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Insecticidal and Nematicidal Contributions of Mexican Flora in the Search for Safer Biopesticides

Plant metabolites have been used for many years to control pests in animals and to protect crops. Here, we reviewed the available literature, looking for the species of Mexican flora for which extracts and metabolites have shown activity against pest insects and parasitic nematodes of agricultural importance, as well as against nematodes that parasitize domestic cattle. From 1996 to 2018, the search for novel and eco-friendly biopesticides has resulted in the identification of 114 species belonging to 36 botanical families of Mexican plants with reported biological effects on 20 insect species and seven nematode species. Most plant species with detected pesticide properties belong to the families Asteraceae, Fabaceae, and Lamiaceae. Eighty-six metabolites have been identified as pesticidal active principles, and most have been terpenoids. Therefore, the continuation and intensification of this area of research is very important to contribute to the generation of new products that will provide alternatives to conventional pesticide agents. In addition, future studies will contribute to the recognition and dissemination of the importance of propagating plant species for their conservation and sustainable use.


Introduction
Pest control in the agricultural sector requires a greater number of alternative products that meet food safety, sustainability, and environmental care requirements. One of the strategies used to obtain new natural agents for protecting crops and domestic animals is the exploration of a diversity of plants and their metabolites [1,2]. Natural products with pesticidal properties have been demonstrated to be an important source of compounds which are used as raw materials in the development of new protective agents, both in their natural form or as semisynthetic derivatives exhibiting better effects. In addition, the chemical structures of the active components of natural products have guided the synthesis of other active compounds [3]. The exploration and use of natural products are currently increasing, with a greater focus on identifying metabolites for use in the treatment of human diseases, including parasistism and plant diseases, as well as products for use in pest control in the agricultural sector [4][5][6][7][8][9].

Coumarin and Ketone
The leaves of R. graveolens were shown to produce psoralen (39) and a median chain ketone 2-undecanone (40), both of which were effective against neonatal S. frugiperda larvae. However, metabolite 39 was more potent than 40, with larval mortalities of 100% and 50% respectively observed at a concentration of 1 mg/mL (Table 4) [30]. Additional compounds with reported activity against S. frugiperda include palmitic (41), oleic (42), linoleic (43), and linolenic (44) acids (Table 5), which exhibited LV 50 values of ≤ 1354 ppm, with the most active compounds being unsaturated fatty acids. These active fatty acids were detected in C. papaya seeds and R. communis leaves grown in Mexico [32,33]. Both of these plant species are widely distributed, and R. communis is recognized for its pesticidal effects and high fatty acid content [34]. Furthermore, the powdered seed of C. papaya has been shown to cause larval mortality and weight reduction in S. frugiperda [35,36].
Against S. exigua, only the activity of an extract from T. havanensis seeds was reported, with an acetonic extract and its supernatant oil causing significant larval mortality and weight reduction. Furthermore, the acetone extract caused a noticeable delay in the development of S. exigua larvae when used at 500 mg/L [38].
The insecticidal activity of V. mollis extracts (dichloromethane, chloroform-methanol, and methanol) towards S. frugiperda was very interesting. A chloroform-methanol (1:1) extract from V. mollis leaves caused noteworthy mortality against S. frugiperda larvae, with an LC50 value of 13.63 ppm observed, greater than that of previously reported terpenes (vide infra). In addition, the percentage of larvae reaching pupation decreased in the presence of all of the extracts [39]. As expected, leaf and flower extracts of T. erecta showed activity against S. frugiperda larvae. At 500 ppm, the acetonic extract from leaves was the most effective, with a 50% reduction in larval weight observed after seven days. However, the hexane, acetone, and ethanol leaf extracts all exhibited lethal activities against S. frugiperda larvae, with observed LC50 values of 312.2, 246.9, and 152.2 ppm, respectively [40].
Other organic plant extracts with activity against S. frugiperda include acetonic extracts of B. copallifera, ethyl acetate extracts of B. lancifolia, and a methanol extract of B. grandifolia, which caused deformations in pupae or adults at different concentrations; acetylcholinesterase is also inhibited by these extracts [41,42]. In addition, I. murucoides, I. pauciflora, S. connivens, and S. microphylla extracts  The crude organic extracts of 10 plant species exhibited effective insecticidal activities against S. frugiperda, with one showing activity against S. exigua, the results of which are shown in Table 7. These plants included Bursera copallifera, Bursera grandiflora, Bursera lancifolia, Ipomoea murucoides, Ipomoea pauciflora, Salvia connivens, Salvia microphylla, Tagetes erecta, Trichilia havanensis, and Vitex mollis. Against S. exigua, only the activity of an extract from T. havanensis seeds was reported, with an acetonic extract and its supernatant oil causing significant larval mortality and weight reduction. Furthermore, the acetone extract caused a noticeable delay in the development of S. exigua larvae when used at 500 mg/L [38].
The insecticidal activity of V. mollis extracts (dichloromethane, chloroform-methanol, and methanol) towards S. frugiperda was very interesting. A chloroform-methanol (1:1) extract from V. mollis leaves caused noteworthy mortality against S. frugiperda larvae, with an LC 50 value of 13.63 ppm observed, greater than that of previously reported terpenes (vide infra). In addition, the percentage of larvae reaching pupation decreased in the presence of all of the extracts [39]. As expected, leaf and flower extracts of T. erecta showed activity against S. frugiperda larvae. At 500 ppm, the acetonic extract from leaves was the most effective, with a 50% reduction in larval weight observed after seven days. However, the hexane, acetone, and ethanol leaf extracts all exhibited lethal activities against S. frugiperda larvae, with observed LC 50 values of 312.2, 246.9, and 152.2 ppm, respectively [40].
Other organic plant extracts with activity against S. frugiperda include acetonic extracts of B. copallifera, ethyl acetate extracts of B. lancifolia, and a methanol extract of B. grandifolia, which caused deformations in pupae or adults at different concentrations; acetylcholinesterase is also inhibited by these extracts [41,42]. In addition, I. murucoides, I. pauciflora, S. connivens, and S. microphylla extracts displayed slight effects against first-stage larvae of S. frugiperda at high concentrations (

Plant Extracts
The screening of extracts from six plants for activity against the fourth-instar A. aegypti larvae identified those of A. mexicana and P. perniciosum as the most effective (Table 9). Hexane and acetone extracts from A. mexicana seeds and hexane extracts from the bark of P. perniciosum showed the lowest larvicidal activities, with LC50 values of, 80, 50, and 20 µg/mL, respectively [51]. Other organic extracts observed to have larvicidal activity against A. aegypti include those of R. chalepensis, T. vulgaris, and Z. fagara, exhibiting notable LC50 values of 1.8, 4.4 and 75.1 µg/mL, respectively [52]. In contrast, the aqueous extract of A. indica showed slight effects towards four different instars of C. quinquefasciatus (LD50 = 410-550 ppm) [53].

Plant Extracts
The screening of extracts from six plants for activity against the fourth-instar A. aegypti larvae identified those of A. mexicana and P. perniciosum as the most effective (Table 9). Hexane and acetone extracts from A. mexicana seeds and hexane extracts from the bark of P. perniciosum showed the lowest larvicidal activities, with LC 50 values of, 80, 50, and 20 µg/mL, respectively [51]. Other organic extracts observed to have larvicidal activity against A. aegypti include those of R. chalepensis, T. vulgaris, and Z. fagara, exhibiting notable LC 50 values of 1.8, 4.4 and 75.1 µg/mL, respectively [52]. In contrast, the aqueous extract of A. indica showed slight effects towards four different instars of C. quinquefasciatus (LD 50 = 410-550 ppm) [53].

Anastrepha ludens
Foliarn and stem extracts from three species of the family Annonaceae, Annona diversifolia, A. lutescens, and A. muricata, as well as one species of the family Magnoliaceae, Magnolia dealbata, showed good activity against the Mexican fruit fly A. ludens (Coleoptera). Among the assayed extracts, the aqueous extracts from stems exhibited the best effect at 100 µg/mL, with the greatest effect (95.9%) caused by A. lutescens (Table 10) [54,55].

Bemisia tabaci
To date, five studies have reported on the use of natural Mexican plant products in whitefly (B. tabaci) management. The results of these studies identified 11 Mexican plants with extracts that are effective against various B. tabaci life stages (eggs, nymphs, and adults). The plant species included Acalypha gaumeri, Agave tequilana, Annona squamosa, A. indica, Capsicum chinense, Carlowrightia myriantha, C. ambrosioides, Petiveria alliacea, Piper nigrum, Pluchea sericea, and Trichilia arborea.

Plant Extracts
Cruz-Estrada [57] investigated the effects of extracts from six plant species against B. tabaci eggs and reported that aqueous extracts from the leaves of A. gaumeri, A. squamosa, P. alliacea, and T. arborea exhibited activity (LC 50 = 0.36-0.42%, w/v), as did the ethanol extracts of P. alliacea (LC 50 = 2.09 mg/mL) and T. arborea (LC 50 = 2.14 mg/mL). The latter two species showed the highest activity against B. tabaci nymphs (LC 50 = 1.27 and 1.61 mg/mL, respectively). In parallel, leaf extracts from A. indica plants grown in Mexico were assayed. The toxic effects of the aqueous extracts of native plants were similar to those of A. indica aqueous extracts (LC 50 = 0.30%, w/v) and were greater than those of the A. indica ethanolic extract against eggs (LC 50 = 3.60 mg/mL) and nymphs (LC 50 = 2.57 mg/mL). A. tequilana juice (undiluted) and its hexanic extract (2%) promoted B. tabaci nymph mortality (100% and 91%, respectively), which is interesting given the significant quantities of juice obtained from the waste of this agave (Table 11) [58].
In another study (Table 11), the ethanol extracts of mature C. chinense fruits (creole orange variety) showed slight repellency and mortality effects against B. tabaci adults (LC 50 = 29.4% w/v, LT 50 = 7.31 h). The concentration of capsaicinoids in the fruit of the habanero pepper was 1193.6 mg/kg. Capsaicinoids have been reported to have toxic and repellent effects against insects [59]. Ethanolic extracts from the leaves of C. ambrosioides and the fruits of P. nigrum showed good lethal activity against B. tabaci, with the lowest LC 50 of 1.6% (w/v) observed for the P. nigrum extracts. Furthermore, P. nigrum produces high ethanolic extract yields (3.69%), and this plant is inexpensive and accessible [60]. Finally, P. sericea is an interesting Asteraceae species which the extracts of have been shown to be effective against B. tabaci adults, with acetone, aqueous, and ethanolic extracts of the leaves shown to have moderate repellence activity (RI 50 of 0.52-0.78) [61].

Prostephanus truncates
The larger grain borer (P. truncates) was shown to be susceptible to EO from the leaves of Lippia palmeri, with an LC50 value of 320.5 µL/L observed after 72 h. After the application of the EOs, a strong repellency against the insect at 200 µL/L was observed, and no insect emerged at 500 µL/L in 24 h. These EOs primarily contained 22 (58.9%) and p-cimene (66, 21.8%) as majority compounds (Table 14, Figure 7) [64].

Prostephanus truncates
The larger grain borer (P. truncates) was shown to be susceptible to EO from the leaves of Lippia palmeri, with an LC50 value of 320.5 µL/L observed after 72 h. After the application of the EOs, a strong repellency against the insect at 200 µL/L was observed, and no insect emerged at 500 µL/L in 24 h. These EOs primarily contained 22 (58.9%) and p-cimene (66, 21.8%) as majority compounds (Table 14, Figure 7) [64].

Sitophilus zeamais
The EOs of 14 plant species with activities against the stored grain pest S. zeamais were compiled. These EOs were primarily derived from members of the Asteraceae family (Aster subulatus, Bahia absinthifolia, Chrysactinia mexicana, Erigeron longipes, Eupatorium glabratum, Heliopsis annua, Heterotheca

EOs
A bioactive EO from E. glabratum exhibited high activity against female and male S. zeamais, with LC50 values of 16 and 20 µL/mL, respectively, and median lethal times of 53 and 70 h, respectively. Chromatographic analyses of E. glabratum EO revealed the presence of α-pinene (59) and αphellandrene (68,19.6%) as the major compounds (29.5%) [66]. In contrast, the pest insect S. zeamais exhibited a slight sensitivity to EO from L. palmeri leaves, with LC50 value of 441.45 µL/L against adults after 48 h. In addition, this EO induced total repellency against maize weevil adults, with no emergence observed using a concentration of 1000 µL/L after 24 h, with major EO components having been previously described (21 and 66) (Table 15, Figure 8) [64].

Plant Extracts
Juárez-Flores [67] screened flower powder and leaf powders from 81 plant species belonging to the Asteraceae family. Among the 162 plant powders tested (1%, w/w), twelve powders showed remarkable lethal activities (>80%) against S. zeamais, but only two inhibited adult emergence (<22 insects), B. absinthifolia and C. Mexicana (Table 15). The most effective of these powders were those produced from the leaves of C. mexicana, which caused a mortality of 98% and no adult emergence. Similarly, the root powder of S. perforates mixed with maize kernel (3%) displayed total mortality against S. zeamais [68], while an acetone extract produced from the roots of H. celastroides and its precipitate resulted in slight antifeeding activity index values of 72.3 and 73.8 against the stored grain pest S. zeamais, respectively (Table 15) [65].

EOs
A bioactive EO from E. glabratum exhibited high activity against female and male S. zeamais, with LC 50 values of 16 and 20 µL/mL, respectively, and median lethal times of 53 and 70 h, respectively. Chromatographic analyses of E. glabratum EO revealed the presence of α-pinene (59) and α-phellandrene (68,19.6%) as the major compounds (29.5%) [66]. In contrast, the pest insect S. zeamais exhibited a slight sensitivity to EO from L. palmeri leaves, with LC 50 value of 441.45 µL/L against adults after 48 h. In addition, this EO induced total repellency against maize weevil adults, with no emergence observed using a concentration of 1000 µL/L after 24 h, with major EO components having been previously described (21 and 66) (Table 15, Figure 8) [64].

Plant Extracts
Juárez-Flores [67] screened flower powder and leaf powders from 81 plant species belonging to the Asteraceae family. Among the 162 plant powders tested (1%, w/w), twelve powders showed remarkable lethal activities (>80%) against S. zeamais, but only two inhibited adult emergence (<22 insects), B. absinthifolia and C. Mexicana (Table 15). The most effective of these powders were those produced from the leaves of C. mexicana, which caused a mortality of 98% and no adult emergence. Similarly, the root powder of S. perforates mixed with maize kernel (3%) displayed total mortality against S. zeamais [68], while an acetone extract produced from the roots of H. celastroides and its precipitate resulted in slight antifeeding activity index values of 72.3 and 73.8 against the stored grain pest S. zeamais, respectively (Table 15) [65].

Tenebrio molitor and Trichoplusia ni
Sterols 15 and 16 (Figure 1) from M. geometrizans (Cactaceae) and their combination (6:4) exhibited a high toxicity against the last-instar larvae of T. molitor, the yellow mealworm, causing acute toxicities with 5, 3, and 0% survival at 100 ppm, respectively. Interestingly, 15, 16, and their combination induced shortened T. molitor pupation and emergence, and many of the pupae died
Only one report described assays against the cabbage looper T. ni, where volatile organic compounds from A. indica stems promoted significant neonatal and larval mortality (24 and 77%, respectively) at 1 g doses and an LD 50 of 5.6 g after 7 days (Table 17) [71].

EOs
Native populations of T. filifola in Mexico contain high proportions of anethole, a phenylpropene present in the EOs from the plant. Therefore, the EOs from the flowers, leaves, and whole plants of T. filifolia were tested together with a commercial standard of trans-anethole (70) against T. vaporariorum. The lowest LC 50 value was observed using 70 ( Figure 10), which produced an LC 50 value of 1.74 mg/mL and a median oviposition inhibition concentration (IOC 50 ) of 1.55 mg/mL, followed by the floral oil (LC 50 = 6.59 mg/mL), the foliar oil (LC 50 = 10.29 mg/mL), and the whole plant oil (LC 50 = 9.99 mg/mL). Another parameter measured was the median repellent concentration (RC 50 ), with the floral oil being the most effective with an RC 50 value of 0.13 mg/mL against T. vaporariorum. The second instar of the nymphal stage of T. vaporariorum was noticeably sensitive to foliar oil (Table 18) [72].
Molecules 2019, 23, x 20 of 36 the floral oil (LC50 = 6.59 mg/mL), the foliar oil (LC50 = 10.29 mg/mL), and the whole plant oil (LC50 = 9.99 mg/mL). Another parameter measured was the median repellent concentration (RC50), with the floral oil being the most effective with an RC50 value of 0.13 mg/mL against T. vaporariorum. The second instar of the nymphal stage of T. vaporariorum was noticeably sensitive to foliar oil (Table 18) [72].

Plant Extracts
Mendoza-García [73] reported that an ethanolic extract of P. auritum was the most toxic extract (LC50 = 116 mg/mL) tested against T. vaporariorum and that an aqueous extract of R. raphanistrum effectively inhibited oviposition (IOC50 = 77.3 mg/mL) against the greenhouse whitefly.

Plant Extracts
Mendoza-García [73] reported that an ethanolic extract of P. auritum was the most toxic extract (LC 50 = 116 mg/mL) tested against T. vaporariorum and that an aqueous extract of R. raphanistrum effectively inhibited oviposition (IOC 50 = 77.3 mg/mL) against the greenhouse whitefly.
Evaluations of extracts applied to tomato crops under greenhouse conditions were reported to control T. vaporariorum. In one study, aqueous, methanol, and dichloromethane extracts from P. alliacea leaves showed remarkable LC 50 values of 16.6, 13.3, and 3.5%, respectively [74]. In contrast, methanolic extracts from A. donax and P. icosandra exhibited slightly higher target LC 50

Zabrotes subfasciatus
The species L. palmeri and Senecio salignus exhibited effective activities against Z. subfasciatus, the main pest of common beans (Phaseolus vulgaris). A 0.07% solution of a root powder of the Asteraceae species S. salignus exerted lethal toxicity by contact against bean weevil adults after five days. When the concentration was increased, fewer days were required to control the pest, with a 0.07% solution producing LC 50 values of 0.03% and 0.08% after 3 days and median lethal times of 1.21 and 3.20 days observed for male and females, respectively. Therefore, males were more sensitive than females. In addition, the authors determined the optimal size of the root powder that should be used (<0.25 mm particles) [76].

EOs
EOs obtained from leaves of L. palmeri collected in the localities of Puerto de Oregano (PO) and Alamo (Al) exhibited lethal and ovicidal activities against Z. subfasciatus at 1.35 µL/g, with two months of persistence. EOs from leaves collected in PO was slightly more lethal than EOs obtained from leaves collected in Al. A comparison of the components of the two EOs revealed a number of differences, with carvacrol (22, 37.35%), thymol (21,24.56%), and p-cimene (64, 15.62%) being abundant in EO from PO, whereas 64 (33.7%) and 22 (18.32%) were abundant in EOs from Al (Table 19) [77].

Plant Extracts Effective against Parasitic Plant Nematodes
Although data on the subject is scarce, we focused on compiling reports on plants that have toxic effects on phytonematodes Meloidogyne incognita, Meloidogyne javanica, and Nacobbus aberrans. A total of twelve metabolites from M. helleri, S. bulbosus, and C. annuum have been purified and identified as active principles against plant parasite nematodes.

Meloidogyne incognita
Plant extracts from Calea urticifolia, E. winzerlingii, and Tephrosia cinerea were shown to have lethal activities against M. incognita (Table 20). An aqueous extract from the roots of C. urticifolia was tested on second-stage M. incognita juveniles under greenhouse conditions. The results showed that 50% (w/v) of the C. urticifolia root extract effectively reduced gall formation (50%) and the number of eggs (72% reduction) on tomato seedlings that had been inoculated with 1000 eggs and 130 M.

Meloidogyne incognita
Plant extracts from Calea urticifolia, E. winzerlingii, and Tephrosia cinerea were shown to have lethal activities against M. incognita (Table 20). An aqueous extract from the roots of C. urticifolia was tested on second-stage M. incognita juveniles under greenhouse conditions. The results showed that 50% (w/v) of the C. urticifolia root extract effectively reduced gall formation (50%) and the number of eggs (72% reduction) on tomato seedlings that had been inoculated with 1000 eggs and 130 M. incognita J 2 [80]. Ethanol extracts from the roots of C. urticifolia, the stems of T. cinerea, and the leaves of E. winzerlingii produced immobility in M. incognita J 2 (>80%) when applied at 250 ppm. Finally, the ethanol extract from E. winzerlingii leaves was very active against M. incognita and had the lowest LC 50 (133.4 ppm) of the tested extracts [81].

Plant Extracts with Activity against Parasitic Animal Nematodes
To date, 27 plant species have been identified with an effect against animal nematodes, 12 of which belong to the family Fabaceae (43%). The relevant studies primarily focused on the control of Haemonchus contortus (93%): one study investigated Haemonchus placei, and three investigated Trichostrongylus colubriformis, zooparasites of sheep. In addition, three studies focused on Cooperia puntacta and Cyatostomin sp., zooparasites of grazing cattle and horses, respectively, and one focused on Ascaridia galli, a bird parasite. Herein, the active plant extracts are included, as well as some fractions or subfractions, with the predominant compounds described by the authors. Only five natural compounds were reported to have an anthelmintic activity against animal nematodes, two of which were purified and identified from plant species and the remaining two as enriched fractions, with compound rutin (35) assayed as a commercial standard.

Ascaridia galli
Only one study investigated the effect of metabolites from T. graveolens (Amaranthaceae) against A. galli. Flavonoid 69 (Figure 9) was the active ingredient isolated from the aerial parts of T. graveolens, and it had an LC 50 of 623.5 µg/mL against A. galli (Table 21) [69].

Cooperia puntacta
Plant species with ovicidal activity against C. puntacta included G. sepium and L. leucocephala. These plants were extracted with water, acetone-water 30:70, and acetone solvents, and all of these fractions were tested. For each plant, at least one of the extracts showed ovicidal activity. The most effective were the acetone extract from G. sepium and the aqueous extract from L. leucocephala, which showed significant LC 50 values of 1.03 and 7.93 mg/mL on egg hatching inhibition (EHI), respectively. The addition of a tannin inhibitor (polyethylene glycol) in all of the extracts showed that, with the exception of the G. sepium acetone extract, all exhibited enhanced ovicidal effects. Next, an aqueous extract of L. leucocephala was fractionated using chromatographic methods. Among the fractions obtained, the highest ovicidal effect was observed in LlC1F3, with an LC 50 value of 0.06 mg/mL detected on Cooperia spp. The analytical data indicated that the majority of components in LlC1F3 were quercetin (83,82.21%) and caffeic acid (84,13.42%) [82,83].

Cyatostomin sp.
An investigation on the control of the zooparasitic nematode Cyatostomin sp. using plant extracts was recently reported [86]. The authors indicated that methanol extracts from the leaves and bark of Diospyros anisandra (Ebenaceae) and the leaves and stems of P. alliacea, which were collected in the rainy seasons, showed promising activities in controlling the eggs and the development of L1 Cyastotomin sp. larvae. The highest ovicidal activity was produced by the bark extract of D. anisandra, followed by the leaf extract, both of which were collected in the rainy season. These extracts presented LC50 values of 10.28 and 18.48 µg/mL on the EHI, respectively, while extracts from P. alliacea exhibited lower lethal activities (LC50 ≥ of 28.27 µg/mL). However, P. alliacea stems, which were also collected in the rainy season, induced the failed eclosion of larvae (90.7% at 75 µg/mL). The continued study of both plant species was highly recommended (Table21) [86].

Haemonchus placei
A hydroalcoholic extract with significant activity against H. placei, was obtained from Caesalpinia coriaria. In this case, the extracts from fruits presented a greater activity than the leaves, with LC50 values of 3.91 and 11.68 mg/mL, respectively [87].

Haemonchus contortus
In ruminants, H. contortus is one of the most important gastrointestinal parasitic nematodes in

Cyatostomin sp.
An investigation on the control of the zooparasitic nematode Cyatostomin sp. using plant extracts was recently reported [86]. The authors indicated that methanol extracts from the leaves and bark of Diospyros anisandra (Ebenaceae) and the leaves and stems of P. alliacea, which were collected in the rainy seasons, showed promising activities in controlling the eggs and the development of L 1 Cyastotomin sp. larvae. The highest ovicidal activity was produced by the bark extract of D. anisandra, followed by the leaf extract, both of which were collected in the rainy season. These extracts presented LC 50 values of 10.28 and 18.48 µg/mL on the EHI, respectively, while extracts from P. alliacea exhibited lower lethal activities (LC 50 ≥ of 28.27 µg/mL). However, P. alliacea stems, which were also collected in the rainy season, induced the failed eclosion of larvae (90.7% at 75 µg/mL). The continued study of both plant species was highly recommended (Table 21) [86].

Haemonchus placei
A hydroalcoholic extract with significant activity against H. placei, was obtained from Caesalpinia coriaria. In this case, the extracts from fruits presented a greater activity than the leaves, with LC 50 values of 3.91 and 11.68 mg/mL, respectively [87].

Haemonchus contortus
In ruminants, H. contortus is one of the most important gastrointestinal parasitic nematodes in sheep and goats, as well as H. placei, a hematophagous parasite in bovines. Several plant extracts exhibited promising activities in controlling the larval stage of H. contortus in vitro (Table 22. Among these extracts, the dichloromethane extract from Phytolaccca icosandra leaves (Phytolaccaceae) was one of the most active, with an LD 50 of 0.90 mg/mL on larval migration inhibition and an LD 50 of 0.28 mg/mL on egg hatch inhibition (EHI) in H. contortus. Additionally, ethanolic extracts from the same plant caused >92% of EHI at a 0.9 mg/mL in vitro level [88]. In addition, the methanolic extract from Gliricidia sepium (Fabaceae) displayed a good EHI effect, with an ED 50 value of 394.96 µg/mL [89]. The hydroalcoholic extract from the leaves of Acacia cochliacantha (Fabaceae) showed total mortality against eggs of H. contortus. However, this extract was used at a high concentration (100 mg/mL), and its organic fraction obtained with ethyl acetate displayed one of the lowest EHI at an LC 50 of 0.33 mg/mL. This EHI effect increased ten-fold when it was subfractionated with dichloromethane to produce soluble and precipitate subfractions, with the low LC 50 values of 0.06 and 0.04 mg/mL observed, respectively. The ethyl acetate fraction was enriched with caffeoyl and coumaroyl derivatives [90]. The hydroalcoholic extract from C. coriaria showed a slightly higher effect against H. contortus larvae than on H. placei. In this case, the extracts from fruits presented LC 50 values of 1.63 and 3.98 mg/mL, respectively [87]. In addition, the ethanol extract from the seeds of C. papaya (Caricaceae) induced an EHI of 92% at 2.5 mg/mL [91].
The extracts of partially purified tannins obtained from the leaves of Arachis pintoi, L. leucocephala, Guazuma ulmifolia, and Manihot esculenta reduced the migration of the third-stage larvae of H. contortus by 69.9-87.4% at 4.5 µg/mL and 74.2-100% at 45 µg/mL after 96 h of exposure. However, an ovicidal effect from these plants was not observed [92]. Alonso-Diaz [93] confirmed the role of tannins in the larvicidal effect of L. leucocephala and other tropical Fabaceae, Acacia pennatula and Lysiloma latisiliquum, with larval migration inhibitions (LMI) of 51-53.6% at 1200 µg/mL through the use of polyvinyl polypyrrolidine, an inhibitor of tannins. In contrast, Piscidia piscipula was not affected. Vargas-Magaña [94] demonstrated that tannins in a 30% acetone-water extract (3600 µg/mL PBS) from the leaves of Laguncularia racemose blocked the eclosion of eggs of H. contortus (50.29%). Besides, Senegalia gaumeri induced an EC 50 of 401.8 and 83.1 µg/mL of EHI and larval mortality on H. contortus, respectively [95].
In in vitro studies, other investigations reported a lesser effect (20-40 mg/mL) on H. contortus larval mortality, including the hexane extract from the aerial parts of Prosopis laevigata, an acetone extract from the stem of B. copallifera [96], a hydro-methanolic extract from Larrea tridentata and aqueous extracts from Cydista aequinoctialis, Heliotropium indicum, and Momordica charantia (Table 22) [97,98].
There are seven reports on in vivo experiments that describe the effects of plant extracts. One of these studies included a mixture of extracts from the bulbs of A. sativum and the flowers of T. erecta. First, the extracts alone or in combination were tested in vitro. After 72 h, the lowest larval mortality of H. contortus (L 3 ) occurred at an LC 50 of 1.3 mg/mL, which was induced by the mixed extract (Table 22). Subsequently, it was administered in one dose of 100 µg/mL (40 mg/mL) to gerbils infected with H. contortus (L 3 ). After 13 days, the nematode in the gastric lumen of both treatment and control animals were counted. The highest larvae population reduction (LPR) was 87.5%, which was induced by the T. erecta and A. sativum mixed extracts. Each extract of these plants alone showed a lower effect in comparison with their combination in both assays, suggesting a synergistic action [99]. Similarly, Zamilpa [100] reported that a combined extract from the aerial parts of Castela tortuosa and C. ambrosioides induced a 57.36% population reduction on L 3 H. contortus in infected gerbils (Table 23). In contrast, in vitro, the lowest lethal activity was produced by a hexane extract of C. ambrosioides (LC 50 = 1.5 mg/mL) at 72 h (Table 22). Other hexane extracts administered (100 µg/mL at 40 mg/mL) to gerbils was from Prosopis laevigata, which reduced parasite population (42.5%) [101].  An organic ethyl acetate fraction obtained from aqueous extracts of Lysiloma acapulcensis leaves showed a high EHI on L 3 (94.85%) at 6.25 g/mL and a 100% larval mortality at 50 mg/mL after 72 h at the in vitro level. Subsequently, an organic fraction of dry and ground leaves of L. acapulcensis and the flavonol rutin (35) used to treat infected sheep were tested in vivo. The reduction in the excretion of eggs per gram (EPGR) of faeces was recorded, with 35 and the ethyl acetate fraction exhibiting a 66.2 and 62.9% EPGR at a concentration of 10 and 25 mg/kg body weight (BW), respectively. The application of the ethyl acetate fraction was more effective than dried leaves (5 g/kg BW), presenting a 62.9% EPGR. The chromatographic separation of the ethyl acetate fraction revealed the presence of the flavonol myricitrin (87) as a major component, though this enriched fraction was not tested (Figure 13). In this experiment, the larvae of Cooperia curticei, H. contortus, and Teladorsagia circumcincta and the eggs of Trichuris sp. from faeces were identified by morphological and morphometric analyses [102]. Another in vivo test was reported with the ethanolic extract from P. icosandra leaves which was encapsuled and orally administered to infected goats. Results showed a reduction of 72% in H. contortus eggs/g of faeces at two doses of 250 mg/kg BW, on day 11 post-treatment (Table 23). Fatty acids and a ketone were detected in the ethanol extract of P. icosandra as major components [103].
circumcincta and the eggs of Trichuris sp. from faeces were identified by morphological and morphometric analyses [102]. Another in vivo test was reported with the ethanolic extract from P. icosandra leaves which was encapsuled and orally administered to infected goats. Results showed a reduction of 72% in H. contortus eggs/g of faeces at two doses of 250 mg/kg BW, on day 11 posttreatment (Table 23). Fatty acids and a ketone were detected in the ethanol extract of P. icosandra as major components [103]. In further studies, a hydroalcoholic extract from Oxalis tetraphylla (Oxalidaceae) leaves was orally applied daily (20 mg/kg BW) for eight days to lambs infected with H. contortus. The results showed a 45.6% reduction in the number of eggs/gram of faeces. Flavonol compounds in O. tetraphylla were also detected [104].
Finally, an in vivo test in goats, Creole male kids, experimentally infected with L3 H. contortus was reported. In this investigation, kids were fed fresh leaves (10% of the total diet) of A. cochliacantha, G. ulmifolia, and Pithecellobium dulce (Fabaceae) for sixty days. A lower EPG was observed in kids fed with A. cochliacantha and P. dulce, with 1.28 Log 10 and 1.48 Log 10 , respectively. Moreover, the total body weight in kids noticeably increased with P. dulce foliage in the diet, with 0.2% (control) to 2.4% kg/animal (treatment) weight gained, which was attributed to the decrease in parasite load [105] ( Table 23).  In further studies, a hydroalcoholic extract from Oxalis tetraphylla (Oxalidaceae) leaves was orally applied daily (20 mg/kg BW) for eight days to lambs infected with H. contortus. The results showed a 45.6% reduction in the number of eggs/gram of faeces. Flavonol compounds in O. tetraphylla were also detected [104].
Finally, an in vivo test in goats, Creole male kids, experimentally infected with L 3 H. contortus was reported. In this investigation, kids were fed fresh leaves (10% of the total diet) of A. cochliacantha, G. ulmifolia, and Pithecellobium dulce (Fabaceae) for sixty days. A lower EPG was observed in kids fed with A. cochliacantha and P. dulce, with 1.28 Log 10 and 1.48 Log 10 , respectively. Moreover, the total body weight in kids noticeably increased with P. dulce foliage in the diet, with 0.2% (control) to 2.4% kg/animal (treatment) weight gained, which was attributed to the decrease in parasite load [105] (Table 23).

Species/Family
Plant Part Extract (Toxicity) Ref.

Conclusions
This review demonstrates the relevant pesticidal activity of several native plant species of Mexico, the majority of which were reported at the in vitro level, while some were reported in in vivo assays. Unfortunately, at present, research on bioprospecting plant species from Mexican flora with the aim of developing natural pesticides against insects and nematode pests is still in its early stages. To date, only 114 species of Mexican plants with biological activity against insects or nematode pests have been reported, most of which belong to the Asteraceae (20%), Fabaceae (15%), and Lamiaceae (11%) families ( Figure 14). The investigations on the activities of these plants have primarily focused on evaluating the biological activity of raw vegetable extracts or their enriched fractions, and less than 35% have led to the purification, identification, and evaluation of the active compounds. Among the most common metabolites with activity detected against some of the tested targets are terpenes (58%), followed by phenols and flavonoids. A mixture of extracts or their pure compounds provides a strategy in the search for natural and safer pesticides. Despite these limitations, species with a high potential for effectiveness were identified for further study in the development of biotechnological products. Evaluations of promising plant extracts in the field are needed to identify appropriate formulations. Therefore, the use of an adequate and low-cost extract should be considered during in vitro evaluations. Although botanical pesticides are less persistent in the environment, toxicological studies on beneficial organisms and mammals should still be performed.
The high diversity of plant species in Mexico coupled with the increasing demand and urgency for new natural pesticides makes it extremely important to continue bioprospecting studies in this country. Additional studies will help generate new and alternative natural products that can improve the biological effectiveness, lower residuals, and increase the innocuousness of agricultural products as well as decrease their presence in foods. These studies will contribute to the recognition and dissemination of the importance of propagating plant species for their conservation and sustainable use. Evaluations of promising plant extracts in the field are needed to identify appropriate formulations. Therefore, the use of an adequate and low-cost extract should be considered during in vitro evaluations. Although botanical pesticides are less persistent in the environment, toxicological studies on beneficial organisms and mammals should still be performed.
The high diversity of plant species in Mexico coupled with the increasing demand and urgency for new natural pesticides makes it extremely important to continue bioprospecting studies in this country. Additional studies will help generate new and alternative natural products that can improve the biological effectiveness, lower residuals, and increase the innocuousness of agricultural products as well as decrease their presence in foods. These studies will contribute to the recognition and dissemination of the importance of propagating plant species for their conservation and sustainable use.