長 泰行

Recently, we reported brood parasitism in the tiny predatory mite Neoseiulus californicus (Acari: Phytoseiidae); adult females of this species prefer to add their eggs to a cluster of eggs of another predatory mite species, Gynaeseius liturivorus (Acari: Phytoseiidae), which guards its own eggs against egg predators. Here, we investigated the cues used by the blind N. californicus to detect eggs of G. liturivorus. We show that N. californicus locates oviposition sites of G. liturivorus using volatiles emanating from eggs of the latter species. Adult female G. liturivorus spent more time guarding oviposition sites that contain more eggs, which resulted in a higher per capita survival of the eggs. We therefore hypothesized that N. californicus would prefer oviposition sites with more G. liturivorus eggs. Indeed, N. californicus preferably laid their egg at oviposition sites containing more than six G. liturivorus eggs, which corresponds to the average number laid by a female G. liturivorus during 1 day. Our results suggest that N. californicus uses egg volatiles to localize oviposition sites of G. liturivorus, where the eggs of the former are effectively protected against egg predators.

Many animal species protect their eggs against predators, and other species may profit from this by adding their eggs to those of the protecting species. We studied two tiny species of predatory mites that share a food source, are engaged in intraguild predation, and which eggs are attacked by the same egg predator. One of these predatory mites (Neoseiulus californicus) adds its eggs to those of the other species (Gynaeseius liturivorus) which guards its eggs from egg predators, resulting in reduced predation of the eggs of the nonguarding species. The guarding species experiences costs in the form of intraguild predation of her offspring, and the addition of eggs to the guarding species therefore qualifies as brood parasitism. In the presence of egg predators, the brood parasite preferentially adds its eggs to those of the guarding host species, not to those of another, nonguarding mite species. This cuckoo behaviour comes with a cost for the parasite when egg predators are absent, and therefore only occurs when egg predators are present. Our findings emphasize the importance of the risk of egg predation as a factor driving facultative brood parasitism. Read the free Plain Language Summary for this article on the Journal blog.

Prey mothers at risk of predation sometimes change the morphology and/or antipredator behaviour of their offspring to reduce predation risk. When maternal exposure to predation risk changes the morphology of some offspring, it is unclear whether and how the other offspring, which have normal morphology, exhibit antipredator behaviour. We aimed to clarify these behaviours using pea aphids, Acyrthosiphon pisum Harris (Hemiptera: Aphididae), and aphidophagous Asian ladybird beetles, Harmonia axyridis Pallas (Coleoptera: Coccinellidae), which induce aphids to release the alarm pheromone (E)-beta-farnesene (EBF) and to exhibit antipredator responses. Pea aphids exposed to EBF reduced reproduction through changes in the number of wingless offspring, producing more winged offspring than unexposed conspecifics. Wingless aphids whose mothers had been exposed to EBF showed higher dispersal from host plants with predators than the offspring of unexposed mothers. These results suggest that pea aphids at risk of predation increase their offspring survival by increasing the number of winged offspring and antipredator dispersal of wingless offspring.

Predators frequently compete with other species for prey but can also interact by preying on each other’s vulnerable stages. Because eggs and juveniles are more vulnerable to this intraguild predation than adults, their survival will depend on maternal strategies to reduce predation risk. Recently, we reported that adult female predatory mites Gynaeseius liturivorus Ehara (Acari: Phytoseiidae) reduce intraguild predation on their eggs by remaining at oviposition sites, thus deterring the egg predators. In addition, they avoid oviposition close to eggs laid by conspecific females. We therefore expected that adult female G. liturivorus protect their own eggs better against these egg predators than eggs of other females. This was tested using juveniles of the predatory mite Neoseiulus californicus McGregor (Acari: Phytoseiidae) as egg predators and the western flower thrips, Frankliniella occidentalis Pergande (Thysanoptera: Thripidae), as the shared prey. When G. liturivorus eggs were kept with their mothers, the presence of juvenile egg predators did not affect the survival of eggs. However, when G. liturivorus eggs were kept with females that were not their mothers, the mortality of eggs in the presence of juvenile egg predators increased. When adult female G. liturivorus were guarding their eggs, they killed a similar number of juvenile egg predators as females that were not kept with their eggs. Hence, adult female G. liturivorus protect their eggs by remaining close to their eggs.

© 2020 The Royal Entomological Society Several animal species are known to distinguish between their own eggs and eggs of unrelated conspecifics. However, the cues involved in this discrimination are often unknown. These cues were studied using the predatory mite Gynaeseius liturivorus Ehara. Adult females of these predatory mites oviposit in clusters and avoid oviposition close to eggs laid by other females, resulting in reduced cannibalism between offspring. Because predatory mites are blind, it was tested whether volatiles of eggs were used as a cue for egg recognition. Adult female predatory mites were offered volatile cues of their own eggs and of unrelated conspecific eggs, and females were prevented from contacting the eggs. Predatory mites oviposited closer to their own eggs than to unrelated eggs. This preference was observed even when one own and one unrelated egg were offered as a volatile source. These results suggest that adult female predatory mites can determine kinship using volatiles released from the eggs.

Intraguild (IG)-prey prefer to oviposit at sites with a low IG-predation risk of their offspring. However, IG-predators sometimes show oviposition preferences similar to those of IG-prey. In such cases, IG-prey eggs might need protection against IG-predators to survive. We tested this possibility using a system that consisted of an IG-prey, the predatory mite Gynaeseius liturivorus, and an IG-predator, the predatory mite Neoseiulus californicus. Both mite species feed on larvae of the western flower thrips, Frankliniella occidentalis, as a shared food source. When offered plastic discs as substrates for oviposition, both mite species preferred to lay eggs on the discs, regardless of the presence of heterospecifics. Subsequently, we examined G. liturivorus egg survival in the presence of only conspecific mothers or N. californicus, and the presence and absence of both mite species. The survival of G. liturivorus eggs was significantly reduced when kept with only N. californicus, but this reduction was not found in the presence of both G. liturivorus and N. californicus. These results indicate that G. liturivorus mothers improved the survival of the eggs in the presence of N. californicus. Behavioural observation revealed that adult female G. liturivorus mostly remained on the plastic discs with their own eggs during experiments. Furthermore, the presence of G. liturivorus mothers reduced the residence time of N. californicus on plastic discs with G. liturivorus eggs, whereas the residence time of G. liturivorus mothers was not affected by the presence of N. californicus. We conclude that mothers of G. liturivorus are able to increase the survival of their eggs by deterring IG-predators.

1. Herbivores sometimes suppress plant defences. This study tested whether the presence of pea aphids (Acyrthosiphon pisum Harris) on broad bean (Vicia faba) led to decreased secretion of extrafloral nectar (EFN) which functions as an indirect plant defence against herbivores. 2. To determine effects of aphid infestation on EFN secretion, a comparison was done between EFN secretion in uninfested plants and that in plants infested by A. pisum and another aphid species (Aphis craccivora Koch). 3. When broad bean plants were infested by A. pisum, they secreted significantly smaller amounts of EFN than did uninfested plants and A. craccivora-infested plants. There was no significant difference in EFN secretion between uninfested plants and A. craccivora-infested plants. The number of extrafloral nectaries did not differ among the three treatments. 4. These results suggest that A. pisum reduced EFN production in broad bean plants.

Animals often select oviposition sites to minimize the predation risk for eggs and juveniles, which are more vulnerable to predation than adults. When females produce eggs in clusters, the eggs and juveniles are likely to suffer from cannibalism. Although cannibalism among siblings is known to be lower than among non-siblings, there have been few investigations into the possibility that females select oviposition sites that reduce the risk of cannibalism for the offspring. To test this possibility, we examined oviposition preference by adult females of the predatory mite Gynaeseius liturivorus in response to the presence of her own eggs and to eggs of other females, offering plastic discs as oviposition substrates. Although females did not clearly show a preference for plastic discs on which they had oviposited, they avoided plastic discs on which other females had oviposited. When eggs of other females were artificially placed on clean plastic discs, adult female mites avoided these discs, suggesting that the eggs were used as cues for oviposition preference. Cannibalism among juvenile siblings was lower than among non-siblings. These observations show that adult females and juveniles of G. liturivorus discriminate kin relationships among conspecific individuals. Therefore, oviposition preference by adult female G. liturivorus may lead to the reduced risk of cannibalism among offspring.

When predators can use several prey species as food sources, they are known to select prey according to foraging efficiency and food quality. However, interactions between the prey species may also affect prey choice, and this has received limited attention. The effect of one such interaction, intraguild predation between prey, on patch selection by predators was studied here. The predatory mite Neoseiulus californicus preys on young larvae of the western flower thrips Frankliniella occidentalis and on all stages of the two-spotted spider mite Tetranychus urticae. The two prey species co-occur on several plant species, on which they compete for resources, and western flower thrips feed on eggs of the spider mites. A further complicating factor is that the thrips can also feed on the eggs of the predator. We found that performance of the predatory mite was highest on patches with spider mites, intermediate on patches with spider mites plus thrips larvae and lowest on patches with thrips larvae alone. Patch selection and oviposition preference of predators matched performance: predators preferred patches with spider mites over patches with spider mites plus thrips. Patches with thrips only were not significantly more attractive than empty patches. We also investigated the cues involved in patch selection and found attractiveness of patches with spider mites was significantly reduced by the presence of cues associated with killed spider mite eggs. This explains the reduced attractiveness of patches with both prey. Our results point at the importance of predatory interactions among prey species for patch selection by predators. Significance statement Patch selection by predators is known to be affected by factors such as prey quality, the presence of competitors and predators, but little is known on the effects of interactions among prey species present on patch selection. In this paper, we show that patch selection by a predator is affected by such interactions,

When intraguild prey and intraguild predators feed and reproduce in the same habitat and relatively immobile juveniles are the vulnerable stage, predation risk depends on oviposition site selection by the adult females. We studied how the availability of oviposition sites affected the distribution of two predatory mite species, Neoseiulus cucumeris (Oudemans) and Iphiseius degenerans (Berlese), over two patches that both contained food. The two plant-inhabiting species feed on pollen and thrips, prey on each other's juveniles, and prefer to oviposit on hairy parts of the leaf. When an artificial oviposition site was provided on one of two connected patches, both predator species strongly preferred this patch. Whereas the distributions of adults and eggs of N. cucumeris over the two patches were not affected by the presence of heterospecifics, the proportions of adults and eggs of I. degenerans on the patch with an oviposition site were reduced by the presence of N. cucumeris. A similar change in distribution was induced by cues of N. cucumeris on the oviposition site, without these mites being present. Hence, intraguild prey can weaken the strength of intraguild predation through patch selection, which in turn may promote coexistence of the two predator species.

Predators are usually larger than their prey, but because size changes during ontogeny, predator and prey roles may be reversed. Hence, an individual may be prey when juvenile, but as an adult, it may counterattack the juveniles of its childhood enemy. Earlier, we showed that juvenile predatory mites, Iphiseius degenerans, recognize adults of another predatory mite species that attacked and killed conspecifics of the juveniles. Upon becoming adult, these former juveniles showed an increase in attacks on juveniles of their enemy. Here, we tested whether adult females of I. degenerans show a similar response after witnessing attack on conspecific juveniles in the presence of suitable alternative food (i.e. pollen). We used three predatory mite species involved in reciprocal intraguild predation. We found mixed results: the rate of attack on juveniles of one species of predator, Neoseiulus cucumeris, did increase after witnessing the killing of conspecific juveniles, but the rate of attack on juveniles of another species, Amblyseius swirskii, did not increase after such an experience. Furthermore, we found no conclusive evidence for species-specific antipredator responses. It is unlikely that cues of previous predation events affected the behaviour of adult predatory mites, because the trials were conducted on new experimental arenas free of predation cues. We conclude that adult predatory mites can change their antipredator behaviour in response to having witnessed predation on vulnerable juvenile conspecifics. The Association for the Study of Animal Behaviour. Published by Elsevier Ltd.

Ants attack and exclude natural enemies of aphids in ant-aphid mutualisms. However, larvae of the green lacewing, Mallada desjardinsi, prey on the cowpea aphid, Aphis craccivora, without exclusion by aphid-tending ants. Lacewing larvae are protected from ants by carrying aphid carcasses on their backs. Here, we tested whether cuticular hydrocarbons (CHCs) of aphid carcasses affected the aggressiveness of aphid-tending ants. Aphid carcasses were washed with n-hexane to remove lipids. Lacewing larvae with washed aphid carcasses were attacked by aphid-tending ants more frequently than those with untreated aphid carcasses. We measured the aggressiveness of aphid-tending ants to lacewing larvae that were either carrying a piece of cotton wool (a dummy aphid carcass) treated with CHCs from aphids or lacewing larvae, or carrying aphid carcasses. The rates of attack by ants on lacewing larvae carrying CHCs of aphids or aphid carcasses were lower than that of attack on lacewing larvae with conspecific CHCs. Chemical analysis by gas chromatography/mass spectrometry showed similarity of CHCs between aphids and aphid carcasses. These results suggest that aphid carcasses on the backs of lacewing larvae function via chemical camouflage to limit attacks by aphid-tending ants.

Plants show defensive responses after exposure to volatiles from neighbouring plants infested by herbivores. When a plant's neighbours host only species of herbivores that do not feed on the plant itself, the plant can conserve energy by maintaining a low defence level. An intriguing question is whether plants respond differently to volatiles from plants infested by herbivores that pose greater or lesser degrees of danger. We examined the secretion of extrafloral nectar (EFN) in lima bean plants exposed to volatiles from cabbage plants infested by common cutworm, two-spotted spider mites, or diamondback moth larvae. Although the first two herbivore species feed on lima bean plants, diamondback moth larvae do not. As a control, lima bean plants were exposed to volatiles from uninfested cabbage plants. Only when exposed to volatiles from cabbage plants infested by spider mites did lima bean plants significantly increase their EFN secretion compared with the control. Increased EFN secretion can function as an indirect defence by supplying the natural enemies of herbivores with an alternative food source. Of the three herbivore species, spider mites were the most likely to move from cabbage plants to lima bean plants and presumably posed the greatest threat. Although chemical analyses showed differences among treatments in volatiles produced by herbivore-infested cabbage plants, which compounds or blends triggered the increased secretion of EFN by lima bean plants remains unclear. Thus, our results show that plants may tune their defence levels according to herbivore risk level. © 2012 Springer Science+Business Media Dordrecht.

Although biologists routinely label animals as predators and prey, the ecological role of individuals is often far from clear. There are many examples of role reversals in predators and prey, where adult prey attack vulnerable young predators. This implies that juvenile prey that escape from predation and become adult can kill juvenile predators. We show that such an exposure of juvenile prey to adult predators results in behavioural changes later in life: after becoming adult, these prey killed juvenile predators at a faster rate than prey that had not been exposed. The attacks were specifically aimed at predators of the species to which they had been exposed. This suggests that prey recognize the species of predator to which they were exposed during their juvenile stage. Our results show that juvenile experience affects adult behaviour after a role reversal.

We previously reported that Cotesia vestalis (Hymenoptera, Braconidae), a parasitoid of diamondback moth (DBM) (Plutella xylostella; Lepidoptera, Plutellidae) larvae, was attracted to volatiles from crucifer plants infested by moth larvae kept in a desktop acrylic box, and that a blend of four DBM-induced plant volatiles was responsible for this attraction. In this study, using a specially designed dispenser to release the four compounds, we demonstrated that the wasp was attracted to intact komatsuna plants (Brassica rapa var. perviridis). The experiments were performed in a climate-controlled room, which was approximately 1000 times larger than the acrylic box used previously. Similarly, using the dispenser in the field, C.vestalis females were attracted to intact komatsuna plants with the dispenser from a distance of three metres. We also examined the effect of the volatile blend on the incidence of parasitism of DBM larvae in the field. Three small containers containing DBM-infested komatsuna plants with dispensers, and three control containers containing only infested plants (control) were arranged in two lines running perpendicular to a komatsuna field in which both DBM larvae and C.vestalis populations were maintained, at distances of 12, 30 and 70 m. The results showed that the incidence of DBM parasitism was significantly higher in containers containing dispensers than in the control containers, suggesting that the blend could potentially be applied to DBM control in agroecosystems.

When herbivorous mites encounter with predatory mites in their colony, they disperse from the colony to an alternative leaf patch to escape from the predators. However, the alternative patch may have been used by other herbivore competitors. We studied whether the herbivorous mites change their dispersal to the alternative patch with either conspecifics, or cowpea aphids, or common cutworms when they perceived volatiles from the patch infested by the competitors. The herbivorous mites reduced the dispersal to the alternative leaf patch with common cutworms that induced resistance to themselves in the leaf patch. We confirmed that the reduced dispersal would be a response to leaf volatiles induced by common cutworms.

Theory on intraguild (IG) predation predicts that coexistence of IG-predators and IG-prey is only possible for a limited set of parameter values, suggesting that IG-predation would not be common in nature. This is in conflict with the observation that IG-predation occurs in many natural systems. One possible explanation for this difference might be antipredator behaviour of the IG-prey, resulting in decreased strength of IG-predation. We studied the distribution of an IG-prey, the predatory mite Neoseiulus cucumeris (Acari: Phytoseiidae), in response to cues of its IG-predator, the predatory mite Iphiseius degenerans. Shortly after release, the majority of IG-prey was found on the patch without cues of IG-predators, suggesting that they can rapidly assess predation risk. IG-prey also avoided patches where conspecific juveniles had been killed by IG-predators. Because it is well known that antipredator behaviour in prey is affected by the diet of the predator, we also tested whether IG-prey change their distribution in response to the food of the IG-predators (pollen or conspecific juveniles), but found no evidence for this. The IG-prey laid fewer eggs on patches with cues of IG-predators than on patches without cues. Hence, IG-prey changed their distribution and oviposition in response to cues of IG-predators. This might weaken the strength of IG-predation, possibly providing more opportunities for IG-prey and IG-predators to co-exist.

Herbivore-induced plant volatiles (HIPV) are emitted by plants in response to herbivory and attract natural enemies of herbivores, thereby inducing an important indirect defence against herbivores. Evidence supports the hypothesis that plants become more defensive against herbivores after exposure to HIPV and that this is a type of priming, or preparation by the plant perceiving an HIPV signal to respond to herbivory. We report the priming of two induced indirect defences: HIPV-mediated induction of predator attraction and the secretion of extrafloral nectar (EFN), known as an alternative food source for natural enemies of herbivores. When uninfested lima bean plants (Phoseolus lunatus) were exposed to HIPV, the plants attracted more predatory mites (Phytoseiulus persimilis) and secreted larger amounts of EFN than unexposed plants. Further, when HIPV-exposed plants were infested by spider mites (Tetranychus urticoe) for 2 days, the plants attracted more predators and secreted larger amounts of EFN than plants that were infested for 2 days after exposure to uninfested plant volatiles. However, there were no differences in the attraction and the EFN secretion when they were infested for 4 days. Predatory mites survived longer when supplied with EFN and stayed longer on uninfested plants that had been supplemented with additional extrafloral nectar. From these results, we conclude that the priming of HIPV-exposed plants recruits predators and induces the secretion of EFN that functions to protect the plants before and after herbivory.

When adult females of the herbivorous mite, Tetranychus urticae, were exposed to the predatory mite, Phytoseiulus persimilis, they laid fewer eggs than females that had not been exposed to P. persimilis when transferred onto a new leaf patch. However, when T. urticae females were exposed to either products of P. persimilis or artificially damaged conspecific eggs on a leaf patch, the number of T. urticae eggs on a new leaf patch did not differ significantly from the control. The reduced oviposition was neither due to the feeding activity on the leaf patch with P. persimilis nor to that on the new leaf patch. There was also no significant difference between the number of T. urticae eggs produced on a new leaf patch following exposure to the odours of a neighbouring leaf patch where there had previously been either P. persimilis or T. urticae adults. However, female T. urticae that had been exposed to odours from neighbouring leaf patches on which both T. urticae and P. persimilis had been placed produced significantly fewer eggs on a new leaf patch than those that had not been exposed to such odours. Neither odours from neighbouring intact leaf patches on which T. urticae eggs were preyed on by P. persimilis, nor odours from a neighbouring Parafilm patch on which T. urticae was preyed on by P. persimilis affected the oviposition of T. urticae. These data suggest that the presence of T. urticae, P. persimilis and a leaf patch are needed for the emission of odours to reduce oviposition in T. urticae.

When predators invade a leaf patch inhabited by herbivores, the herbivores disperse to a neighboring predator-free leaf patch, thus escaping from the predators. However, the neighboring patch might already be used by con- or heterospecific herbivores. We used laboratory bioassays to examine whether perception of odor from con- or heterospecific competitors on a neighbored lima bean leaf patch influences dispersal behavior of the herbivorous mite Tetranychus urticae when attacked by predatory mites Phytoseiulus persimilis. The dispersal rates of T. urticae that perceived odors from leaf patches infested by conspecifics or cowpea aphids (Aphis craccivora) did not differ from the control (the dispersal rate of T. urticae that perceived odor from uninfested leaf patches). By contrast, the dispersal rate of T. urticae was reduced when they perceived odors from leaf patches that were currently or had previously been infested by larvae of the common cutworm (Spodoptera litura). Previous herbivory by S. litura larvae induced resistance in leaf patches to T. urticae as indicated by the reduced number of eggs laid by T. urticae. Our results are discussed with respect to the feeding behavior of the tested competitors of T. urticae and the impact of the plant and arthropod community on the dispersal behavior of these mites. ©Springer Science+Business Media, LLC 2010.

1. When offered a choice, female diamondback moths (Plutella xylostella) oviposited more eggs on plants with non-parasitised conspecific larvae than on plants with parasitised larvae. 2. The leaf area consumed by parasitised larvae was significantly lower than that by non-parasitised larvae. However, this quantitative difference in larval damage did not explain the female's ability to discriminate between plants with parasitised and non-parasitised larvae, as females showed an equal oviposition preference for plants infested by higher or lower densities of non-parasitised larvae. 3. Pupal weight and duration of the larval stage of P. xylostella were independent of whether larvae were reared on plants that were previously infested by either non-parasitised or parasitised larvae. 4. The larval parasitoid Cotesia vestalis did not distinguish between plants infested by non-parasitised larvae and plants infested by larvae that had already been parasitised by conspecific wasps. 5. Based on these data, it can be concluded that the moth oviposition preference for plants infested by non-parasitised conspecifics relative to plants infested by parasitised conspecifics was not explained by plant quality or by the attractiveness of plants towards wasps. It is hypothesised that one of the reasons for this preference is avoidance of plants where a relatively high risk of parasitism is expected due to the emergence of parasitoids from the parasitised host larvae.

We studied whether volatiles released by putative host plants affect the antipredator response of an herbivorous mite, Tetranychus urticae, when the patch was invaded by Phytoseiulus persimilis. Tetranychus urticae laid a lower number of eggs on tomato leaves than on lima bean leaves, suggesting that lima bean is a preferred host food source for T. urticae. In addition, T. urticae preferred lima bean plant volatiles to tomato plant volatiles in a Y-tube olfactometer test. To investigate the antipredator response of T. urticae, we examined the migration of T. urticae from a lima bean leaf disc to a neighbouring leaf disc (either a tomato or lima bean leaf disc) when ten predators were introduced into the original lima bean disc. A Parafilm bridge allowed for migration between the leaf discs. No migrations occurred between leaf discs when there were no predators introduced to the original leaf disc. However, when predators were introduced migrations did occur. When the neighbouring leaf disc was upwind of the original disc, the migration rate of the mite from original lima bean leaf disc to a neighbouring tomato leaf disc was significantly lower than that to a neighbouring lima bean leaf disc. By contrast, when the neighbouring leaf disc was downwind of the original leaf disc, there was no difference in the migration rates between lima bean leaf discs and tomato leaf discs. The number of T. urticae killed by P. persimilis for each treatment was not different, and this clearly shows that the danger was the same in all treatments regardless of the decision made by T. urticae. From these results, we conclude that T. urticae change their antipredator response by evaluating the difference in host plant volatiles in the patch they inhabit.

When plants are infested by herbivores, they emit herbivore-induced plant volatiles (HIPVs) that attract carnivorous natural enemies of herbivores. Furthermore, there are increasing evidences that defenses of intact plants against herbivores are primed when exposed to HIPVs. We previously reported that lima bean leaf volatiles induced by the herbivorous mites Tetranychus urticae primed two T. urtiae-induced indirect defenses in neighboring conspecific plants: HIPV emission and extrafloral nectar (EFN) secretion. An intriguing unanswered question is whether the durations of these two defenses are the same. Here, we show that the durations of the two defenses were the same for up to two days after the initiation of T. urticae damage. The two induced primed defense would act as a battery of defense in exposed plants. ©2007 Landes Bioscience.

In response to herbivory by spider mites (Tetranychus urticae), lima bean plants produced significantly greater quantities of extrafloral nectar (EFN) than intact conspecific plants. Moreover, EFN amounts of infested plants depended on exposure to odor of infested neighbor plants. Two d after spider mite infestation, a test plant produced more EFN when exposed prior to infestation to volatiles from infested neighbor plants than when exposed to volatiles from uninfested conspecific plants. However, this effect was only detectable 2 d after spider mite infestation and vanished 4 d after infestation. These results suggest that EFN production is enhanced during the earlier stages of damage by T. urticae in response to previous exposure to volatiles from infested neighbor plants.

Previous studies have shown that intact lima bean plants exposed to volatiles emitted from conspecific plants infested by two-spotted spider mites, Tetranychus urticae (Acari: Tetranychidae), attract Phytoseiulus persimilis (Acari: Phytosciidae), a carnivorous natural enemy of spider mites. Here, we investigated the olfactory responses of P persimilis and T urticae to different parts of intact lima bean plants exposed to these volatiles using a Y-tube olfactometer. Predators responded in greater number to volatiles from the first trifoliate leaves compared to those from primary leaves, and to volatiles from the parts above the first trifoliate leaves compared to those from the first trifoliate leaves. Conversely, spider mites responded more to volatiles from primary leaves compared to those from the first trifoliate leaves, and showed equal preference for volatiles released from the first trifoliate leaves or the parts above the first trifoliate leaf. The reproduction of spider mites in primary leaves was higher than those on trifoliate leaves. Based on these data, the potential adaptive value of differential attractiveness of different parts of intact lima bean plants to T urticae and P persimilis is discussed.

We found that intact lima bean plants increased the secretion of extrafloral nectar (EFN) after exposure to Tetranychus urticae-induced plant volatiles. Predatory mites, Phytoseiulus persimilis, dispersed more slowly from an exposed intact plant than from a control plant (plant exposed to volatiles from intact conspecific). The predators also dispersed more slowly from those plants that were provided with extra EFN than from untreated plants. We further show that EFN was a potential alternative food source for P. persimilis. From these results, we concluded that increased EFN was involved in the slow dispersal of P. persimilis from the plants exposed to herbivore-induced plant volatiles. Our data suggest that the increase of EFN in an HIPV-exposed intact plant could be an induced indirect defense against spider mites.

There is increasing evidence that volatiles emitted by herbivore-damaged plants can cause responses in downwind undamaged neighboring plants, such as the attraction of carnivorous enemies of herbivores. One of the open questions is whether this involves an active (production of volatiles) or passive ( adsorption of volatiles) response of the uninfested downwind plant. This issue is addressed in the present study. Uninfested lima bean leaves that were exposed to volatiles from conspecific leaves infested with the spider mite Tetranychus urticae, emitted very similar blends of volatiles to those emitted from infested leaves themselves. Treating leaves with a protein-synthesis inhibitor prior to infesting them with spider mites completely suppressed the production of herbivore-induced volatiles in the infested leaves. Conversely, inhibitor treatment to uninfested leaves prior to exposure to volatiles from infested leaves did not affect the emission of volatiles from the exposed, uninfested leaves. This evidence supports the hypothesis that response of the exposed downwind plant is passive. T. urticae-infested leaves that had been previously exposed to volatiles from infested leaves emitted more herbivore-induced volatiles than T. urticae-infested leaves previously exposed to volatiles from uninfested leaves. The former leaves were also more attractive to the predatory mite, Phytoseiulus persimilis, than the latter. This shows that previous exposure of plants to volatiles from herbivore-infested neighbors results in a stronger response of plants in terms of predator attraction when herbivores damage the plant. This supports the hypothesis that the downwind uninfested plant is actively involved. Both adsorption and production of volatiles can mediate the attraction of carnivorous mites to plants that have been exposed to volatiles from infested neighbors.

The effects of jasmonic acid (JA) and benzo (1,2,3) thiadiazole-7-carbothioic acid S-methyl ester (BTH), a functional analogue of salicylic acid, treatment of lima bean plants on the egg production were investigated in a herbivorous mite, Tetranychus urticae. JA and BTH were applied at three concentrations for each treatment to soil in pots containing plants. Only the 0.1 mm JA-treatment significantly reduced the number of eggs laid by T. urticae over a three day period, whereas higher (1 mm) and lower (0.01 mm) concentrations did not affect the egg production of T. urticae. Fewer eggs were laid by T. urticae on lima bean plants treated with 1 mm and 10 mm BTH than with 0.1 mm BTH. These data suggest that JA and BTH are involved in the direct defense of the lima bean plant against T. urticae.