Californicus Eggs Research Articles

Mechanisms underlying the impact and interaction of temperature and UV-B on the hatching of spider mite and phytoseiid mite eggs.

A spider mite control method using night-time ultraviolet (UV)-B irradiation was recently developed for strawberry greenhouses (UV method). The control effect of this UV method is negatively affected by increasing temperature. Tetranychus urticae eggs are more resistant to a single dose of UV-B irradiation than Neoseiulus californicus eggs. By contrast, N. californicus can better survive nightly UV-B irradiation with the UV method compared with T. urticae. To elucidate the mechanism underlying these phenomena, we explored the hypotheses that higher temperature promotes photoenzymatic repair (PER) and that mortality is determined by UV-B susceptibility in the embryonic stage exposed to UV-B. PER efficacy was not promoted by increasing temperature. The lowest hatchability (around zero) of T. urticae eggs after a single dose of UV-B irradiation (0.288 and 0.432 kJ m-2 ) without photoreactivation was seen in the morphogenesis stages between "cleavage ended" and "eye points became colored". Based on these results, we developed a linear function of daily UV-B irradiance and deviation of cumulative irradiance during vulnerable embryonic developmental phases from 50% lethal dose (LD50 ) after a single dose of UV-B irradiation. The difference between T. urticae and N. californicus and changes in UV-B vulnerability due to temperature could be explained by this simple relationship. Slower development in T. urticae than N. californicus in nature and developmental delay under low temperatures increase the ovicidal effects of the UV method. This shows the advantage of the simultaneous use of the UV method and biological control, contributing to the development of integrated pest management. © 2022 Society of Chemical Industry.

A vegetable oil-based biopesticide with ovicidal activity against the two-spotted spider mite, Tetranychus urticae Koch.

A recently developed biopesticide made of safflower and cottonseed oils has excellent ovicidal activity against the hard‐to‐control spider mite Tetranychus urticae Koch (Acari: Tetranychidae). It has attracted attention as a sustainable treatment for controlling T. urticae because it has low potential for promoting resistance and little effect on the predatory mite Neoseiulus californicus (McGregor) (Acari: Phytoseiidae), which is an important natural enemy of spider mites. Here, we investigated the mechanism of its ovicidal activity against T. urticae. The oil droplets in the oil‐in‐water emulsion of the biopesticide strongly adhered to T. urticae eggs, seeped through the chorion being cut during hatching, and inhibited the embryonic rotational movement necessary for cutting and hatching. No adverse effect was observed on N. californicus eggs even in undiluted biopesticide. We conclude that this biopesticide and N. californicus can be used simultaneously in the integrated management of T. urticae in oily biopesticide‐tolerant plant species.

Dose-Response and Temperature Dependence of the Mortality of Spider Mite and Predatory Mite Eggs Caused by Daily Nighttime Ultraviolet-B Irradiation.

The two-spotted spider mite, Tetranychus urticae, is an economically important agricultural pest. A novel physical control method involving daily nighttime UV-B irradiation was recently developed for use in strawberry greenhouses. However, the overlapping of leaves after March prevents direct irradiation to T.urticae on the lower leaf surface, decreasing control effect. Excessive UV-B irradiation causes leaf sunscald in winter. Therefore, optimization of UV-B irradiance and a compensatory control agent are desired. Temperature may affect the survival of organisms exposed to UV-B, although the temperature dependence of UV-B damage is controversial. A phytoseiid mite, Neoseiulus californicus, is a prominent predator but vulnerable to a single UV-B irradiation. We compared dose-response and temperature dependence of UV-B damage between T.urticae and N.californicus eggs under daily nighttime UV-B irradiation. Unexpectedly, N.californicus showed greater resistance to UV-B than T.urticae, and the mortality was increased and decreased at low and high temperatures, respectively. This makes possible the application of UV-B doses that are lethal for spider mites but safe for phytoseiid mites. Overall, we concluded that combined use of phytoseiid mites with UV-B lamps is advantageous to spider mite management in strawberry greenhouses.

<p class="Body"><strong>The effect of con/heterospecific diet on predation, oviposition and longevity of <em>Amblyseius swirskii</em>, <em>Neoseiulus californicus</em> and <em>Phytoseiulus persimilis</em> (Acari: Phytoseiidae)</strong></p>

Intraguild predation (IGP) consists of interacting individuals with context dependent roles that compete for food. Information about the predator trophic interactions i.e. cannibalism or feeding on heterospecific juveniles, is a key to understand the real impact of their combinations when introduced in biological control systems. The hypothesis here, assumed that the pairwise introduction of the female predatory mites, N. californicus (predator) + P. persimilis (heterospecific prey) and vice versa, A. swirskii (predator) + P. persimilis (heterospecific prey) and vice versa could exist in the Tetranychus urticae (main prey) scarcity. Three diets consisted of either conspecific or heterospecific six eggs, four eggs + four larvae and four protonymphs were introduced to the guilds. The predation and oviposition rates and the longevity of each female intraguild predator on detached bean leaf disc was recorded every three hours for 12 consecutive days. Neoseiulus californicus predation rate was estimated to be highest on conspecific eggs + larvae (11.35 ± 1.12) and so was on those of P. persimilis (55.7 ± 3.42). No significant difference was observed in N. californicus oviposition rate on three conspecific diets (P > 0.05), while its oviposition rate was highest on P. persimilis eggs + larvae (7.15 ± 0.80). Phytoseiulus persimilis predation rate was estimated to be highest on eggs + larvae both on N. californicus and P. persimilis as prey. Its oviposition rate was estimated to be highest when feeding on conspecific eggs (2.25 ± 0.19) and N. californicus eggs + larvae. Amblyseius swirskii fed on 45 ± 2.79 P. persimilis and 12.90 ± 1.51 A. swirskii eggs + larvae, which was significantly higher than predation rates on other stages (P < 0.01). Amblyseius swirskii oviposition rate was not significantly different on each of the three diets or on A. swirskii or P. persimilis as prey (P > 0.05). The oviposition rate of P. persimilis was the highest on A. swirskii eggs + larvae (1.45 ± 0.19). When N. californicus fed on each of the three diet types, no significant difference was observed in its longevity. The greatest longevity of P. persimilis was recorded when feeding on N. californicus/P. persimilis eggs. Longevity of A. swirskii was the greatest on P. persimilis eggs and protonymphs. Similarly, P. persimilis had the greatest longevity feeding on A. swirskii eggs. We concluded that the predator species were capable of surviving under conditions of scarce prey when heterospecific species are present.

Laboratory assays on the effects of a novel acaricide, SYP-9625 on Tetranychus cinnabarinus (Boisduval) and its natural enemy, Neoseiulus californicus (McGregor).

ObjectiveTetranychus cinnabarinus (Boisduval) is an agricultural mite pest threatens crops throughout the world, causing serious economic loses. Exploring the effects of acaricides on predatory mites is crucial for the combination of biological and chemical control of T. cinnabarinus. Neoseiulus californicus (McGregor) is one of the principal natural enemies of T. cinnabarinus, which can be applied in protected agriculture. In this study, the effects of sublethal concentrations of a new acaricide, SYP-9625 on two mite species, and the effects of the application concentration on predatory mite, N. californicus were assessed. The aim of the present study was to evaluate the effect of SYP-9625 on life parameters and predation capacity of N. californicus based on the concentration-response bioassay of T. cinnabarinus to explor the application of the new acaricide with natural enemy N. californicus.MethodAll of the experiments were conducted under laboratory conditions [25 ± 1°C, 16: 8 h (L: D) and 75 ± 5% RH]. The sublethal concentrations LC10 (0.375μg/mL) and the LC30 (0.841μg/mL) against T. cinnabarinus and the application concentration (100μg/mL) against N. californicus were used to evaluate the effects of SYP-9625 on population parameters of N. californicus based on an age-stage, two-sex life table and its predation capacity by functional response.Resultcinnabarinus females treated with LC30 exhibited significantly reduced net reproductive rates (R0 = 11.02) in their offspring compared with females treated with LC10 (R0 = 14.96) and untreated females (R0 = 32.74). However, the intrinsic rate of increase (rm) and the finite rate of increase (λ) of N. californicus indicated that the application concentration of SYP-9625 had no significant negative effect on N. californicus eggs (rm = 0.277, λ = 1.319) compared to the control (rm = 0.292, λ = 1.338). Additionally, most population parameters of N. californicus showed a dose-dependent manner with the increase of the concentration of SYP-9625 against T. cinnabarinus. SYP-9625 also stimulated the control efficiency of N. californicus against immobile stages including eggs and larvae.ConclusionThis study demonstrated that sublethal concentrations of SYP-9625 can inhibit the population growth of T. cinnabarinus. In addition, the sublethal concentrations and the application concentration showed no effect on the population growth of N. californicus. These two advantages described above showed great commercial potential of this new acaricide based on population parameters of the two mite species and predation capacity of the predatory mite under laboratory conditions.

Ontogenetic stage-specific reciprocal intraguild predation

The size or stage of interacting individuals is known to affect the outcome of ecological interactions and can have important consequences for population dynamics. This is also true for intraguild predation (the killing and eating of potential competitors), where the size or ontogenetic stage of an individual determines whether it is the intraguild predator or the intraguild prey. Studying size- or stage-specific interactions is therefore important, but can be challenging in species with complex life histories. Here, we investigated predatory interactions of all feeding stages of the two predatory mite species Neoseiulus californicus and Phytoseiulus macropilis, both of which have complex life cycles, typical for predatory arthropods. Populations of these two species compete for two-spotted spider mites, their prey. We evaluated both the capacity to kill stages of the other predator species and the capacity to benefit from feeding on these stages, both prerequisites for the occurrence of intraguild predation. Ontogeny played a critical role in the occurrence of intraguild predation. Whereas the juveniles of P. macropilis developed from larva until adulthood when feeding on N. californicus eggs, interestingly, adult female P. macropilis did not feed on the smaller stages of the other species. We furthermore show that intraguild predation was reciprocal: both juveniles and adult females of N. californicus preyed on the smallest stages of P. macropilis. These results suggest that a proper analysis of the interactions between pairs of species involved in intraguild predation should start with an inventory of the interactions among all ontogenetic stages of these species.

Synergism to acaricides in resistant Neoseiulus californicus (Acari: Phytoseiidae), a predator of Tetranychus urticae (Acari: Tetranychidae)

Tetranychus urticae Koch is one of the most important phytophagous mite species worldwide, and Neoseiulus californicus (McGregor) is the main predatory mite species marketed for control of this pest in Brazil. The present study aimed to evaluate the toxicity of acaricides on both prey and predator mites and to assess mechanisms of resistance to acaricides in the predator. Concentration-response curves for the mite populations were established using the acaricides abamectin, chlorfenapyr, diafenthiuron, spiromesifen and fenpyroximate. Acaricide field dose effect on predator survival was also assessed. Additionally, synergism of PBO, TPP and DEM to fenpyroximate and chlorfenapyr was performed on the predator to preliminarily assess the involvement of detoxification enzymes on their toxicities. Ovicidal effects of acaricides were also evaluated on N. californicus eggs. Abamectin was the most toxic acaricide for both T. urticae (LC50 varying from 0.02 to 0.24 mg/L) and N. californicus (LC50 varying from 3.92 to 4.94 mg/L). Chlorfenapyr, diafenthiuron, fenpyroximate and spiromesifen are promising acaricides for the integrated management of T. urticae in combination with N. californicus. However, spiromesifen efficacy is stage dependent. Resistance of N. californicus to chlorfenapyr (RR50 = 14.69-times) and fenpyroximate (RR50 = 113.96-times) was observed for Bonito and Brejão populations, respectively. Synergism of chlorfenapyr toxicity in both N. californicus populations suggested an involvement of CYP450-dependent monooxygenases in the resistance, while these and esterases seem to be involved in the resistance to fenpyroximate. Survival of N. californicus was reduced to zero in a maximum of 12 h, to abamectin only. Excepting abamectin, the other acaricides must have their use encouraged regarding chemical-biological control association.

Effects of Low Temperature on Spider Mite Control by Intermittent Ultraviolet-B Irradiation for Practical Use in Greenhouse Strawberries.

The application of ultraviolet-B (UVB) radiation to control spider mites is challenging as a key technology for integrated pest management (IPM) in greenhouse strawberries in Japan. To address this, concurrent use of phytoseiid mites and reduced UVB irradiance is desirable to ensure control effects in areas shaded from UVB radiation and to minimize the sunscald in winter, respectively. We designed experiments reproducing the UVB dose on the lower leaf surfaces in strawberry and evaluated the effects of intermittent UVB irradiation at midnight for practical application in the greenhouse and low temperature on the survival of the spider mite Tetranychus urticae Koch (Acari: Tetranychidae) and damage to the phytoseiid mite Neoseiulus californicus (McGregor) (Acari: Phytoseiidae). The midnight intermittent UVB irradiation effectively suppressed egg hatching and development of larvae of T. urticae, and the control effect was reinforced at 20°C (no eggs hatched at 0.13 kJ m-2 d-1) rather than, at 25°C (70.8% eggs hatched). In contrast, the hatchability of N. californicus eggs was unaffected by intermittent UVB irradiation at 0.27 kJ m-2 d-1 at 25°C and 20°C. However, residual effects of UVB irradiation to N. californicus eggs on survival of hatched larvae were seen, so that reducing the UVB dose is also advantageous for this phytoseiid mite. N. californicus showed a photoreactivation capacity, whereas their UVB tolerance was improved by prey species, suggesting the possibility of the improvement of phytoseiid mites by diet. The reduction of UVB dose and concurrent use of phytoseiid mites increase reliability of the UVB method in IPM strategies in strawberry greenhouse.

Different responses to hypobaria between spider mites and a predatory mite

ABSTRACTSpider mites are a quarantine pest for different agricultural products imported to Japan, which may require phytosanitary treatments. To develop an environmental-friendly physical method to control agricultural pests, with minimal harm to natural enemies, we evaluated the effect of hypobaria (reduced atmospheric pressure) on three pest spider mites (Tetranychus urticae, T. kanzawai, Panonychus citri) and their natural enemy, the predatory mite Neoseiulus californicus. None of the spider mite eggs hatched when exposed to 17 kPa (lower partial pressure of oxygen, pO2 ≈ 3.5 kPa) at 25°C or 30°C for 24 h. The hatchability of N. californicus eggs was slightly reduced when the eggs were exposed to hypobaria at 30°C for 24 h. However, N. californicus adult females were more susceptible to hypobaria than females of the three species of spider mites. Adult survival of T. urticae and P. citri was significantly reduced by exposure to hypobaria at 30°C for 12 or 24 h, while adult survival of N. californicus was significantly reduced at 20°C, 25°C, and 30°C for ≥12, ≥12, and ≥6 h, respectively. For most species in most of the exposures, the adult survivabilities could be recovered by supplying water during the treatment. The exception was N. californicus when exposed to hypobaria at 30°C for 24 h. These results suggest that hypobaric-induced desiccation rather than hypoxia (pO2 ≈ 3.5 kPa) causes the mortality of adult females and that hypobaric treatments can be useful for selectively controlling spider mite eggs for phytosanitary treatment of several commercially important fresh commodities.

Influence of various preys in soybean and the biological performance of the predatory mite Neoseiulus californicus (Phytoseiidae)

Mites and insects cause damage to soybean crops (Glycine max (L.): Fabaceae). Mononychellus planki McGregor, Tetranychus ludeni Zacher (Acari: Tetranychidae) and Caliothrips phaseoli Hood (Insecta: Thripidae) have been mentioned as pests of soybean crops in Brazil, while Neoseiulus californicus McGregor (Acari: Phytoseiidae) is considered a generalist predatory mite. This work aimed to determine the biological parameters of N. californicus feeding on T. ludeni, M. planki and C. phaseoli on transgenic soybean leaves. Thirty N. californicus eggs were individually placed in arenas with T. ludeni, M. planki and C. phaseoli. Egg-to-adult duration (in days) was longest when fed T. ludeni (5.52±0.06) and shortest when fed C. phaseoli (4.89±0.06). Mean fertility was approximately 32 eggs/female and did not differ significantly when N. californicus fed on T. ludeni or M. planki. During the adult stage, N. californicus did not lay eggs when feeding on C. phaseoli and survived for only a few days. The net reproductive rate (Ro) of N. californicus was larger when fed T. ludeni (20.30±0.68) than M. planki (14.66±0.29). Both M. planki and T. ludeni were suitable prey for N. californicus, while C. phaseoli was not.

The use of the cannibalistic habit and elevated relative humidity to improve the storage and shipment of the predatory mite Neoseiulus californicus (Acari: Phytoseiidae).

This study investigated the feasibility of using the cannibalistic habits of the mite Neoseiulus californicus (McGregor) and controlling the relative humidity (RH) to prolong the survival time during the storage or shipment of this predatory mite. Three-day-old mated and unmated females were individually kept at 25±1°C in polypropylene vials (1.5mL), each containing one of the following items or combinations of items: a kidney bean leaf disk (L), N. californicus eggs (E), and both a leaf disk and the eggs (LE). Because the leaf disk increased the RH in the vials, the RH was 95±2% under the L and LE treatments and 56±6% under the E treatment. The median lethal time (LT50) exceeded 50days for the mated and unmated females under the LE treatment. However, it did not exceed 11 or 3days for all females under the L or E treatments, respectively. Under the LE treatment, the mated and unmated females showed cannibalistic behavior and consumed an average of 5.2 and 4.6 eggs/female/10days. Some of the females that survived for LT50 under each treatment were transferred and fed normally with a constant supply of Tetranychus urticae Koch. Unmated females were provided with adult males for 24h for mating. Only females previously kept at LE treatment produced numbers of eggs equivalent to the control females (no treatment is applied). The results suggested that a supply of predator eggs and leaf material might have furnished nutrition and water vapor, respectively, and that this combination prolonged the survival time of N. californicus during storage. Moreover, this approach poses no risk of pest contamination in commercial products.

Anoxia treatment for selectively controlling spider mites Tetranychus urticae and Panonychus citri with little impact on the predatory mite Neoseiulus californicus

ABSTRACTAnoxia treatment with a deoxidant consisting of iron, calcium chloride and silicon dioxide was evaluated at different temperatures for pest spider mites (Tetranychus urticae and Panonychus citri) and their natural enemy, the predatory mite Neoseiulus californicus. No spider mite eggs survived when exposed to anoxia for 18 h at 20°C or for 12 h at 25°C, whereas the survival of N. californicus eggs under these conditions was 53% and 72%, respectively. No adult female spider mites survived when exposed to anoxia for 15 h at 20°C or for 8 h at 25°C, whereas >95% of adult N. californicus females survived under these conditions. These results indicate that anoxia has potential as a selective method for controlling pest mites, such as T. urticae and P. citri, but has little impact on their natural enemy, N. californicus.

사막이리응애의 살응애제에 대한 감수성

Effects of 9 acaricides to the predatory mite, Neoseiulus californicus were evaluated. Seven of the acaricides tested, cyenopyrafen. spirodiclofen, spiromesifen, acequinocyl, bifenazate, flufenoxuron and cyflumetofen exhibited low toxicity to adult females and nymphs of N. californicus and had little effect on the reproduction and eclosion of eggs deposited by treated predators. Moreover, hatch percentage of N. californicus eggs was unaffected by exposure to these seven acaricides. Etoxazole did not significantly affect the survival and reproduction of adult female predators but caused very low eclosion in eggs laid by treated females and high egg mortality. Pyraclofos was extremely toxic to adult female predators and caused 100% mortality. Adult female predators survived on a diet of spider mites treated with cyenopyrafen. spirodiclofen, spiromesifen, acequinocyl, bifenazate, flufenoxuron and cyflumetofen and their fecundity was not substantially affected. Based on the results, cyenopyrafen. spirodiclofen, spiromesifen, acequinocyl, bifenazate, flufenoxuron and cyflumetofen are appeared to be promising candidates for use in integrated mite management program where N. californicus is the major natural enemy.

Effect of hot-water treatment on the two-spotted spider mite, Tetranychus urticae, and its predator, Neoseiulus californicus (Acari: Tetranychidae, Phytoseiidae)

Hot-water treatment has been used on various kinds of plants to control plant diseases and pests. Here, we determined the lethal times (LT50 and LT100) for various temperatures for the two-spotted spider mite, Tetranychus urticae, and the predatory mite, Neoseiulus californicus (Spical®). Mites were placed on strawberry leaf discs that were dipped in hot water. For T. urticae eggs, LT50 ranged from 250 s at 47.5°C to 1 s at 57°C, while LT100 ranged from 600 s at 47.5°C to 7 s at 57°C. For T. urticae females, LT50 ranged from 380 s at 47.5°C to 4 s at 57°C, while LT100 ranged from 1200 s at 47.5°C to 9 s at 57°C. For N. californicus eggs, LT50 ranged from 68 s at 45°C to 7 s at 50°C, while LT100 ranged from 300 s at 45°C to 6 s at 52.5°C. For N. californicus females, LT50 ranged from 107 s at 45°C to 6 s at 50°C, while LT100 ranged from 180 s at 45°C to 6 s at 52.5°C. LT50s for N. californicus eggs and females were 4–10 and 13–32 times shorter than those of T. urticae, respectively. The strawberry leaves did not appear to be damaged (i.e., they did not show significant wilting) when treated for 150 s at 50°C, 30 s at 55°C or 20 s at 57°C. Together, these results suggest that hot-water treatment can be used to control spider mites on strawberry, without much damage to the plants, but predatory mites may need to be replaced due to their sensitivity to hot water.

Life history and population growth parameters of Neoseiulus californicus (Acari: Phytoseiidae) fed on Thrips tabaci (Thysanoptera: Thripidae) in laboratory conditions

The onion thrips, Thrips tabaci Lindeman, is an important polyphagous pest of vegetables and ornamentals in greenhouses. Neoseiulus californicus (McGregor) is a biological control agent of spider mites that also preys on thrips. Little is known about the biology and life table of N. californicus fed on Thrips tabaci. We evaluated the development, survivorship and life-history parameters of the Boku strain of N. californicus feeding on first instar larvae of T. tabaci. Total prey consumption by protonymphs and deutonymphs were 3.85 and 3.50, respectively. Total prey consumption during the adult period in the Boku strain was 65.1 first instar larvae of T. tabaci. Ninety percent of N. californicus eggs hatched but just over 16% of newly hatched larvae attained maturity at 25°C. Developmental time was 9.00 days with T. tabaci as prey. Oviposition rate was 2.42 eggs/ female/ day. The average pre-oviposition, oviposition and post-oviposition periods were 3.54, 22 and 3.91 days, respectively. The low estimated intrinsic rate of natural increase (rm) of N. californicus (0.041 per day with T. tabaci) was due to high juvenile mortalities.

Effect of temperature on life history of the predatory mite Amblyseius (Neoseiulus) californicus (Acari: Phytoseiidae).

Amblyseius (Neoseiulus) californicus is an indigenous mite in Japan that feeds on many spider mite species. We evaluated the development, survivorship and life-history parameters of A. californicus on a diet of eggs of Tetranychus urticae (red form). More than 97.3% of A. californicus eggs hatched and more than 81.6% of newly hatched larvae attained maturity at temperatures between 15 and 35 degrees C. Females oviposited at 37.5 degrees C, but no eggs hatched. At 40 degrees C, no females laid eggs. The lower threshold temperature from egg to oviposition was 10.3 degrees C and the thermal constant was 86.2 degree-days. Based on these data, the maximum number of generations that could complete development in a year under field conditions in Ibaraki, central Japan, would be between 21 and 28. At 25 degrees C, females laid a mean of 41.6 eggs during a mean oviposition period of 19.4 days. The intrinsic rates of natural increase (rm) were 0.173 at 20 degrees C, 0.274 at 25 degrees C and 0.340 at 30 degrees C.

Comparative Behavioural Studies of Larval and Adult Stages of the Phytoseiids (Acari: Mesostigmata) Typhlodromus Athiasae and Neoseiulus Californicus

We compared the behaviours of the indigenous Typhlodromus athiasae Porath and Swirski and the exotic Neoseiulus californicus (McGregor) (= Amblyseius chilenensis Dosse) relative to their persistence in apple orchards in Israel. We studied (1) larval feeding, walking, intraspecific interactions (cannibalism, touch-avoidance responses and/or touching with palps and tarsi) and tendency to aggregate (when resting), (2) predation and cannibalism on phytoseiid eggs by young females and (3) the effects of starvation for 10 days on young females relative to ambulation speed, longevity, fecundity, progeny survival and sex ratio. Larvae of T. athiasae were almost inert, did not feed and hardly walked or interacted whereas larvae of N. californicus fed, walked and interacted, mainly by touching with palps and tarsi. No cannibalism in the larval stage was observed for either species. The presence of prey increased the larval walking and intraspecific interactions of N. californicus but not of T. athiasae. Egg predation by adult females of both species was substantially higher than cannibalism, implying that both are capable of distinguishing their eggs from those of other species. Soaking eggs for 30 min in deionized water increased cannibalism in both species. During the 10 days of starvation, the ambulation speed of adult female N. californicus ranged from 1.8 to 10.1 times that of T. athiasae. The 50% lethal time value (LT50) of T. athiasae (6.0 days) was significantly lower than that of N. californicus (10.4 days). None of the starved T. athiasae recuperated following the reintroduction of prey, whereas 75% of N. californicus did and oviposited after 2 days. These traits should enable N. californicus to persist when prey is scarce; however the selective predation of N. californicus eggs by T. athiasae could prevent establishment of N. californicus. The degree of specialization of these two predators is discussed.