Arthropod Pest Populations Research Articles

Virulência de fungos entomopatogênicos sobre larvas de Lepidoptera: Noctuidae

ABSTRACT Currently, agricultural cropping systems have adopted integrated pest management (IPM) as a successful model for pest control. The use of entomopathogenic fungi in IPM has increased because of their great potential for reducing arthropod pest populations without causing harm to human health and ecosystems. Beauveria bassiana and Metarhizium anisopliae stand out among the most used fungi in biological control, with many isolates commercialized worldwide. Helicoverpa armigera is an agriculturally important pest in Brazil and worldwide, causing damage to several crops. In this context, the objective of this study was to evaluate the biological control potential of Beauveria bassiana, Metarhizium anisopliae, and M. rileyi on H. armigera. The results indicated that the entomopathogenic fungi B. bassiana (strain ESALQ PL63), M. anisopliae (strain ESALQ E9), and M. rileyi (strain UFMS 03), applied using different methods (direct application and dry film) and concentrations (1 × 107, 1 × 108, and 1 × 109 conidia mL-1), resulted in low mortality and no virulence in first-, third-, and fifth-instar larvae of H. armigera. The death of all individuals subjected to treatment with B. bassiana (strain ESALQ PL63) was confirmed by conidiogenesis. Considering the importance of H. armigera as an agricultural pest and the biodiversity of entomopathogenic fungi in Brazil, further investigations on the virulence of fungal strains are necessary to improve the integrated management of lepidopteran pests through microbial control, explore the potential of new strains, and understand the relationships between microorganisms and host defense mechanisms.

Photo-selective nets (PSNs) affect predation by Harmonia axyridis on Myzus persicae

Photo-selective nets (PSNs) can increase agricultural crop production by modifying the quantity and quality of light that reaches the plants. PSNs also have the potential to affect arthropod pest populations and their natural enemies. The present study aimed to assess the impact of PSN systems on coccinellid predation. Experiments were carried out in microcosm conditions to evaluate the efficiency (prey localization and predation) of the multicolored Asian lady beetle, Harmonia axyridis (Pallas), when preying on the green peach aphid, Myzus persicae (Sulzer), on potato plants. Three colors of nets were tested and compared to control (no net): black SN (standard net), pearl PSN, and red PSN, using H. axyridis third-instar larvae (L3), females and males. We hypothesized that pearl and red PSN and black SN would alter the predator behavior, delaying the time to aphid colony localization, or by reducing overall aphid predation. Our results showed that aphid colonies were not affected by any PSN or the black SN in the absence of predators. Aphid colony localization by adult coccinellids was delayed under black SN, and favored under pearl PSN, but overall aphid predation was unaffected by net type. There were no significant differences among treatments in interplant movement of L3, females, or males. We conclude that, under laboratory conditions, pearl PSN, red PSN, and black SN can affect aphid colony localization by H. axyridis, but do not affect predation efficiency. Subsequent trials in the field would be required to further clarify the effects of PSNs on H. axyridis foraging behavior.

New subdivision of cotton production area of Côte d’Ivoire based on the infestation of main arthropod pests

Variations in populations of arthropod pests, under the influence of climate change, compromise the effectiveness of the cotton phytosanitary protection strategy in Côte d'Ivoire. This study aims to establish a new classification of cotton production areas, on the basis of predominant pests. A monitoring was therefore carried out from 2016 to 2019 in 400 farmers' fields. In these fields, surveys were conducted weekly, from the 30th to the 122nd day after emergence. Data analysis, through Principal Component Analysis, identified four groups of localities. The first group includes the northeastern localities (4°W to 5°W: 8°N to 10.5°N) such as Kong, Ouangolodougou, Sordi, Tiékpè, Kaouara. This area is characterized by high infestations of most pests (jassid, white flies, exocarpic lepidoptera, endocarpic lepidoptera, phyllophagous lepidoptera and mites). The second group is intermediate between northeast and central (5.5°W to 6.2°W: 8.3°N to 10.5°N). This area is characterized by infestations of jassid, white flies and exocarpic lepidoptera (H. armigera and D. watersi). It remains less infested by endocarpic lepidoptera (T. leucotreta and P. gossypiella). The third area is located in the South (4.5°W to 8.5°W: 6°N to 8.5°N). It is essentially infested by endocarpic lepidoptera T. leucotreta and P. gossypiella. Jassid and whitefly infestations are less important in this part, compared to the northern part. The fourth and last area extends from the center to the west (6°W to 8°W: 8°N to 10.5°N). Pest infestations are lower in this area compared to other areas.

Do the beneficial fungi manage phytosanitary problems in the tea agro-ecosystem?

In recent years, Fungal Biocontrol Agents (FBCAs) have played a significant role in the biological control of pests and plant pathogens of several economically important crops, including tea. Although such agents are environment friendly, the risk of their effect on non-target organisms in tea gardens remains elusive. Among those FBCAs commercialized for field application, their impacts on the populations of arthropod pests and the prevalence of pathogens in tea ecosystems are still limited. Some products based on FBCAs have been applied for the control of pests and plant pathogens in tea crop. This review focuses on the biological potential of the fungal entomopathogens and antagonists against prevalent pests and diseases of tea crop, and their practical applications as bio-pesticides to minimize the load of chemical pesticides. The roles of FBCAs in plant growth promotion, their suitability as alternatives of chemical pesticides, challenges in the use of FBCAs, and perspectives are also discussed.

Weed species, not mulching, affect web‐building spiders and their prey in organic fruit orchards in South Africa

AbstractWeed infestation affects economically relevant orchard properties, including tree performance, yield, and fruit quality negatively, and weeds are therefore often controlled by herbicide application in conventional farming. The addition of organic mulch below tree canopies has been proposed as an alternative reliable practice to suppress weeds and preserve soil moisture in organic farming. Mulching, however, may also affect arthropod pest and natural enemy populations, which highlights the need for simultaneously assessing weed, natural enemy, and animal pest communities in mulch experiments. This study addresses the limited knowledge about nonchemical ground cover management strategies for the control of plant and animal pests in orchards as a major constraint for organic growers. Here, we hypothesize that decisions about ground cover management practices in organic temperate fruit orchards affect the composition of web‐building spider communities and their functional role as natural enemies of pest arthropods through effects on weed and insect pest communities. We studied weed, prey, and spider communities, as well as spider diet composition, in four temperate fruit types (apricot, peach, plum, and quince) on a single farm in the Western Cape, South Africa. We established experimental plots with and without addition of dead organic mulch under fruit tree canopies. Addition of organic mulch did not significantly affect weed cover under trees or the taxonomic composition of weed or spider communities over the eight‐month study period. However, independent of mulching, the taxonomic composition of weed communities was significantly related to the composition of potential prey and spider communities. These relationships indirectly affected the prey composition of web‐building spiders. These results suggest that the identity of weed species in the study orchards had a pronounced effect on the diet composition and functional role of web‐building spiders. Future research should focus on the value of individual plant species for the promotion of pest control services provided by spiders across larger spatial scales and with higher levels of replication to allow for wider generalizations. The expected results would not only be relevant for weed control but could also be considered during the development of future flower strips in orchards.

Insect herbivory antagonizes leaf cooling responses to elevated temperature in tomato

As global climate change brings elevated average temperatures and more frequent and extreme weather events, pressure from biotic stresses will become increasingly compounded by harsh abiotic stress conditions. The plant hormone jasmonate (JA) promotes resilience to many environmental stresses, including attack by arthropod herbivores whose feeding activity is often stimulated by rising temperatures. How wound-induced JA signaling affects plant adaptive responses to elevated temperature (ET), however, remains largely unknown. In this study, we used the commercially important crop plant Solanum lycopersicum (cultivated tomato) to investigate the interaction between simulated heat waves and wound-inducible JA responses. We provide evidence that the heat shock protein HSP90 enhances wound responses at ET by increasing the accumulation of the JA receptor, COI1. Wound-induced JA responses directly interfered with short-term adaptation to ET by blocking leaf hyponasty and evaporative cooling. Specifically, leaf damage inflicted by insect herbivory or mechanical wounding at ET resulted in COI1-dependent stomatal closure, leading to increased leaf temperature, lower photosynthetic carbon assimilation rate, and growth inhibition. Pharmacological inhibition of HSP90 reversed these effects to recapitulate the phenotype of a JA-insensitive mutant lacking the COI1 receptor. As climate change is predicted to compound biotic stress with larger and more voracious arthropod pest populations, our results suggest that antagonistic responses resulting from a combination of insect herbivory and moderate heat stress may exacerbate crop losses.

Effect of azadirachtin pre-treatment on major pests, diseases and yield of seed yam.

Pests and diseases infested material of seed yams have led to sub optimal yield levels. Neem was applied as substitute for chemical pesticides and as environmentally safe bio-pesticide to reduce the crops annual loss due to herbivore pests and their resulting diseases. Field trials were conducted during the 2016 and 2017 major planting seasons in four communities each of Ejura-Sekyedumase and Atebubu-Amantin districts of the Ashanti and Brong Ahafo regions respectively. Yam minisetts sizes were pre-treated with Mancozeb at a rate of 100 g and Lambda cyhalothrin at 40 ml in 10 L water as cocktail. Yam minisetts of 30 g each were planted on ridges at 100 cm between and 30 cm within rows on a 20 m × 20 m plot size. Neem leaf powder was applied on five rows per plot and another five served as check for assessment. Harvesting was done approximately 6 to 7 months after planting. Scale insects, mealybugs, beetles, termites and millipedes infestations. Galling due to root-knot nematodes, cracks, soft and wet rot were assessed on a scale of 1-5. Tuber yields were also assessed. Neem treated plots were observed to have significantly reduced arthropod pest populations and nematode galling as well as damage signs compared to the control plots. Yields of seed yam were higher on the neem treated plots than the control, probably due to the reduced damage on the treated plots. Seed yam yield increased for plots treated with Azadirachta indica leaves by 40 and 41% at Ejura-Sekyedumase district as well as 45 and 20% at Atebubu-Amantin district for 2016 and 2017 respectfully. Plots of seed yams treated with neem recorded reduced pests and damages in terms of parameters measured and subsequently translated into yield. It is paramount to seed yam producers to adopt neem leaf powder as pre-treatment for higher productivity.

Short-term toxicity of insecticides residues to key predators and parasitoids for pest management in cotton

The cotton ecosystem comprises various arthropod pest and natural enemies with simultaneous occurrence irrespective of growing region. The use of insecticides with reduced impact on natural enemies is a major goal to conserve them and, therefore, to reduce populations of arthropod pests. The survival of twelve key natural enemies for cotton pest management exposed to dried residues using the highest and lowest recommended rates representing old and new insecticides recommended to control cotton pests (chlorantraniliprole, chlofernapyr, spinosad, lambda-cyhalotrin, methidathion, pymetrozine, and thiamethoxam) was determined. The study included parasitoids [Aphelinus gossypii Timberlake, Bracon vulgaris Ashmead, Lysiphlebus testaceipes (Cresson), Telenomus podisi (Ashmead), Trichogramma pretiosum (Riley)] and predators [Hippodamia convergens Guerin-Meneville, Euborellia annulipes (Lucas), Podisus nigrispinus (Dallas), Solenopsis invicta Buren), Orius insidiosus (Say), Chrysoperla externa Hagen and Eriopis connexa (Germar)], with two different cohorts for these last two species. All natural enemies exposed to methidathion exhibited 100% mortality. Thiamethoxam, lambda-cyhalothrin and chlorfenapyr also caused high mortality of P. nigrispinus, S. invicta, H. convergens, O. insidiosus and all tested parasitoids. Among the natural enemies, E. annulipes exhibited high survival when exposed to all tested insecticides, except methidathion. Chlorantraniliprole and pymetrozine caused overall lower impact on the natural enemies tested followed by spinosad; hence, they are options for cotton pest management. Furthermore, the outcomes highlight the implication of knowing the background susceptibility of the species tested when addressing the impact of insecticides on natural enemies.

Fitness costs of key point mutations that underlie acaricide target-site resistance in the two-spotted spider mite Tetranychus urticae.

The frequency of insecticide/acaricide target‐site resistance is increasing in arthropod pest populations and is typically underpinned by single point mutations that affect the binding strength between the insecticide/acaricide and its target‐site. Theory predicts that although resistance mutations clearly have advantageous effects under the selection pressure of the insecticide/acaricide, they might convey negative pleiotropic effects on other aspects of fitness. If such fitness costs are in place, target‐site resistance is thus likely to disappear in the absence of insecticide/acaricide treatment, a process that would counteract the spread of resistance in agricultural crops. Hence, there is a great need to reliably quantify the various potential pleiotropic effects of target‐site resistance point mutations on arthropod fitness. Here, we used near‐isogenic lines of the spider mite pest Tetranychus urticae that carry well‐characterized acaricide target‐site resistance mutations to quantify potential fitness costs. Specifically, we analyzed P262T in the mitochondrial cytochrome b, the combined G314D and G326E substitutions in the glutamate‐gated chloride channels, L1024V in the voltage‐gated sodium channel, and I1017F in chitin synthase 1. Five fertility life table parameters and nine single‐generation life‐history traits were quantified and compared across a total of 15 mite lines. In addition, we monitored the temporal resistance level dynamics of populations with different starting frequency levels of the chitin synthase resistant allele to further support our findings. Three target‐site resistance mutations, I1017F and the co‐occurring G314D and G326E mutations, were shown to significantly and consistently alter certain fitness parameters in T. urticae. The other two mutations (P262T and L1024V) did not result in any consistent change in a fitness parameter analyzed in our study. Our findings are discussed in the context of the global spread of T. urticae pesticide resistance and integrated pest management.

Spinosad- and Deltamethrin-Induced Impact on Mating and Reproductive Output of the Maize Weevil Sitophilus zeamais.

Assessments of acute insecticide toxicity frequently focus on the lethal effects on individual arthropod pest species and populations neglecting the impacts and consequences of sublethal exposure. However, the sublethal effects of insecticides may lead to harmful, neutral, or even beneficial responses that may affect (or not) the behavior and sexual fitness of the exposed insects. Intriguingly, little is known about such effects on stored product insect pests in general and the maize weevil in particular. Thus, we assessed the sublethal effects of spinosad and deltamethrin on female mate-searching, mating behavior, progeny emergence, and grain consumption by maize weevils. Insecticide exposure did not affect the resting time, number of stops, and duration of mate-searching by female weevils, but their walking velocity was compromised. Maize weevil couples sublethally exposed to deltamethrin and spinosad exhibited altered reproductive behavior (walking, interacting, mounting, and copulating), but deltamethrin caused greater impairment. Curiously, higher grain consumption and increased progeny emergence were observed in deltamethrin-exposed insects, suggesting that this pyrethroid insecticide elicits hormesis in maize weevils that may compromise control efficacy by this compound. Although spinosad has less of an impact on weevil reproductive behavior than deltamethrin, this bioinsecticide also benefited weevil progeny emergence, but did not affect grain consumption. Therefore, our findings suggest caution using either compound, and particularly deltamethrin, for controlling the maize weevil, as they may actually favor this species population growth when in sublethal exposure requiring further assessments. The same concern may be valid for other insecticides as well, what deserves future attention.

Sublethal and transgenerational effects of short-term and chronic exposures to the neonicotinoid nitenpyram on the cotton aphid Aphis gossypii

Aphis gossypii Glover (Hemiptera: Aphididae) is a polyphagous pest worldwide. Neonicotinoid insecticides, such as nitenpyram, are widely used for its control in cotton crops. Sublethal or low exposure to these insecticides can cause contrasting effects on arthropod pest populations. Through laboratory experiments, we assessed the impact of low nitenpyram concentrations on the exposed A. gossypii generation (F0) and on its progeny (F1). Nitenpyram caused sublethal effects on reproduction and longevity in the aphids directly exposed (F0) to low doses. However, the estimated demographic indexes of the progeny (F1) of those individuals exposed for 72 h were higher than those of the control population. This is the first laboratory evidence of a transgenerational hormesis owing to low lethal and sublethal nitenpyram concentrations. Although these findings must be validated in real cropping conditions, it could be expected that, in addition to the acute effects that usually occur at high (label) doses, sublethal effects and hormesis can occur on the pest populations over time among insecticide applications in the field.

Site-specific temporal and spatial validation of a generic plant pest forecast system with observations of Bactrocera dorsalis (oriental fruit fly)

This study introduces a simple generic model, the Generic Pest Forecast System (GPFS), for simulating the relative populations of non-indigenous arthropod pests in space and time. The model was designed to calculate the population index or relative population using hourly weather data as influenced by developmental rate, high and low temperature mortalities and wet soil moisture mortality. Each module contains biological parameters derived from controlled experiments. The hourly weather data used for the model inputs were obtained from the National Center of Environmental Prediction Climate Forecast System Reanalysis (NCEP-CFSR) at a 38 km spatial resolution. A combination of spatial and site-specific temporal data was used to validate the GPFS models. The oriental fruit fly, Bactrocera dorsalis (Hendel), was selected as a case study for this research because it is climatically driven and a major pest of fruit production. Results from the GPFS model were compared with field B. dorsalis survey data in three locations: 1) Bangalore, India; 2) Hawaii, USA; and 3) Wuhan, China. The GPFS captured the initial outbreaks and major population peaks of B. dorsalis reasonably well, although agreement varied between sites. An index of agreement test indicated that GPFS model simulations matched with field B. dorsalis observation data with a range between 0.50 and 0.94 (1.0 as a perfect match). Of the three locations, Wuhan showed the highest match between the observed and simulated B. dorsalis populations, with indices of agreement of 0.85. The site-specific temporal comparisons implied that the GPFS model is informative for prediction of relative abundance. Spatial results from the GPFS model were also compared with 161 published observations of B. dorsalis distribution, mostly from East Asia. Since parameters for pupal overwintering and survival were unknown from the literature, these were inferred from the distribution data. The study showed that GPFS has promise for estimating suitable areas for B. dorsalis establishment and potentially other non-indigenous pests. It is concluded that calibrating prediction models with both spatial and site-specific temporal data may provide more robust and reliable results than validations with either data set alone.

Key and Secondary Arthropod Pest Population Trends in Apple Cultivated over Four Seasons with No Insecticides and a Legume Cover

The reduced use of insecticides in apple orchards has caused many to expect secondary pests to become a serious problem. To assess the validity of this concern, we monitored arthropod populations in apple orchards cultivated with no insecticides and an alfalfa or grass cover over four seasons. Codling moths became economically injurious, while leafroller populations declined to sub-economic levels. No other species caused economic injury. Our results suggest that secondary pests may be, to some extent, pesticide induced. We did not observe any significant effect of cover treatment on arthropod populations. However, some evidence suggests that an alfalfa cover may contribute modestly to increased biological control.

Thresholds, Injury, and Loss Relationships for Thrips inPhleum pratense(Poales: Poaceae)

Timothy (Phleum pratense L.) is an important forage crop in many Western U.S. states. Marketing of timothy hay is primarily based on esthetics, and green color is an important attribute. The objective of these studies was to determine a relationship between arthropod populations, yield, and esthetic injury in timothy. Economic injury levels (EILs) and economic thresholds were calculated based on these relationships. Thrips (Thripidae) numbers were manipulated with insecticides in small plot studies in 2006, 2007, and 2008, although tetranychid mite levels were incidentally flared by cyfluthrin in some experiments. Arthropod population densities were determined weekly, and yield and esthetic injury were measured at each harvest. Effects of arthropods on timothy were assessed using multilinear regression. Producers were also surveyed to relate economic loss from leaf color to the injury ratings for use in establishing EILs. Thrips population levels were significantly related to yield loss in only one of nine experiments. Thrips population levels were significantly related to injury once before the first annual harvest and twice before the second. Thrips were the most important pest in these experiments, and they were more often related to esthetic injury rather than yield loss. EILs and economic thresholds for thrips population levels were established using esthetic injury data. These results document the first example of a significant relationship between arthropod pest population levels and economic yield and quality losses in timothy.

Biostable agonists that match or exceed activity of native insect kinins on recombinant arthropod GPCRs

The multifunctional arthropod ‘insect kinins’ share the evolutionarily conserved C-terminal pentapeptide motif Phe-X 1-X 2-Trp-Gly-NH 2, where X 1 = His, Asn, Ser, or Tyr and X 2 = Ser, Pro, or Ala. Insect kinins regulate diuresis in many species of insects. Compounds with similar biological activity could be exploited for the control of arthropod pest populations such as the mosquito Aedes aegypti (L.) and the southern cattle tick Rhipicephalus ( Boophilus) microplus (Canestrini), vectors of human and animal pathogens, respectively. Insect kinins, however, are susceptible to fast enzymatic degradation by endogenous peptidases that severely limit their use as tools for pest control or for endocrinological studies. To enhance resistance to peptidases, analogs of the insect kinins incorporating bulky α,α-disubstituted amino acids in positions adjacent to both primary and secondary peptidase hydrolysis sites were synthesized. In comparison with a control insect kinin, several of these analogs are highly stable to hydrolysis by degradative enzymes ANCE, neprilysin and Leucine aminopeptidase. Six analogs were evaluated by calcium bioluminescence assay on recombinant receptors from mosquito and tick. Four of these analogs either matched or exceeded the potency of the control kinin peptide agonist. One of these was about 5-fold more potent than the control agonist on the tick receptor. This analog was 8-fold more potent than the control agonist on the mosquito receptor, and twice more potent than the endogenous Aedes kinin-II. The analog also demonstrated potent activity in an in vitro Aedes Malpighian tubule fluid secretion assay. Similar comparisons of analog potency cannot be made to tick kinins because no endogenous kinin has yet been identified. These potent, biostable analogs represent ideal new tools for endocrinologists studying arthropod kinin-regulated processes in vivo, particularly for ticks in which their role remains to be established.

Developing a generic sampling system for monitoring the key arthropod pests of table grapes, Vitis vinifera L.

We describe a system developed for monitoring arthropod pests of table grapes in the Hex River Valley, South Africa. The system has wide applicability for monitoring pests at grape-producing localities in the country. Six Vitis vinifera cv. Barlinka and six V. vinifera cv. Dauphine vineyards were used as sampling sites. In each vineyard, 100 vines were inspected bi-weekly, to record damage or the presence of arthropod pests on the cordon, one bunch and one leaf per vine. Sampling precision and operating characteristic (OC) curves were estimated for each of the pests. Using previously determined economic thresholds together with the OC curves, action thresholds were determined for Tetranychus urticae Koch (Prostigmata: Tetranychidae) (11–29% leaf infestation), Planococcus ficus (Signoret) (Hemiptera: Pseudococcidae) (2% cordon infestation), Epichoristodes acerbella (Walker) (Lepidoptera: Tortricidae) and Phlyctinus callosus Boh. (Coleoptera: Curculionidae) (1% bunch damage). This novel system can be used for monitoring arthropod pest population levels in all types of South African vineyards, providing a basis for the development of integrated pest management (IPM) systems in these vineyards.

The use of ultraviolet‐blocking films in insect pest management in the UK; effects on naturally occurring arthropod pest and natural enemy populations in a protected cucumber crop

AbstractStudies in polytunnels were conducted to investigate the effects of ultraviolet (UV)‐blocking films on naturally occurring insect pests and their arthropod natural enemies on a cucumber crop. Within tunnels clad with Antibotrytis (blocks light < 400 nm) and UVI/EVA (UV transmitting), 5.8 and 23.4 times more aphids, respectively, were recorded on traps compared with those on traps within tunnels clad with XL 385 (blocks light < 385 nm). When all plants within the UVI/EVA tunnels had become heavily infested with aphids, half of the plants in XL 385 tunnels were uninfested. More Coleoptera and thrips (approximately two times) were recorded under the UVI/EVA film than under the UV‐blocking films, but for other arthropod pests (e.g. whitefly, leafhoppers), clear conclusions could not be drawn as low numbers were recorded. Substantial numbers of chalcid parasitoids and syrphids were found under the UV‐blocking films, but further research is needed to evaluate fully the effect of such films on biological control of aphids. Higher syrphid numbers and more aphid mummies were recorded under the UVI/EVA film, probably because of the higher numbers of aphids present in tunnels clad with this film. The potential that UV‐blocking films have as an effective component of commercial Integrated Pest Management (IPM) systems, for protected horticultural crops, is discussed.

Suppression of two-spotted spider mite ( Tetranychus urticae), mealy bug ( Pseudococcus sp) and aphid ( Myzus persicae) populations and damage by vermicomposts

A vermicompost, produced commercially from food wastes, was tested for its capacity to suppress populations and damage to plants, by two-spotted spider mites ( Tetranychus urticae), mealy bugs ( Pseudococcus sp.) and aphids ( Myzus persicae), in the greenhouse. A range of mixtures of food waste vermicompost and a soil-less bedding plant growth medium Metro-Mix 360 (MM360) was tested in cages (40 cm × 40 cm × 40 cm) (0.2 mm mesh aperture) into which known numbers of greenhouse-bred pests were released. The crops tested were cucumbers and tomatoes for mealy bugs, bush beans and eggplants for spider mites, and cabbages for aphids. In all experiments, four 10 cm diameter pots, each containing one seedling, grown in the same MM360/vermicompost mixture were exposed to either 50 mealy bugs, 100 spider mites, or 100 aphids in cages, with each cage treatment replicated 4 times per treatment. The five growth mixtures tested were: (i) 100% MM360; (ii) 90% MM360 with 10% vermicompost; (iii) 80% MM360 with 20% vermicompost; (iv) 60% MM360 with 40% vermicompost; and (v) 20% MM360 with 80% vermicompost. Almost all of the mixtures containing vermicomposts suppressed the arthropod pest populations, and decreased pest damage significantly, compared with the MM360 controls. Not only did the vermicomposts make the plants less attractive to the pests, but they also had considerable effects on pest reproduction over time. The effects of the vermicompost substitutions tended to be least on spider mites, intermediate on mealy bugs, and greatest on aphids; however this may relate to the motility of the pests, as well as to the suppression potential of vermicomposts. Possible mechanisms for the suppression discussed include: the form of nitrogen available in the leaf tissues, the effects of vermicomposts on micronutrient availability, and the possible production of phenols, by the plants after applications of vermicomposts, making the tissues unpalatable.

Effect of Stocked Fish on Rice Leaffolder Cnaphalocrocis medinalis and Rice Caseworm Nymphula depunctalis Populations in Intensive Rice Culture

It is often claimed that fish stocked in rice fields have a significant impact on the rice pest population. However, there is little experimental evidence for this. We used the data of six experiments to find out whether a polyculture of silver barb Barbodes gonionotus (Bleeker), common carp Cyprinus carpio (L.) and Nile tilapia Oreochromis niloticus (L.) has any effect on the population of rice leaffolders Cnaphalocrocis medinalis (Guenée) and rice caseworms Nymphula depunctalis (Guenée), two common pests in intensively cultured rice fields. Fish had no effect on the rice leaffolder population, but significantly lowered the number of rice caseworm adults and larvae. We concluded that fish have some effect on the arthropod pest population in rice fields, although, most probably, only on sluggish pests living in the water or on the water surface.

Comparison of Different Sampling Methods and Effect of Pesticide Application on Spider Populations in Lime Orchards in South Florida

A survey of predatory arthropods in lime orchards at Homestead, FL, showed that spiders significantly outnumbered the other predatory arthropods (the green lacewing Chrysoperla rufilabris, coccinellid Harmonia sp., and the ant Myrmelachista sp.). The spider community consisted of nine families, 25 genera, and 15 species. The abundance and diversity of the predatory spiders in lime orchards suggests their possible role in regulating the increase of arthropod pest populations. In general, comparison of three sampling methods revealed that the visual sampling method provided the highest number of spiders collected followed by the shake-cloth method and the DVAC suction method collected the least. However, our data showed that the choice of sampling method depends on the species of interest. For instance, spider species in the hunting group were collected frequently using the visual method followed by the shake-cloth method; whereas, most of the species in the web-building group were collected by the three sampling methods with similar frequencies. The difference in the efficiency of the sampling methods may be explained by the retreating habits of the different spider species. The data gathered in sampling the predatory arthropods in sprayed and nonsprayed lime orchards demonstrated the probable nontarget effect of the different pesticides used in the orchards.