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.     

有益真绥螨与巴氏新小绥螨的集团内捕食和同类相残作用

【目的】有益真绥螨Euseius utilis是北方地区广泛分布的一种多食性植绥螨,而巴氏新小绥螨Neoseiulus barkeri目前在我国广泛应用于农业害虫的生物防治中。本研究旨在对巴氏新小绥螨在本地的应用进行风险评估及为与有益真绥螨的联合释放提供依据。【方法】本研究在室内通过一系列实验,比较了实验室饲养的巴氏新小绥螨和采自内蒙古农业大学校园的有益真绥螨的雌成螨对同种或异种未成熟螨的捕食量、存活时间及产卵量的差异,检测了有益真绥螨与巴氏新小绥螨两种植绥螨相互之间的攻击强度以及种内和种间的相互作用。【结果】两种植绥螨都难以刺吸同种或异种植绥螨的卵,而对同种或异种植绥螨幼螨的捕食量最大,其次是对若螨。在无共同食物的情况下,有益真绥螨雌成螨对同种植绥螨幼螨的攻击性比对异种植绥螨幼螨的攻击性强(BreslowDay检验:χ~2=13.84,df=1,P0.001),且有益真绥螨对同种植绥螨幼螨的捕食量(9.10±1.65头)高于对异种植绥螨幼螨的捕食量(5.31±1.43头)(T检验:t=5.487,P0.001),巴氏新小绥螨对异种植绥螨幼螨的捕食量(7.48±0.75头)高于对同种植绥螨幼螨的捕食量(4.75±0.58头)(T检验:t=9.110,P0.05)。【结论】有益真绥螨更倾向于捕食同种幼螨而发生同类相残;巴氏新小绥螨更倾向于捕食异种幼螨而发生集团内捕食。     

Factors determining species displacement of related predatory mite species (Acari: Phytoseiidae)

Neoseiulus womersleyi (Acari: Phytoseiidae) used to be the dominant species in fruit-tree orchards throughout Japan, but starting in the 1990s, N. womersleyi began to be displaced by Neoseiulus californicus in central and southwestern Japan. The present study was conducted to examine factors explaining the displacement of N. womersleyi by N. californicus. First, we confirmed under laboratory conditions that N. californicus could exclude N. womersleyi if they initially coexisted in a 1:1 ratio. During a 2-h continuous observation period, none of the heterospecific pairs had copulated and after 5 days together with heterospecific males, none of the females had laid eggs. When these females were placed with conspecific males, normal numbers of offspring were produced. Moreover, conspecific matings were not substantially disturbed in the presence of heterospecific males or females. Total fecundity was significantly lower in N. womersleyi than in N. californicus, but their r _m values did not differ from each other. On the other hand, the frequency of intraguild predation by N. californicus on N. womersleyi was significantly higher than vice versa. From these results, we concluded that not reproductive interference nor differential female fecundity but asymmetrical intraguild predation seemed to explain the competitive exclusion of N. womersleyi by N. californicus.     

Cannibalism and intraguild predation in Typhlodromus exhilaratus and T. phialatus (Acari: Phytoseiidae) under laboratory conditions

Two species of Phytoseiidae are found in the same agroecosystem: Typhlodromus exhilaratus prevails in vine plots, while T. phialatus prevails in uncultivated surrounding areas. The objective of the present paper was to investigate whether the poor settlement of T. phialatus in vine plots can be explained by intraguild predation of these two species and/or cannibalism. Predatory abilities of the females on larvae and protonymphs were studied under laboratory conditions. A first experiment was conducted with only conspecific or heterospecific phytoseiid prey, in a second experiment Tetranychus urticae eggs were added to the phytoseiid prey. Oviposition, prey consumption, and escape rates of females were recorded. Oviposition and intraguild predation rates were higher for T. exhilaratus than for T. phialatus. Typhlodromus exhilaratus consumed fewer conspecifics than heterospecific phytoseiids, and oviposited when feeding on both diets. Typhlodromus phialatus consumed equal amounts of con- and heterospecifics. Although these two generalist predators belong to the type III defined by McMurtry and Croft (Annual Review of Entomology 42:291–321, 1997), our results suggest that they have different predation behaviour. However, because these results were obtained in experiments where no choice was given between the two phytoseiid species, they are difficult to link to previous studies conducted on the intraguild predation of the Phytoseiidae. The greater voracity and prolificacy of T. exhilaratus could partially explain the poor settlement of T. phialatus in vineyards and the predominance of T. exhilaratus. However, a full understanding of this phenomenon will require the study of other factors, such as susceptibility to pesticides and micro-climatic conditions, as well as the ability to cope with different food sources and host plants.     

Nutritional benefits of intraguild predation and cannibalism among generalist and specialist phytoseiid mites

1. Intraguild predation and cannibalism are common among predaceous phytoseiid mites (Acari, Phytoseiidae) but the nutritional benefits gained by these processes are poorly understood. 2. The study reported here addressed the questions of whether cannibalism and intraguild predation provide different nutritional benefits and whether the ability to utilise cannibalism and intraguild predation is linked to the diet specialisation of phytoseiid mites. Specialists tested were Phytoseiulus macropilis, Galendromus occidentalis, and Neoseiulus longispinosus; generalists tested were Amblyseius andersoni, Neoseiulus cucumeris, and Neoseiulus fallacis. 3. All generalists and the specialist P. macropilis were able to complete juvenile development with both con‐ and hetero‐specific prey. Juvenile development of generalists was shorter with heterospecific prey than with conspecific prey, whereas development of the specialist P. macropilis did not differ between prey types. Only a few N. longispinosus and G. occidentalis, both specialists, reached adulthood by cannibalism but none reached adulthood by intraguild predation. 4. All generalists were able to sustain oviposition by intraguild predation. Neoseiulus cucumeris and A. andersoni laid more eggs with heterospecific prey than with conspecific prey, whereas N. fallacis had similar oviposition rates with both prey types. No specialist sustained oviposition by intraguild predation or cannibalism. 5. Overall, generalists gained equal or more nutritional benefits by intraguild predation than by cannibalism and were able to utilise phytoseiid intraguild prey as an alternative food source. Specialists gained equal or more nutritional benefits from cannibalism than from intraguild predation. For specialists, con‐ and hetero‐specific phytoseiids may be considered only a supplemental food.     

Predation preferences and discrimination between con- and heterospecific prey by the phytoseiid mites Phytoseiulus persimilis and Neoseiulus californicus

Discrimination between and predation preference for con- or heterospecific larvae was examined for adult females of P. persimilis and N. californicus in plexiglass cages with and without their primary prey T. urticae. Rates of intra- and interspecific predation on larvae were measured for females held on leaves and provided with excess amounts of spider mites. Females of the generalist N. californicus distinguished con- and heterospecific larvae and preferred to prey upon the latter. Females of the specialist P. persimilis appeared to lack discrimination ability and fed equally on con- and heterospecifics. When spider mites and phytoseiids were offered simultaneously, all P. persimilis females chose to first attack T. urticae, whereas N. californicus females attacked both tetranychids and heterospecific phytoseiids. Females of both predators preyed upon phytoseiid larvae when held on leaves with surplus T. urticae: while P. persimilis fed on both con- and heterospecifics, N. californicus attacked larvae of P. persimilis but avoided cannibalizing larvae. The different behaviors of P. persimilis and N. californicus are discussed with regard to different predation types (generalists vs. specialists) and the possible consequences of mixed release for biological control of spider mites in greenhouses.     

Cannibalism and interspecific predation in the phytoseiid mites Phytoseiulus persimilis and Neoseiulus californicus: predation rates and effects on reproduction and juvenile development

We examined intra- and interspecific predation of adult females and immature stages of the generalist Neoseiulus californicus and the specialist Phytoseiulus persimilis. Adult females and immatures of both predators exhibited higher predation rates on larvae than on eggs and protonymphs. N. californicus fed more inter- than intraspecifically. Predation on P. persimilis by N. californicus was more severe than vice versa. P. persimilis had higher predation rates on conspecifics than heterospecifics and was more prone to cannibalism than N. californicus. When provided with phytoseiid prey, P. persimilis suffered higher mortality than N. californicus. When held without food, adult females and protonymphs of N. californicus survived longer than the corresponding stages of P. persimilis. N. californicus females were able to sustain oviposition when preying upon P. persimilis, whereas cannibalizing females did not lay eggs. Females of P. persimilis were not able to sustain oviposition, irrespective of con- or heterospecific prey. Immatures of both predators were able to reach adulthood when provided with either con- or heterospecifics. Juvenile development of N. californicus was shorter with heterospecific vs. conspecific larvae; mortality of P. persimilis immatures was less when feeding on conspecific vs. heterospecific larvae. Different behavioral pattern in intra- and interspecific predation are discussed in regard to their feeding types (generalist vs. specialist).     

Diet-dependent life history,feeding preference and thermal requirements of the predatory mite <Emphasis Type="Italic">Neoseiulus baraki</Emphasis> (Acari: Phytoseiidae)

Neoseiulus baraki Athias-Henriot (Acari: Phytoseiidae) has been reported from the Americas, Africa and Asia, often in association with Aceria guerreronis Keifer (Acari: Eriophyidae), one of the most important pests of coconut (Cocos nucifera L.) in different parts of the world. That phytoseiid has been considered one of the most common predators associated with A. guerreronis in Brazil. The objective of this study was to evaluate the feeding preference and the effect of food items commonly present on coconut fruits and several temperature regimes on the life history of a Brazilian population of N. baraki. Completion of immature development was possible when N. baraki was fed A. guerreronis, Steneotarsonemus concavuscutum Lofego and Gondim Jr., and Tyrophagus putrescentiae (Schrank). Fecundity was highest on T. putrescentiae (39.4 eggs), followed by A. guerreronis (24.8 eggs). In choice tests, irrespective of the food on which N. baraki was reared, a larger number of adults of this predator chose leaf discs containing A. guerreronis than discs containing other food items, demonstrating a preference of the former for the latter as food. Egg to adult thermal developmental time was calculated as 84.2 degree-days, above a threshold of 15.8°C. This lower developmental threshold is higher than previously published for phytoseiid species from higher latitudes. Neoseiulus baraki was shown to have higher biotic potential at 30°C (r _m 0.29). The results suggest N. baraki to be a promising biological control agent of A. guerreronis, well adapted to survive and develop in areas with relatively high temperatures, where that pest prevails.     

Risk assessment of non-target effects caused by releasing two exotic phytoseiid mites in Japan: can an indigenous phytoseiid mite become IG prey?

Two exotic phytoseiid mites, Neoseiulus cucumeris and Amblyseius swirskii, are commercially available in Japan for the control of thrips and other pest insects. As part of a risk assessment of the non-target effects of releasing these two species, we investigated intraguild predation (IGP) between these exotic phytoseiid mites and an indigenous phytoseiid mite Gynaeseius liturivorus, which is promising as an indigenous natural enemy for the control of thrips in Japan. To understand IGP relations between the exotic and indigenous phytoseiid mites after use of the exotic mites for biological control, we investigated IGP between them in the absence of their shared prey. When an IG prey was offered to an IG predator, both exotic and indigenous females consumed the IG prey at all immature stages (egg, larva, protonymph, deutonymph), especially at its larval stages. The propensity for IGP in a no-choice test was measured by the survival time of IG prey corrected using the survival time of thrips offered to the IG predator. There was no significant difference in the propensity for IGP between N. cucumeris and G. liturivorus, but the propensity was significantly higher in A. swirskii than G. liturivorus. The propensity for IGP in a choice test was measured by the prey choice of the IG predator when a conspecific and a heterospecific larva were offered simultaneously as IG prey. Both exotic females consumed the heterospecific larva only. The indigenous female preferentially consumed the heterospecific larva when the heterospecific larva was N. cucumeris, but consumed the conspecific larva when the heterospecific larva was A. swirskii. We concluded that further investigation would be necessary for the exotic mites’ risk assessment, since the propensity for IGP of the two exotic females was similar to or higher than that of the indigenous female in both the no-choice and choice tests.     

Neoseiulus paspalivorus,a predator from coconut,as a candidate for controlling dry bulb mites infesting stored tulip bulbs

The dry bulb mite, Aceria tulipae, is the most important pest of stored tulip bulbs in The Netherlands. This tiny, eriophyoid mite hides in the narrow space between scales in the interior of the bulb. To achieve biological control of this hidden pest, candidate predators small enough to move in between the bulb scales are required. Earlier experiments have shown this potential for the phytoseiid mite, Neoseiulus cucumeris, but only after the bulbs were exposed to ethylene, a plant hormone that causes a slight increase in the distance between tulip bulb scales, just sufficient to allow this predator to reach the interior part of the bulb. Applying ethylene, however, is not an option in practice because it causes malformation of tulip flowers. In fact, to prevent this cosmetic damage, bulb growers ventilate rooms where tulip bulbs are stored, thereby removing ethylene produced by the bulbs (e.g. in response to mite or fungus infestation). Recently, studies on the role of predatory mites in controlling another eriophyoid mite on coconuts led to the discovery of an exceptionally small phytoseiid mite, Neoseiulus paspalivorus. This predator is able to move under the perianth of coconuts where coconut mites feed on meristematic tissue of the fruit. This discovery prompted us to test N. paspalivorus for its ability to control A. tulipae on tulip bulbs under storage conditions (ventilated rooms with bulbs in open boxes; 23 °C; storage period June–October). Using destructive sampling we monitored predator and prey populations in two series of replicated experiments, one at a high initial level of dry bulb mite infestation, late in the storage period, and another at a low initial dry bulb mite infestation, halfway the storage period. The first and the second series involved treatment with N. paspalivorus and a control experiment, but the second series had an additional treatment in which the predator N. cucumeris was released. Taking the two series of experiments together we found that N. paspalivorus controlled the populations of dry bulb mites both on the outer scale of the bulbs as well as in the interior part of the bulbs, whereas N. cucumeris significantly reduced the population of dry bulb mites on the outer scale, but not in the interior part of the bulb. Moreover, N. paspalivorus was found predominantly inside the bulb, whereas N. cucumeris was only found on the outer scale, thereby confirming our hypothesis that the small size of N. paspalivorus facilitates access to the interior of the bulbs. We argue that N. paspalivorus is a promising candidate for the biological control of dry bulb mites on tulip bulbs under storage conditions in the Netherlands.     

Intraguild predation among Scolothrips longicornis (Thysanoptera: Thripidae), Neoseiulus californicus and Typhlodromus bagdasarjani (Acari: Phytoseiidae) under laboratory conditions

This study was carried out on the ability of predatory thrips Scolothrips longicornis Priesner to feed on 2 phytoseiid species and vice versa. Also the effect of predation of Neoseiulus californicus (McGregor) on Typhlodromus bagdasarjani Wainstein and Arutunjan and vice versa was evaluated. The larvae, prepupae, and pupae of thrips and the eggs, larvae, and protonymphs of phytoseiids were selected as intraguild prey. The intraguild predation (IGP) among S. longicornis and 2 phytoseiid species was unidirectional and in favor of phytoseiids, i.e., S. longicornis was not able to feed on larval stages of 2 phytoseiids. However, N. californicus and T. bagdasarjani fed on the 1st instar larvae (1.39 and 0.80 per day), 2nd instar larvae (0.87 and 0.55 per day), prepupae (0.51 and 0.48 per day), and pupae of thrips (0.51 and 0.49 per day, respectively). Both phytoseiids fed on eggs, larvae, and protonymphal stages of each other. Females of N. californicus consumed more phytoseiid larvae (2.49 per day) than T. bagdasarjani, which consumed 1.08 N. californicus larvae per day. When Tetranychus urticae was presented as an extraguild prey, intensity of IGP between 2 species of phytoseiids and on larval stages of S. longicornis reduced significantly. Therefore, it is concluded that (i) IGP existed among the 3 examined species and lack of feeding of S. longicornis on 2 phytoseiid species can be justified by its feeding type (monophagy), (ii) N. californicus was much more prone to IGP than was T. bagdasarjani.     

Intra- and interspecific predation on four life stage groups by the adult females of Metaseiulus occidentalis, Typhlodromus pyri, Neoseiulus fallacis and Amblyseius andersoni

Do adult females of oligophagous species such as Neoseiulus fallacis (Garman) and Metaseiulus occidentalis (Nesbitt) show less intra- and interspecific predation on phytoseiids when other foods are scarce than polyphagous species such as Amblyseius andersoni Chant and Typhlodromus pyri Scheuten? We caged single adult females of each species without food with ten of their own eggs or larvae, with ten eggs or larvae of the other species or with ten nymphs or adult females of M. occidentalis (T. pyri for M. occidentalis). We assessed the ambulatory activity, survival time, egg levels and prey loss in each test. Polyphages (in particular T. pyri) lived longer than oligophages (in particular N. fallacis) without food. The small T. pyri detected its own stages and benefited most by feeding on small active stages of other species. Amblyseius andersoni, the largest mite, fed and gained the most of any species when held with nymphs and female adults. Metaseiulus occidentalis fed on eggs of all four species to enhance survival. The large hyperactive N. fallacis gained the least from these behaviours. Each mite seemed uniquely adapted to survive conditions of scarce prey and these behaviours may explain their roles in phytoseiid mite complexes. Overall, oligophagous adult females fed less and gained less by feeding on phytoseiids than did polyphagous adult females.     

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.     

Survival and behavioural response to acaricides of the coconut mite predator Neoseiulus baraki

The coconut mite, Aceria guerreronis Keifer, is a major pest of coconut palm in the world. The control of this pest species is done through acaricide applications at short time intervals. However, the predators of this pest may also be affected by acaricides. Among the predators of A. guerreronis, Neoseiulus baraki (Athias-Henriot) has potential for biological control. The objective of this study was to assess the effect of acaricides on the survival and behavior of N. baraki. The survivorship of N. baraki was recorded in surface-impregnated arenas. Choice and no-choice behavioral bioassays were carried out using a video tracking system to assess the walking behavior of the predator under acaricide exposure. Although all acaricides negatively affected the survival of N. baraki, chlorfenapyr and azadirachtin caused lower effect than the other acaricides. No significant differences in walking behavior were observed under exposure to fenpyroximate, chlorfenapyr and chlorpyrifos on fully-contaminated arenas. Azadirachtin and chlorpyrifos caused repellence. Irritability was observed for all acaricides, except for abamectin. Chlorfenapyr was the most suitable product for managing the coconut mite because of its low effect on survival and behavior of N. baraki.     

Leaf domatia reduce intraguild predation among predatory mites

1. Although theory suggests that intraguild predation destabilises food webs and may result in exclusion of species, empirical observations of food webs reveal that it is a common interaction. It has been proposed that habitat structure reduces the interaction strength of intraguild predation, thus facilitating the coexistence of species. 2. This was tested using acarodomatia, tiny structures on plant leaves, and predatory mites, which usually reside in these domatia. Sweet pepper plants (Capsicum annuum L.) were used, which possess domatia consisting of tufts of hair, and coffee plants (Coffea arabica L.) with pit‐shaped domatia. 3. On sweet pepper, the predatory mites Neoseiulus cucumeris Oudemans and Iphiseius degenerans Berl. feed on each other's juveniles. Larvae of each of the species were therefore used as intraguild prey with adult females of the other species as intraguild predators. On coffee, a similar set‐up was used, with larvae and adult females of Amblyseius herbicolus Chant and Iphiseiodes zuluagai Denmark & Muma as intraguild prey and intraguild predators, respectively. 4. Domatia on detached, isolated sweet pepper and coffee leaves were either closed with glue or left open, after which larvae and adult predators were released. As a control, larvae were released on leaves with open or closed domatia without an adult predator. 5. Survival of larvae was high in the absence of the adult (intraguild) predator. In the presence of the intraguild predator, survival was significantly higher on leaves with open domatia than on leaves with closed domatia. 6. This shows that even such tiny structures as plant domatia may significantly affect the interaction strength of intraguild predation.     

Evaluation of the predacious mite Hemicheyletia wellsina (Acari: Cheyletidae) as a predator of arthropod pests of orchids

The cheyletid predator Hemicheyletia wellsina was found in association with orchid pests in a Florida greenhouse. The life history of H. wellsina was determined using the two-spotted spider mite, Tetranychus urticae, as prey in the laboratory. Hemicheyletia wellsina is arrhenotokous, with mated females producing a female-biased sex ratio of 3.4:1. Adult longevity averaged 30.2 days, with females producing an average of 18.5 eggs. Adult females live up to 17 days without food, surviving an average of 9.7 days. Hemicheyletia wellsina will readily feed on the phytoseiid Metaseiulus occidentalis, suggesting intraguild predation by H. wellsina on phytoseiids could be important in pest management programs. The average prey consumption of H. wellsina is 1.5 T. urticae females per day. The results of this study provide information on an under-studied group of mite predators. Although H. wellsina does not have the qualities that would be necessary for its use in an augmentative or classical biological control program, its use in naturally occurring biological control could be beneficial.     

Predation Preference of Typhlodromus Pyri and Kampimodromus Aberrans (Acari: Phytoseiidae) When Offered Con- and Heterospecific Immature Life Stages

The predation preference of singly caged adult females and nymphs of Typhlodromus pyri and Kampimodromus aberrans for con- or heterospecific immature stages as prey was tested in the laboratory. Both polyphagous predatory mite species have been previously shown to interact directly through predation on each other. The present study demonstrated that the adult females of T. pyri and K. aberrans are able to discriminate between con- and heterospecific larvae and protonymphs and that they prefer to prey upon heterospecifics when given the choice. Hunger did not reduce the propensity of the females to prefer heterospecifics over conspecifics. For proto-and deutonymphs the trends followed the results obtained with the adult females, but the preference for heterospecifics was not distinct enough to be significant. In competitive situations reciprocal predation may be a crucial mechanism in the interaction of polyphagous phytoseiid species and may contribute significantly to population persistence. The results are discussed with regard to possible associations between the ability to discriminate con- and heterospecifics and the type of feeding specialization (generalists versus specialists).     

Predators induce egg retention in prey

To prevent predation on their eggs, prey often avoid patches occupied by predators. As a result, they need to delay oviposition until they reach predator-free patches. Because many species allocate energy to egg production in a continuous fashion, it is not clear what kind of mechanism prey use to delay oviposition. We used females of the phytoseiid mite Neoseiulus cucumeris to study these mechanisms. Females were placed in patches with pollen, a food source they use for egg production, and they were exposed to another phytoseiid mite, Iphiseius degenerans, which is an intraguild predator of N. cucumeris juveniles. We found that the oviposition of N. cucumeris females on patches with the predator was lower than on patches without the predator. Cues left by the intraguild predator were not sufficient to elicit such behaviour. Females of N. cucumeris reduced oviposition when exposed to the predator by retaining the egg inside their body, resulting in a lower developmental rate once these eggs were laid. Hence, females are capable of retaining eggs, but the development of these eggs continues inside the mother’s body. In this way, females gain some time to search for less risky oviposition sites.     

Intraguild predation among the predatory mites Amblyseius eharai,Amblyseius cucumeris and Amblyseius barkeri

Predator species with the same prey interact not only by competition for food and space but also by intraguild predation (IGP). The impact of IGP on introduced phytoseiid mites and native species in the context of biological control is a matter of considerable debate. Amblyseius eharai is the dominant native citrus species in central China, while Amblyseius cucumeris and Amblyseius barkeri are candidates for importation. All three species can feed on the spider mite Panonychus citri, which is the main pest in citrus. This study investigated, in the laboratory, possible IGP among these species in the absence and presence of P. citri, respectively. IGP in different densities of shared prey and intraguild (IG) prey was also studied. All three species consumed heterospecific larvae and eggs but not adults, and the IGP rate of larvae was significantly higher than that of eggs in the absence of shared prey. Additionally, the IGP rate of each group was reduced dramatically in the presence of both shared and IG prey when compared to the absence of shared prey. This occurs most likely because the three species prefer to feed on their natural prey P. citri, rather than on IG prey. Our results showed that A. eharai seems to be a more voracious IG predator than A. cucumeris. A. eharai was much more prone to IGP than A. barkeri.     

Intra- and interspecific predation by adult female Metaseiulus occidentalis and Typhlodromus pyri (Acari: Phytoseiidae) when provisioned with varying densities and ratios of Tetranychus urticae (Acari: Tetranychidae) and phytoseiid larvae

The phytoseiid mites Metaseiulus occidentalis (Nesbitt) and Typhlodromus pyri Schueten are used together and alone as biological control agents against tetranychid pest mites of apple. Their effectiveness as control agents may be impacted by intraguild predation. The effects of prey species and prey density on the rates of inter- and intraspecific predation and oviposition by these two predators were investigated through a series of experiments. Adult female predators were given prey as mixed populations of phytoseiid larvae and larvae of a more preferred species, the spider mite, Tetranychus urticae Koch, at different densities and ratios. Typhlodromus pyri, more of a generalist predator, showed higher rates of predation and cannibalism on phytoseiid immatures at most prey densities and ratios. Manly preference indices indicated that T. pyri switched to feed on phytoseiid larvae at higher prey levels and ratios of T. urticae than M. occidentalis. This greater ability to use phytoseiid larvae as prey may help stabilize T. pyri populations when more preferred prey is unavailable. This may, in part, explain the observed persistence of T. pyri populations when M. occidentalis populations were decreasing in orchard test plots.