Limitations of <Emphasis Type="Italic">Neoseiulus baraki</Emphasis> and <Emphasis Type="Italic">Proctolaelaps bickleyi</Emphasis> as control agents of <Emphasis Type="Italic">Aceria guerreronis</Emphasis>

Several predatory mites have been found in association with the coconut mite, Aceria guerreronis Keifer, in northeast Brazil. However, the latter still causes damage to coconut in that region. The objectives of this work were to compare the frequencies of occurrence of Neoseiulus (Phytoseiidae) and Proctolaelaps (Melicharidae) species on standing and aborted coconuts in coastal Pernambuco State, northeast Brazil and to analyze their possible limitations as control agents of the coconut mite, based on evaluations of the restrictions they may have to access the microhabitat inhabited by the pest and their functional and reproductive responses to increasing densities of the latter. Neoseiulus baraki (Athias-Henriot) was found mostly on standing coconuts whereas Proctolaelaps bickleyi (Bram) was found mostly on aborted coconuts. Measurements of the entrance to the microhabitat occupied by the coconut mite, between the bracts and the subjacent fruit surface, showed that this different pattern of predator prevalence could be related to predator sizes, although other environmental factors could not be disregarded. Progressively higher predation rate of N. baraki was observed up to an experimental density that corresponded to 1,200 coconut mites per fruit, which is close to the average number determined in northeast Brazil, reducing slightly afterwards. Predation rate of P. bickleyi reduced consistently but slightly with increasing prey densities, but in absolute values, rates were always much higher than determined for N. baraki. The excessively high killing capacity of P. bickleyi, probably related to its high feeding requirement, may be detrimental in terms of stability. In fact, such high requirement for food suggests that P. bickleyi might not have a strong relation with the coconut mite and that the latter may not be its main food source under natural conditions. It is concluded that body sizes of both predators and the exceedingly high feeding requirement of P. bickleyi may limit their performance as control agents of the coconut mite.     

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

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

Life history of the predatory mites <Emphasis Type="Italic">Neoseiulus paspalivorus</Emphasis> and <Emphasis Type="Italic">Proctolaelaps bickleyi</Emphasis>, candidates for biological control of <Emphasis Type="Italic">Aceria guerreronis</Emphasis>

The eriophyoid mite Aceria guerreronis Keifer (Eriophyidae), commonly called the coconut mite, is a key pest of coconut fruits. Surveys conducted on coconut palms in Brazil revealed the predatory mites Neoseiulus paspalivorus DeLeon (Phytoseiidae) and Proctolaelaps bickleyi Bram (Ascidae) as the most commonly associated natural enemies of A. guerreronis on coconut fruits. However, virtually nothing is known about the life history of these two predators. We conducted laboratory experiments at 25 ± 0.1°C, 70–90% RH and 12:12 h L:D photoperiod to determine the life history characteristics of the two predatory mites when feeding on A. guerreronis and other potential food sources present on coconut fruits such as Steneotarsonemus furcatus DeLeon (Tarsonemidae), coconut pollen and the fungus Rhizopus cf. stolonifer Lind (Mucoraceae). In addition, the two-spotted spider mite Tetranychus urticae Koch (Tetranychidae) was tested for its suitability as prey. Both predators, N. paspalivorus and P. bickleyi, thrived on A. guerreronis as primary food source resulting in shorter developmental time (5.6 and 4.4 days, respectively), higher oviposition rate (1.7 and 7.0 eggs/female/day, respectively) and higher intrinsic rate of increase (0.232 and 0.489 per female/day, respectively) than on any other diet but were unable to develop or lay eggs when fed T. urticae. Coconut pollen and S. furcatus were adequate alternative food sources for N. paspalivorus and Rhizopus for P. bickleyi. We discuss the relevance of our findings for natural and biological control of the coconut mite A. guerreronis.     

Life history of <Emphasis Type="Italic">Proctolaelaps bulbosus</Emphasis> feeding on the coconut mite <Emphasis Type="Italic">Aceria guerreronis</Emphasis> and other possible food types occurring on coconut fruits

Aceria guerreronis Keifer (Acari: Eriophyidae) is a major pest of coconut fruits (Cocos nucifera L.) in many countries of the Americas, Africa, and parts of Asia. Considerable attention has been given to studies of biological control agents of A. guerreronis. Proctolaelaps bulbosus Moraes, Reis and Gondim Jr. is a predator recently discovered in association with A. guerreronis. Nothing is known about its biology. The aim of this study was to determine suitable food sources for P. bulbosus, among items commonly found on coconut fruits, including A. guerreronis. Food sources evaluated included the mites A. guerreronis, Steneotarsonemus concavuscutum Lofego and Gondim Jr., and Tyrophagus putrescentiae (Schrank), the fungus Rhizopus aff. stolonifer (Ehrenb.) Vuill and coconut pollen; the mite Tetranychus urticae Koch was also included in the assessments, for being a commonly used prey for mass production and laboratory rearing of predatory mites. Proctolaelaps bulbosus was able to develop up to adulthood when fed A. guerreronis, R. aff. stolonifer and T. putrescentiae. It had the highest population growth rates when feeding on the former (R _o = 17.5; r _m = 0.392). These results indicate that A. guerreronis is the most suitable food for P. bulbosus among the possible food sources found on coconut fruits and that P. bulbosus can survive in the absence of eriophyid using R. aff. stolonifer as a food source.     

Population dynamics of <Emphasis Type="Italic">Aceria guerreronis</Emphasis> (Acari: Eriophyidae) and its predatory mite, <Emphasis Type="Italic">Neoseiulus baraki</Emphasis> (Acari: Phytoseiidae) in two coconut growing areas in Sri Lanka

Densities of coconut mite, Aceria guerreronis Keifer (Acari: Eriophyidae) and its predatory mite, Neoseiulus baraki Athias-Henriot (Acari: Phytoseiidae) were monitored on coconut fruits in two coconut mite infested areas, Kalpitiya and Madurankuliya, in Sri Lanka, over a period of 3 years and were compared with local rainfall records. Significant differences in A. guerreronis densities were observed among years and months of the year. Rainfall (amount and frequency, i.e. the total number of days with rainfall of >5 mm) was not significantly correlated with the variation of A. guerreronis densities. But the drought length (i.e. the number of days without rainfall of >5 mm) significantly influenced A. guerreronis densities. Generally, peak densities of A. guerreronis were observed during February–March and June–September in both areas. The differences in the N. baraki densities were significantly different between the two areas and among the 3 years but not among months of the year. Although the amount of rainfall was not significantly correlated with the population densities of N. baraki, frequency of rainfall showed a negative significant correlation and drought length showed a positive significant correlation with the population densities. The results of this experiment indicated that the application of control methods for A. guerreronis may be more advantageous if they are carried out at the onset and during the dry seasons.     

Chemosensory cues of predators and competitors influence search for refuge in fruit by the coconut mite <Emphasis Type="Italic">Aceria guerreronis</Emphasis>

Organisms are adapted to recognize environmental cues that can provide information about predation risk or competition. Non-vagrant eriophyoid mites mainly avoid predation by using habitats that are difficult for predators to access (galls or confined spaces in plants) such as the meristematic region of the coconut fruit, which is inhabited by the phytophagous mites Aceria guerreronis and Steneotarsonemus concavuscutum. The objective of this study was to investigate the response of A. guerreronis to cues from the predators Neoseiulus baraki and Amblyseius largoensis in coconut fruits, cues from conspecifics (A. guerreronis injured) and cues from the phytophage S. concavuscutum. The test was carried out through the release of about 300 A. guerreronis on coconut fruits previously treated with cues from predators, conspecific or heterospecific phytophagous. We also observed the walking behaviour of A. guerreronis exposed to the same chemical cues using a video tracking system. The infestation of fruits by A. guerreronis was greater in the presence of predator cues and reduced in the presence of S. concavuscutum cues, but cues from injured conspecifics did not interfere in the infestation process. In addition, the cues also altered the walking parameters of A. guerreronis: it walked more in response to cues from predators and the heterospecific phytophage. Aceria guerreronis spent more time in activity in the treatments with clues than in the control treatment. These results suggest that A. guerreronis recognizes cues from predators and competitors and modifies its behaviour to increase its fitness.     

Toxicity of some insecticides to <Emphasis Type="Italic">Tetranychus urticae</Emphasis>, <Emphasis Type="Italic">Neoseiulus californicus</Emphasis> and <Emphasis Type="Italic">Tydeus californicus</Emphasis>

Three mite species are frequently found on vegetable crops in Italy: the pest Tetranychus urticae Koch (Acari: Tetranychidae), the predator Neoseiulus californicus (McGregor) (Acari: Phytoseiidae) and the unspecialised feeder Tydeus californicus (Banks) (Acari: Tydeidae). In laboratory trials, the direct and residual effects of six insecticides recommended for the control of aphids, whiteflies and thrips in vegetable crops, (Biopiren® plus (pyrethrins), Confidor® (imidacloprid), Oikos® (azadirachtin), Plenum® (pymetrozine), Naturalis® (Beauveria bassiana) and Rotena® (rotenone)), were evaluated for the three mite species. All the products affected the mites and their effect was often favourable towards T. urticae and unfavourable towards N. californicus and T. californicus. Rotenone was more toxic to eggs than females of T. urticae. It was highly toxic to N. californicus and caused the death of all treated females of T. californicus. Pyrethrins and imidacloprid increased T. urticae fecundity, but decreased fecundity of N. californicus. Imidacloprid decreased T. californicus fecundity more than pyrethrins. Beauveria bassiana was not toxic to T. urticae and T. californicus, but induced high mortality in the progeny of treated females of N. californicus. Azadirachtin and pymetrozine were the least toxic to T. urticae and N. californicus, but decreased production of larvae in T. californicus. Implications for integrated pest management on vegetables are discussed.     

Acaricide toxicity and synergism of fenpyroximate to the coconut mite predator Neoseiulus baraki

The non-target effects of acaricides, used against Aceria guerreronis (Acari: Eriophyidae) the coconut mite, on its natural enemies are not known. Therefore we assessed the susceptibility of A. guerreronis and its predator Neoseiulus baraki (Acari: Phytoseiidae) to selected acaricides, their impact on N. baraki rate of increase, and the synergism of fenpyroximate towards this predator. Toxicity bioassays and synergism of fenpyroximate (with piperonyl butoxide, triphenyl phosphate and diethyl maleate) were performed by spraying the mites under a Potter tower. The instantaneous rate of increase (r _i ) was calculated ten days after spraying the predator. Chlorfenapyr and fenpyroximate were selective (both LC₅₀ and LC₉₀ were higher for N. baraki than for A. guerreronis) and did not affect the predator r _i . Only piperonyl butoxide significantly synergized fenpyroximate suggesting the involvement of cytochrome P450 monooxygenase in the N. baraki tolerance. Fenpyroximate and chlorfenapyr are promising agents for managing A. guerreronis in combination with N. baraki because both are selective and do not affect its predator r _i .     

The coconut mite, Aceria guerreronis, in Benin and Tanzania: occurrence, damage and associated acarine fauna

The coconut mite Aceria guerreronis (Eriophyidae) is considered the most important pest of coconut fruits in Africa; however, quantitative knowledge about its distribution and abundance is lacking. We conducted four diagnostic surveys—three in Southern Benin and one along the coast of Tanzania—to determine the distribution of A. guerreronis and the severity of its damage to coconut fruits, as well as the diversity and abundance of other associated mites and potential natural enemies. Aceria guerreronis was found in all visited plantations with the percentage of damaged fruits varying considerably among plantations—67–85% in Benin and 43–81% in Tanzania. Overall, 30–40% of the fruit surfaces were damaged by A. guerreronis. Damage severity increased with fruit age and negatively affected fruit weight of 7- to 12-months-old fruits. Aceria guerreronis was by far the most abundant mite on coconut fruits but its abundance depended on fruit age. The highest densities of A. guerreronis were observed on 3- to 4-months-old fruits. Neocypholaelaps sp. (Ameroseiidae) was the most abundant mite on inflorescences. Three species of predatory mites (Phytoseiidae)—Neoseiulus baraki, N. neobaraki and N. paspalivorus—were the most commonly found predatory mites beneath the coconut bracts in association with A. guerreronis. Neoseiulus neobaraki was the prevailing predator in Tanzania while N. paspalivorus was the most frequent predator in Benin. Other mites found beneath the bracts were the herbivore Steneotarsonemus furcatus (Tarsonemidae) and the detritivore and fungivore Tyrophagus putrescentiae (Acaridae).     

Genetic diversity in <Emphasis Type="Italic">Hirsutella thompsonii</Emphasis> isolates based on random amplified polymorphic DNA analysis

Hirsutella thompsonii Fisher is a host-specific fungal pathogen of the diverse group of arthropods known as the Acari. It particularly affects eriophyid mites, and the identification of its isolates is a difficult task due to its pleomorphic nature. Seven isolates of H. thompsonii var. thompsonii and H. thompsonii var. synnematosa collected from various agro-climatic regions of India were subjected to PCR analysis using random decamer primers to differentiate between them. Random amplified polymorphic DNA analysis revealed that all of the isolates from the citrus rust mite, Phyllocoptruta oleivora Ashmead (Acari: Eriophyidae), clustered together, with the exception of one, HtCRMB. The only isolate of H. thompsonii from Aceria guerreronis keifer (Acari: Eriophydae), HtPDBC, clustered separately.     

Life history of the predatory mite <Emphasis Type="Italic">Phytoseiulus fragariae</Emphasis> on <Emphasis Type="Italic">Tetranychus evansi</Emphasis> and <Emphasis Type="Italic">Tetranychus urticae</Emphasis> (Acari: Phytoseiidae,Tetranychidae) at five temperatures

Tetranychus evansi Baker and Pritchard and Tetranychus urticae Koch (Acari: Tetranychidae) are important pests of Solanaceae in many countries. Several studies have demonstrated that T. urticae is an acceptable prey to many predatory mites, although the suitability of this prey depends on the host plant. T. evansi, has been shown to be an unfavorable prey to most predatory mites that have been tested against it. The predator Phytoseiulus fragariae Denmark and Schicha (Acari: Phytoseiidae) has been found in association with the two species in Brazil. The objective of this work was to compare biological parameters of P. fragariae on T. evansi and on T. urticae as prey. The study was conducted under laboratory conditions at 10, 15, 20, 25 and 30°C. At all temperatures, survivorship was lower on T. evansi than on T. urticae. No predator reached adulthood at 10°C on the former species; even on the latter species, only about 36% of the predators reached adulthood at 10°C. For both prey, in general, duration of each life stage was shorter, total fecundity was lower and intrinsic rate of population increase (r _m ) was higher with increasing temperatures. The slower rate of development of P. fragariae on T. evansi resulted in a slightly higher thermal requirement (103.9 degree-days) on that prey than on T. urticae (97.1 degree-days). The values of net reproduction rate (R ₀), intrinsic rate of increase (r _m ) and finite rate of increase (λ) were significantly higher on T. urticae, indicating faster population increase of the predator on this prey species. The highest value of r _m of the predator was 0.154 and 0.337 female per female per day on T. evansi and on T. urticae, respectively. The results suggested that P. fragariae cannot be considered a good predator of T. evansi.     

Biological control of the citrus red mite <Emphasis Type="Italic">Panonychus</Emphasis><Emphasis Type="Italic">citri</Emphasis> by the predator mite <Emphasis Type="Italic">Typhlodromus athiasae</Emphasis> on two citrus cultivars under greenhouse conditions

This study examined the efficacy of the predatory mite Typhlodromus athiasae Porath and Swirski (Acari: Phytoseiidae) as a biological control agent of the citrus red mite Panonychus citri (McGregor) (Acari: Tetranychidae) on seedlings of Washington and Valencia citrus cultivars at 1:10, 1:20 and 1:40 predator:prey release ratios under greenhouse conditions. At predator:prey ratios of 1:10, significant reductions on P. citri populations were observed one week after release of T. athiasae, and populations remained at low levels thereafter. The highest mean numbers of P. citri were found in the third week on the Washington cultivar and in the fourth week on Valencia, in a control group with no predators. This study demonstrates the potential of T. athiasae to effectively control P. citri on Washington and Valencia cultivars under greenhouse conditions at predator:prey ratios of 1:10. However, T. athiasae was unable to control the citrus red mite populations when the predator:prey ratio was reduced to 1:40. We therefore recommend a release ratio of 1:10 for effective control of P. citri in greenhouses on seedlings of Washington and Valencia citrus.     

Acaricides impair prey location in a predatory phytoseiid mite

The use of predatory mites as the sole management tactic in biological control programmes frequently does not fully and reliably prevents damage of phytophagous mites on plants. Therefore, as an alternative, the integration of predatory mites with acaricides can provide more effective control of phytophagous mites than that of the predators only. However, for such integration, acaricides minimal negative impacts on predatory mites are required. In this study, we evaluated the sublethal effects of three acaricides on the foraging behaviour of Neoseiulus baraki (Athias‐Henriot) (Acari: Phytoseiidae) in a coconut production system. The acaricides were assessed for interference with the location of prey habitat using a Y‐tube olfactometer and for interference with the location of the prey colony within the habitat using a video‐tracking system. In addition to the choice of odour source, the time required and the distance walked to make the choice were assessed. The acaricides tested were abamectin, azadirachtin and fenpyroximate. The predatory mite preferred coconuts infested with the coconut mite Aceria guerreronis Keifer (Acari: Eriophyidae) over uninfested coconuts when not exposed to acaricides. However, when exposed to acaricides, the predator did not distinguish between infested and uninfested fruits. When exposed to abamectin, N. baraki spent more time resting and walked greater distances before making the choice of an odour source. Thus, the acaricides impair the ability of the predatory mite N. baraki to locate a prey habitat and to locate a prey within that habitat. The acaricides differentially affected prey foraging by interfering with odour perception.     

Rearing of coconut mite Aceria guerreronis and the predatory mite Neoseiulus baraki in the laboratory

A method was developed for the rearing of coconut mite, Aceria guerreronis Keifer (Acari: Eriophyidae), and its predatory mite Neoseiulus baraki (Athias-Henriot) (Acari: Phytoseiidae) on embryo culture seedlings of coconut (Cocos nucifera) in the laboratory. Seedlings in the ages of <2, 2–4 and 4–6 months were infested with 75 field-collected coconut mites and the population growth was determined up to six weeks after introduction. The populations of coconut mites increased exponentially up to five weeks after introduction and declined thereafter on seedlings of all ages with significant differences among the three groups of seedlings occurring over time. At week 5, a significantly higher mean number (±SE) of coconut mites (20,098 ± 3,465) was bred on 4–6-month-old seedlings than on smaller seedlings, and on the largest seedlings the numbers were highest at all time intervals, except at week 2. Neoseiulus baraki was reared on embryo culture seedlings of the three age groups infested with coconut mites, by introduction of five female deutonymphs and one male, three weeks after introducing coconut mites. Predator numbers progressed significantly over time, but the size of seedlings did not significantly influence the numbers. On all groups of seedlings, the mean number of N. baraki increased up to two weeks after introduction on to seedlings and then declined. Many coconut mites were successfully reared in the laboratory for a longer period by this method and it could also be used as an alternative method to rear N. baraki. Development of this method may contribute to the progress of studies on the biology and ecology of coconut mite and its interactions with natural enemies.     

Effects of <Emphasis Type="Italic">Euseius stipulatus</Emphasis> on establishment and efficacy in spider mite suppression of <Emphasis Type="Italic">Neoseiulus californicus</Emphasis> and <Emphasis Type="Italic">Phytoseiulus persimilis</Emphasis> in clementine

The two-spotted spider mite, Tetranychus urticae, is one of the most problematic phytophagous pests in Spanish clementine orchards. The most abundant predatory mites in this ecosystem are Euseius stipulatus, Phytoseiulus persimilis and Neoseiulus californicus. Euseius stipulatus is dominant but poorly adapted to utilize T. urticae as prey. It mainly persists on pollen and citrus red mite, Panonychus citri. A recent study suggested that the more efficacious T. urticae predators P. persimilis and N. californicus are negatively affected by lethal and non-lethal intraguild interactions with E. stipulatus. Here, we investigated the potential of N. californicus and P. persimilis to colonize and thrive on young clementine trees infested by T. urticae in presence and absence of E. stipulatus. Presence of E. stipulatus interfered with establishment and abundance of P. persimilis and negatively affected the efficacy of N. californicus in T. urticae suppression. In contrast, the abundance of E. stipulatus was not affected by introduction of a second predator. Trait-mediated effects of E. stipulatus changing P. persimilis and N. californicus behavior and/or life history were the most likely explanations for these outcomes. We conclude that superiority of E. stipulatus in intraguild interactions may indeed contribute to the currently observed predator species composition and abundance, rendering natural control of T. urticae in Spanish clementine orchards unsatisfactory. Nonetheless, stronger reduction of T. urticae and/or plant damage in the predator combination treatments as compared to E. stipulatus alone indicates the possibility to improve T. urticae control via repeated releases of N. californicus and/or P. persimilis.     

Control of <Emphasis Type="Italic">Bemisia tabaci</Emphasis> and <Emphasis Type="Italic">Frankliniella occidentalis</Emphasis> in cucumber by <Emphasis Type="Italic">Amblyseius swirskii</Emphasis>

Bemisia tabaci Genn. (Hemiptera: Aleyrodidae) and Frankliniella occidentalis (Thysanoptera: Thripidae) are major pests in greenhouse grown cucumber crops. Recently, Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae) was shown an effective biological control agent of both pests. Hence, perhaps both pests can be controlled simultaneously by this predator. However, with simultaneous infestation of both pests, synergistic effects, or interference could affect biological control and perhaps require changes in release rates of the predator. Thus, the aim of the present study was to evaluate different release rates of A. swirskii to control both pests under a worst case scenario of rapid immigration into a cucumber greenhouse. Two experiments were conducted, one simulating the influx of whiteflies alone (whitefly experiment) and the other immigration of whiteflies and thrips together (whitefly plus thrips experiment). Three treatments were compared in the whitefly experiment: (1) B. tabaci alone, (2) B. tabaci + 25 A. swirskii m⁻² and (3) B. tabaci + 75 A. swirskii m⁻². The high release rate was more effective than the low rate in controlling B. tabaci alone. The high rate was subsequently tested against B. tabaci and F. occidentalis for the whitefly and thrips experiment in which five treatments were compared: (1) B. tabaci alone, (2) F. occidentalis alone, (3) B. tabaci + 75 A. swirskii m⁻², (4) F. occidentalis + 75 A. swirskii m⁻² and (5) B. tabaci + F. occidentalis + 75 A. swirskii m⁻². This rate of A. swirskii controlled whiteflies and thrips either alone or together. Therefore, 75 A. swirskii m⁻² should be an adequate rate for controlling both pests either alone or simultaneously in cucumber greenhouses.     

Interspecific hybridization of <Emphasis Type="Italic">Cucumis anguria</Emphasis> and <Emphasis Type="Italic">C. zeyheri via</Emphasis> embryo-rescue

Embryo-rescue was used to facilitate interspecific hybridization of Cucumis anguria L. and C. zeyheri Sond. Embryos were excised from developing fruits at one week intervals for six weeks after hand pollination. Medium containing coconut water was the most suitable for initial germination, and a medium with ascorbic acid was the best for embryo development and plant recovery. Viable plants were obtained from embryos and these plants showed morphological characteristics different from both parents. The analysis of the leucine aminopeptidase (LAP) locus revealed three hybrid types, H1.1, H1.2 and H2.     

Experimental study on possible transmission of the bacterium <Emphasis Type="Italic">Erysipelothrix rhusiopathiae</Emphasis> to chickens by the poultry red mite, <Emphasis Type="Italic">Dermanyssus gallinae</Emphasis>

The vector potential of the poultry red mite, Dermanyssus gallinae De Geer (Acari: Dermanyssidae), in relation to chicken erysipelas was investigated under experimental conditions. Chickens were inoculated intramuscularly with the bacterium Erysipelothrix rhusiopathiae, and mites were allowed to feed on the inoculated chickens for 5 days. After 20 days of starvation, the mites were allowed to feed on healthy chickens to enable transmission of bacteria. Blood samples were collected from the birds and analysed for the presence of E. rhusiopathiae, and ELISA tests were performed for seropositivity. The internal presence of E. rhusiopathiae in the mites after feeding of inoculated birds was also investigated. It could not be demonstrated that mites take up and transmit E. rhusiopathiae under the experimental conditions described. However, since there are case reports as well as other in vitro studies indicating the potential of D. gallinae to act as a reservoir and potential vector for infections agents, we cannot exclude the possibility that the red poultry mite transmits E. rhusiopathiae between chickens under field conditions.     

Relationship between <Emphasis Type="Italic">Psoroptes cuniculi</Emphasis> and the Internal Bacterium <Emphasis Type="Italic">Serratia marcescens</Emphasis>

The bacterium Serratia marcescens isolated from surface-sterilised Psoroptes cuniculi was found sensitive to the antibiotic Amikacin. Mites placed in this antibiotic for 48–72 h and then washed by centrifugation were found to be alive and S. marcescens-free. Two experimental infestations were undertaken in order to verify the ability of the S. marcescens-free mites to infect and to give ear skin lesions in healthy rabbits and to evaluate the differential ability of the S. marcescens-free and S. marcescens-infected mites to give ear skin lesions. All rabbits were found to be infested, but only rabbits infested with S. marcescens-free mites presented crusts in their ears, whereas mites and/or eggs were only detected in the ear cerumen of all rabbits infested with S. marcescens-infected mites. S. marcescens was isolated only from P. cuniculi mites taken from these latter rabbits. Results indicate that P. cuniculi mites do not need S. marcescens to live and to be able to infest a healthy rabbit. In addition, S. marcescens was not isolated from eggs and newly born larvae of S. marcescens-infected P. cuniculi, demonstrating that in a population of P. cuniculi this bacterium is not transmitted transovarially.     

Predation by <Emphasis Type="Italic">Nesidiocoris tenuis</Emphasis> on <Emphasis Type="Italic">Bemisia tabaci</Emphasis> and injury to tomato

Tomato is the most important vegetable crop in Spain. The mirid bug Nesidiocoris tenuis (Reuter) commonly appears in large numbers in protected and open-air tomato crops where little or no broad-spectrum insecticides are used. Nesidiocoris tenuis is known to be a predator of whiteflies, thrips and several other pest species. However, it is also considered a pest because it can feed on tomato plants, causing necrotic rings on stems and flowers and punctures in fruits. Our objectives were to evaluate predation by N. tenuis on sweetpotato whitefly Bemisia tabaci Gennadius under greenhouse conditions and establish its relationship to N. tenuis feeding on tomato. Two different release rates of N. tenuis were compared with an untreated control (0, 1 and 4 N. tenuis plant⁻¹) in cages of 8 m². Significant reductions of greater than 90% of the whitefly population and correspondingly high numbers of N. tenuis were observed with both release rates. Regression analysis showed that necrotic rings on foliage caused by N. tenuis were best explained by the ratio of B. tabaci nymphs:N. tenuis as predicted by the equation y = 15.086x − 0.6359.