Localization and electrical activity of the distance chemoreceptors that mediate predator avoidance behaviour in Acmaea limatula and Acmaea scutum (gastropoda, prosobranchia).

1. The marine gastropods Acmaea (Collisella) limatula and Acmaea (Notoacmea) scutum respond to distant predatory starfish (i.e. to starfish scent) by moving up a vertical surface. 2. The distance chemoreceptors that mediate this avoidance behaviour are located on the mantle margin. Heat cauterization of the limpets' mantle margin eliminates their responsiveness to Pisaster ochraceus scent, while a similar cauterization of the ctenidium and the osphradia does not diminish the avoidance behaviour. 3. Primary afferent electrical activity can be recorded from the chemoreceptors on the mantle margin that are responsive to starfish scent and also from other physiologically distinct receptors that are responsive to contact with starfish tube feet.     

Avoidance and escape responses of the gastropod mollusc Olivella biplicata (Sowerby) to predatory asteroids

The sand-dwelling gastropod Olivella biplicata (Sowerby) gives two chemically-mediated defensive responses to predatory asteroids — an avoidance and an escape response. An avoidance response is triggered by water-borne chemicals diffusing from distant starfish. When snails on the surface of the sand sense a distant predatory starfish, they avoid the predator by burying themselves in the sand. Strong avoidance responses are given to the predatory asteroids Pisaster brevispinus (Stimpson), P. ochraceus (Brandt), and Pycnopodia helianthoides (Brandt). Little or no response is given to the omnivorous asteroid Patiria miniata (Brandt) or to the predatory gastropod Polinices lewisii (Gould). An escape response is given when a snail on the surface is contacted by the starfish Pisaster brevispinus. Upon contact, the snail immediately retracts the propodium, sometimes throwing the metapodium forward at the same time; the snail then turns sharply away from the point of contact, and buries itself. Both avoidance and escape responses can be observed in the field and laboratory.     

Activity pattern as a mechanism of predator avoidance in two species of acmaeid limpet

Activity patterns in the foraging activity of two species of acmaeid limpets, Collisella limatula (Carpenter, 1864) and C. scabra) (Gould, 1846) were documented over the entire tidal cycle. C. limatula was found to be active only while awash by the tide and during night-time emergence; periods of inactivity were spent in crevices and on the undersides of boulders. C. scabra, which homes to a scar on the upper surfaces of rocks, foraged only while awash in daylight. The activity pattern of C. limatula was demonstrated to be an effective mechanism for avoiding predation by Octopus, a major visual predator of limpets, in both laboratory and field experiments. The homing habit of Collisella scabra was also shown to reduce the rate of predation in the laboratory. It is suggested that the observed activity patterns have evolved in response to predation pressure from swift-moving visual predators.     

The impact of predation by Kelp GullsLarus dominicanus on the sub-Antarctic limpetNacella delesserti

Summary The Southern Kelp GullLarus dominicanus derives about 45% of the mass of its marine diet from the limpetNacella delesserti at sub-Antarctic Marion Island. It selectively feeds on the largest limpets (35–65 mm) —a pattern most obvious in adult gulls — and eliminates about 19.6% of these limpets per year in the intertidal zone and in shallow waters, thus accounting for about 50% of the known annual mortality of limpets of this size. The gulls cannot forage for limpets in water more than 40 cm deep, and in the intertidal zone boulder-fields provide the limpets a refuge against the gulls. The gulls are also selective in feeding most often on limpets with pale shells. This alters the colour composition of limpet populations in habitats where predation is most intense.Larus dominicanus seldom feeds on limpets on the mainland of South Africa, and only on small limpets, probably because a greater range of food is available, but possibly also because the limpet species that occur on South African shores attach with forces that are three to six times those ofN. delesserti.     

Defensive responses of gastropods to the predatory flatworms Freemania litoricola (Heath and McGregor) and notoplana acticola (Boone)

Three species of gastropods were tested in the laboraory and in the field for responses to contact with the polyclad flatworms Freemania litoricola (Heath and McGregor) and Notoplana acticola (Boone). The three limpets differed considerably in their responses to Freemania litoricola All specimens of Notoacmea scutum (Rathke) responded in some way to this flatworm, mostly by running. Fewer than half of the Collisella digitalis (Rathke) responded to Freemania litoricola, and these responded by mushrooming - elevating the shell several millimeters off the substratum. Collisella scabra (Gould) did not respond any differently to contact with Freemania litoricola than to contact with a control probe. Differences in the responses of these limpets to Freemania litoricola are discussed in relation to the characteristic intertidal distributions of this flatworm and the limpets. In contrast to Freemania litoricola, the polyclad Notoplana acticola typically did not elicit defensive responses. This difference is related to the diets of the two flatworms. Freemania litoricola was found to be a predator on limpets, whereas no evidence was found that Notoplana acticola eats limpets.     

The Asian grass lizard (Takydromus sexlineatus) does not respond to the scent of a native mammalian predator

Lacertid lizards use chemical cues emitted by saurophagous snakes to evade predation. Whether these lizards can detect and respond to the chemical cues of predatory mammals has not been studied. As many mammals carry distinct body odours and/or use chemical cues for intraspecific communication, lizards can be expected to use these chemicals as early warning cues. To test this idea, we observed the behaviour of Asian grass lizards (Takydromus sexlineatus) that had been transferred to an unfamiliar test arena containing one of four scent treatments. No particular scent was applied to the arena in the control situation. Diluted aftershave served as a pungency control. In the snake treatment, scent of the Oriental whip snake (Ahaetulla prasina) was applied. We included this treatment to learn how Asian grass lizards react to predator chemical cues. Finally, in the mongoose treatment, the lizards were confronted with scent cues of several small Indian mongooses (Herpestes auropunctatus). Snake scent elicited foot shakes, startles and tail vibrations. These are behaviours that in lacertid lizards are associated with stressful situations such as predatory encounters. Surprisingly, lizards confronted with mongoose scent exhibited none of these stress-indicating behaviours. In fact, their behaviour did not differ from that of lizards subjected to an odourless control treatment. These results raise concern. Mongooses are rapidly invading ecosystems worldwide. If lizards that have co-evolved with mongooses are unable to detect these predators’ presence through chemical cues, it seems highly unlikely that evolutionary naïve lizards will develop this ability rapidly.     

Patterns of secondary succession in a mangrove forest of Southern Florida

Summary Successional patterns were studied in mangrove forests which had developed recently in response to salinization of areas formerly supporting freshwater marshes along Biscayne Bay in North Miami, Florida. The population structures of these Induced Forests were compared with an adjacent Historical Forest which consisted of a nearly pure stand ofRhizophora mangle. A mixed forest ofRhizophora andLaguncularia racemosa had developed in intertidal areas, while areas above the mean high water elevation supported a scrub community dominated byLaguncularia. Maximum growth of bothRhizophora andLaguncularia occurred in intertidal areas, while both species were stunted and had sparse, poorly formed canopies in drier environments above the mean high water level. Analysis of population structure suggests that Induced Forests in intertidal areas are undergoing succession to a stand ofRhizophora. Laguncularia is unable to compete effectively withRhizophora in these areas and it is suggested that it eventually will be limited to the drier areas, where competition fromRhizophora will be reduced or absent.formely Kimball     

Chemical discrimination among predators by lizards: Responses of three skink species to the odours of high‐ and low‐threat varanid predators

Animals must balance the benefits of predator avoidance with costs. Costs of predator avoidance, such as being forced to spend long periods inactive, should select for careful discrimination among predator species. Although prey responses to multiple predators have been well researched across many taxa, no studies have tested whether lizards discriminate among larger lizard predators. We examined the responses of three species of skink to two species of predatory goanna, one that occasionally consumes skinks, and the other a skink specialist. Three litter‐dwelling, tropical skink species, Carlia rostralis, C. rubrigularis and C. storri, were given a choice between a retreat site treated with the odour of one of the goanna species, and an odourless control. The two goanna species used for stimulus scents were: Varanus tristis, a species that consumes skinks as a major proportion of its diet, and Varanus varius, a species that consumes skinks occasionally. Both goannas are broadly sympatric with all three skink species. Carlia rostralis and C. storri both avoided the scent of V. tristis, whereas C. rubrigularis did not. However, no skink species avoided the odour of V. varius. Prey are clearly able to avoid predators based on chemical cues, and can discriminate among similar predators that pose different levels of threat.     

Predation by small mobile aquatic predators regulates populations of the intertidal limpet Patella vulgata (L.)

Highly mobile aquatic predators are known to forage in the intertidal during periods of immersion. There is limited quantitative information, however, on the extent to which these predators influence the abundance of grazing molluscs which are known to have a key role in structuring intertidal assemblages. Our preliminary video observations revealed that crabs and small fish were abundant on shores in southwest England during high-tide. We then used manipulative experiments to quantify the effect of small mobile aquatic predators on the abundance of limpets (Patella vulgata L.). On the lower shore at two moderately sheltered rocky shores three treatments were established: complete cage, partial cage (cage control) and uncaged (natural condition). The complete cages excluded all predators. The partial cage treatment allowed full access to small predators and the uncaged treatment allowed access to all predators. After two months, limpet abundance in uncaged and partial cage treatments had declined by around 50% compared to the complete cage treatment. Population structure also changed with survival of larger individuals being greater than smaller individuals in the open and partial cage treatments compared to the complete cage treatment. The effects of excluding predators were consistent at small (meters) and large spatial scales (kilometres) and hence, it would appear that the outcomes of our research are generally applicable to similar shores in the region.To explore the mechanism behind the differential effects of predators according to prey size, we compared the detachment force required to remove limpets of differing sizes from the shore. This was around four times greater for larger individuals than for smaller ones indicating that smaller limpets were more vulnerable to predation. These effects were also consistent between locations. Subsequent laboratory observations showed that the crabs Carcinus maenas (L.), Necora puber (L.) and Cancer pagurus (L.) which are locally abundant predators of limpets, had differing handling behaviour but were all highly efficient at removing limpets from substratum. Hence, shell width and attachment force appeared to be critical factors influencing the vulnerability of limpets to predation by these crabs. Limpets are known to control the abundance of macroalgae on shores in the North-east Atlantic and so our conclusions about the role of mobile predators in regulating the abundance of these grazers are important to our broader understanding of the ecology of these shores.     

Life-history patterns of populations of the limpet Patella granularis: the dominant roles of food supply and mortality rate

Summary Rates of algal production were measured at 6 rocky intertidal sites on the southwestern Cape coast, South Africa, where populations of the limpet Patella granularis occur. Rates of algal production and limpet mortality were recorded at each site and both factors affected limpet reproductive fitness. Limpet growth rates and biomass at different sites were significantly correlated with rates of algal production, and limpet mortality was related to the density of African Black Oystercatchers, important predators of P. granularis. Life-time gametic output of a hypothetical cohort of limpets at each site was modelled using the measurements of growth, reproduction and mortality made at each site. Limpet cohorts at sites with rapid rates of algal production were predicted to have a larger life-time production of gametic material than cohorts at sites with slow algal production rates, except in instances of acute predatory pressure. In the light of the overriding influence of food supply on the expression of limpet life-history parameters, it is imperative that researchers consider food availability before assuming that local, population-specific differences in life-history patterns are due to genetic differences.     

The importance of predation and competition in organizing the intertidal epifaunal communities of Barnegat Inlet,New Jersey

Summary Community organization was studied by experiment and observation from October 1972–October 1974 in the marine epifaunal assemblages at each end of Barnegat Inlet, New Jersey. The rock jetty at the wave-exposed eastern end of the inlet possesses an intertidal community with the following attributes: (1) a high intertidal zone dominated by the barnacle, Balanus balanoides, but also occupied by the blue mussel, Mytilus edulis, in rock crevices, (2) a mid and low intertidal zone with usually <10% free space and extreme numerical dominance by Mytilus edulis (usually >85% cover) during summer and fall, and (3) almost no intertidal predators or herbivores. The predatory seastar, Asterias forbesi, is abundant subtidally. Controlled removal experiments indicate that in the mid and low intertidal underlying barnacles perish as a consequence of the establishmentof extensive secondary cover by Mytilus, probably because Mytilus outcompetes Balanus through suffocation or starvation. Mytilus transplants demonstrate that the mussels do not survive outside of crevices in the high intertidal, which thus may represent for Balanus a refuge from competition by Mytilus.The pilings on docks at the protected western end of Barnegat Inlet possess an intertidal epifaunal community with the following characteristics: (1) a high intertidal zone that includes Balanus balanoides, a second barnacle, Balanus eburneus, and an herbivorous gastropod, Littorina littorea, (2) a mid and low intertidal zone with usually >40% free space in the summer and fall and the remaining area covered by several abundant species with no extreme dominant, and (3) abundant predators, chiefly the oyster drill, Urosalpinx cinerea, the blue crab, Callinectes sapidus, and a mud crab, Neopanope texana sayi. Asterias forbesi, while abundant subtidally, is also occasionally present on intertidal surfaces. Controlled exclusion of predators by caging several replicate pilings at the western end of the inlet reveals that predation prevents monopolization of mid and low intertidal space by the apparent competitive dominant, Mytilus. Predation appears to be a direct cause of the relatively great temporal and spatial heterogeneity in the mid and low intertidal of these pilings.Thus, although the Barnegat Inlet intertidal system appears to follow closely the patterns of community organization described for several other rocky intertidal coastlines, this organizational pattern is noteworthy because it is repeated here in a far more seasonal environment and with a new cast of interacting competitors and predators. That crabs play an important role as predators is novel for North America, but only perhaps because all previous North American studies have ignored the rocky intertidal zones of quiet, estuarine waters where in Europe predatory crabs are known to be extremely significant.This paper is dedicated to the memory of Robert H. MacArthur     

Type and nature of cues used by Nucella lapillus to evaluate predation risk

The ability of prey to detect and adequately respond to predation risk influences immediate survival and overall fitness. Chemical cues are commonly used by prey to evaluate risk, and the purpose of this study was to elicit the nature of cues used by prey hunted by generalist predators. Nucella lapillus are common, predatory, intertidal snails that evaluate predatory risk using chemical cues. Using Nucella and a suite of its potential predators as a model system, we explored how (1) predator type, (2) predator diet, and (3) injured conspecifics and heterospecifics influence Nucella behavior. Using laboratory flumes, we determined that Nucella responded only to the invasive green crab (Carcinus maenas), the predator it most frequently encounters. Nucella did not respond to rock crabs (Cancer irroratus) or Jonah crabs (Cancer borealis), which are sympatric predators but do not frequently encounter Nucella because these crabs are primarily subtidal. Predator diet did not affect Nucella responses to risk, although starved predator response was not significantly different from controls. Since green crabs are generalist predators, diet cues do not reflect predation risk, and thus altering behavior as a function of predator diet would not likely benefit Nucella. Nucella did, however, react to injured conspecifics, a strategy that may allow them to recognize threats when predators are difficult to detect. Nucella did not react to injured heterospecifics including mussels (Mytilus edulis) and herbivorous snails Littorina littorea, suggesting that they are responding to chemical cues unique to their species. The nature of cues used by Nucella allows them to minimize costs associated with predator avoidance.     

Influence of rearing and experimental temperatures on predator avoidance behaviour in a freshwater pulmonate snail

1. Predicted increases in the temperature of freshwaters is likely to affect how prey species respond to predators. We investigated how the predator avoidance behaviour of the freshwater pulmonate snail Lymnaea stagnalis is influenced by the temperature at which it was reared and that at which behavioural trials were carried out. 2. Crawl‐out behaviour of juvenile snails from two populations (high predation risk versus low predation risk) reared at either 15 or 20 °C was assessed in response to predation cues (predatory fish kairomones and conspecific alarm cues) in behavioural trials at both 15 and 20 °C. 3. Trial temperature had a significant effect on the time that snails spent in avoidance, regardless of their population of origin. Crawl‐out behaviour was greater during behavioural trials at 15 °C, but there was no effect of trial temperature on the speed with which animals showed avoidance behaviour. 4. There was no interactive effect of rearing temperature (RT) and trial temperature, but the effect of RT on avoidance behaviour did differ between populations. For an RT of 15 °C, snails from the South Drain (high risk) population showed a more rapid and longer avoidance response than those from the Chilton Moor (low risk) population. In contrast, for snails reared at 20 °C, there was no difference between populations for the duration of the avoidance response and snails from Chilton Moor crawled out faster than those from South Drain. 5. Hence, whilst (predictable) differences relative to natural predation threat in crawl‐out behaviour were apparent at 15 °C, raising the developmental temperature to 20 °C eliminated or, in the case of latency, reversed these differences. This suggests that L. stagnalis populations that cohabit with predatory fish and experience high developmental temperatures may have a reduced ability to respond to fish predation risk.     

Know thy enemy: Behavioural response of a native mammal (Rattus lutreolus velutinus) to predators of different coexistence histories

Abstract Predation is recognized as a major selective pressure influencing population dynamics and evolutionary processes. Prey species have developed a variety of predator avoidance strategies, not least of which is olfactory recognition. However, within Australia, European settlement has brought with it a number of introduced predators, perhaps most notably the red fox (Vulpes vulpes) and domestic cat (Felis catus), which native prey species may be unable to recognize and thus avoid due to a lack of coexistence history. This study examined the response of native Tasmanian swamp rats (Rattus lutreolus velutinus) to predators of different coexistence history (native predator‐ spotted‐tail quoll (Dasyurus maculatus), domestic cats and the recently introduced red fox). We used an aggregate behavioural response of R. l. velutinus to predator integumental odour in order to assess an overall behavioural response to predation risk. Rattus lutreolus velutinus recognized the integumental odour of the native quoll (compared with control odours) but did not respond to either cat or fox scent (compared with control odur). In contrast, analyses of singular behaviours resulted in the conclusion that rats did not respond differentially to either native or introduced predators, as other studies have concluded. Therefore, measuring risk assessment behaviours at the level of overall aggregate response may be more beneficial in understanding and analysing complex behavioural patterns such as predator detection and recognition. These results suggest that fox and cat introductions (and their interactive effects) may have detrimental impacts upon small native Tasmanian mammals due to lack of recognition and thus appropriate responses.     

Understanding the toad code: Behavioural responses of cane toad (Chaunus marinus) larvae and metamorphs to chemical cues

Abstract Larvae of many anuran taxa display strong behavioural responses to chemical cues, including alarm signals from injured conspecific tadpoles. We exposed tadpoles and metamorphs from an Australian population of the invasive cane toad (Chaunus[Bufo] marinus) to a range of chemical stimuli and quantified their responses both in the laboratory and in the field. Filtered fluids containing scent cues from crushed conspecifics elicited strong avoidance from tadpoles, whereas other cues (e.g. scent of food, of native‐range fish or urodele predators, and thermal stimuli) did not. Apparent aggregation of tadpoles in response to scent cues proved to be an artifact of tank design, and was an indirect consequence of avoidance of those cues. Field trials confirmed that free‐ranging toad tadpoles and metamorphs avoided chemical cues from crushed conspecifics, suggesting that the chemicals inducing this response might provide an opportunity to develop targeted control methods for this invasive species.     

Short-term predator avoidance behavior by invasive and native amphipods in the Great Lakes

Understanding predator avoidance behavior by prey remains an important topic in community and invasion ecology. Recently, the Ponto-Caspian amphipod Echinogammarus ischnus (Stebbing 1898) was accidentally introduced into the Great Lakes. Since its introduction, it has displaced the native amphipod, Gammarus fasciatus (Say 1818), from several locations in the lower lakes. To assess whether behavioral differences in predator avoidance might be a causal mechanism increasing the success of the invasive amphipods, two experiments were conducted examining (1) native and invasive amphipod behavioral responses to five fish species with different foraging behaviors, and (2) amphipod responses to different densities of round gobies, a hyper-abundant benthic invertivore. Echinogammarus reduced its distance moved in the presence of all fish species tested, whereas Gammarus reduced its distance moved only after exposure to round gobies, black crappies, and rainbow darters. Both amphipod species increased the time spent motionless following exposure to round gobies, but not after encountering the scent of most of the remaining fish predators. The exception was that Echinogammarus also responded to black crappie scent whereas Gammarus did not. Although both amphipod species exhibited behavioral responses to many of the fish predators, the magnitude of their responses differed only after exposure to the brown bullhead. In the bullhead trials, Echinogammarus reduced its distance traveled significantly more than Gammarus. Both amphipod species increased their avoidance response to increasing goby density, however, the pattern of avoidance behavior was different. Invasive E. ischnus exhibited a consistently strong avoidance response to round gobies over the test duration. Native G. fasciatus initially avoided goby scent, but then either ceased their avoidance response or showed a hyper-avoidance response, depending on goby density. These results suggested (1) both species of amphipods were able to differentiate and react to a variety of fish predators, (2) invasive Echinogammarus amphipods avoided a larger range of fish predators than the native Gammarus, (3) increased avoidance behavior was associated with an increased density of fish, and (4) the avoidance response patterns of invasive Echinogammarus when faced with round goby predators might lead to increased predation on native Gammarus in habitats where they co-occur.     

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.     

Does human scent bias the survival of bird nests?

Human-scent contamination of bird nests and the human-made trails leading to them is suspected to influence nest survival by attracting or deterring predatory mammals. This paper (1) reviews studies in which human-scent contamination was suspected to have biased the survival of real and artificial nests by influencing the behaviour of predatory mammals, (2) summarizes the procedures used in attempts to mitigate human-scent contamination in nest-survival studies, and (3) describes procedures to enhance the design and interpretation of nest-survival experiments. The behaviour of various non-domesticated mammals is confirmed or suspected to be affected by human scent, so similar effects on nest predators are plausible. However, suggestions that human scent affects nest survival by influencing the behaviour of predatory mammals are poorly supported, due to a dearth of appropriately designed experiments. Some studies failed to include measures to reduce human-scent contamination, and the effectiveness of scent-mitigation methods used in other studies has seldom been verified. In addition, volatile compounds arising from soil and vegetation disturbed underfoot by field researchers may have confounded many nest-survival studies. Investigators have routinely inferred human-scent effects from post hoc predation patterns or have simply acknowledged possible human-scent effects among other potential influences of nest fate. Studies are needed of the effects of human scent using uniform methods of scent application and verified methods of scent mitigation, where the fates of different types of nests are examined under a range of field conditions. More fundamentally, studies of naïve and experienced mammals are needed to assess their responses to human scent and clarify its salience in wildlife disturbance.     

4. SOME BIRDS OBSERVED AT LAKE MENTZ

Randall, R. M. &; Randall, B. M. 1900. The hard-shell4 diet of African Black Oystercatcher chicks at St Croix Island, South Africa. Ostrich 53:157-163.

The hard-shelled diet of African Black Oystercatcher Haematopus moquini chicks was established by monitoring piles of food remains brought to the chicks. Mussels were the dominant prey species constituting about 90% numerically and about 95% by mass. Limpets were the next most abundant prey item, while false limpets, keyhole limpets and whelks were present in small numbers. Transects down the intertidal area showed that African Black Oystercatchers ignored some abundant species such as barnacles and small gastropods. They took most prey species in the same relative proportion that they were represented in transects, but there was evidence of selection for limpets and avoidance of false limpets and whelks. The modal size class of mussels in feeding piles was greater than in transects.     

Selection for non-diapause inAmblyseius cucumeris andAmblyseius barkeri and exploration of the effectiveness of selected strains for thrips control

In Europe and North America the western flower thrips,Frankliniella occidentalis, is an important pest in various greenhouse crops, such as sweet pepper and cucumber. Two species of predatory mite are commercially applied for biological control of this pest:Amblyseius cucumeris andA. barkeri. Thrips control is generally successful from March onwards. During winter, however, thrips control by these predatory mites is less effective. An important reason for this is that the commercially applied strains of both mite species enter reproductive diapause under short-day photoperiods, whereas the western flower thrips does not enter diapause. In this paper we report on selection experiments for non-diapause in strains of both mite species, aimed at obtaining predators that do not enter diapause under light- and temperature conditions prevailing in winter. Additional experiments were done to estimate the potential of the selected lines as control agents ofF. occidentalis. Selection for non-diapause proved highly successful in both predatory mite species. In a New Zealand strain ofA. cucumeris diapause incidence decreased from 41% to 0% in about ten generations; in a Dutch strain ofA. barkeri diapause incidence decreased from 67% to 0% in about six generations. Furthermore, selection for non-diapause had no influence on predator performance, measured as predation rate and oviposition rate on a diet of first instar thirps larvae. Rates of predation and oviposition were the same for selected and unselected lines in both species; rates of predation and oviposition were higher forA. cucumeris than forA. barkeri. After 18 months under non-diapause conditions, no less than 92% of a sample of the selected non-diapause line ofA. cucumeris did not enter diapause when tested under diapause-inducing conditions. This indicates that ‘non-diapause’ is a stable trait in these predatory mites. Finally, a small-scale greenhouse experiment in a sweet pepper crop showed that the selected non-diapause line ofA. cucumeris established successfully under diapause-inducing short-day conditions.