Relationship between predation by Podisus nigrispinus and developmental phase and density of its prey,Plutella xylostella

This study evaluated the predation by Podisus nigrispinus (Dallas) (Hemiptera: Pentatomidae) at various densities of larvae and pupae of the pest Plutella xylostella (L.) (Lepidoptera: Plutellidae). We tested predator behavior of female P. nigrispinus at six experimental densities (1, 5, 10, 15, 20, or 25 prey items in a 1‐l transparent plastic container, replicated 15 times for each density) of both the fourth instar and pupae of P. xylostella. The number of prey consumed was monitored every 15 min for 12 h and was subsequently monitored at 24 h. Podisus nigrispinus females were weighed before and after the experiments to determine the effect of different densities of prey on their weight gain. Female predators had a Type‐II functional response, with attack rate estimated at 1.387 and 0.260 and a handling time of 0.091 and 0.183 h^?1 for larvae and pupae, respectively. Podisus nigrispinus consumed on average 10.9 larvae or 5.5 pupae in 24 h. Despite the similarity of the response type, P. nigrispinus preferred to feed on larvae, rather than on pupae.     

How predation by Podisus nigrispinus is influenced by developmental stage and density of its prey Alabama argillacea

The functional response of a predator to the density of its prey is affected by several factors, including the prey's developmental stage. This study evaluated the functional response of Podisus nigrispinus (Dallas) (Hemiptera: Heteroptera: Pentatomidae) females to fourth instars and pupae of Alabama argillacea (Hübner) (Lepidoptera: Noctuidae), an important pest of cotton (Gossypium hirsutum L., Malvaceae) in Brazil. The prey were exposed to the predator for 12 and 24 h, and in densities of 1, 6, 12, 18, 24, and 30 items per predator female. The predation data were subjected to polynomial regression logistic analysis to determine the type of functional response. Holling and Rogers' equations were used to estimate parameters such as attack rate and handling time. Podisus nigrispinus females showed functional response types II and III by preying on larvae and pupae, respectively. The attack rate and handling time did not differ between the 12 and 24 h exposure times. Predation rate was higher at higher larval and pupal densities; predation was highest at a density of 30 prey items per female, and it was similar at 18 and 24 prey per predator. Understanding the interaction of predators and their food resources helps to optimize biological control strategies. It also helps the decision‐making and the improvement of release techniques of P. nigrispinus in the field.     

Functional response of Nesidiocoris tenuis (Hemiptera: Miridae) to Trialeurodes vaporariorum (Hemiptera: Aleyrodidae): effect of different host plants

The influence of three host plants, namely cucumber, tomato and eggplant, on functional response of male, virgin and mated female predatory bug Nesidiocoris tenuis was investigated on different densities of Trialeurodes vaporariorum nymphs. The 24-h experiment conducted at laboratory conditions revealed that N. tenuis exhibited a type II functional response to T. vaporariorum on host plants. There were no significant differences between attack rates, as well as handling times estimated for each adult stage of the predator between host plants. However, on each host plant, the handling time estimated for the mated female in comparison with two other adult stages had lower values (0.7952, 0.6827 and 0.8884?h^?1 on cucumber, tomato and eggplant, respectively). Handling time estimated for the mated female on cucumber was significantly lower than that estimated for the male predator. The highest maximum handling rate (T/T_h) was estimated for the mated female followed by the virgin female and male on all host plants. For three adult stages of the predator, the highest value of this parameter was determined on tomato followed by cucumber and eggplant. Unlike virgin and mated females, the host plant significantly affected prey consumption by the male. Prey consumed by mated females was higher than those obtained for two other adult stages of the predator on each host plant. The difference in trichome density between three host plants may be responsible for the obtained results. These results revealed that N. tenuis is more effective in the biological control of T. vaporariorum on tomato in comparison with cucumber and eggplant.     

Functional responses of Iphiseius degenerans and Neoseiulus teke (Acari: Phytoseiidae) to changes in the density of the cassava green mite, Mononychellus tanajoa (Acari: Tetranychidae)

The functional responses of protonymph and adult female Iphiseius degenerans and Neoseiulus teke to increasing density of three stages of their prey, the cassava green mite (CGM), Mononychellus tanajoa, were studied on excised cassava leaf discs under laboratory conditions. The responses obtained were predominantly sigmoid type III curves with the highest plateau when both stages of I. degenerans and N. teke were preying on CGM eggs. In all cases, the predation rate of the former species exceeded that of the latter. The empirical data were fitted by four different models. From the models, the attack coefficient (a) and handling time (T _h) were estimated. For a given predator stage (protonymph or adult female), the predator's attack coefficient declines and handling time increases as the prey gets larger. For a given prey stage, the predator's attack coefficient increases and handling time decreases as the predator stage becomes larger.     

Effect of habitat complexity on the predation of Buenoa fuscipennis (Heteroptera: Notonectidae) on mosquito immature stages and alternative prey

Notonectids are well‐known predators in aquatic habitats, where mosquito larvae, chironomids, and cladocerans constitute their main diet. Our purpose was to assess the effect of structural complexity on the predatory ability of Buenoa fuscipennis, a common predator in aquatic habitats of Buenos Aires city (Argentina). Buenoa fuscipennis showed type 2 functional responses in both the presence and absence of prey refuge and no differences in attack rate or handling time between refuge treatments. Regarding mosquito size classes, B. fuscipennis exhibited a significantly higher preference for 2^nd instar larvae and no predation on pupae. In the presence of mosquito larvae and alternative prey, B. fuscipennis preferred mosquitoes over chironomid larvae and adult cladocerans over mosquito larvae. No switching behavior was detected in our experiments. Habitat structure only slightly affected the predator´s consumption rates on mosquito larvae. Overall, preference for prey did not vary with the presence of refuge, except for the preference for mosquitoes over chironomid larvae, which was significantly decreased in the presence of refuge as a consequence of reduced predation on mosquito larvae. The results suggest that B. fuscipennis could efficiently control mosquitoes in structurally simple habitats where chironomids are the most abundant alternative prey but not in temporary pools where cladocerans are abundant.     

Assessment of the functional response parameters of Coccinella septempunctata to varying densities of Acyrthosiphon pisum

The functional response of a predator describes the rate at which it kills its prey at different prey densities and is, therefore, an important tool to determine the efficiency of a predator in regulating the population dynamics of a prey. We investigated the functional response of Coccinella septempunctata L. (Coleoptera: Coccinellidae) to varying densities of Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae). The results revealed that the linear coefficient, P₁ in the reduced logistic model was found significantly negative for the 4^th instar larvae and adult male and female of C. septempunctata (?0.002, ?0.004 and???0.002, respectively) indicating a type II functional response. The parameter estimates of adult male, female and 4^thinstar larvae of C. septempunctata calculated through Holling's disc model revealed that the highest attack rate (a) (1.047?±?0.014), shortest handling time (T_h) (0.0984?±?0.024?h) and largest maximum capture rate (T/T_h) (243.902) was exhibited by female. Parameter estimates calculated through Rogers’s equation also showed the same sequence where maximum attack rate (a) of 0.00256?±?0.0003 was exhibited by female followed by 4^th instar larvae (0.00251?±?0.0005). The shortest handling time (T_h) (0.210?±?0.003?h) and highest maximum capture rate (T/T_h) (114.17) was also exhibited by female. Comparison of functional response curves of adult male, female and 4^th instar larvae revealed that maximum consumption of prey at all the densities offered was shown by female followed by 4^thinstar larvae. The study manifested that C. septempunctata could be an efficient biocontrol agent of pea aphid, A. pisum.     

Nitrogen fertiliser affects the functional response and prey consumption of Harmonia axyridis (Coleoptera: Coccinellidae) feeding on cereal aphids

Predator–prey interactions are influenced by nitrogen availability. Wheat (Triticum aestivum cv. Solstice) plants were provided with four levels of nitrogen and examined the responses of coccinellid predator, Harmonia axyridis to cereal aphids, Rhopalosiphum padi and Sitobion avenae. Increased nitrogen application improved nitrogen contents of the plants and also the body weight of cereal aphids feeding on them. In no‐choice feeding trials, H. axyridis consumed more aphids on low fertilised plants, suggesting a compensatory consumption to overcome reduced biomass (lower aphid size). Total biomass devoured by H. axyridis on all nitrogen fertiliser treatments was not statistically different. Logistic regression analysis of the proportion of prey consumed demonstrated that all developmental stages (larval and adult) of H. axyridis exhibited the type II functional response on all nitrogen fertiliser treatments. The rate of successful search (a′) of third and fourth instars and adults were the same across all fertiliser treatments suggesting that nitrogen fertilisation did not affect a′. Maximum handling time for the first instars of H. axyridis on R. padi (3.81 h^?1) and S. avenae (4.59 h^?1) was on the highest nitrogen treatment while minimum handling time was for the adults of H. axyridis on R. padi (0.20 h^?1) and S. avenae (0.20 h^?1) on the lowest nitrogen treatment. Handling time varied at varying fertiliser treatments within all instars and affected the predator's efficiency. The functional response curve, rate of successful search and handling time provide the information needed to understand the predator–prey interaction between H. axyridis and these cereals aphids. This could lead to the development of a better strategy for the biological control of R. padi and S. avenae at any particular level of nitrogen fertiliser regime in the field crops.     

Functional response of Chrysoperla carnea (Neuroptera: Chrysopidae) to Helicoverpa armigera (Lepidoptera: Noctuidae): Effect of prey and predator stages

Abstract Understanding predator–prey interactions has a pivotal role in biological control programs. This study evaluated the functional response of three larval instars of the green lacewing, Chrysoperla carnea (Stephens), preying upon eggs and first instar larvae of the cotton bollworm, Helicoverpa armigera Hübner. The first and second instar larvae of C. carnea exhibited type II functional responses against both prey stages. However, the third instar larvae of C. carnea showed a type II functional response to the first instar larvae of H. armigera, but a type III functional response to the eggs. For the first instar larvae of C. carnea, the attack rate on H. armigera eggs was significantly higher than that on the larvae, whereas the attack rate of the second instar C. carnea on H. armigera larvae was significantly higher than that on the eggs. For the third instar larvae of C. carnea, the attack rate on the larvae was 1.015 ± 0.278/h, and the attack coefficient on the eggs was 0.036 ± 0.005. The handling times of the third instar larvae on larvae and eggs were 0.087 ± 0.009 and 0.071 ± 0.001 h, respectively. The highest predation rate was found for the third instar larvae of C. carnea on H. armigera eggs. Results of this study revealed that the larvae of C. carnea, especially the third instar, had a good predation potential in controlling H. armigera eggs and larvae. However, for a comprehensive estimation of the bio‐control abilities of C. carnea toward H. armigera, further field‐based studies are needed.     

Functional response of different stages of Hippodamia variegata (Col.: Coccinellidae) to Diuraphis noxia (Hemiptera: Aphididae) on two wheat cultivars

As one of the most important natural enemies of aphids, lady beetles have been widely used for the control of pest aphids. Important to the efficiency of natural enemies is their functional response to varying prey densities. In this study, the functional response of Hippodamia variegata Goeze (Col.: Coccienllidae) to different densities of Diuraphis noxia Mordvilko was examined on two wheat cultivars with different resistance levels under laboratory conditions (25 ± 1°C, 65 ± 5% RH and 16:8 L:D photoperiod). Our results revealed that all stages of H. variegata exhibited a type II functional response, in that predation decreased with increasing prey density. Searching efficiency (a) and handling time (T_h) of third instar larvae on the Sardari cultivar were 0.0285/h and 0.0079 h, while for fourth instar larvae these values were 0.0561/h and 1 × 10^?8 h, for males these values were 0.0412/h and 0.0173 h and for females were 0.059/h and 0.0168 h. The corresponding values for the back cross cultivar for third instar larvae were 0.0475/h and 0.0782 h, for fourth instar larvae were 0.0753/h and 0.0529 h, for males were 0.045/h and 0.0060 h and for females were 0.0516/h and 0.0077 h. This study demonstrated that these wheat cultivars do not have a significant effect on the functional response parameters of H. variegata life stages, except for the searching efficiency of third instar larvae and the handling time of male adults. The possible application of this species against Russian wheat aphids in an integrated pest management programme is also discussed.     

Oviposition pattern of the predator Podisus nigrispinus (Heteroptera: Pentatomidae) under different temperatures

The daily reproductive rate of Podisus nigrispinus (Dallas) (Heteroptera: Pentatomidae) fed with Alabama argillacea (Hübner) (Lepidoptera: Noctuidae) larvae was studied at constant temperatures of 20, 23, 25, 28, 30 and 33±0.2°C, relative humidity of 60±10% and photoperiod of L:D 14:10. Daily reproductive rate of P. nigripinus was affected by age of this predator. Each P. nigrispinus female laid 5.3 (20°C) to 19.9 eggs/day (28°C) which developed into 4.3–16.5 nymphs, respectively. Highest daily reproductive rate of P. nigrispinus was recorded at 28 and 30°C for 5–30-day-old females. This predator showed higher daily reproductive rate than its prey A. argillacea at 25°C. It was also able to reproduce at temperatures from 20 to 33°C with maximum daily reproductive rate between 25 and 30°C. These results are important for optimizing mass rearing of P. nigrispinus in the laboratory.     

Morphology and defensive structures in the predator-prey interaction: an experimental study of Parabroteas sarsi (Copepoda,Calanoida) with different cladoceran prey

Parabroteas sarsi is a predaceous calanoid copepod commonly found in South Andes lakes. Feeding experiments were carried out in order to estimate the predation rates and attack patterns on different cladoceran prey. Predation rates were related with prey sizes. The smallest prey, Bosmina longirostris, was ingested up to 5 prey pred^–1 h^–1 while the largest, Daphnia middendorffiana, only at 0.12 prey pred^–1 h^–1. The functional response of P. sarsi differed when confronted with different prey although in all cases, the number of kills increased with prey density. A saturation of ingestion rates at high prey densities was only observed for B. longirostris and Ceriodaphnia dubia juveniles. Remains seldom appeared at the end of the experiments, implying that the predator consumed prey totally. Yet, in all experiments carried out with Daphnia ambigua and D. middendorffiana, remains, including soft parts, were found. Direct observations of attack and of number and types of remains showed interference of handling by tail, helmet, and size of the prey.     

Predation and functional response of the multi-coloured Asian ladybeetle Harmonia axyridis on the adult Asian citrus psyllid Diaphorina citri

Diaphorina citri (Hemiptera: Liviidae) is a vector for the citrus Huanglongbing greening disease, which can reduce crop yields. Harmonia axyridis (Coleoptera: Coccinellidae) is known to prey on D. citri nymphs; we investigated the predation capacity and functional response of H. axyridis on adult D. citri. H. axyridis larvae exhibited Holling’s type II functional response to different densities of adult D. citri. For second, third and fourth instar H. axyridis larvae, the successful attack rates were 0.75?±?0.22, 1.06?±?0.11, and 1.04?±?0.26, respectively; the handling times were 18.08?±?5.37, 0.45?±?0.07, and 0.24?±?0.07?h, respectively; and the estimated maximum predation rates were 4, 54, and 102, respectively. Fourth instar larvae had the lowest handling time. Adult H. axyridis consumed more D. citri adults maintained at 15–20°C than at 30–35°C, with an optimal temperature of 17.28°C. More adults were consumed during the day than at night, with peak consumption between 12:00 and 14:00?h, not differing significantly differ between predator genders. Adult H. axyridis reared on the aphid Acyrthosiphon pisum were tested for D. citri predation; these H. axyridis had successful attack rates, handling times, and estimated maximal predation rates of 0.66?±?0.18, 0.82?±?0.26?h, and 29, respectively. Conversely, those fed and tested on D. citri had corresponding rates of 0.99?±?0.17, 0.38?±?0.12?h, and 63, respectively. Significant H. axyridis predation on adult D. citri indicated its enhanced role in suppressing both nymph and adult D. citri.     

Parasitism-mediated prey selectivity in laboratory conditions and implications for biological control

In agroecosystems, parasitoids and predators may exert top-down regulation and predators for different reasons may avoid or give preference to parasitised prey, i.e., become an intraguild predator. The success of pest suppression with multiple natural enemies depends essentially on predator–prey dynamics and how this is affected by the interplay between predation and parasitism. We conducted a simple laboratory experiment to test whether predators distinguished parasitised prey from non-parasitised prey and to study how parasitism influenced predation. We used a host-parasitoid system, Spodoptera frugiperda and one of its generalist parasitoids, Campoletis flavicincta, and included two predators, the stinkbug Podisus nigrispinus and the earwig Euborellia annulipes. In the experiment, predators were offered a choice between non-parasitised and parasitised larvae. We observed how long it took for the predator to attack a larva, which prey was attacked first, and whether predators opted to consume the other prey after their initial attack. Our results suggest that, in general, female predators are less selective than males and predators are more likely to consume non-parasitised prey with this likelihood being directly proportional to the time taken until the first prey attack. We used statistical models to show that males opted to consume the other prey with a significantly higher probability if they attacked a parasitised larva first, while females did so with the same probability irrespective of which one they attacked first. These results highlight the importance of studies on predator–parasitoid interactions, as well as on coexistence mechanisms in agroecosystems. When parasitism mediates predator choice so that intraguild predation is avoided, natural enemy populations may be larger, thus increasing the probability of more successful biological control.     

Functional response of Macrolophus pygmaeus (Rambur) and Nesidiocoris tenuis (Reuter) feeding on two different prey species

Functional response type and predatory parameters of Macrolophus pygmaeus and Nesidiocoris tenuis (Hemiptera: Miridae), the two important predators widely used in IPM programmes at tomato greenhouses, were investigated. The predators fed on Tuta absoluta (Lepidoptera: Gelechiidae) or Ephestia kuehniella (Lepidoptera: Pyralidae) eggs. Different densities of prey eggs including 1, 2, 3, 4, 5, 8, 10, 15, 20, 30 and 40 (latest only for E. kuehniella) were used at laboratory conditions. The results showed that both predatory bugs had type II functional response. Also, predation indices were significantly different between the predators. Although N. tenuis was more efficient against T. absoluta eggs than M. pygmaeus, M. pygmaeus predatory indices showed that this predator was more efficient on E. kuehniella eggs. Thus, minimum and maximum attack rate were observed in N. tenuis fed on E. kuehniella (0.0871 h^?1) and T. absoluta (0.2514 h^?1) eggs, respectively. Whilst, the minimum and maximum handling time were observed in M. pygmaeus fed on E. kuehniella (1.8695 h) and T. absoluta (2.7415 h) eggs, respectively.     

Selection of healthy and nuclear polyhedrosis virus infectedAnticarsia gemmatalis [Lep.: Noctuidae] as prey by nymphalNabis roseipennis [Hemiptera: Nabidae] in laboratory and on soybean

Nabis roseipennis Reuter nymphs demonstrated a preference for nuclear polyhedrosis virus (NPV) — infected over healthyAnticarsia gemmatalis Hübner larvae when offered a choice of larval prey in Petri dishes and on soybean. In Petri dishes, small (second-third instar) and large (fifth-sixth instar) nymphs attacked a significantly greater number of diseased than healthy larvae at all larval instars tested (first-fifth instars) and exposure periods (2, 5 and 24 h), except that at 2 h the number of 1^st and 3^rd instar larvae attacked by large nymphs did not differ significantly (P≤0.05). Nabis roseipennis caged with larvae on individual soybean plants in the greenhouse resulted in a generally low percentage of attack by small and large nymphs after 2 days, ranging from 5.6 to 36.7%. As in the Petri dishes, the nabids showed a significant preference for diseased larvae over healthy larvae attacked for all nabid and larval sizes on soybean, with the percentage of diseased larvae attacked ranging from 28.0 to 65.4% (P≤0.05). This preference for diseased larvae on soybean as well as in Petri dishes demonstrates that the preference was not due to the close proximity in which the host and prey were found in the Petri dishes. The preference for diseased larvae may be due to a reduction in a defensive response in late stages of disease. This material is based upon work supported in part by USDA Grant No. 83-CRCR-1-1212.     

Oviposition patterns in a predatory mite reduce the risk of egg predation caused by prey

Abstract 1. Predatory arthropods lay their eggs such that their offspring have sufficient prey at their disposal and run a low risk of being eaten by conspecific and heterospecific predators, but what happens if the prey attacks eggs of the predator? 2. The egg distribution and time allocation of adult female predatory mites Iphiseius degenerans as affected by predation of their eggs by prey, the western flower thrips Frankliniella occidentalis, were studied on sweet pepper plants. The predatory mites attack the first instar of thrips but all active stages of thrips are capable of killing the eggs of the predator; however the predatory mite is used for biological control of thrips. 3. The majority of predatory mite eggs was laid on the underside of leaves in hair tufts (domatia). During the experiment, females spent increasing amounts of time in flowers where they fed on pollen and thrips larvae. The risk of predation on predator eggs by thrips was lower on leaves than in flowers where the majority of thrips resides. Moreover, predation risk was higher outside leaf domatia than inside. 4. This suggests that predators avoid ovipositing in places with abundant prey to prevent their eggs from being eaten by thrips.     

Consumption rate and functional response of the predaceous mite<Emphasis Type="Italic"> Kampimodromus aberrans</Emphasis> to two-spotted spider mite <Emphasis Type="Italic">Tetranychus urticae</Emphasis> in the laboratory

Prey stage preference of female Kampimodromus aberrans (Oudemans) (Phytoseiidae) at constant densities of different stages of Tetranychus urticae Koch (Tetranychidae), functional response types and parameters of the predator females to the varying densities of eggs, larvae, protonymphs and deutonymps of T. urticae were determined in order to establish its potential for the mite biological control. Experiments were conducted at 25 ± 1°C, 65 ± 10% RH and 16:8 (L:D) photoperiod. Our results indicated that the predator consumed significantly more prey larvae than other prey stages. Functional response type of predator was determined by a logistic regression model. The predator exhibited a Type II response on all prey stages. The attack rate (α) and handling time (T _h ) coefficients of a Type II response were estimated by fitting a “random-predator” equation to the data. The lowest estimated value α and the highest value of T _h (including digestion) were obtanined for the predator feeding on deutonmph. The lowest value of T _h were obtained for the predator feeding on prey larvae, but the attack rate value obtained on larva wasn’t different than that obtained on egg and protonymph. According to our results, K. aberrans could be an efficient biological control agent of T. urticae at least at low prey densities. However, further field based studies are needed to draw firm conclusions.     

Foraging behavior of the coccinellid Nephus includens (Coleoptera: Coccinellidae) in response to Aphis gossypii (Hemiptera: Aphididae) with particular emphasis on larval parasitism

This study assessed the effect of parasitism of Nephus includens (Col.: Coccinellidae) larvae by Homalotylus flaminius (Hym.: Encyrtidae) on the predation rates of the predator on the cotton aphid, Aphis gossypii Glover (Hem.: Aphididae) by deriving functional responses for second- and fourth-instar predators at prey densities ranging from 10 to 80 aphids per arena. The relationship between the functional and numerical responses of adult females of N. includens also was determined for prey densities ranging from 10 to 140 aphids per arena. Predation rates of unparasitized and parasitized second-instar N. includens were both fit by a type II functional response model with parameters as follows: unparasitized (a = 0.0768 hours(-1) and T(h) = 0.975 h) and parasitized (a = 0.0787 hours(-1) and T(h) = 0.8823 hours). Predation rates of unparasitized and parasitized fourth-instar N. includens were fit by type III and II models, respectively, with the following parameters: unparasitized (b = 0.1702 hours(-1) and T(h) = 0.2369 hours) and parasitized (a = 0.038 h(-1) and T(h) = 0.539 h). The unparasitized fourth-instar was the most voracious stage, having the highest attack rate and lowest handling time. Considering these attributes, it would seem to be the most effective stage of this predator against A. gossypii. Adult female lady beetles (N. includens) showed a type III functional response and their numerical response increase to prey density was curvilinearly related to prey density, with the highest number of eggs being produced at highest prey densities. The maximum saturation level for both predation and egg production for adult females occurred at a prey density of 120 aphids. Thus, a ratio 1:120 (predator:prey) should be used when releasing this species for augmentative biological control. Release of either fourth-instar or adult stage N. includens should be minimized the potentially negative effect of parasitism by H. flaminius on early developmental stages, and hence increase its efficiency in biocontrol programs.     

Host plant effects on the functional response of Stethorus gilvifrons to strawberry spider mites

The functional response of adult females of the coccinellid beetle Stethorus gilvifrons Mulsant to juveniles of strawberry spider mite, Tetranychus turkestani Ugarov & Nikolski was determined on cowpea, castor bean and cucumber leaves in the laboratory at 25°C and a 14 h L: 10 h D photoperiod. Beetles were isolated singly for 24 h in 9-cm Petri dishes with either 2, 4, 8, 16, 32, 64, or 128 nymphal stages of T. turkestani. Results showed a typical type II response on all plants tested, with up to 110.7, 100.8, and 53.0 prey attacked when 128 nymphal stages were provided on cowpea, castor bean, and cucumber leaves, respectively. Based on the Rogers random attack equation, the highest estimated attack rate and the lowest handling time were obtained on cowpea. It was therefore concluded that the host plant species can affect the predation rate and functional response components of S. gilvifrons, a specific and effective predator of spider mites.     

Environmental variation and the predator-specific responses of tropical stream insects: effects of temperature and predation on survival and development of Australian Chironomidae (Diptera)

The threat posed by predation varies among predator species and with environmental context, and prey species often adjust their responses accordingly. We investigated such effects within an insect assemblage from a tropical Australian stream. These systems are frequently subjected to catastrophic floods, often suggested to reduce the importance of predation in streams, and invertebrate faunas are characterised by relatively broad environmental tolerances. Impacts of the hunting predator Australopelopia prionoptera (Diptera: Chironomidae) and an undescribed ambush predator from the Polycentropodidae (Trichoptera) on survival and development of two species of tubicolous Chironomidae, Echinocladius martini (Orthocladiinae) and Polypedilum australotropicus (Chironominae), were assessed in laboratory microcosms. A further experiment investigated how impacts of Australopelopia varied over a broad range of temperatures, exceeding that experienced annually by the studied populations. Neither predator impacted survivorship for E. martini, but the presence of the polycentropodid caused E. martini to spend longer as larvae and reduced adult longevity, and adult females were smaller-sized and had smaller oocytes. In contrast, both predators reduced survivorship of P. australotropicus, but only Australopelopia affected its development, causing reductions in pupal duration and oocyte size. The observed non-lethal impacts of predation reflect the threat each predator is known to pose to each prey species in situ. Impacts of predation varied little with temperature, reflecting the broad thermal tolerances of all study species. The predator-specific responses of the prey species imply that predation is a significant selective force in tropical Australian streams, although fluctuation in intensity of predation associated with flooding may limit its importance for community structure and prey diversity at larger scales. Our results indicate a more limited scope for environmental modification of predator–prey relationships in faunas characterised by broad physiological tolerances.