Blattisocius Tarsalis Research Articles

Postharvest Biological Control of Guatemalan Potato Moth, Tecia solanivora, by Trichogramma euproctidis and Blattisocius tarsalis

Tecia solanivora (Povolný 1973), is a quarantine pest in Europe. Identified in Guatemala in the 1970s, it spread throughout Central and South America, reaching the Canary Islands in 1999 and mainland Spain in 2015. The pest has caused prohibitive economic losses both in the field and in storage, where losses can reach 100%. In the absence of approved chemical treatments, the use of an egg predatory mite, Blattisocius tarsalis (Berlese 1918), and the egg parasitoid, Trichogramma euproctidis (Girault 1911), is being studied for use in storage. Previous laboratory studies have confirmed their potential for use in non-refrigerated stores, typically between 15 and 20 °C. In the present work, we compared the efficacy of both natural enemies under semi-storage conditions. We observed that while both T. euproctidis and B. tarsalis reduced the T. solanivora populations (with an efficacy of 82.95 ± 7.32% and 49.06 ± 2.69%, respectively) and the number of mites per tuber, only B. tarsalis resulted in undamaged tubers (65%). For this reason, the mite was selected and tested in storage conditions, obtaining promising results in the protection of infested tubers, suggesting potential for further investigation, adaptation and standardization of its use in real conditions.

Evaluation of the Egg Predator Blattisocius tarsalis (Mesostigmata: Blattisociidae) for the Biological Control of the Potato Tuber Moth Tecia solanivora under Storage Conditions

Tecia solanivora is the most prevalent pest causing damage to potato crops in fields in the Canary Islands, but even more so in the postharvest storage period. However, currently, there are no authorised chemical insecticides for potato storage facilities. Analysis of the viability of the predator mite Blattisocius tarsalis as a biological control agent for this moth was carried out. A study of the temperature effect showed B. tarsalis maintains predatory capacity in the range of 10–27 °C. Though predatory activity increases with temperature, no differences in mortality rates were observed between 10 and 20 °C (33.52 ± 2.44 and 40.14 ± 3.54% efficacy rate, respectively), nor between 25 and 27 °C (59.26 ± 4.59 and 75.19 ± 4.64% efficacy rate, respectively). Under microcosm conditions, at low pest infestation (10 eggs), B. tarsalis achieved the highest mortality of eggs at a density of 5 mites, with an efficacy rate of 91.67 ± 8.33%. At high infestation levels (50 eggs), maximum mortality was achieved with a density of 10 mites and efficacy of 98.52 ± 1.48%. The choice-assay showed no preference of B. tarsalis between T. solanivora and Phthorimaea operculella, suggesting this mite could be useful in mixed infestations of potato moths. The results show B. tarsalis is a very good candidate as a control agent in storage conditions and even in mixed infestations of T. solanivora and P. operculella.

Potential for the Postharvest Biological Control of Phthorimaea operculella (Lepidoptera, Gelechiidae) by Blattisocius tarsalis (Mesostigmata, Blattisociidae)

Phthorimaea operculella is one of the most important pests causing damage to stored potatoes. In this work, the effect of temperature (at 10, 20 and 30 °C) on the predation of pest eggs by Blattisocius tarsalis was studied in the laboratory. In addition, the effect of three predatory release rates on two pest densities was studied under microcosm conditions. The results showed that B. tarsalis maintains its predatory capacity at low temperatures (10 °C), obtaining an efficiency of 49.66 ± 5.06% compared to the control. In turn, at 20 °C, a maximum efficacy of 78.17 ± 4.77% was achieved, very similar to that presented at 30 °C (75.57 ± 4.34%). Under microcosm conditions and at low pest density (10 eggs/container), the mortality due to the mite was 96.97 ± 3.03%, 81.82 ± 8.84%, and 84.85 ± 8.30%, respectively, for the three predatory release rates (5, 10 or 20 mites/container). At the high infestation level, the pest control ranged from 61.54 ± 9.21% to 92.31 ± 2.74%, depending on the predatory release rate. The results obtained show that B. tarsalis could be a relevant control agent against P. operculella under non-refrigerated potato storage conditions, as well as in the first stages of their storage under refrigerated conditions.

Biological control of Acanthoscelides obtectus and Zabrotes subfasciatus in stored dried beans

This study assesses the feasibility of using natural enemies for the control of Acanthoscelides obtectus Say and Zabrotes subfasciatus Boheman (Coleoptera: Chrysomelidae), key pests of stored dried beans, Phaseolus vulgaris L. (Fabales: Fabaceae). The predatory mites Blattisocius tarsalis Berlese (Acari: Ascidae) and Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae) were able to prey on A. obtectus eggs, reducing the bruchid population by more than 60% under both controlled and warehouse conditions. Therefore, they show good potential as biological agents for controlling this pest. The larval parasitoids Anisopteromalus calandrae Howard and Lariophagus distinguendus Forster (Hymenoptera: Pteromalidae) were both moderately effective (34–38% reduction) at suppressing A. obtectus populations, but when A. calandrae was combined with B. tarsalis, a significant improvement in control efficacy (81% reduction in emergence) was observed. Therefore, the release of A. calandrae combined with B. tarsalis seems to be a promising strategy for controlling A. obtectus. Neither B. tarsalis nor A. swirskii were able to prey on Z. subfasciatus eggs. Only the parasitoid A. calandrae was moderately effective (39% reduction) at supressing Z. subfasciatus populations. Further testing is needed to identify other natural enemies that can complement the action of A. calandrae in reducing Z. subfasciatus populations.

Biological control of Callosobruchus chinensis (Coleoptera: Chrysomelidae) in stored chickpeas through the release of natural enemies

In this study, two predatory mites and two parasitoid wasps were evaluated for their effectiveness in controlling Callosobruchus chinensis (Coleoptera: Chrysomelidae), a common pest in stored chickpeas. The predatory mite Amblyseius swirskii (Acari: Phytoseiidae) preyed on the bruchid’s eggs but did not consume a large amount; the mite Blattisocius tarsalis (Acari: Ascidae) did not consume C. chinensis eggs. However, the larval parasitoids Anisopteromalus calandrae and Lariophagus distinguendus (Hymenoptera: Pteromalidae) were effective at reducing the bruchid’s larval population, producing mortality rates above 90% in controlled conditions (28 ± 2 °C, 75 ± 5% relative humidity [RH]). In tubes of 20-cm diameter filled with 9–35 kg of chickpeas, both parasitoids were able to parasitize the host at depths of 40, 100, and 150 cm, even when larvae were offered simultaneously at all depths. This indicates that parasitoids will probably be able to locate hosts at least at 150 cm of distance in a storage facility. A. calandrae was similarly effective at reducing the bruchid population at different parasitoid-to-host ratios (1:7, 1:15, 1:30, and 1:60). Moreover, A. calandrae efficiently reduced C. chinensis populations when released in 25-kg commercial polypropylene bags of chickpeas in simulated warehouse conditions (27 ± 2 °C and 65 ± 4% RH). This is the first time that A. calandrae and L. distinguendus are shown to be effective biological control agents for the integrated management of C. chinensis in stored chickpeas and can be an alternative to the application of pesticides for maintaining low bruchid population levels.

Selection of Predatory Mites for the Biological Control of Potato Tuber Moth in Stored Potatoes.

Worldwide, the potato tuber moth (PTM), Phthorimaea operculella (Zeller), is one of the most severe pests affecting potato (Solanum tuberosum L.), whether in open-air crops or during tuber storage. This work examines the potential control of this pest by two species of predatory mites, Macrocheles robustulus (Berlese) and Blattisocius tarsalis (Berlese), on pest eggs under laboratory conditions. In the two first assays, the acceptance rate of the pest eggs was assessed for each predatory mite. Then, in a third assay, the functional response of B. tarsalis was studied. The results showed that Macrocheles robustulus did not prey on the pest eggs (number of eggs surviving = 4.33 ± 0.38), whereas B. tarsalis did (number of eggs surviving = 0.5 ± 0.5). Likewise, B. tarsalis showed a type II functional response when it killed the eggs. The results showed the potential use of Blattisocius tarsalis as a biological control agent of P. operculella in potato under storage conditions.

Mites in spice and medicinal dehydrated plants stored in bulk in the metropolitan area of São Paulo

Mites can occur in large numbers in storage units, causing serious economic damage to stored products, as well as health problems such as asthma, diarrhea, acute enteritis, and allergic reactions. In Brazil, spice and medicinal dehydrated plants are widely sold in bulk, but almost nothing is known about mite infestations. Thus, the objective of this research was to evaluate the diversity and relative abundance of mites in samples of Coriandrum sativum L., Pimpinella anisum L., Petroselinum sativum Hoffm., Matricaria chamomilla L., Baccharis trimera (Less) DC, Bixa orellana L., Senna alexandrina Mill., Origanum vulgare L., Ocimum basilicum L., Melissa officinalis L., Mentha piperita L., Rosmarinus officinalis L., Peumus boldus Molina, Salvia officinalis L., Thymus vulgaris L., Laurus nobilis L., Hibiscus sabdariffa L., Myristica fragans Houtt., Capsicum annuum L., and Curcuma longa L., collected from food retailers in the metropolitan area of São Paulo, Brazil, from October 2015 to March 2016. A total of 2584 mites, distributed into 13 families, were found in the samples of these dehydrated plants. The most abundant mite species (families) were: Tyrophagus putrescentiae (Schrank) (Acaridae) (84.6%), Cheyletus malaccensis Oudemans (Cheyletidae) (5.4%), Blattisocius tarsalis (Berlese) (Blattisociidae) (4.6%), Suidasia sp. (Astigmata: Suidasiidae) (3.2%), and Typhlodromus transvaalensis (Nesbitt) (Phytoseiidae) (1.4%). Other families (Glycyfagidae, Ameroseiidae, Bdellidae, Iolinidae, Raphignatidae, Stigmaeidae, Tydeidae) together represented less than 1.0% of the mites. T. transvaalensis is recorded for the first time in stored products in Brazil. Differences among the plant species in terms of diversity, frequency and abundance of mites were observed. Although there is a regulatory standard for good food production and service practices, the results of this study demonstrate that the bulk retail market for dehydrated plants has failed to control hygiene and quality, considering the relatively high mite infestations in most of the evaluated plant species.

<p class="Body">Mites in dried figs of Turkey: diversity, species composition and density

This study was conducted to determine mite species in dried figs in Aydin, Turkey between August 2014 and November 2016. A total of 141 dried fig samples were taken from producers’ storage, commercial storages and fig processing factories in Buharkent, Germencik, Incirliova, Kocarli, Kosk, Kuyucak, Merkez, Nazilli, Sultanhisar and Yenipazar districts. In addition, 24 dried fig samples were kept in storage for 8 months and the changes in mite species composition and their densities in stored figs were determined. As a result, 8 mite species belonging to 3 orders and 5 families were identified from the dried figs. Acarus siro L., Carpoglyphus lactis (L.), Glycyphagus destructor (Schrank), G. domesticus (De Geer) and Tyrophagus putrescentiae (Schrank) as pest species, and Blattisocius tarsalis (Berlese), B. mali (Oudemans) and Cheyletus eruditus (Schrank) as predatory mite species were found. Out of 141 samples, 133 were infested with mites and the infestation ratio was 94.3%. Tyrophagus putrescentiae was the most common pest species with an infestation rate of 72.3%, followed by C. lactis with 34.8%, A. siro, G. destructor and G. domesticus with 0.7% contamination, respectively. Carpoglyphus lactis was found to have the highest density with 10,488 individuals/kg in contaminated fig samples. Blattisocius tarsalis was the most common predatory mite species with an infestation rate of 77.3%. Blattisocius mali and C. eruditus were found in 9.2% and 4.3% of dried figs, respectively. This study showed that the dried fig samples kept in storage were always vulnerable to contamination with mites. Mite species composition and their densities also fluctuated over time.

Mite fauna (Acari) associated to commercial laying hens and bird nests in Vale do Taquari, Rio Grande do Sul, Brazil

The control of ectoparasites is essential for maintaining biosafety in a poultry farm. This paper aimed to analyze the mite fauna associated to abandoned nests and commercial laying hens in the towns of Lajeado and Teutonia, Vale do Taquari, Rio Grande do Sul, Brazil. Samplings were conducted from December 2010 to July 2011. A total of 11,757 mites belonging to 21 families and 31 species were found. Cheyletidae showed the highest number of species (4), followed by Blattisocidae (3 species). Dermanyssus gallinae (De Geer) showed the highest number of individuals (5,689), followed by Megninia gynglimura Megnin (2,175), and Chortoglyphus arcuatus Troupeau (1,488). Blattisocius tarsalis Berlese, C. arcuatus, and D. gallinae were found on traps, feathers, poultry farm nests without cages (free), and abandoned bird nests.

Spatial Associations of Insects and Mites in Stored Wheat

The spatial association pattern of insect and mite populations in a steel bin containing stored wheat, Triticum durum Desf., in central Greece, was studied using the Spatial Analysis by Distance IndicEs (SADIE). The monitoring was carried out for 7 mo by using grain trier samples and probe traps. The most abundant insect species were Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae) and Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae). For mites, the most abundant species were the phytophagous Lepidoglyphus destructor (Schrank) (Acari: Glycyphagidae) and the predator Blattisocius tarsalis (Berlese) (Mesostigmata: Ascidae). Both for P. interpunctella and C. ferrugineus, trap catches were associated with numbers of individuals in the trier samples, but the overall association index calculated among trap and sample counts was significant only in the 33% of trap-sample pairs of values. Generally, P. interpunctella had the main patch areas in the central part of the bin, with few exceptions, during the entire monitoring period. Similar trends also were noted in the case of C. ferrugineus, which was clearly aggregated in the center of the grain mass. Spatial association maps indicated a stable positive association in the central part of the bin, but in most of the other sampling zones the association was negative. However, distribution of L. destructor, based on trier samples, indicated increased presence in peripheral zones of the grain sampling area. Moreover, B. tarsalis presented the most dispersed distribution among all four species. For each species, the association between two consecutive samplings was significant in the majority of cases, indicating a stable spatial pattern. Finally, B. tarsalis was spatially associated to a higher degree with the insects found rather than with L. desctructor. Moreover, there was no association of insect and mite presence with grain temperature and moisture content. The results of the current study suggest that the coexistence of insects and mites in bulked grain follows a complex pattern, with significant interactions, especially in the case of mite predators, which are spatially associated with insect species.

Edaphic ascid mites (Acari: Mesostigmata: Ascidae) from the state of São Paulo, Brazil, with description of five new species

This paper reports the occurrence of 11 species of edaphic mites of the family Ascidae collected from soil and litter in southeastern Brazil. Five are new to science, namely Cheiroseius neophalangioides sp. nov., Gamasellodes magniventris sp. nov., Lasioseius latinoamericanus sp. nov., Proctolaelaps paulista sp. nov. and Protogamasellus sigillophorus sp. nov.. Among the other species collected, diagnoses and collection data are provided for Asca garmani Hurlbutt, 1963, Blattisocius tarsalis (Berlese, 1918), Proctolaelaps diffissus Karg, 1976 and Protogamasellus mica (Athias-Henriot, 1961 ); these are the first Brazilian collection records for these species other than B. tarsalis in stored products. Lasioseius helvetius Chant, 1958 is considered a senior synonym of L. saltatus Karg, 1980 (new synonymy), the latter reported previously from Brazil. Lasioseius quinisetosus Lindquist & Karg, 2006 (= Cheiroseius inguinalis Karg, 1977) is newly recorded from Brazil. Diagnoses and redescriptions are provided for L. helvetius and L. quinisetosus. Proctolaelaps intermedius Athias-Henriot, 1959 is considered a senior synonym of P. orientalis (Chant, 1963) and P. wenkochingi “(Samšinák, 1964)” (new synonymies).

Survey on Mites Associated with Major Insect Pests Infesting Stored Grains in Middle Delta

The present study was directed towards the habitat of various mite species as predators, fungivores or as parasitesassociated with insects inhabiting grains and stored products. Samples were collected monthly from maize, wheat flour,broad bean, wheat and rough rice in four governorates, Kafr El-Sheikh, Dakahleya, Gharbeya and Menoufeya duringthe period between March 2003 and February 2004. The results revealed that: 1) The mite survey revealed theoccurrence of 13 predatory species belonging to one family of the suborder Gamasida, and 6 families of the suborderActinedida. Also 7 species belong to 4 families of the suborder Acaridida, were recorded as scavengers or fungivores.2) The most abundant predaceous mites were: Blattisocius keegani Fox followed by Cheyletus malaccensis Oudemans,then Blattisocius tarsalis (Berlese). 3) The most abundant fungivore mites were: Tyrophagus putrescentiae (Shranck),Rhizoglyphus robini Claparede, and Acarus siro Linnaeus. 4) The most infested stored grains with mites was maizefollowed by wheat, rough rice, broad bean seeds then wheat flour. 5) The major insect pests of stored grains and seedsand associated mites were listed herein.

The effect of different temperatures and food densities on development of Blattisocius tarsalis (Berlese) (Acari: Ascidae) reared on Mediterranean flour moth Ephestia kuehniella Zeller (Lepidoptera: Pyralidae)

Blattisocius tarsalis (Berlese) (Acari: Ascidae) is an effective predatory mite species on eggs of Mediterranean flour moth Ephestia kuehniella Zeller (Lepidoptera: Pyralidae). Mediterranean flour moth is an important pest of flour storages and mills in Turkey. The aim of this paper is to investigate the possibilities for the use of B. tarsalis as a biological control agent to control moth. The effect of different temperatures (15±1 oC and 25±1 oC) on development time of B. tarsalis at different food density levels (5, 10, 15 and 20 eggs densities) has been investigated. For 15 oC; the development times of immature stages were 5,53 (1-6); 4,86 (3-5); 4,53 (0-5) and 4,86 (1-6) days while adults life span were determined 52,00 (3-67); 42,77 (5-67); 29,85 (1-66) and 27,36 (7-39) days for 5, 10, 15 and 20 moth egg densities. For 25 oC the development times of immature stages were 5,00 (5-5) days at 10 prey eggs and 6,00 (6-6) days at the rest of prey densities, beside this life span of adults were determined 32,00 (20-39); 30,67 (15-40); 42,20 (10-64) and 38,67 (4-69) days at each food densities consequently.

Laboratory Studies on the use of Two New Arenas to Evaluate the Impact of the Predatory Mites Blattisocius tarsalis and Cheyletus eruditus on Residual Populations of the Stored Product Mite Acarus siro

Residual populations of storage mites sheltering in crevices and cracks escape conventional control treatments and are implicated in the infestation of newly harvested grain. In a series of 24 h laboratory tests, the performance of solitary adults of two predatory mite species, Cheyletus eruditus (Schrank) and Blattisocius tarsalis (Berlese), were assessed for controlling small numbers of the flour mite Acarus siro (L.). Tests were carried out in the presence or absence of prey refuges or grain debris to afford shelter to the flour mites. While C. eruditus had a significant effect on the motile stages of A. siro, in contrast B. tarsalis had a significant effect on the eggs. The maximum percentage of motile stages of A. siro eaten by C. eruditus was 82%, whereas the minimum percentage of A. siro eggs eaten by B. tarsalis was 99%. While the performance of C. eruditus in predating on motile stages of the flour mite was hindered by the presence of the prey refuge (38% eaten) and grain debris (25% eaten), the performance of B. tarsalis in predating on flour mite eggs was unaffected (100% eaten in presence of prey refuge or grain debris). In prolonged exposures (36 days) the performance of 2, 4 or 8 adult predators, either a single species or a combination of both, was assessed for their ability to control a population of the flour mite developing up to F(2) from an initial inoculum of 80 females and 20 males, allowed to oviposit for 72 h in the absence of predatory mites. The maximum reduction in prey population of 80% was achieved with eight B. tarsalis. Combining the two predatory species did not enhance the reduction of A. siro population.

Arthropod pests and their natural enemies in stored crops in northern Namibia

A survey of stored product pests, their natural enemies, grain storage and pest management approaches in northern Namibia was conducted. The survey revealed five types of crop commodities (pearl millet, sorghum, cowpea, maize, feed mixture) stored in four types of grain stores (baskets, bag stags-flat stores, concrete bin, metal containers). No synthetic pesticides or plastic sheeting was recorded. Wooden-ash natural pesticide is the only protectant used. Ten insect pest species were found affiliated to the orders of Coleoptera (Attagenus fasciatus, Callosobruchus subinnotatus, Cryptolestes ferrugineus, Oryzaephilus surinamensis, Rhyzopertha dominica and Tribolium castaneum), Lepidoptera (Corcyra cephalonica, Sitotroga cerealella), Psocoptera (Liposcelis paeta) and Blattodea (Blattella germanica). Out of these, seven species were recognized as new stored-products pests for Namibia. Although listed for southern Africa region, no storage pest-mites (Acari) and Sitophilus spp., Prostephanus sp. or Trogoderma sp. beetles were traced. We found four new species of natural enemies of storage pests recruiting from insects (Habrobracon hebetor, Cephalonomia wattersoni, Brachymeria sp.) and mites (Blattisocius tarsalis). The occurrence of natural enemies indicates a potential for pest bio-control in Namibian grain stores.

Developmental time of Blattisocius tarsalis (Acari: Ascidae) at different temperatures.

The developmental time of the predatory mite Blattisocius tarsalis (Berlese) (Acari: Ascidae) was investigated at temperatures of 15, 21 and 25 degrees C and 75% r.h. Eggs 1-3 days old of Ephestia kuehniella Zeller (Lep.: Pyralidae), killed by freezing, were used as food. Mean developmental times were found to be 22.4, 8.5 and 7.0 days, respectively. Within the investigated thermal limits the developmental rate showed a linear relationship with temperature and the corresponding thermal threshold for development was calculated to 10.2 degrees C.

The impact of temperature on activity and consumption rate of moth eggs by Blattisocius tarsalis (Acari: Ascidae)

The activity of adult female Blattisocius tarsalis was investigated at temperatures of 7–13°C. At 7°C only 33% of the mites walked and these individuals all walked less than 1.5 cm min–1. All mites walked at 9°C and at 12°C all were highly active, walking more than 1.5 cm min–1. Daily food consumption rates of adult female B. tarsalis offered young eggs of Ephestia kuehniella as food were investigated at temperatures of 9–27°C. Food consumption below 13°C was very low. At temperatures of 13–19°C the mean number of fully ingested eggs had a level of between 0.5 and 1.0 egg in 24 h. At temperatures of 21–27°C the mean number of fully ingested eggs was above 1.0 egg in 24 h. The mean number of destroyed eggs per female at temperatures above 13°C ranged from three to five eggs per day. © Rapid Science Ltd. 1998

Warehouse ecology studies of bagged maize in Kenya—II: Ecological observations of an infestation by Ephestia (Cadra) cautella (Walker) (Lepidoptera, Phycitidae)

The build-up through three generations, and the decline and control of a tropical warehouse moth infestation is described. The measured temperature changes in the stack are related to the distribution and increase in numbers of Ephestia (Cadra) cautella (Walker) larvae. Mortality of E. cautella is considered, and it is concluded that the egg predating mite, Blattisocius tarsalis Berlese, was the major controlling factor. Several aspects of the biology and distribution of B. tarsalis were investigated. Other factors possibly contributing to the decline and control of E. cautella were disease (assumedly Bacillus thuringiensis), predation by ants and spiders, indirectly the presence of Tribolium castaneum (Herbst), the trapping techniques used and auto-contamination of the environment by E. cautella. The findings of this study are discussed against the background of maize storage problems in Kenya.

Regulatory processes and population cyclicity in laboratory populations of Anagasta Kühniella (Zeller) (Lepidoptera: Phycitidae) II. Parasitism, predation, competition and protective cover

SummaryThe population dynamics of Anagasta kühniella has been studied in standardized conditions in replicated ecosystems in which the variables have been increased one at a time. Additional to the variables reported earlier (WHITE and HUFFAKER, 1969), the present ecosystems included larval and pupal parasitism by Venturia canescens, both in the presence and absence of the egg‐predator Blattisocius tarsalis, and also in the presence and absence of two levels of protective cover for the host. In the presence of V. canescens, parasitism was generally of major importance as a regulating instrument in determining host population densities and it characteristically produced cycling and discrete host generations that arose from a parasite‐induced discontinuity in the age‐structure of the host populations. When the predatory mite and/or protective cover was also present, modifying interactions arose but these were not sufficient to dispel completely the discontinuous age‐structure and the cycling induced by the parasite. The actual degree of protective cover was particularly important insofar as it modified the levels and patterns of parasitism and permitted competition for food among host larvae to assume greater importance in the collective regulating process.Three forms of population cyclicity are described and discussed: a four‐generation cyclicity which was the basic pattern of cycling and occurred both in the presence and absence of protective cover; an eight‐generation cyclicity that arose from disturbed four‐generation cycling in the presence of a minimal level of host protection; and a nine‐generation cyclicity in which extensive protection compounded the collective nature of density‐dependent regulation.

Searching Success of Predators in Artificial Leaf Litter

To study the effects on searching success of some of the purely geometrical properties of leaf litter, the author constructed artificial litter components leaves, twigs, and in the laboratory, and allowed a parasitoid wasp (Trichogramma brasiliaense) and a gamasine mite (Blattisocius tarsalis) to search among these in the dark for eggs of the flour moth (Sitotroga cerealella). The distribution of parasitoid wasps and gamasine mites in natural habitats suggests that the wasps would be able to search more effectively among the leaves, and the mite among the twigs and chunks. This prediction was confirmed. Two different sizes for each type of structure were used; the wasp was in every case less efficient when searching among smaller pieces, whereas the mite showed no such differences. This suggests that the mite may be better able to search among small crevices, which fact perhaps also explains its superior ability to search among the chunks. INTRODUCTION A small arthropod searching for prey in leaf litter finds itself in a habitat of bewildering structural complexity. There are large flat surfaces (leaves), cylindrical ones (twigs) and polyhedral chunks (dried fruits, etc.). Disturbance from wind and mice tends to produce stratification, with the leaves more on top and the solid pieces nearer the soil. What are the opportunities for specialized searching behavior in such a habitat? There will, of course, be more light towards the top and more moisture towards the bottom, with consequent gradients in fungal and other growth. But to what extent are the opportunities for specialization related to enviromental features of a purely geometrical character? E.g., does the locomotory pattern best suited for searching along sticks differ from that best suited for searching the surface of a leaf? As a preliminary approach to this problem, I set up a laboratory model, using eggs of the flour moth Sitotroga cerealella (Olivier) as prey and comparing the performances of two predatorsa chalcidoid parasitoid wasp (Trichogramma brasiliaense Ashmead) and a phytoseiid gamasine mite (Blattisocius tarsalis (Berlese) ). These can beregarded as representatives of whole groups of arthropods that one sees distributed from the top to the bottom of leaf litter. The wasps are found abundantly on the broad surfaces of growing vegetation and to some extent on the surface of litter, but are conspicuously uncommon in the deeper parts of leaf litter. Exactly the opposite holds true for gamasine mites. In the laboratory model, all non-geometrical variables are eliminated. There are no light gradients: the animals are forced to search I M.A. dissertation, University of California, Los Angeles. 2 Present address: Dpto. de Zoologia Agricola, Universidad Central de Venezuela, Maracay.