**2. Exposure to systemic insecticides**

Unlike typical contact insecticides, that are usually taken up through the arthropod's cuticle or skin of animals, systemic insecticides get into the organisms mainly through feeding on the treated plants or contaminated soil. Thus, monocrotophos and imidacloprid are more le‐ thal to honey bees (*Apis mellifera)* through feeding than contact exposure [143]. Residual or contact exposure affects also some pests and non-target species alike.

Systemic insecticides are applied directly to the crop soil and seedlings in glasshouses using flowable solutions or granules, and often as seed-dressings, with foliar applications and drenching being less common. Being quite water soluble (Table 1), these insecticides are readily taken up by the plant roots or incorporated into the tissues of the growing plants as they develop, so the pests that come to eat them ingest a lethal dose and die. Sucking insects in particular are fatally exposed to systemic insecticides, as sap carries the most concentrat‐ ed fraction of the poisonous chemical for a few weeks [124], whereas leaf-eating species such as citrus thrips and red mites may not be affected [30]. Systemic insecticides contaminate all plant tissues, from the roots to leaves and flowers, where active residues can be found up to 45-90 days [175, 187], lasting as long as in soil. Thus, pollen and nectar of the flowers get contaminated [33], and residues of imidacloprid and aldicarb have been found at levels above 1 mg/kg in the United States [200]. Guttation drops, in particular, can be contaminat‐ ed with residues as high as 100-345 mg/L of neonicotinoids during 10-15 days following ap‐ plication [272]. Because these insecticides are incorporated in the flesh of fruits, the highly poisonous aldicarb is prohibited in edible crops such as watermelons, as it has caused hu‐ man poisoning [106].

As with all poisonous chemicals spread in the environment, not only the target insect pests get affected: any other organism that feeds on the treated plants receives a dose as well, and may die or suffer sublethal effects. For example, uptake of aldicarb by plants and worms re‐ sults in contamination of the vertebrate fauna up to 90 days after application [41], and honey bees may collect pollen contaminated with neonicotinoids to feed their larvae, which are thus poisoned and die [125]. Newly emerged worker bees are most susceptible to insecti‐ cides, followed by foraging workers, while nursery workers are the least susceptible within 72 h of treatment [80]. Insects and mites can negatively be affected by systemic insecticides whenever they feed on:

**1.** pollen, nectar, plant tissue, sap or guttation drops contaminated with the active ingredi‐ ent (primary poisoning);

ical used in pest control, resistance to imidacloprid by whitefly (*Bemisia tabaci*), cotton aphids (*Aphis gossypii*) and other pests is rendering ineffective this and other neonicotinoids

This chapter examines the negative impacts that systemic insecticides have on organisms, populations and ecosystems. The efficacy of these products in controlling the target pests is assumed and not dealt with here – only the effects on non-target organisms and communi‐

Unlike typical contact insecticides, that are usually taken up through the arthropod's cuticle or skin of animals, systemic insecticides get into the organisms mainly through feeding on the treated plants or contaminated soil. Thus, monocrotophos and imidacloprid are more le‐ thal to honey bees (*Apis mellifera)* through feeding than contact exposure [143]. Residual or

Systemic insecticides are applied directly to the crop soil and seedlings in glasshouses using flowable solutions or granules, and often as seed-dressings, with foliar applications and drenching being less common. Being quite water soluble (Table 1), these insecticides are readily taken up by the plant roots or incorporated into the tissues of the growing plants as they develop, so the pests that come to eat them ingest a lethal dose and die. Sucking insects in particular are fatally exposed to systemic insecticides, as sap carries the most concentrat‐ ed fraction of the poisonous chemical for a few weeks [124], whereas leaf-eating species such as citrus thrips and red mites may not be affected [30]. Systemic insecticides contaminate all plant tissues, from the roots to leaves and flowers, where active residues can be found up to 45-90 days [175, 187], lasting as long as in soil. Thus, pollen and nectar of the flowers get contaminated [33], and residues of imidacloprid and aldicarb have been found at levels above 1 mg/kg in the United States [200]. Guttation drops, in particular, can be contaminat‐ ed with residues as high as 100-345 mg/L of neonicotinoids during 10-15 days following ap‐ plication [272]. Because these insecticides are incorporated in the flesh of fruits, the highly poisonous aldicarb is prohibited in edible crops such as watermelons, as it has caused hu‐

As with all poisonous chemicals spread in the environment, not only the target insect pests get affected: any other organism that feeds on the treated plants receives a dose as well, and may die or suffer sublethal effects. For example, uptake of aldicarb by plants and worms re‐ sults in contamination of the vertebrate fauna up to 90 days after application [41], and honey bees may collect pollen contaminated with neonicotinoids to feed their larvae, which are thus poisoned and die [125]. Newly emerged worker bees are most susceptible to insecti‐ cides, followed by foraging workers, while nursery workers are the least susceptible within 72 h of treatment [80]. Insects and mites can negatively be affected by systemic insecticides

such as acetamiprid, thiacloprid and nitenpyram [247, 269].

366 Insecticides - Development of Safer and More Effective Technologies

contact exposure affects also some pests and non-target species alike.

**2. Exposure to systemic insecticides**

ties are considered.

man poisoning [106].

whenever they feed on:

**2.** prey or hosts that have consumed leaves contaminated with the active ingredient (sec‐ ondary poisoning).

Parasitoids may be indirectly affected because foliar, drench or granular applications may decrease host population to levels that are not enough to sustain them. Furthermore, host quality may be unacceptable for egg laying by parasitoid females [54]. Small insectivorous animals (e.g. amphibians, reptiles, birds, shrews and bats) can also suffer from primary poi‐ soning if the residual insecticide or its metabolites in the prey are still active. It should be noticed that some metabolites of imidacloprid, thiamethoxam, fipronil and 50% of carba‐ mates are as toxic as the parent compounds [29]. Thus, two species of predatory miridbugs were negatively affected by residues and metabolites of fipronil applied to rice crops [159]. However, since systemic insecticides do not bioaccumulate in organisms, there is little risk of secondary poisoning through the food chain.

Apart from feeding, direct contact exposure may also occur when the systemic insecticides are sprayed on foliage. In these cases, using a silicone adjuvant (Sylgard 309) reduces the contact exposure of honey bees to carbofuran, methomyl and imidacloprid, but increases it for fipronil [184]. In general the susceptibility of bees to a range of insecticides is: wild bees > honey bee > bumble bee [185]. In reality a combination of both contact and feeding exposure occurs, which is more deadly than either route of exposure alone [152, 218].

In soil, residues of acephate and methomyl account for most of the cholinesterase inhibition activity found in mixtures of insecticides [233]. Fortunately, repeated applications of these insecticides induces microbial adaptation, which degrade the active compounds faster over time [250]. Degradation of carbamates and OPs in tropical soils or vegetation is also faster than on temperate regions, due mainly to microbial activity [46]. Some neonicotinoids are degraded by soil microbes [172], and the yeast *Rhodotorula mucilaginosa* can degrade acet‐ amiprid but none of the other neonicotinoids [63], which are quite persistent in this media (Table 2).



**Chemical Group Water Field**

aldicarb C 8 **189** 6 10 (1-60) bendiocarb C 13 25 2 4 (3-20 butocarboxim C Sta ble stable - 4 (1-8) butoxycarboxim C Stable 18 (510-16) - 42 carbofuran C 71 37 (46-0.1) 9.7 14 (1-60) ethiofencarb C - 16 52 37 (34-131) methomyl C Stable stable 4 7 (5-30) oxamyl C 7 8 <1 11 pirimicarb C 6 stable **195** 9 (5-13) thiodicarb C 9 30 (69-0.3) <1 18 (1-45) thiofanox C 1 30 - 4 (2-6) triazamate C 301 2 <1 <1 cartap D - - - 3

halofenozide IGR 10 stable - **219** (60-219)

hexaflumuron IGR 6 stable - **170** novaluron IGR Stable stable 18 97 (33-160) teflubenzuron IGR 10 stable 16 14 (9-16) acetamiprid N 34 **420**<sup>a</sup> - 3 (2-20) clothianidin N 0.1 14 a 56 **545** (13-1386) dinotefuran N 0.2 stable - 82 (50-100) imidacloprid N 0.2 ~ **365** <sup>a</sup> **129 191** (104-228)

nitenpyram N NA 2.9 a - 8 thiacloprid N stable stable 28 16 (9-27) thiamethoxam N 2.7 11.5 a 40 50 (7-72) acephate OP 2 50 - 3 demeton-S-methyl OP - 56 (63-8) - 2.7 dicrotophos OP - - - 28 dimethoate OP 175 68 (156-4) 15 7 (5-10) disulfoton OP 4 **300** 15 30 fenamiphos OP <1 **304** 60 2 (1-50) fosthiazate OP Stable **104** (178-3) 51 13 (9-17) heptenophos OP - 13 7 1 methamidophos OP 90 5 24 4 (2-6) mevinphos OP 27 17 21 1 (1-12) monocrotophos OP 26 **134** - 30 (1-35) omethoate OP Stable 17 5 14 oxydemeton-methyl OP 222 73 (96-41) 3 5

phorate OP 1 3 - 63 (14-90)

Photolysis (pH 7) Hydrolysis (pH 5-7) Water-sediment Soil (range)

Impact of Systemic Insecticides on Organisms and Ecosystems

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369

**Table 1.** Physicochemical properties of systemic insecticides. C = carbamates; D = dithiol; IGR = Insect growth regulator; N = neonicotinoid; OP = organophosphate; PP = phenylpyrazole
