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1 Introduction

Spiders are an abundant and important group of predators that inhabit many ecosystems and play a major role in the regulation of pest species (Riechert and Lockley 1984). Because many species inhabit agricultural ecosystems or their surroundings, they have the potential to be exposed to pesticides. Spiders are in general quite susceptible to pesticides, especially synthetic insecticides (Stark et al. 1994; Pekár 2013). However, much less work has been published on the effects of pesticides on spiders compared to insects. Certain natural insecticides, including those of plant origin, appear to be less toxic to spiders compared to synthetic insecticides. Pesticides from the neem tree fall into this category.

The neem tree, Azadirachta indica, is native to Southern Asia and has been known for centuries to have medicinal and pest control properties. More recently, commercial pesticides have been developed from the neem tree, and today, neem pesticides are used to control various pests throughout the world. In the developed world, neem-based pesticides are often used by organic farmers. Neem pesticides are produced primarily from the seed kernels which are crushed and extracted with water or alcohol. Neem oil, which is obtained by cold pressing the seeds, also has pesticidal properties. Neem soap is another product that is used as a pesticide.

More than 70 chemicals have been identified in the neem tree. The major insecticidal component is azadirachtin (Fig. 33.1), a triterpenoid compound that exhibits insect growth regulatory properties. Azadirachtin interferes with molting by inhibiting production of the insect hormone, ecdysone. Neem products also act as antifeedants causing insects to stop feeding after ingestion. Furthermore, neem can act as an egg-laying deterrent, whereby volatile compounds from neem are repulsive to some insects, and this stops them from laying eggs on plant surfaces. Neem pesticides are considered to be broad-spectrum insecticides because they are toxic to most major groups of insects. Furthermore, they work by contact and/or ingestion and are systemic, being taken into plants via leaves and roots. For a list of neem products and pest insect species controlled by neem, see the following web page: http://web.pppmb.cals.cornell.edu/resourceguide/mfs/08neem.php.

Fig. 33.1
figure 00331

The chemical structure of azadirachtin, the main active compound of the neem tree (Wikipedia Commons)

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In this chapter, I will discuss the literature pertaining to the effects of neem pesticides on spiders. I have limited this review to include papers published only in peer-reviewed scientific journals. Papers presented at meetings, published meeting proceedings, book chapters, theses/dissertations, or reports published in newsletters are not considered. Furthermore, only studies where spiders were evaluated separately and not lumped in with predators in general are discussed. Furthermore, I have also separated out laboratory and field studies.

2 Laboratory Studies

A number of laboratory studies have been conducted to determine the effects of neem on spiders. One of the earliest studies to evaluate the effects of a neem-based pesticide on spiders was published by Saxena et al. (1984). In this study, topical application of 50 μg of a neem seed kernel extract had no effect on the lycosid Pardosa pseudoannulata. In another study, Mansour et al. (1986) evaluated the effects of a 2.5 % extract of neem seed prepared with several different solvents. They found that certain extracts were not toxic to the miturgid Cheiracanthium mildei but that 4 % extracts made with pentane, acetone, and ethanol resulted in 71 %, 54 %, and 33 % mortality, respectively.

Mansour and Nentwig (1988) evaluated the toxicity of 30 pesticides, including neem, to juvenile and adult web-building and hunting spiders from the tropics, Europe and the Middle East, in laboratory studies. The philodromid hunting spider, Philodromus sp., was not susceptible to any of the pesticides evaluated. The web-building spiders, Argiope sp. (Araneidae) and Linyphia sp. (Linyphiidae), and the hunting spider, Cheiracanthium sp., were moderately to highly susceptible to these pesticides. Botanical insecticides, herbicides, and fungicides were not very toxic to these spider species, while most acaricides were highly toxic.

The effects of three neem pesticides, Margosan-O, Azatin, and RD9-Repelin, were evaluated on the pest mite, Tetranychus cinnabarinus, the predacious mite, Typhlodromus athiasae, and the predatory spider, C. mildei, in laboratory studies (Mansour et al. 1993). None of these products were toxic to the spider species.

Two neem pesticides, Neemgard, an acaricidal and fungicidal formulation obtained from neem seed kernels, and Neemix 4.5 were tested as controls for the pest mite, T. cinnabarinus, the predacious mite, Phytoseiulus persimilis, and the predatory spider, C. mildei (Mansour et al. 1997). Neemgard was found to be highly toxic to T. cinnabarinus, but was not toxic to C. mildei or P. persimilis. Neemix 45 was repellent but caused no mortality in T. cinnabarinus.

Punzo (1997) studied the effects of azadirachtin on the wolf spider Schizocosa humilis (sub S. episina). In this study, azadirachtin’s effects on mortality, survivorship, and immunological competency were evaluated. Adults and spiderlings were fed prey that had been injected with several concentrations of azadirachtin. Significant mortality over a 30-day period was observed when spiders ingested prey injected with 1.0 and 10.0 ppm azadirachtin. Additionally, ingestion of azadirachtin-treated prey led to significant negative effects on spiderlings body mass and the width of the prosoma as well as a significant decrease in total hemocyte counts.

Amalin et al. (2000) tested the toxicity of 14 pesticides used in the production of Tahiti lime to the anyphaenid spider, Hibana velox, in the laboratory. Many of the pesticides evaluated were highly toxic to this spider. However, exposure to azadirachtin resulted in the lowest impact on H. velox with less than 20 % mortality at the highest concentration tested.

The effects of several pesticides on the survival and web-building potential of the eresid spider, Stegodyphus sarasinorum, were evaluated in laboratory studies (Kumar and Yashkamal 2009). Neem pesticides were the least toxic to this spider species compared to the other insecticides tested.

The toxicity of five insecticides, including neem (NeemAzal) on the functional response of the spider, Philodromus cespitum, was evaluated in a laboratory study (Řezáč et al. 2010). Exposure of this spider to NeemAzal resulted in less than 10 % mortality. However, NeemAzal exposure resulted in significantly lower predation rates compared to the control.

3 Field Studies

In 1988 and 1989, two field experiments were conducted to study the effects of different neem products and the synthetic insecticide, monocrotophos, on rice pests and the spider, Pardosa pseudoannulata (Mohan et al. 1991). The neem products were effective as controls for rice pests. After application of neem, there were initial reductions in spider populations, but spiders recolonized neem-treated plots while populations remained low in monocrotophos-treated plots.

Stark (1992) found that applications of the commercial neem pesticide Margosan-O had no significant effect on spiders inhabiting turf grass. In a follow-up study, Stark and Crawford (2005) found that the synthetic insecticide chlorpyrifos significantly reduced spider species diversity, whereas Margosan-O had no significant negative effect on these spiders inhabiting turf grass.

Baitha et al. (2000) evaluated the efficacy of several insecticides on control of insect pests in rice. They found that a neem seed kernel extract was the least effective at controlling pest species but also had the lowest impact on spiders.

A neem seed extract was evaluated along with a synthetic insecticide for control of insect pests of cotton in Australia (Ma et al. 2000). The neem pesticide was moderately effective as a control for cotton pests and resulted in higher control yields than the control. Spiders and other predators were found to be unaffected by the neem extract.

Chakraborti (2001) evaluated neem pesticides along with application of the synthetic insecticide, phosphamidon, for their potential to control insect pests of mustard. Neem cake was applied to soil; a neem seed kernel extract and phosphamidon were applied to mustard foliage. Effects on aphids, diamond back moth, and several predators were recorded. This combination treatment effectively controlled the pest species but was safe for spiders, coccinellids, and syrphid flies.

Three neem pesticides—NeemAzal, Rakshak Gold, and ICIPE Neem—were evaluated against beneficial arthropods in a cotton agroecosystem (Mann and Dhaliwal 2001). Numbers of spiders were found to be higher in the NeemAzal treatment of 1 l/ha and the same as the control in a higher rate of NeemAzal (2 l/ha).

The effects of two concentrations of neem on the pest species, the alfalfa weevil Hypera variabilis (Coleoptera: Curculionidae) and aphids and the predators (coccinellids, anthocorids, chrysopids, and spiders) were compared to malathion in field experiments (Yardim et al. 2001). Malathion was more effective at reducing weevil numbers than neem, but the neem treatments significantly reduced weevil numbers and were more effective than malathion at controlling aphids. The number of predators was not significantly affected by the neem treatments.

The effectiveness of a sustainable management program targeting sucking pests that transmit leaf curling in chilli was conducted in West Bengal, India (Chakraborti 2004). Both neem cake and foliar applications of neem oil and azadirachtin were applied. These treatments were effective controls for the pest species and were safe to coccinellids, syrphids, and spiders compared to conventional chemical control.

The efficacy of neem oil and the synthetic insecticides, imidacloprid and carbosulfan, as a seed dress to control sucking insect pests of okra was conducted in the field (Indira Gandhi et al. 2006). Neem oil provided good control of the pest species. Additionally, numbers of coccinellids and the spiders, Oxyopes sp. (Oxyopidae) and Clubiona sp. (Clubionidae), were higher in neem-treated plots than in okra treated with synthetic pesticides.

A study was conducted to evaluate the effects of various plant extracts including neem alone and in combination with synthetic insecticides for control of bollworms in cotton in the field (Sinzogan et al. 2006). All treatments, except neem alone, significantly reduced populations of lady beetles, ants, and spiders compared to the control.

Ishtiyaq and Shaw (2008) studied the effects of several plant extracts on the host location and acceptance by the egg parasitoid, Trichogramma japonicum, parasitizing the yellow stem borer, Scirpophaga incertulas, in a Chhattisgarh agroecosystem in India. They found that applications of a neem extract (0.5 %) resulted in reductions in spider populations in the field.

Ravi et al. (2008) compared the efficacy of sequential applications of the natural pesticides, nucleopolyhedrovirus, of the cotton bollworm Helicoverpa armigera (HaNPV @ 1.5 × 1012 OB/ha), Bacillus thuringiensis var. kurstaki (Delfin® 25 WG @1 kg/ha), spinosad 45 SC (@ 75 g a.i./ha), and neem (neemazol 1.2 EC @ 1,000 ml/ha) as controls for H. armigera to sequential application of synthetic insecticides and untreated control on tomato F1 hybrid Ruchi. The sequential applications of the natural pesticides were as effective as the synthetic products for control of H. armigera. Furthermore, higher numbers of predators, including spiders, were found in the plots that received applications of the natural products.

A field study was conducted to evaluate the effectiveness of synthetic insecticides, biopesticides/bio-agents, botanicals, and their combinations, cartap hydrochloride 4 G @ 0.75 kg a.i./ha, Beauveria bassiana @ 2.5 kg/ha, B. thuringiensis @ 1.5 kg/ha, imidacloprid 17.8 SL @ 0.05 %, T. japonicum @ 100,000 eggs/ha, neem gold @ 5 ml/l, and neem gold @ 3 ml/l + T. japonicum @ 75,000 eggs/ha for control of the yellow stem borer (Singh et al. 2008). The synthetic pesticides were most effective for control of the pest species but were detrimental to spider populations. The biopesticides, including neem, conserved spider populations.

Anis Joseph et al. (2010) conducted a field study to evaluate the toxicity of several insecticides, including neem to two major tetragnathid spiders found in rice fields, Tetragnatha mandibulata and T. maxillosa. These species were highly susceptible to synthetic insecticides, but exposure to a neem seed kernel extract resulted in the least mortality.

Applications of neem oil at 1 %, 2 %, and 3 % applied at 10 days intervals were used to control tukra mealy bug Maconellicoccus hirsutus and leaf webber Diaphania pulverulentalis infestations on mulberry (Ravikumar et al. 2010). The neem treatments were effective at reducing the pest species and populations of coccinellids, spiders, and soil macrofauna in mulberry ecosystem increased.

A field study was conducted to evaluate the effectiveness of seven botanical pesticides, including neem oil, on pest and beneficial insect species inhabiting eggplant and okra in Ghana (Mochiah et al. 2011). All of the pesticides evaluated significantly reduced pest insect species in both crops compared to the control. These pesticides were relatively benign to the natural enemies, including spiders and lady beetles.

Tiwari et al. (2011) evaluated the effects of neem and the synthetic insecticides, imidacloprid and cypermethrin, on populations of the natural enemies, braconid wasps, coccinellids, and predatory spiders, in eggplants. They found that neem pesticides were less harmful to the natural enemies than the synthetic insecticides.

4 Conclusions

The majority of the laboratory and field studies with neem have shown that pesticides derived from this tree have little impact on spiders. Some neem products and certain spider species are sensitive to neem. However, compared to synthetic insecticides, neem pesticides are much less damaging to spiders and other beneficial insects.