Leaf pubescence mediates intraguild predation between predatory mites

Plant morphological traits such as leaf pubescence may affect herbivores and their natural enemies at the individual, population and community levels. Leaf pubescence has been repeatedly shown to mediate predator‐herbivore interactions whereas the influence of leaf pubescence on predator–predator interactions such as intraguild predation (IGP) has seldom been investigated. Using a three‐pronged approach we assessed the influence of leaf pubescence on the predatory mites Kampimodromus aberrans and Euseius finlandicus. Both predators occur on broad‐leaved trees in Europe. Euseius finlandicus is mostly found on trees with glabrous leaves whereas K. aberrans mainly occurs on trees with pubescent leaves. We hypothesized that leaf pubescence mediates IGP between K. aberrans and E. finlandicus and thereby determines their dominance and proportional abundance. A field survey on apple revealed that the abundance of K. aberrans and E. finlandicus is negatively correlated, with the former predominating on cultivars with strongly pubescent leaves and the latter predominating on cultivars with little pubescent or glabrous leaves. Microhabitat choice tests showed that K. aberrans preferentially resides on pubescent leaves whereas E. finlandicus preferentially resides on glabrous leaves. The effects of leaf pubescence on survival and development of immature IG predators and IG prey were reversed for K. aberrans and E. finlandicus. In the presence of the IG predator E. finlandicus, immature K. aberrans had higher survival probabilities on pubescent leaves than on glabrous ones. In contrast, the survival chances of immature E. finlandicus were higher on glabrous leaves than on pubescent ones when the IG predator K. aberrans was present. Artificial leaf pubescence enhanced IG prey capture by immature K. aberrans and prolonged their longevity but impaired IG prey capture by immature E. finlandicus and shortened their longevity. We conclude that leaf pubescence mediates IGP strength and symmetry and discuss the implications to natural and biological control.     

Cannibalism and Intraguild Predation Among Phytoseiid Mites: Are Aggressiveness and Prey Preference Related to Diet Specialization?

We tested whether specialist and generalist phytoseiid mites differ in aggressiveness and prey choice in cannibalism and intraguild predation. Specialists tested were Galendromus occidentalis, Neoseiulus longispinosus, Phytoseiulus persimilis, and P. macropilis; tested were Amblyseius andersoni, Euseius finlandicus, E. hibisci, Kampimodromus aberrans, Neoseiulus barkeri, N. californicus, N. cucumeris, N. fallacis, and Typhlodromus pyri. Aggressiveness of cannibalistic females against larvae was not related to diet specialization except that highly aggressive species were exclusively generalists. Seldom to moderately cannibalizing species occurred in both generalist and specialist phytoseiids. In contrast to aggressiveness in cannibalism, generalists and specialists differed in aggressiveness in intraguild predation. Adult females of specialists were only slightly aggressive against heterospecific larvae, whereas adult females of all generalists except T. pyri were highly aggressive. Adult females of generalists were able to discriminate between con- and heterospecific larvae and preferentially consumed the latter when given a choice. Adult females of specialists except G. occidentalis showed no preference when given a choice between con- and heterospecific larvae. We conclude that aggressiveness in intraguild predation, species recognition and subsequent preferential consumption of heterospecifics when given a choice is common in generalist but not specialist phytoseiids. We discuss the evolutionary pathways that might have led to the difference between specialists and generalists in species discrimination.     

Correspondence of trichome mutations in diploid and tetraploid cottons

Quantitative variation for leaf trichome number is observed within and among Gossypium species, varying from glabrous to densely pubescent phenotypes. Moreover, economically important cotton lint fibers are modified trichomes. Earlier studies have mapped quantitative trait loci (QTLs) affecting leaf pubescence in Gossypium using allotetraploids. In this study, we mapped genes responsible for leaf trichome density in a diploid A genome cross. We were able to map 3 QTLs affecting leaf pubescence based on trichome counts obtained from young leaves (YL) and mature leaves (ML). When the F(2) progeny were classified as pubescent versus glabrous, their ratio did not deviate significantly from a 3:1 model, suggesting that glabrousness is inherited in a simple Mendelian fashion. The glabrous mutation mapped to linkage group A3 at the position of major QTL YL1 and ML1 and appeared orthologous to the t1 locus of the allotetraploids. Interestingly, a fiber mutation, sma-4(ha), observed in the same F(2) population cosegregated with the glabrous marker, which indicates either close linkage or common genetic control of lint fiber and leaf trichomes. Studies of A genome diploids may help to clarify the genetic control of trichomes and fiber in both diploid and tetraploid cottons.     

Intraguild interactions between Euseius stipulatus and the candidate biocontrol agents of Tetranychus urticae in Spanish clementine orchards: Phytoseiulus persimilis and Neoseiulus californicus

Spanish clementine orchards are frequently infested by the two-spotted spider mte Tetranychus urticae. Natural control of T. urticae is insufficient despite the presence of Neoseiulus californicus and Phytoseiulus persimilis. The phytoseiid community is dominated by the generalist Euseius stipulatus which is poorly adapted to exploit T. urticae. Having the intention to promote biological control of T. urticae by augmentative releases we were interested whether P. persimilis and N. californicus are negatively affected by intraguild (IG) interactions with E. stipulatus. Two experiments were conducted. Firstly, we assessed female aggressiveness (quantified as combination of attack probability and latency) in IG predation on larvae. Secondly, we measured mortality, escaping rate and developmental time of immature IG prey in presence and absence of an adult IG predator female. Euseius stipulatus appeared the strongest IG opponent but microhabitat structure modulated the IG interactions and the advantage of E. stipulatus was partially offset when spider mite webbing was present. Implications of these IG interactions for natural and biological control of T. urticae in clementine orchards are discussed.     

Distribution of the Predatory Mite Typhlodromus pyri (Acari: Phytoseiidae) on Different Apple Cultivars

The effect of apple cultivar on the distribution of the predatory mite Typhlodromus pyri was studied in an experimental orchard where spider mites occurred at negligible densities. Seven apple scab-resistant cultivars, showing some differences in their leaf morphology, were considered. In particular, their leaf blade was classified according to four levels of pubescence. The distribution of T. pyri along the shoots was also studied. In the first experimental year the colonization of different cultivars by T. pyri showed definite patterns, sometimes influenced by the occurrence of eriophyids. One year later, T. pyri abundance again showed some differences among cultivars in conditions of prey scarcity. In both years large phytoseiid populations were recorded on the cultivar N.Y. 18491, despite the low eriophyid occurrence, probably because of its highly pubescent leaf undersurfaces. In contrast, Prima and TSR 29T219, characterized by slightly pubescent leaf undersurfaces, supported low phytoseiid densities independently of prey availability.     

Intraguild Interactions Between the Predatory Mites Neoseiulus californicus and Phytoseiulus persimilis

Species at the same trophic level may interact through competition for food, but can also interact through intraguild predation. Intraguild predation is widespread at the second and third trophic level and the effects may cascade down to the plant level. The effects of intraguild predation can be modified by antipredator behaviour in the intraguild prey. We studied intraguild predation and antipredator behaviour in two species of predatory mite, Neoseiulus californicus and Phytoseiulus persimilis, which are both used for control of the two-spotted spider mite in greenhouse and outdoor crops. Using a Y-tube olfactometer, we assessed in particular whether each of the two predators avoids odours emanating from prey patches occupied by the heterospecific predator. Furthermore, we measured the occurrence and rate of intraguild predation of different developmental stages of P. persimilis and N. californicus on bean leaves in absence or in presence of the shared prey. Neither of the two predator species avoided prey patches with the heterospecific competitor, both when inexperienced with the other predator and when experienced with prey patches occupied by the heterospecific predator. Intraguild experiments showed that N. californicus is a potential intraguild predator of P. persimilis. However, P. persimilis did not suffer much from intraguild predation as long as the shared prey was present. This is probably because N. californicus prefers to feed on two-spotted spider mites rather than on its intraguild prey.     

The significance of prey in the diet of the phytophagous thrips, Frankliniella schultzei

1. Patterns of mite egg consumption by the phytophagous thrips Frankliniella schultzei Trybom were investigated. Although F. schultzei predation is somewhat similar to that of F. occidentalis (Pergande), the understanding of predation by these two phytophagous thrips was extended, allowing the functional significance of flower thrips’ predatory behaviour to be reinterpreted. 2. Second-instar larvae consumed significantly more eggs than any other life-stage, and the daily intake of eggs by second-instar larvae declined significantly with each successive day of the 4-day duration of instar two. 3. Mite eggs that had had their silken webbing removed were consumed at a significantly greater rate than those with their webbing intact. 4. Frankliniella schultzei immatures developed successfully both on diets containing cotton (Gossypium hirsutum L.) leaf tissue plus mite eggs and on cotton leaf tissue alone. Supplementing a leaf tissue larval diet with mite eggs lowered the developmental time from egg to adult significantly, as well as lowering the percentage mortality. Continuation of the mite egg supplement beyond adult eclosion increased fecundity significantly and extended life span over that achieved on a leaf diet alone. 5. In laboratory choice tests, mite eggs and pollen of Wax Mallow (Malvaviscus arboreus Cav.), the usual host of F. schultzei in Brisbane, were encountered with similar frequencies. Furthermore, the mean proportion of encounters with pollen grains that resulted in consumption of pollen did not differ significantly from the encounter : consumption rate for mite eggs. 6. Frankliniella schultzei, like F. occidentalis, does not seem to be specifically adapted for preying on mite eggs, even though such predation enhances performance and reproductive output of F. schultzei when constrained on cotton leaves. Comparison of performance results with those published for F. schultzei when reared on the floral parts of one of its primary hosts (M. arboreus) (Milne et al., 1996), indicates that mite egg predation does not make up completely for a deficient adult or larval diet.     

Factors affecting biological control of apple mites by mixed populations ofMetaseiulus occidentalis andTyphlodromus pyri

Metaseiulus occidentalis (Nesbitt) andTyphlodromus pyri Scheuten have complementary features/ traits that enable them to control effectively plant-feeding mites on apple. Populations of both predators gave as good or better biological control of the apple rust mite (Aculus schlechtendali Nalepa), European red mite (Panonychus ulmi Koch) and two-spotted spider mite (Tetranychus urticae (Koch)) than single-predator populations. With mixed predators,M. occidentalis provided better control of spider mites the first season after release, butT. pyri gave better control in the second season. Several factors affected the ability of predators to provide biological control: When prey were dense,M. occidentalis rapidly increased during the warm mid-summer, whileT. pyri provided greater predation when it was cool at the start or end of the growing season. When few prey were present, searching byM. occidentalis was more confined on individual apple leaves, but it migrated between leaves and trees more often. Pollen feeding, cannibalism and interspecific predation were more common byT. pyri. In fall, oviposition byM. occidentalis stopped sooner and in the following spring,T. pyri reproduced beforeM. occidentalis. Research needs and management of mixed-predator populations are discussed.     

Prey preference of the phytoseiid miteTyphlodromus pyri 1. Response to volatile kairomones

Using a Y-tube olfactometer, a study has been made of the response of females of the predatory miteTyphlodromus pyri Scheuten (Acarina: Phytoseiidae) to volatile kairomones of three prey species: the European red spider mite (Panonychus ulmi (Koch)), the two-spotted spider mite (Tetranychus urticae Koch) and the apple rust mite (Aculus schlechtendali (Nalepa)).Predators that had been reared onT. urticae responded only to the volatile kairomone ofP. ulmi. In contrast, when reared onVicia faba L. pollen, they responded to the kairomones of all three prey species. Pollen-reared predators, offered a choice between kairomones of two different prey species, prefer theP. ulmi kairomone to those ofA. schlechtendali orT. urticae.The difference in response between predators reared onV. faba pollen andT. urticae seems to be caused by the low carotenoid content ofV. faba pollen. Predators that had been reared onV. faba pollen mixed with crystalline -carotene behaved in a way similar to conspecific that had been reared on the carotenoid-rich prey miteT. urticae. Obviously, pollen-rearedT. pyri females are in need of carotenoids, which can be obtained from, e.g.,P. ulmi, T. urticae orA. schlechtendali. This may explain why pollen-reared predators respond to more prey species thanT. urticae-reared predators.WhyT. pyri females need carotenoids has not been established. The only known function of carotenoids in mites is involvement in diapause induction. However, as pollen-rearedT. pyri enter reproductive diapause under short-day conditions, they either extract sufficient amounts of carotenoids fromV. faba pollen, or do not need carotenoids for diapause induction.Apart from the effect of dietary requirements on prey selection, food deprivation also affects the predator's response to kairomones. All the data mentioned above have been obtained for predators that had been starved for 20 h. Predators that had been reared onT. urticae and starved for 48 h before the experiment did respond to the volatile kairomone ofT. urticae in contrast to predators from the same culture that had been starved for 20 h. Thus foraging decisions byT. pyri are affected by both starvation time and specific hunger for carotenoids.     

Long-term stability in the interaction betweenTetranychus urticae andPhytoseiulus persimilis producing successful integrated control on roses in southeast Queensland

Phytoseiulus persimilis Athias-Henriot successfully controlledTetranychus urticae Koch on rose hedges in an integrated mite control programme in two unheated plastic-covered tunnels at Cleveland in southern Queensland. Mite populations were monitored fortnightly for nearly three years in one tunnel and for two years in a second. Once established,P. persimilis quickly suppressedT. urticae and then persisted. A relatively stable, long-term, low-level interaction developed between the two species under normal commercial conditions. In one tunnel, the production (upper) level of the four rose hedges contained fewer mites of both species per compound leaf (1.71 of all stages ofT. urticae, 0.38 motiles; 0.25 of all stages ofP. persimilis, 0.12 motiles) than the maintenance (lower) layer (2.02 of all stages ofT. urticae, 0.75 motiles; 0.35 of all stages ofP. persimilis, 0.21 motiles). On 68% of sampling occasions, 10% or less of compound leaves in the production layer were infested withT. urticae (all stages including eggs) and control was excellent throughout the 30-month period afterP. persimilis was established, there being no economic losses. In the second tunnel, there was no significant difference between mite numbers in the production and maintenance layers of the two hedges examined. The overall mean number of all stages ofT. urticae per compound leaf was 3.2 (1.45 motiles), and ofP. persimilis 0.46 (0.25 motiles). Control here was slightly less effective than in the first tunnel, but was still satisfactory, with 10% or less of leaves being infested on 45.5% of sampling occasions (20% or less on 66% of sampling occasions) withT. urticae (all stages including eggs).Phytoseiulus persimilis was not reintroduced or redistributed during the course of the observations. An auxiliary miticide (clofentezine) was applied on only one occasion to selected areas in the second tunnel. The influence of high temperatures on control byP. persimilis is discussed.     

Behavioral responses to prey density by three acarine predator species with different degrees of polyphagy

Behavioral responses by three acarine predators, Phytoseiulus persimilis, Typhlodromus occidentalis, and Amblyseius andersoni (Acari: Phytoseiidae), to different egg and webbing densities of the spider mite Tetranychus urticae (Acari: Tetranychidae) on rose leaflets were studied in the laboratory. Prey patches were delineated by T. urticae webbing and associated kairomones, which elicit turning back responses in predators near the patch edge. Only the presence of webbing affected predator behavior; increased webbing density did not increase patch time. Patch time increased with increased T. urticae egg density in the oligophagous P. persimilis, but was density independent in the polyphagous species T. occidentalis and A. andersoni. Patch time in all three species was more strongly correlated with the number of prey encounters and attacks than with the actual prey number present in the patch. Patch time was determined by (a) the turning back response near the patch edge; this response decayed through time and eventually led to the abandonment of the patch, and (b) encounters with, and attacks upon, prey eggs; these prolonged patch time by both an increment of time spent in handling or rejecting prey and an increment of time spent searching between two successive prey encounters or attacks. Although searching efficiency was independent of prey density in all three species, the predation rate by P. persimilis decreased with prey density because its searching activity (i.e. proportion of total patch time spent in searching) decreased with prey density. Predation rates by T. occidentalis and A. andersoni decreased with prey density because their searching activity and success ratio both decreased with prey density. The data were tested against models of predator foraging responses to prey density. The effects of the degree of polyphagy on predator foraging behavior were also discussed.     

Absorption and cannibalism: do phytoseiids conserve egg resources when prey densities decline rapidly?

The number of eggs oviposited or left in the opisthosomas of dead mites (total eggs) was assessed for Metaseiulus occidentalis (Nesbitt), Neoseiulus fallacis (Garman), Typhlodromus pyri Scheuten or Amblyseius andersoni Chant when each was caged with either (1) no Tetranychus urticae Koch, (2) only odours of T. urticae, (3) ten eggs of M. occidentalis or (4) ten nymphs of M. occidentalis (T. pyri for M. occidentalis). The total eggs for the no prey versus odour tests did not differ within species; the levels were the greatest for N. fallacis > T. pyri > A. andersoni > M. occidentalis. Among treatments, egg means did not differ for M. occidentalis but they did for N. fallacis and T. pyri and similar trends were seen for A. andersoni. Egg means were usually less for mites held with ten predator nymphs than mites held with ten predator eggs or with no prey. Were adult females with nymphs absorbing rather than ovipositing their eggs or dying with them in their opisthosomas? Activity levels (walking) for adult females were no more for mites held with nymphs versus no food. The data indicated that interference by nymphs was not increasing the energy use of females and thus reducing egg levels. However, tests with ten nymphs, one egg and no adult female had egg losses from nymphal predation that could account for fewer eggs in cage tests. Overall, no evidence for absorption was found. If it occurs, it must be among younger eggs or mites exposed to less rapid prey losses than were the mites tested here; in addition, other stimuli may cause absorption. The total eggs in sticky-tape tests were greatest for N. fallacis > M. occidentalis > T. pyri > A. andersoni. Cage versus stick-tape data differed most for M. occidentalis because of cannibalism. All four mites cannibalized eggs but M. occidentalis did most rapidly and extensively. When starved, it laid all of its eggs before the other three species did. Such behaviours may enhance survival of M. occidentalis when prey become scarce.     

Diapause induction and duration in the phytoseiid miteTyphlodromus pyri

A photoperiod of 8L/16D for two weeks was used to distinguish between diapausing and non-diapausingTyphlodromus pyri Scheuten. A diet ofPanonychus ulmi orTetranychus urticae, or pollen ofVicia faba did not influence preovipositional periods of diapausing mites. In mid-September, 88% ofT. pyri collected from an insectary were in diapause. The critical day-length appeared to be between 12.5 and 13.5 h. Diapause duration was greatest in mites collected in September–November, becoming progressively less in mites collected later in the winter. By mid-April, ca. 50% of mites collected from the orchard and insectary oviposited promptly when cultured in the laboratory.Typhlodromus pyri eggs and larvae were present on leaves in early May. At this time, only 4% ofP. ulmi winter eggs had hatched. Diapause terminated most quickly inT. pyri kept in an 18L/6D photoperiod, followed by 24L/0D and 0L/24D. Longest preoviposition periods were recorded for mites kept in 8L/16D photoperiods.     

Pear rust mite,Epitrimerus pyri (Acari: Eriophyidae) oviposition and nymphal development on Pyrus and non-Pyrus hosts

The ovipositional response of deutogynes of the pear rust mite, Epitrimerus pyri Nalepa, and the rate of development of E. pyri nymphs differed according to the host plant to which mites were exposed. Among the fourteen Pyrus hosts examined, leaves from the Clapp's Favorite cultivar of P. communis elicited the strongest egg-laying response and the fastest rate of nymphal development, whereas egg-laying was least and nymphal development slowest on leaves from P. calleryana. Among the three non-Pyrus hosts, E. pyri oviposited and completed nymphal development on apple and quince leaves, but would not deposit eggs on apricot. Antixenosis appears to be the primary mechanism of resistance, although antibiosis may be operating to a lesser extent. These results are discussed in relation to the resistance of Pyrus to other arthropod pests.     

Chemically mediated arrestment of the predaceous mitePhytoseiulus persimilis by extracts ofTetranychus evansi andTetranychus urticae

SinceTetranychus evansi Baker and Pritchard had been observed to be unfavorable prey for several species of phytoseiid mite predators, a study was conducted to determine the possible existence of an allomone produced by this species againstPhytoseiulus persimilis Athias-Henriot. Instead,P. persimilis was strongly arrested by extracts of eggs, adults and, especially, webbing plus excreta ofT. evansi. Methanol extracts ofTetranychus urticae (Koch) showed a stronger arrestment than extracts ofT. evansi.     

Interactions among phytophagous mites, and introduced and naturally occurring predatory mites, on strawberry in the UK

In choice test experiments on strawberry leaf disc arenas the phytoseiid mites Neoseiulus californicus and N. cucumeris were more effective than Typhlodromus pyri as predators of the phytophagous mites Tetranychus urticae and Phytonemus pallidus. There were no preferences shown for either prey by any of these predators. In multiple predator leaf disc experiments both Phytoseiulus persimilis and N. cucumeris significantly reduced numbers of T. urticae eggs and active stages; this effect was seen when the two species were present alone or in combination with other predator species. Neoseiulus californicus was less effective at reducing T. urticae numbers, and T. pyri was not effective; no interaction between predator species was detected in these experiments. When T. urticae alone was present as prey on potted plants, P. persimilis and N. californicus were the only phytoseiids to significantly reduce T. urticae numbers. These two predator species provided effective control of T. urticae when P. pallidus was also present; however, none of the predators reduced numbers of P. pallidus. There were no significant negative interactions when different species of predators were present together on these potted plants. In field experiments, releases of both P. persimilis and N. cucumeris significantly reduced T. urticae numbers. However, there was a significant interaction between these predator species, leading to poorer control of T. urticae when both species were released together. These results show the importance of conducting predator/prey feeding tests at different spatial scales.     

The geographic distribution of pubescence in the sea daisy, Borrichia aborescens, on Bahamian Islands

Borrichia aborescens (L.) DC. is a salt‐tolerant perennial herb that is common on small islands in the central Bahamas. Two morphotypes are present: one with densely pubescent leaves and one with glabrous leaves. I conducted surveys in three archipelagos to document the geographical distribution of pubescence in this species and to infer the underlying mechanisms. B. aborescens was also grown from seed in a greenhouse. The pubescent form of B. aborescens was relatively more abundant on small islands than on nearby large ‘mainland’ islands. In two of the three archipelagoes, pubescence increased with distance on small islands. The pubescent form was relatively more abundant on small islands exposed to the open ocean compared to small islands that were protected by mainland islands or reefs on all sides. On a large mainland island, the pubescent form decreased in relative abundance inland from the coast. B. aborescens cultivated in a greenhouse revealed the effect of a genetic factor on the expression of pubescence. The observed patterns of variation are consistent with a physiological explanation for the adaptive benefit of pubescence. Trichomes may prevent physical blockage of the stomata by accumulation of salt in areas near breaking waves and salt spray.     

The benefits of clustering eggs: the role of egg predation and larval cannibalism in a predatory mite

Many arthropods produce clusters of eggs, but an unambiguous explanation for the evolution of egg clustering is still lacking. We test several hypotheses for the production of egg clusters by the predatory mite Iphiseius degenerans. This predator feeds on pollen, thrips larvae and nectar in flowers, but oviposits in clusters in tufts of leaf hairs (acarodomatia), where eggs run a lower risk of being killed by thrips, the prey of this predatory mite. The observed clustering is not caused by a shortage of oviposition sites; females preferably oviposit in a domatium containing eggs rather than in an empty domatium. To explain this preference, we first examined the effect of egg clusters on the risk of cannibalism. We found that eggs are invulnerable to cannibalism, whereas larvae emerging from single eggs or from clusters were equally vulnerable. Subsequently, we considered the killing of eggs resulting from counter-attacks by prey, i.e. the western flower thrips. We found no indication that a cluster of eggs protects eggs from predation by thrips. However, when eggs were clustered in a domatium rather than scattered over domatia, the proportion of eggs killed by thrips was lower. Hence, oviposition in clusters has no effect on its own and oviposition in domatia reduces predation risk by thrips, but oviposition in clusters in domatia leads to a synergistic effect on the survival of predator eggs. This synergism probably arises because eggs in clusters within tufts of leaf hairs are more difficult for thrips to reach. These experiments highlight a novel explanation of egg clustering, i.e. adaptation to counter-attacking prey. Moreover, they show that plant domatia protect predator eggs from predation.     

The predatory mite Typhlodromalus aripo prefers green-mite induced plant odours from pubescent cassava varieties

It is well known that plant-inhabiting predators use herbivore-induced plant volatiles to locate herbivores being their prey. Much less known, however, is the phenomenon that genotypes of the same host plant species vary in the attractiveness of these induced chemical signals, whereas they also differ in characteristics that affect the predator’s foraging success, such as leaf pubescence. In a series of two-choice experiments (using a Y-tube olfactometer) we determined the preference of Typhlodromalus aripo for pubescent versus glabrous cassava cultivars infested with the cassava green mite Mononychellus tanajoa and also the preference for cultivars within each of the two groups. We found that when offered a choice between pubescent and glabrous cassava cultivars (either apex or leaves), T. aripo was significantly more attracted to pubescent cultivars. For each cultivar, M. tanajoa infested leaves and apices were equally attractive to T. aripo. There was however some variation in the response of T. aripo to M. tanajoa-infested plant parts within the group of pubescent cultivars, as well as within the group of glabrous cultivars. Our study confirms not only that T. aripo uses herbivore-induced plant volatiles to search for prey in cassava fields, but it also shows that it can discriminate between glabrous and pubescent cultivars and prefers the latter. This knowledge can be useful in selecting cultivars that are attractive and suitable to T. aripo, which, in turn, may promote biological control of the cassava green mite.     

Intraguild Predation and Feeding Preferences in Three Species of Phytoseiid Mite Used for Biological Control

The ecological impact of introduced biological control agents on native species of arthropods is a matter of considerable debate. This study investigated the ability of the non-native predatory mite Neoseiulus californicus to feed on the native Typhlodromus pyri and vice versa, as both species now co-occur in UK orchards. Typhlodromips montdorensis is a candidate for introduction into the UK as a glasshouse biological control agent. The ability of T. montdorensis to feed on the widely used N. californicus was investigated to identify possible intraguild predation, which might influence the effectiveness of either or both species as predators of Tetranychus urticae. Both N. californicus and T. pyri consumed larval stages of each other, but in choice experiments both showed a preference for T. urticae. Both N. californicus and T. montdorensis also fed on each other, but whereas N. californicus again showed a preference for T. urticae, T. montdorensis fed equally on T. urticae and N. californicus. Interactions between N. californicus and T. pyri and N. californicus and T. montdorensis are discussed in relation to their effectiveness as biological control agents in the glasshouse and the natural control of spider mite in the field.