Introduction

In Mexico there is no precise information indicating the volume of loss of grains and seeds. However, it is estimated that annually is lost between 5% and 25% of total production of corn, wheat and beans, the main staple grains in the country (Hernández and Carballo, 2014). The grain and seed are living things that breathe oxygen from the environment and produce carbon dioxide, water and energy is transformed into heat; consequently, to the extent that the breathing process is accelerated, it will also deterioration grain or seed, causing the development of insects, mites, fungi and microorganisms, which by feeding decrease the amount and food and commercial quality grain (^{Lagunes and Rodríguez, 1989}; ^{Lannacone and Lamas, 2003a}).

The insects also represent one of the main causes in post-harvest losses of grains or seeds. These mainly they affect small producers and in particular temporary, for lack of appropriate storage media, as well as the misuse of pesticides and sometimes complete lack of them, for their high costs (^{FAO, 2010}). In Mexico, there are more than twenty species of economically important insects that attack stored grains and seeds; fifteen species of which belong to the Coleoptera and Lepidoptera orders (^{Moreno, 1992}, ¹⁹⁹⁶). Among the most important insects that damage and affect the quality of grains and seeds, are the weevil or bruco bean (Acanthoscelides obtectus Say), the weevil wheat (Sitophilus granarius L.) and maize weevil (Sitophilus zeamais M.) (^{FAO, 2010}).

The chemical insecticides generate negative effects on humans for its high potential for bioaccumulation and prolonged residual power. An alternative to this problem is the use of natural products derived from plants, usually biodegradable and do not produce an imbalance in the ecosystem (^{Lannacone and Reyes, 2001}; ^{Lannacone and Lamas, 2003a}).

The use of plant extracts is a technique recovered from subsistence farming countries in Africa and Central America mainly (^{Lagunes and Rodríguez, 1989}). Among the plant species that have been used for insect control in grain or seed is garlic (Allium sativum) for their active agents of allicin and disulphide alipropilo, castor oil plant (Riccinus communis) for their active ingredients ricin and ricinina and the governor (Larrea trindetata) for its active ingredients of the resin (^{Seigler, 1998}; ^{Rodríguez, 2000}).

The seed quality is one of the most important factors affecting a greater extent the potential of a variety performance and therefore success in agriculture. On the other hand, the high moisture content in the grain during storage, favors the development of insects, mites, fungi and microorganisms, which by feeding reduce the amount and food and commercial quality of grain and seed (^{Ramírez et al., 1993}). The germination capacity and vigor are the main attributes involved in the physiological component of seed quality. The vigor of the seed is the biological potential that favors the rapid establishment and uniform under field conditions, including unfavorable. Whereas germination is the physiological process by which emerge and develop, from the embryo, the essential structures for the formation of a normal plant under favorable conditions (^{Delouche, 2002}). The ability to germinate and vigor are the two most important indicators of the quality of the seed (^{Odindo, 2007}).

Based on the above objectives of this research were to evaluate the control storage pests in corn, wheat and beans with garlic powder, oils castor oil plant and governor, and the effect that causes tríese bio-insecticides in the physiological seed quality.

Materials and methods

The work was done in 2011, at the Seed Analysis Laboratory Institute of Technology Roque, located in Celaya, Guanajuato, Mexico (20° 31' north latitude, 100° 45' west longitude and 1 765 masl). The climate of the experimental site is semi warm BS1Hw (e), with a rainfall of 550-710 mm during the year and annual average temperature of18.4 °C (^{INEGI, 2012}).

Vegetable powders

The garlic powder (Allium sativum), leaf, stem and cascara, castor seed oil (Riccinus communis) and leaf and stem governor (Larrea trindetata) for the active ingredients of the resin (Table 1) were evaluated.

Table 1 Description of treatments consisting powders and vegetable oils and combinations thereof at two concentrations. Roque. Celaya, Guanajuato, Mexico. 2011. 

C₁, concentración de 0.1 g y C₂, concentración 0.2 g.

For the preparation of coal dust, plants were collected in flowering stage castor oil plant young leaves, stems and leaves of governor, and the extract of garlic bulbs were acquired business. Each of the parts of the plants for the extraction of insecticide products were washed with running water to eliminate possible contamination present in them, then washed with distilled water. Subsequently they were placed on paper and protected from sunlight. Seven days then placed in an incubator convention gravity (Precision Scientific Model J1755-1A), at 60 °C until the constant weight. Once the dry samples were ground separately in a coffee grinder (Braun model KSM-2) to a fine powder which was sieved in a number 20 mesh with holes of 0.84 mm diameter. Each extract was passed through Whatman filter paper WL No.1 to remove residues of plant tissue.

The extract castor oil, was performed on previously collected seed, these were dried in an oven for three days at 200 °C, then ethyl alcohol was added 95% and allowed to stand for three days, giving washings continuous during this period with distilled water. Immediately proceeded to grind the seed and placed in 95% ethanol for 72 h, performing every 24 h continuous washing with the same solution. Immediately thereafter, the two liquid phases were separated by decantation, the upper phase was taken and placed in Eppendorf tubes and centrifuged at 400 rpm to finally obtain the oil.

For increasing the mother colony insect populations under study, 50 adult weevils corn (Sitophilus zeamais), 50 weevils (Sitophilus granarius) and 50 weevils bean (Acanthoscelides obtectus) were placed in 200 g of sample seed corn, wheat and beans, respectively.After oviposition period, adults were removed and the plastic containers and bottles corn, wheat and beans were kept at a temperature of 25 ± 3 °C and 67 ± 8% relative humidity. For species identification keys used ^{Pereira and Massutti, (2001)}.

For conducting bioassays, were placed 50 insects of Sitophilus zeamais, Sitophilus granarius and Acanthoscelides obtectus in 200 g in seed corn, wheat and beans respectively. The seed of each crop was placed in square plastic containers of 1000 mL. In all treatments, powder oils plants and two concentrations were used: 0.1 g and 0.2 g per 200 g of seed species tested (^{Lannacone et al, 2004}). In addition, a control was used (without application of powders and oil). Each experimental unit was represented by a vessel, repeated three times. The experimental design was completely randomized factorial arrangement, factor A. extracts and factor B, concentrations, 11 treatments and three replications (Table 1).

The mortality was assessed at 24, 48 and 144 h after infestation, registering the dead and live insects, insect was considered dead if this upon receiving a stimulus of heat through an iron laboratory was still motionless. The data obtained mortality count underwent processing for statistical analysis.

The evaluation of physiological seed quality testing was performed with standard germination test and vigor by emergency speed evaluated on the fourth day (ISTA, 1995). To carry out these tests as sanita paper substrate is used, 50 seeds per treatment were placed in three replications, under a completely randomized design. Two counts were made; the first four days after sowing to evaluate the effect quantifying total normal seedlings germinated to determine emergency speed. The second count was performed at seven days, in which the total number of normal seedlings, abnormal seedlings, hard seeds and dead seeds were evaluated. Both variables were transformed to percentage.

For all characters was evaluated by analysis of variance using the PROC GLM procedure of SAS statistical package (^{SAS, 1999}) see. 8.1. The multiple comparison of means was performed according to the minimum significant difference test (DMS, p≤ 0.05 and 0.01).

Results and discussion

For variables of mortality at 24, 48 and 144 h, vigor and germination percentage of the extracts evaluated for control of Sitophilus zeamais M. in corn seeds, significant differences (p≤ 0.01) was observed; which means that at least one treatment is different. Coefficients of variation range from 9.51 to 17.43%. On the other hand, for the source of variation treatments evaluated for weevil control in wheat significant difference (p≤ 0.01) was found for the variable mortality at 24, 48 and 144 h, whereas for the given force by the speed of germination 4 day effect was significant (p≤ 0.05) and the percentage of germination no difference was observed. For this study the coefficient of variation ranged between 3.9 to 19.88%. In the trial of Acanthoscelides obtectus in bean seeds, treatments significant differences (p≤0.01) for mortality was observed in all evaluation times and for the vigor of the seed and the final percentage of germination. Variation coefficients ranging from 6.38 to 22.89% (Table 2).

Table 2 Mean squares for the percentage mortality of the weevils Sitophilus zeamais, Sitophilus granarius and Acanthoscelides obtectus, and quality of seeds of maize, wheat and beans. Roque, Celaya, Guanajuato, Mexico. 2011. 

¹Vigor (%); ² Porcentaje de germinación. SM= semilla de maíz; ST= semilla de trigo y SF= semilla de frijol.

In the Table 3, shows that the best treatment to control Sitophilus zeamais in corn seed was castor oil in both concentrations C₂ and C₁, 100% of the population of this insect was monitored from the first sampling (24 h). Similar results reported ^{Cerna et al. (2010)}, who in a similar study found an insect control store corn 92% and 100% at 92 h with soybean oil and castor, respectively, whereas in trials where they used extract cilantro as biopesticide in weevils corn 25% observed mortality (^{Lannacone et al, 2004)}. lower than those observed in this study percentages are reported by ^{Andrews (1989}) who mentions that an organic treatment was showed better result in controlling maize weevil with Azadirachta indica with 2.98% and with chemical treatment, using aluminum phosphide 6 months storage showed more effective damage control to 1.96%.

Table 3 Average mortality of Sitophilus zeamais M., vigor and germination percentage of seed corn bio-insecticides. Roque, Celaya, Guanajuato, Mexico. 2011. 

C₁, concentración de 0.1 g y C₂, concentración 0.2 g.

Treatment garlic powder concentration 1 (C₁) at all exposure times was the least deaths caused weevil (34.92, 50.83 and 75.69%, respectively). Our results agree with those reported by ^{Issa et al. (2011)} with garlic extracts Sitophilus 96 h assessment. These results indicate that as the extract this for long periods contact weevil mortality increases thereof, this is observed in the other treatments evaluated as time elapses contacting the extract with insect mortality increases. It is important to note that the costs in control of this weevil increase with garlic for being a plant of great economic importance, in contrast to other treatment, which virtually come from wild plants where the farmer can obtain them free of charge. Meanwhile, ^{Cerna et al. (2010)} in a study of Sitophilus zeamais reported that soybean oil showed the best control by causing higher mortality at 92 and 100% at 192 h of exposure.

With regard to seed vigor, evaluated on the fourth day (first count) by the rate of germination; It found that garlic powder treatment concentration 0.2 g (C₂) expressed the highest value (56.10%), followed by treating leaf and stem castor at the same concentration, with a value of54.46%. These results exceed the witness in which 48.02% was observed. On the other hand, castor oil treatments in both concentrations (C₁ and C₂) controlled 100% of the insect (Table 3) expressed the lowest percentage of force with values of27.35 and 9.85%.

The standard germination test is not affected by most of plant extracts used for insect control in stored seed. Although it is important to indicate that the castor oil applied to 0.2 g (C₂) significantly decreased the percentage of normal seedlings (51.4%). These results are partly similar to those reported by ^{Cerna et al. (2010)} who conclude that soybean oil significantly affect germination at doses of2 000 to 10 000 ppm with values below 90%. Also, ^{Salas (1985)} castor oil use in maize seed, observed low germination; similarly, ^{Hall and Harman (1991)} reported 75% germination in maize seeds treated with soybean oil. While ^{Silva-Aguayo et al. (2004)} found that diatomaceous earth and calcium carbonate control up to 80% to Sitophilus zeamais and the percentage of germination was not affected. In other research has identified different compounds that meet the definition of secondary metabolite and revealing regulatory activity or stimulatory growth of the plant, among these are the abscisic acid, sterols, cucurbitacins and naphthoquinonejuglone (^{Schnabl et al, 2001}). In this topic, ^{Macías et al. (2005)} confirmed that the sesquiterpene lactones present in strigolactones are specific inducers of Orobanche cumana Wallr germination.

In the Table 4, shows that the best treatment for controlling weevil wheat was castor oil in both concentrations, killing 100% of wheat weevil from the first sampling (24 h), these results outperform reported by ^{Arango et al. (2008)}) who in a study extracts Verbena offinalis at concentrations of 0.16% reported a mortality of wheat weevil 50%, similarly, in a study to control pests on the foliage of tomato confirms that the castor at a concentration 50% presented a 81% mortality of whitefly (^{Carrillo-Rodriguez et al, 2008}). In all treatments at 0.2 g concentration (C₂) the highest mortality was observed compared with the concentration of 0.1 g (C₁) at the three extract-weevil exposure.

Table 4 Percentage of mortality of Sitophilus granarius L. and its relationship with quality of wheat seed. Roque, Celaya, Guanajuato, Mexico, 2011. 

C₁, concentración de 0.1 g y C₂, concentración 0.2g.

Treatment garlic powder 0.1 g (C₁) was the least efficient to control weevils in wheat seed in all exposure times (24, 48 and 144 h). However, when the concentration twice the active ingredient (C₂) was used, the amount of dead weevils increase with exposure time. It is noteworthy that the number of dead weevils increase over time and the largest concentration with all extracts; this means that there is a high probability that those extracts that did not reach 100% control at 144 h, achieve more contact time with weevils. In this regard, ^{Guillen-Sanchez et al. (2001)} suggest exposure times of 24 and 48 h to achieve at least 50% of dead insects. However, a higher mortality rate at 50% is acceptable and defines the response threshold (^{Lagunes and Rodríguez, 1989}) therefore, these treatments are acceptable for controlling storage pests.

With regard to seed vigor, it was found that the treatment consisting of leaves and stems of governor (C₁ and C₂), shell castor oil plant (C₁ and C₂) and garlic in C₁, exceed the control (41.86%) in the variable first count to normal plantlets. Therefore, these plant extracts can be considered as stimulators of the vigor of wheat seed.

For standard germination test it found that castor oil applied to the seed to C₂ reduces the percentage of germination by 41% compared with the control. On the other hand, plant extracts composed peel castor oil plant in C₂, leaf and stem castor in C₁ and garlic powder in C₁ showed 100% normal germinated seedlings. In this regard, it has proven that there are secondary metabolites that besides insect biocontrol, can also show biostimulator activity in the same plant (in the vigor and germination). For example, plant hormones brassinosteroids increase performance and efficiency cultivation and seed vigor (^{Mandava, 1988}).

In the Table 5, shows the comparison of means test for treatments composed of plant extracts for control of bean seed weevil. The best treatment to control Acanthoscelides obtectus was castor oil in both concentrations (C₁ and C₂); controlling 100% of the insect population from the first sampling at 24 h. Similar results were found ^{Javanovic et al. (2007)} with Urtica dioica extract or controlled 100% of this weevil. Similarly, (^{Salas, 1985}) reported a 100% mortality of Sitophilus oryzae of a dose of castor oil 10 000 ppm. Furthermore, ^{Okonkwo and Okoye (1992)} reported a 100% mortality of Callosobruchus maculatus with 10 000 ppm castor oil. Matching results of this work at the two concentrations of castor oil. Treatment of leaf and stem the C₁ governor had the lowest number of dead weevils in all samples made (55.8 to 66.42%).

Table 5 Response of bio-insecticides to control of Acanthoscelides obtectus Say and its relationship to quality bean seed. Roque, Celaya, Guanajuato, Mexico. 2011. 

C₁, concentración de 0.1 g y C₂, concentración 0.2 g.

For the variable seed vigor it found that treatments leaf and stem castor 0.2 g (C₂) and peel castor oil plant to 0.1 g (C₁) were those with the best answer to this variable, presenting the highest values normal seedlings to the first count (44.48 and 43.95%). These treatments exceed that caused by the control (33.98%) value. The opposite occurred with castor oil in both concentrations, as this treatment drastically affected the formation of normal seedlings during the first count, which was considered a seed vigor test (Table 5).

Finally, in the comparison test averages for the percentage of germination it can be observed that all treatments had values higher germination to 97%, except for the treatment of castor oil to the C₂ which decreased by 25.87% germination. In this regard, ^{Hernández et al. (2006)} reported that seeds treated with different vegetable oils germination decreases and there is a 50% reduction to the seedling height, fresh and dry seedling weight is reduced from 35 to 45%. Furthermore, ^{Babu et al. (1989)} reported 75% germination of bean seeds treated with castor oil (Table 5).

Conclusions

The three bio-insecticides to control two concentrations showed Acanthoscelides obtectus, Sitophilus granarius and maize weevil Sitophilus zeamais above 50% mortality rate is considered acceptable and defines the response threshold.

The castor oil assessed in the first sampling at 24 h showed 100% dead weevils with the two concentrations for the three species, corn, beans and wheat. The lowest mortality at 24, 48 and 144 h treatment was composed of garlic powder Sitophilus zeamais and Sitophilus granarius. For Acanthoscelides obtectus, except castor oil, both the governor, garlic, and castor (stem, leaf and seed hulls) C₁ and C₂, control was less than 144 h with values ranges from 66.42 to 79.74%.

The physiological seed quality was more affected by treatment of castor oil, and the damage was greater in the seed corn and wheat, reducing germination to 41.4 and 48.98%, respectively. This treatment shows the highest negative effect on seed vigor of the three species, although the effect was more severe in bean seed.