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 .     

Bioinsecticide-Predator Interactions: Azadirachtin Behavioral and Reproductive Impairment of the Coconut Mite Predator Neoseiulus baraki

Synthetic pesticide use has been the dominant form of pest control since the 1940s. However, biopesticides are emerging as sustainable pest control alternatives, with prevailing use in organic agricultural production systems. Foremost among botanical biopesticides is the limonoid azadirachtin, whose perceived environmental safety has come under debate and scrutiny in recent years. Coconut production, particularly organic coconut production, is one of the agricultural systems in which azadirachtin is used as a primary method of pest control for the management of the invasive coconut mite, Aceria guerreronis Keifer (Acari: Eriophyidae). The management of this mite species also greatly benefits from predation by Neoseiulus baraki (Athias-Henriot) (Acari: Phytoseiidae). Here, we assessed the potential behavioral impacts of azadirachtin on the coconut mite predator, N. baraki. We explored the effects of this biopesticide on overall predator activity, female searching time, and mating behavior and fecundity. Azadirachtin impairs the overall activity of the predator, reducing it to nearly half; however, female searching was not affected. In contrast, mating behavior was compromised by azadirachtin exposure particularly when male predators were exposed to the biopesticide. Consequently, predator fecundity was also compromised by azadirachtin, furthering doubts about its environmental safety and selectivity towards biological control agents.     

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.     

Comparative demography and diet breadth of Brazilian and African populations of the predatory mite Neoseiulus baraki,a candidate for biological control of coconut mite

Neoseiulus baraki Athias-Henriot (Phytoseiidae) is one of the few predators associated with the coconut mite Aceria guerreronis Keifer (Eriophyidae), the most damaging pest of coconut fruits in the Americas, Africa and more recently in Oman, Sri Lanka and parts of India. As Brazil is presently considered the putative origin of A. guerreronis, a large effort is presently underway to develop a classical biological control strategy for this pest in Africa and Asia. In this study, we investigated the life history of a Brazilian (NbBr) and a Beninese (NbBe) population of N. baraki on prey and non-prey diets under laboratory conditions (25 ± 1 °C 70–90% RH and 12:12 h L:D). Both populations were able to complete juvenile development and reproduce when feeding on A. guerreronis, Tetranychus urticae Koch eggs—a prey commonly used in the maintenance of phytoseiid mite colonies—and maize pollen. The two predators developed faster on A. guerreronis than on any other diet. The longest developmental time was recorded for NbBe on castor bean pollen (12.3 days), which also was not suitable at all for the development of NbBr. The longest developmental time of NbBr was 8.94 days on T. urticae eggs, whereas NbBe needed only 5.86 days to develop from eggs to adult stage on the same diet. For both populations, oviposition rate and longevity as well as demographic parameters were most favorable on A. guerreronis, the target prey. Intrinsic rate of natural increase (r_m) and net reproductive rate (R_o) were significantly higher for NbBr (0.19 and 24.9) than for NbBe (0.16 and 18.0). Taken together, the life history data from this study predict that NbBr is a more specialized and efficient predator of A. guerreronis compared with NbBe. The ability of the latter to utilize alternative food types, however, predicts that it would be able to persist longer in coconut habitat in the absence of its primary prey A. guerreronis. Implications for the implementation of a sustainable control strategy against A. guerreronis are discussed.     

Residual bioassay to assess the toxicity of Acaricides against Aceria guerreronis (Acari: Eriophyidae) under laboratory conditions

Aceria guerreronis Keifer (Acari: Eriophyidae) is considered a major pest of the coconut (Cocos nucifera L.), and the use of pesticides is the current method to control it. However, no standard toxicological tests exist to select and assess the efficiency of molecules against the coconut mite. The aim of this study was to develop a methodology that allows for the evaluation of the relative toxicity of acaricides to A. guerreronis through rapid laboratory procedures. We confined A. guerreronis on arenas made out of coconut leaflets and tested two application methods: immersing the leaf fragments in acaricides and spraying acaricides on the leaf fragments under a Potter spray tower. In the latter application method, we sprayed leaf fragments both populated with and devoid of mites. We evaluated the comparative toxicity of two populations (Itamaracá and Petrolina, Pernambuco, Brazil) by spraying on leaflets without mites and submitted the mortality data to probit analysis after 24 h of exposure. No difference was observed in the LC50, regardless of whether the leaflets were immersed or sprayed with acaricide (abamectin, chlorfenapyr or fenpyroximate). The toxicity of chlorfenapyr and fenpyroximate did not differ, irrespective of whether it was applied directly to the leaflet or to the mite; however, the toxicity of abamectin was higher when applied directly to the mite. Chlorpyrifos and abamectin toxicities were lower for the Petrolina population than for the Itamaracá population. Immersing and spraying coconut leaflets can be used to assess the mortality of A. guerreronis under laboratory conditions.     

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.     

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.     

Status of Aceria guerreronis Keifer (Acari: Eriophyidae) as a Pest of Coconut in the State of Sao Paulo, Southeastern Brazil

The coconut mite, Aceria guerreronis Keifer, is one of the main pests of coconut palms (Cocos nucifera) in northeastern Brazil. The objective of this study was to evaluate the levels of the coconut mite and other mites on coconut palms in the state of S?o Paulo and to estimate the possible role of predatory mites in the control of this pest. The effect of cultivated genotypes and sampling dates on the mite populations was also estimated. We sampled attached fruits, leaflets, inflorescences, and fallen fruits. The coconut mite was the main phytophagous mite found on attached and fallen fruits, with average densities of 110.0 and 20.5 mites per fruit, respectively. The prevalent predatory mites on attached and fallen fruits were Proctolaelaps bulbosus Moraes, Reis & Gondim Jr. and Proctolaelaps bickleyi (Bram), both Melicharidae. On leaflets, the tenuipalpids Brevipalpus phoenicis (Geijsks) and Tenuipalpus coyacus De Leon and the tetranychid Oligonychus modestus (Banks) were the predominant phytophagous mites. On both leaflets and inflorescences, the predominant predatory mites belonged to the Phytoseiidae. Neoseiulus baraki (Athias-Henriot) and Neoseiulus paspalivorus (De Leon), predators widely associated with the coconut mite in northeastern Brazil and several other countries, were not found. The low densities of the coconut mite in S?o Paulo could be related to prevailing climatic conditions, scarcity of coconut plantations (hampering the dispersion of the coconut mite between fields), and to the fact that some of the genotypes cultivated in the region are unfavorable for its development.     

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.     

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).     

Distribution of <Emphasis Type="Italic">Aceria guerreronis</Emphasis> and <Emphasis Type="Italic">Neoseiulus baraki</Emphasis> among and within coconut bunches in northeast Brazil

Aceria guerreronis Keifer (Acari: Eriophyidae) is considered a major pest of coconut in many countries in the Americas, Africa and parts of Asia. Neoseiulus baraki Athias-Henriot (Acari: Phytoseiidae) is one of the predatory mites most commonly found in association with A. guerreronis in parts of northeast Brazil. The objective of this work was to study the distribution of A. guerreronis and N. baraki among and within coconut bunches. The hypothesis was tested that A. guerreronis and N. baraki are homogenously distributed over the fruits in a bunch, independent of the fruits’ age and position. Five collections of bunches, each corresponding to leaves 12–16 from apex (about 2–6 month-old), were conducted in each of three fields in northeastern Brazil, from February to October, 2007. A total of 1,986 fruits were examined. The number of mites, the percentage of fruits hosting them and the level of damage caused by A. guerreronis were evaluated. The highest density of A. guerreronis was observed on fruits of bunch 4 whereas the highest density of N. baraki was observed on bunch 5. Considering all fruits together, no significant differences were observed between densities of either A. guerreronis or N. baraki among the basal, median and apical thirds of the bunches. In younger bunches, fruits of the apical region tend to have lower densities of both mites than fruits of the basal region. This pattern, in association with a similar pattern for the percentage of fruits hosting N. baraki, suggests that the predator initially reaches the basal bunch region, from where it moves to the apical region. The results of the present study suggest that the pest population reduction in bunches older than bunch 4 could be due to (1) an effect of the predator, (2) reduction of the proportion of undamaged tissues amenable to attack, and/or (3) less favorable characteristics of the fruits to attack by A. guerreronis, as indicated by their increasing lignin content as they get older.     

Toxicity of acaricides to Raoiella indica and their selectivity for its predator, Amblyseius largoensis (Acari: Tenuipalpidae: Phytoseiidae)

Raoiella indica Hirst (Acari: Tenuipalpidae) is considered a pest of coconut palm in Asia and the Middle East. This mite was recently introduced in the Americas, where it spread to several countries and expanded its range of hosts, causing heavy losses to coconut and banana production. The phytoseiid mite Amblyseius largoensis (Muma) is one of the predators most often encountered in coconut palms. Because the current prospects for the control of R. indica in the New World indicate the use of acaricides and the management of their natural enemies, the objective of this study was to evaluate the toxicity of selected acaricides to R. indica and the selectivity (i.e., toxicity to the predator relative to toxicity to the prey) for A. largoensis. Assays were performed by the immersion of banana leaf discs in acaricide solutions, followed by the placing of adult females of the pest or predator on the discs. Mortality of the mites was evaluated after 24 h, and the data obtained were subjected to probit analysis. Abamectin, fenpyroximate, milbemectin and spirodiclofen were the products most toxic to R. indica adults, whereas fenpyroximate and spirodiclofen were the most selective for A. largoensis.     

Plant structural changes due to herbivory: Do changes in <Emphasis Type="Italic">Aceria</Emphasis>-infested coconut fruits allow predatory mites to move under the perianth?

Being minute in size, eriophyoid mites can reach places that are small enough to be inaccessible to their predators. The coconut mite, Aceria guerreronis, is a typical example; it finds partial refuge under the perianth of the coconut fruit. However, some predators can move under the perianth of the coconut fruits and attack the coconut mite. In Sri Lanka, the phytoseiid mite Neoseiulus baraki, is the most common predatory mite found in association with the coconut mite. The cross-diameter of this predatory mite is c. 3 times larger than that of the coconut mite. Nevertheless, taking this predator’s flat body and elongated idiosoma into account, it is—relative to many other phytoseiid mites—better able to reach the narrow space under the perianth of infested coconut fruits. On uninfested coconut fruits, however, they are hardly ever observed under the perianth. Prompted by earlier work on the accessibility of tulip bulbs to another eriophyoid mite and its predators, we hypothesized that the structure of the coconut fruit perianth is changed in response to damage by eriophyoid mites and as a result predatory mites are better able to enter under the perianth of infested coconut fruits. This was tested in an experiment where we measured the gap between the rim of the perianth and the coconut fruit surface in three cultivars (‘Sri Lanka Tall’, ‘Sri Lanka Dwarf Green’ and ‘Sri Lanka Dwarf Green × Sri Lanka Tall’ hybrid) that are cultivated extensively in Sri Lanka. It was found that the perianth-fruit gap in uninfested coconut fruits was significantly different between cultivars: the cultivar ‘Sri Lanka Dwarf Green’ with its smaller and more elongated coconut fruits had a larger perianth-fruit gap. In the uninfested coconut fruits this gap was large enough for the coconut mite to creep under the perianth, yet too small for its predator N. baraki. However, when the coconut fruits were infested by coconut mites, the perianth-rim-fruit gap was not different among cultivars and had increased to such an extent that the space under the perianth became accessible to the predatory mites.     

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.     

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.     

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.     

Females as intraguild predators of males in cross-pairing experiments with phytoseiid mites

Studies on intraguild interactions between phytoseiid species have shown that intraguild predation occurs and is most commonly manifested as adult females of one species feeding on juveniles of another. Whether such intraguild interactions can also occur between adult females of one species and adult males of another, is not known. Herein, we report on intraguild interactions between adults of the two sexes in cross-pairing experiments involving three related phytoseiid species (Neoseiulus paspalivorus, N. baraki and N. neobaraki) that are potential candidates for controlling the coconut mite Aceria guerreronis, a serious pest of coconut palms in tropical countries. For comparative reasons, the experiments were repeated with larvae instead of males, and with only males or only females of two different species together. In the presence of an ample supply of prey, females of N. neobaraki never fed on individuals of their own species, yet appeared to be very aggressive against males, as well as larvae of the other two phytoseiid species. They also fed on females of N. paspalivorus, but rarely on females of N. baraki. Males of N. neobaraki did not suffer mortality when together with females of either of the two other phytoseiid species. Males of N. baraki did not suffer predation from females of N. paspalivorus, but males of N. paspalivorus suffered some mortality (15 %) from N. baraki females. Larvae of each of the three species were vulnerable to intraguild predation by heterospecific adult females, except for N. neobaraki larvae when together with N. baraki females. The absence or presence of intraguild predation is largely explained by the size ratios of the individuals that were put together: large individuals feed on smaller ones, but never the reverse. For each sex, size declines in the following order: N. neobaraki > N. baraki > N. paspalivorus. Moreover, for each species, females are larger than males and males are larger than larvae. Strikingly, however, females did not kill males and larvae of their own species. We propose that niche competition between related phytoseiid species is not only determined by intraguild predation on heterospecific larvae, but also by imposing great mortality on males from the intraguild prey because phytoseiid females being pseudo-arrhenotokous require insemination to produce offspring of both sexes.     

Control effects and sublethal effects of four pesticides on Atheloca bondari (Lepidoptera: Pyralidae) caterpillars

Atheloca bondari Heinrich is an opportunistic lepidopteran that uses necrosis caused by the mite Aceria guerreronis Keifer, the most important pest of the coconut palm, to access the meristematic region of coconuts. Because of this moth-mite positive association, pesticides used to control A. guerreronis (abamectin, azadirachtin, fenpyroximate, and pyridaben) may impact A. bondari caterpillar behavior and/or survival. Thus, we used three methodologies (toothpick, triangle, and mesocarp fragment) to evaluate mortality caused by abamectin, the most commonly used pesticide to control A. guerreronis. The toothpick method proved to be suitable for toxicity tests of A. bondari caterpillars. Subsequently, the mortality caused by these four pesticides was evaluated, and abamectin caused 100% mortality in A. bondari caterpillars. Abamectin showed higher toxicity than the other pesticides to A. bondari caterpillars, with LC₅₀ and LC₉₅ values of 1.35 and 3.64 mg/L, respectively. The preference test showed that A. bondari caterpillars infested pesticide-treated fruits in the same proportion as untreated fruits. In the behavioral test, A. bondari caterpillars showed lower locomotor speed when exposed to surfaces with abamectin, azadirachtin, and fenpyroximate residues. Our study presented that pesticides used to control A. guerreronis affect the behavior and survival of A. bondari caterpillars. We discuss how spraying these pesticides can indirectly control the population of A. bondari, reducing the impact of this moth on coconut production, and modifying the importance of this species as a pest of coconut palm.     

Dispersal strategies of Aceria guerreronis (Acari: Eriophyidae), a coconut pest

The dispersal of plant-feeding mites can occur involuntarily, through transportation of infested plant parts, or voluntarily, by walking to new plant parts or to suitable spots where biotic (phoresis) or abiotic (wind, agricultural tools, etc.) factors carry them over long distances. Elucidating the dispersal mechanisms of the coconut mite, Aceria guerreronis Keifer, is important for understanding the process of colonization of new fruits of a same or different plants, essential for the improvement of control strategies of this serious coconut pest. Thus, the objective of this work was to investigate the voluntary dispersal mechanisms of this mite. The hypothesis that the coconut mite disperses by walking, phoresis or wind were tested. The coconut mite was shown to be able to walk short distances between fruits of the same bunch or between bunches of the same plant. Phoresis on insects of the orders Hymenoptera (Apidae), Coleoptera (Curculionidae) and Lepidoptera (Phycitidae) was evaluated in the laboratory and in the field. Although in the laboratory mites were shown to be able to climb onto honeybees, field investigations failed to show these insects as important carriers of the pest, corroborating findings of previous works; however, both laboratory and field investigations suggested the curculionid Parisoschoenus obesulus Casey to be able to transport the coconut mite between plants. Similarly, laboratory and field investigations suggested wind to be important in the dispersal of the coconut mite between plants.     

Olfactory response of predatory mites to vegetative and reproductive parts of coconut palm infested by <Emphasis Type="Italic">Aceria guerreronis</Emphasis>

The phytophagous mite Aceria guerreronis Keifer is an important pest of coconut worldwide. A promising method of control for this pest is the use of predatory mites. Neoseiulus baraki (Athias-Henriot) and Proctolaelaps bickleyi Bram are predatory mites found in association with A. guerreronis in the field. To understand how these predators respond to olfactory cues from A. guerreronis and its host plant, the foraging behavior of the predatory mites was investigated in a Y-tube olfactometer and on T-shaped arenas. The predators were subjected to choose in an olfactometer: (1) isolated parts (leaflet, spikelet or fruit) of infested coconut plant or clean air stream; (2) isolated parts of non-infested or infested coconut plant; and (3) two different plant parts previously shown to be attractive. Using T-shaped arenas the predators were offered all possible binary combinations of discs of coconut fruit epidermis infested with A. guerreronis, non-infested discs or coconut pollen. The results showed that both predators were preferred (the volatile cues from) the infested plant parts over clean air. When subjected to odours from different infested or non-infested plant parts, predators preferred the infested parts. Among the infested plant parts, the spikelets induced the greatest attraction to predators. On the arenas, both predators preferred discs of coconut fruits infested with A. guerreronis over every other alternative. The results show that both predators are able to locate A. guerreronis by olfactory stimuli. Foraging strategies and implications for biological control are discussed.