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

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

Mating, cross-mating and related behaviours of Neoseiulus californicus and Neoseiulus fallacis (Acari: Phytoseiidae)

The pairings of Neoseiulus californicus (McGregor) and Neoseiulus fallacis (Garman) from western North America were monitored for tending by adult males, males in the mating position and oviposition and the activity of female deutonymphs and adults. The N. fallacis × N. californicus (♂ × ♀) tests had fewer males tending the deutonymphs but more in the mating position with new females than the reciprocal test. Afterwards, most of the females appeared gravid and approximately 20% produced an egg. Some eggs did not hatch but others became adult males, which mated with their mothers, but no eggs were produced. F1 males tended and mated with new N. fallacis females which had normal offspring. When held with new N. californicus females, F1 males tended the deutonymphs but were not seen mating and no eggs were laid. The pairings of N. californicus× N. fallacis had more males tending, less in the mating position and the females appeared non-gravid and produced no eggs. When same-species males were added to females held with F1 males for 15–20 days, normal levels and sexes of the progeny were produced. The female and male adults of N. fallacis were more active (ambulatory) than those of N. californicus. In within-species tests, the males had a high activity except while tending and mating, the female deutonymphs were inactive and the just mated females were more active than the ovipositing females. The timing of the tending and mating differed in the cross-pairings. Overall, these and other life-history data show that these two mites are distinct species, but that their males are promiscuous in tending and mating. This revised version was published online in November 2006 with corrections to the Cover Date.     

Effect of Amblyseius cucumeris and Amblyseius barkeri as biological control agents of thrips tabaci on glasshouse cucumbers

Biological control of Thrips tabaci by the phytoseiid mites Amblyseius cucumeris and Amblyseius barkeri was investigated on glasshouse parthenocarpic cucumbers. The mite species were used in combination and singly. Successful thrips control was obtained with A. cucumeris alone, whereas control was not reliable with A. barkeri alone nor with the combination of A. cucumeris and A. barkeri. The establishment period was long for both phytoseiid species. At the beginning of the trial, when thrips were absent or very low in numbers, only A. cucumeris was found on the leaves. Mite populations did not increase until the number of thrips were ca. two and five per leaf for A. cucumeris and A. barkeri, respectively. A. cucumeris seemed to show a better numerical response to T. tabaci than A. barkeri. At the end of the trial (three months after the last introduction of mites) only A. barkeri was found in the combination plot, indicating that A. cucumeris is displaced by A. barkeri in situations of interspecific competition between the two species on glasshouse parthenocarpic cucumbers.     

Purification and characterization of 5-aminolevulinic acid dehydratase from Methanosarcina barken

Abstract 5-Aminolevulinic acid dehydratase from the archaebacterium Methanosarcina barken resembles the mammalian and yeast enzymes in its activation by Zn²⁺, whereas its activation by K⁺ resembles the characteristic of bacterial enzymes. This enzyme is activated with Ni²⁺ which is a component of F₄₃₀, a cofactor present mainly in methanogens. The M _r of 280000 for the native enzyme and 30 000 ± 2000 for the individual subunit suggest that the enzyme is composed of eight apparently indentical subunits similar to mammalian and yeast enzymes. The enzyme has two pH optima, at 8.5 and 9.4. Higher levels of 5-aminolevulinic acid dehydratase in acetate-grown cells suggest the possibility that regulation and control of this enzyme could be different on various growth substrates.     

Kanzawa spider mites acquire enemy‐free space on a detrimental host plant,oleander

Studies have proposed that predators of herbivores suffer significant fitness losses from the defense chemicals of host plants, and that herbivores adapted to these chemicals may experience reduced predation risk when residing on such plant species. We examined the effects of oleander, Nerium indicum Mill. (Apocynaceae), a host plant of the spider mite, Tetranychus kanzawai Kishida (Acari: Tetranychidae), on their prime predator, Neoseiulus womersleyi (Schicha) (Acari: Phytoseiidae), and tested the hypothesis that this host plant provides enemy‐free space. At the study sites, T. kanzawai occurred on oleander shrubs; in contrast, although N. womersleyi was present in the area, no individuals were found on oleander. Tetranychus kanzawai feeding on oleander negatively affected the settlement, development, and egg production of N. womersleyi. The lower egg production was a result of both the direct effects of oleander and the indirect effects via T. kanzawai. Previous studies showed that the fitness of T. kanzawai in the presence of N. womersleyi was lower than that in the absence of the predator, and lower on oleander than on other palatable host plant species in the absence of predators. Our findings suggest that N. womersleyi may not be able to invade T. kanzawai patches on oleander shrubs, which results in the fitness of T. kanzawai being higher on oleander than on other host plant species in the same area when N. womersleyi is present. This supports the hypothesis that T. kanzawai acquires enemy‐free space on oleander using the direct and indirect adverse effects of oleander on their predators as major defense mechanisms.     

Suseptibility of the Predatory Mite,Neoseiulus californicus (Acari: Phytoseiidae), to Seven Insecticides

Susceptibility of the predatory mite, Neoseiulus californicus (McGregor) (Acari: Phytoseiidae), to the field rates of seven commercial insecticides was evaluated in laboratory bioassays. In direct treatments with lufenuron, novaluron, pyrifluquinazon, and sulfoxaflor, 82–88% of N. californicus adult females survived 168 h after exposure. Females exposed to these four insecticides produced 14–19% fewer eggs compared to females in the control group. Eclosion of eggs deposited by treated females was not affected. The percentage of eggs that hatched and larval survival following direct exposure to these four insecticides were not seriously reduced. A total of 72–82% of immature N. californicus survived on leaf discs with residues of lufenuron, novaluron, pyrifluquinazon, and sulfoxaflor matured to adults. Emamectin benzoate, lepimectin and spirotetramat were highly toxic to both N. californicus adult females and larvae. Based on these results, lufenuron, novaluron, pyrifluquinazon and sulfoxaflor are promising candidates for use in integrated pest management programs where N. californicus is a major natural enemy.     

Dehalogenation of trichlorofluoromethane (CFC-11) by Methanosarcina barkeri

Methanobacterium barkeri was found to catalyze the reductive dehalogenation of trichlorofluoromethane (CFC-11), also known as FREON 11. Products detected were CHFCl2, CH2FCl, CO and fluoride.     

Effects of starvation on reproduction of the predacious mite <Emphasis Type="Italic">Neoseiulus californicus</Emphasis> (Acari: Phytoseiidae)

Effects of starvation on gravid females of Neoseiulus californicus were investigated at 20°C and 85% RH. When females that had been reared with abundant prey were swapped, just after laying their first egg, to conditions without any prey and water, they laid 1.8 eggs and survived for 4.3 days. In the body of well-fed females, an egg with eggshell and/or two oocytes were observed in the ventral and dorsal regions, respectively. The larger oocyte had two roundish nuclei and abundant yolk granules, and was enveloped with a vitelline membrane. These two nuclei were not fused but were just close to each other. The smaller oocyte had a nucleus, but had not yet formed yolk granules and vitelline membrane. Females after 12 h starvation had an egg in the ventral region and an oocyte in the dorsal region of the body. After more than 24 h starvation females maintained an oocyte in the dorsal region of the body, but had no egg in the ventral region. The oocyte was filled with abundant yolk granules and contained two irregular nuclei when females were starved for 24 h, but when starved for more than 36 h it contained one irregular nucleus. These findings suggest that (1) gravid females maintained an oocyte in the dorsal region after laying two eggs during starvation, (2) the oocyte was not absorbed during starvation, (3) the oocyte advanced vitellogenesis and the fusion of two nuclei, and (4) the vitellogenic oocyte was not enveloped with an eggshell and had not started embryogenesis.     

Food scarcity reduces female longevity of <Emphasis Type="Italic">Neoseiulus californicus</Emphasis> (Acari: Phytoseiidae)

A commercial strain of Neoseiulus californicus (Spical^®) has a conspicuously long postoviposition period in comparison with other strains of N. californicus or other phytoseiid mites. In many insects and mites, life span is shorter for multiple-mated females than for single-mated females, and is shorter under poor prey conditions than under ample prey conditions. We previously showed that the postoviposition period of multiple-mated females was 40% shorter than that of single-mated females, but that it was never shorter than 30 days. Here we focused on the effect of prey abundance on the postoviposition period. We examined three groups of multiple-mated females: mites that were fed ample prey (group I), mites that were subjected to repeated cycles of 2 days of fasting followed by 2 days of ample prey (group II), and mites that were subjected to repeated cycles of 4 days of fasting followed by 2 days of ample prey (group III). The postoviposition periods of groups II and III were 90% shorter than that of group I. Also the total adult longevity was significantly shorter in groups II and III than in group I. Total egg production in group III was about half that in groups I and II, although the oviposition periods in groups II and III were significantly longer than that in group I. These results suggest that the prolonged postoviposition period in single-mated females of the Spical strain may only appear under laboratory conditions, without multiple mating or starvation.     

Influence of prey on developmental performance, reproduction and prey consumption of Neoseiulus californicus (Acari: Phytoseiidae)

The Spical strain of the predatory mite Neoseiulus californicus (McGregor) is used as a biological control agent, but little is known about its preferred prey and host plants in Japan. Here we studied the development, reproduction and prey consumption of the Spical strain when fed on eggs of five different spider mite species deposited on both their laboratory-rearing plant and cherry, on which all five spider mite species developed well. The developmental periods of immature N. californicus females and males were significantly affected by the prey species they fed on, but not by the plants. No difference was found between males and females. The developmental period was shorter on eggs of two Tetranychus species than on eggs of Panonychus ulmi. Immature females had a higher predation rate than immature males. Preoviposition period, oviposition period and the number of eggs laid per female were not significantly affected by either the plants or the type of prey eggs. The postoviposition period and total adult longevity were shorter on eggs of P. ulmi than of the other four prey species, but there was no effect of plant substrate. The postoviposition period of the Spical strain was much longer than that of other N. californicus strains or other predatory mite species: the postoviposition period of the Spical strain was more than three times longer than the oviposition period, accounting for more than 75% of the total adult longevity. This suggests that the females need multiple mating to reach full egg load, but this remains to be tested. Total consumption by N. californicus adults was lower for eggs of P. ulmi than for eggs of the other four species, apparently because of the shorter postoviposition period when fed on eggs of P. ulmi. The intrinsic rates of natural increase (r _m) on the rearing plant did not differ among prey species, whereas those on cherry were significantly different: the value was higher on Tetranychus urticae eggs than on eggs of other species. Only when N. californicus fed on T. urticae eggs, the r _m-values were significantly different between the rearing plant and cherry (higher on cherry). Thus, the Spical strain of N. californicus could feed on eggs of all five spider mite species, deposited on a variety of plants with similar r _m-values, suggesting that it could be successfully used to control spider mites in orchards and various crop fields of Japan.