mortality in the supplemental sucrose treatment than in the vegetation-removal treatment or the control. Parasitoids of older larvae did not respond to the treatments. Larger-scale treatments may be necessary to elicit a response by the larger parasitoids that attack older larvae.     

Can imitation companion planting interfere with host selection by Brassica pest insects?

• 1 Companion planting with nonhosts may offer a non‐insecticidal means of controlling pests, although the results of studies can be variable and species‐dependent.
• 2 The effect of companion planting on two pests of Brassica crops, Plutella xylostella (L.) and Brevicoryne brassicae (L.), was examined using Brussels sprout as the host plant and imitation cereal plants made from green plastic as the nonhost. For P. xylostella, the effect of nonhost density was also investigated.
• 3 Oviposition (P. xylostella) and abundance (B. brassicae) were lower on Brussels sprout plants presented on a background of high‐density imitation cereal plants (reductions of 59% and 85%, respectively).
• 4 The results are discussed in the context of host location by pest insects and the selection of nonhost companion plants for pest management.
• 5 It is concluded that nonhost plants interfere with pest host selection through disruption to visual host location processes.

     

Leaf nutrient levels and the spatio-temporal distributions of <Emphasis Type="Italic">Plutella xylostella</Emphasis> and its larval parasitoids <Emphasis Type="Italic">Diadegma insulare</Emphasis> and <Emphasis Type="Italic">Microplitis plutellae</Emphasis> in canola

Seasonal distribution patterns of the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), and its principal parasitoids Diadegma insulare (Cresson) (Hymenoptera: Ichneumonidae) and Microplitis plutellae (Muesebeck) (Hymenoptera: Braconidae) were investigated over three site-years in commercial fields of canola (Brassica napus L.) in southern Alberta, Canada. The sampling of P. xylostella, D. insulare, and M. plutellae from points arranged in grid patterns, together with the mapping and analysis of their spatial distributions over time, generated a detailed picture of the pattern of crop infestation by the herbivore and its parasitoids. Plutella xylostella exhibited significant aggregations on different scales most often when its host plants were in early flowering. Diadegma insulare adults exhibited significant aggregated distributions during early flowering and distributions subsequently became more uniform as the wasps moved into the crop later in the season. However, M. plutellae distributions were aggregated in mid flowering in only one site-year. The close spatial associations between densities of D. insulare and P. xylostella indicated that host abundance was the main determinant of parasitoid distribution patterns. Spatial distributions of nutrient contents in leaf tissue and their spatial associations with the herbivore and parasitoids were also investigated. Significant spatial associations existed between certain nutrients (e.g. nitrogen, sulfur, and potassium) and P. xylostella distributions. Sulfur exhibited a positive effect on the distributions of D. insulare but not of M. plutellae. We observed similar relationships between nutrients and the distribution of P. xylostella parasitoids as for nutrients and P. xylostella, but these relationships lacked consistency and may be the results of the spatial associations between the parasitoids and their hosts. Aggregated distributions of adults and larvae of P. xylostella hold promise for spatially targeted insecticidal applications as a means for reducing the environmental impact of insecticides on nontarget and beneficial species in canola agroecosystems.     

Crop–noncrop spillover: arable fields affect trophic interactions on wild plants in surrounding habitats

Ecosystem processes in agricultural landscapes are often triggered by resource availability in crop and noncrop habitats. We investigated how oilseed rape (OSR; Brassica napus, Brassicaceae) affects noncrop plants in managed systems and semi-natural habitat, using trophic interactions among wild mustard (Sinapis arvensis, Brassicaceae), rape pollen beetles (Meligethes aeneus, Nitidulidae) and their parasitoids (Tersilochus heterocerus, Ichneumonidae). We exposed wild mustard as phytometer plants in two cropland habitat types (wheat field, field margin) and three noncrop habitat types (fallow, grassland, wood margin) across eight landscapes along a gradient from simple to complex (quantified as % arable land). Both landscape and local factors affected the abundance of rape pollen beetles and parasitoids. Rape pollen beetle infestation and parasitism rates on these plants were lower in noncrop habitats and higher in wheat fields and field margins, whereas beetles and parasitoids responded differently to landscape scale parameters. We found the hypothesized spillover from OSR crop onto wild plants in surrounding habitats only for parasitoids, but not for pollen beetles. Parasitism rates were not related to landscape simplification, but benefited from increasing proportions of OSR. In contrast, rape pollen beetles benefited from simple landscape structures, presumably due to multi-annual population build-ups resulting from long-term OSR planting (as part of the crop rotation). In conclusion, we showed that spillover from cropland affects parasitism rates on related wild plants outside cropland, which has not been shown so far, but can be expected to be a widespread effect shaping noncrop food webs.     

Wind‐modulated landscape effects on colonization of Brussels sprouts by insect pests and their syrphid antagonists

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Impact of a glossy collard trap crop on diamondback moth adult movement, oviposition, and larval survival

One component of developing a systematic approach for deployment of trap crops is to understand how the trap crop modifies pest behavior. Glossy‐leafed collards, Brassica oleracea L. var. acephala (Brassicaceae), were evaluated as a potential trap crop for diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), because they are attractive to P. xylostella adults and are a poor host for P. xylostella larvae compared to cabbage, Brassica oleracea L. var. capitata. We used large field plots to measure the changes in adult, egg, and larval P. xylostella densities in cabbage when the trap crop was planted in the field. Furthermore, we planted the trap crop in dispersed and concentrated spatial arrangements to determine the impact of trap crop arrangement on the behavior of P. xylostella. In 2002, results showed that the presence of collards within a cabbage field reduced larval density on cabbage. In 2003, neither trap crop arrangement had a significant impact on P. xylostella larval density on cabbage. Adult moths aggregated in proximity to collards in 2002, but not in 2003. Egg and larval data in both years in all treatments showed that total oviposition was highest near a central release point, indicating that females lay many eggs before dispersing very far when suitable host plants are available. The mean direction of P. xylostella movement and oviposition from a central release point was not consistent or correlated to wind direction. Plant size of the trap crop in relation to the main crop and environmental factors may have been responsible for the inconsistent effectiveness of the trap crop.     

The effect of host developmental stage at parasitism on sex‐related size differentiation in a larval endoparasitoid

• 1 For their larval development, parasitoids depend on the quality and quantity of resources provided by a single host. Therefore, a close relationship is predicted between the size of the host at parasitism and the size of the emerging adult wasp. This relationship is less clear for koinobiont than for idiobiont parasitoids.
• 2 As size differentiation in host species exhibiting sexual size dimorphism (SSD) is likely to occur already during larval development, in koinobiont larval endoparasitoids the size of the emerging adult may also be constrained based on the sex of the host caterpillar.
• 3 Sex‐specific growth trajectories were compared in unparasitised Plutella xylostella caterpillars and in second and fourth instar hosts that were parasitised by the solitary larval koinobiont endoparasitoid Diadegma semiclausum. Both species exhibit SSD, where females are significantly larger than males.
• 4 Healthy female P. xylostella caterpillars developed significantly faster than their male conspecifics. Host regulation induced by D. semiclausum parasitism depended on the instar attacked. Parasitism in second‐instar caterpillars reduced growth compared to healthy unparasitised caterpillars, whereas parasitism in fourth‐instar caterpillars arrested development. The reduction in growth was most pronounced in hosts producing male D. semiclausum.
• 5 Parasitism itself had the largest impact on host growth. SSD in the parasitoid is mainly the result of differences in growth rate of the parasitoid–host complex producing male and female wasps and differences in exploitation of the host resources. Female wasps converted host biomass more efficiently into adult biomass than males.

     

Influence of crop background on natural enemies of aphids on Brussels sprouts

The most abundant natural enemies of aphids on Brussels sprout crops were Syrphidae, different species being attracted differentially to weedy or weed-free plots according to whether they were more host-plant-orientated (e.g. Melanostoma spp., Platycheirus spp.) and thus affected directly by the background, or more aphid-orientated (e.g. Syrphus balteatus) and so less affected by background than by aphid numbers. Oviposition by Melanostoma spp. was usually much greater in weedy sprout crops than on sprouts in bare soil, and their eggs were also very abundant on weeds. Eggs of other syrphid species were scarcer on weeds. In contrast to Melanostoma, Platycheirus spp. usually oviposted preferentially on sprouts growing in bare soil. Oviposition by S. balteatus was in response to aphid abundance and thus tended to become greater on sprouts in bare soil. Notably more adults of non-aphido-phagous Syrphidae were caught over weedy than over non-weedy Brussels sprout plants. Anthocoris nemorum nymphs and adults were very common on sprout plants and weeds in the weedy crop but were scarce on sprouts in bare soil; A. nemorum oviposited on white and yellow charlock (Raphanus raphanistrum and Sinapis arvensis) occasionally. Parasitism of Brevicoryne brassicae by Diaeretiella rapae appeared to be related to aphid numbers and was only indirectly influenced by the crop background. Field experiments with green and brown cloth backgrounds showed that some syrphids were attracted to green; A. nemorum was relatively scarce over both artificial backgrounds. It is concluded that decreased natural enemy action is partly responsible for the initially greater abundance of B. brassicae in a weed-free crop of Brussels sprouts than in a weedy crop.     

Parasitoid Preference for Host-Infested Plants Is Affected by the Risk of Intraguild Predation

Flowering Rorippa indicaplants are attended by ants that collect nectar and, at the same time, prey on herbivorous insects, including larvae of the diamondback moth, Plutella xylostella.Here, we showed that P. xylostellalarvae suffered higher predation on R. indicawhose flowers were accessible by ants than on plants those whose flowers were inaccessible. Ants showed equal predation preference between unparasitized and larvae parasitized by Cotesia plutellae,a dominant specialist parasitic wasp of P. xylostellalarvae. C. plutellaepreferred non-flowering, host-infested R. indicato flowering, host infested R. indica.Based on these results, we infer that the preference of C. plutellaefor non-flowering, host-infested plants is in part explained by the avoidance of intraguild predation by attending ants.