Melika, Cibrián-Tovar, Cibrián-Llanderal, Tormos, and Pujade-Villar (2009) indicate that the gall wasp Andricus quercuslaurinus Melika & Pujade-Villar (Hymenoptera: Cynipidae) was first reported in Acaxochitlán, Hidalgo, Mexico on the branches and leaves of the Quercus laurina Bonpl. oak. In field tours after 2009, it was found that the main host is Quercus affinis Scheidw. Cibrián-Tovar et al. (2013) confirm that the insect distributes itself in the municipalities of Tenango de Doria, Metepec, Agua Blanca, and Acaxochitlán, although only in Acaxochitlán is it a significant plague. According to Valencia (2004), Q. affinis is distributed at 1,200 to 2,600 m in the states of Guanajuato, Hidalgo, Nuevo León, Oaxaca, Puebla, Querétaro, San Luis Potosí, Tamaulipas, and Veracruz. There are areas of hybridization between Q. affinis and Q. laurina in the zones where these species overlap; Acaxochitlán adjoins this overlapping zone (González- Rodríguez, Arias, Valencia, & Oyama, 2004).
Melika et al. (2009) indicate that A. quercuslaurinus shows a forced alternation between sexual reproduction that causes galls on the leaves, with asexual reproduction that causes galls on the branches; the duration of which is at least 30 months. Cibrián-Tovar et al. (2013) report that the galls of this Cynipidae are found in individuals of any age and health condition. The main damage caused to the host by sexual reproduction is the deformation of the infested leaves, whereas the damage caused by asexual reproduction infestation includes a decrease in growth, branch dieback, opening of the canopy due to the dieback with effects on the capacity of water catchment, and substitution of tree species. It is important to mention that not all individuals present the same levels of infestation (Cibrián-Tovar et al., 2013).
The A. quercuslaurinus wasp is a plague of great significance in the municipality of Acaxochitlán, having caused the loss of more than 85 % of the population of Q. affinis in some particular plots. In Mexico, the severity of this plague is unique for the Cynipidae family, although in the United States exist the Callirhytis quercusclaviger (Ashmead) (Ashmead, 1881; Dixon, 1992) and C. cornigera (Osten Sacken) (Dixon, 1992; Eliason & Potter, 2000, 2001), both with similar biology and damages to the A. quercuslaurinus. Other examples of Cynipidae plagues are Dryocosmus kuriphilus Yasumatsu (Anonymous, 2005), A. breviramuli Pujade-Villar (Pujade-Villar, Cibrián-Tovar, Barrera- Ruiz, & Melika, 2014), Plagiotrochus amenti Kieffer and Disholcaspis cinerosa (Bassett) (Melika et al., 2009). There have been some studies carried out for the control of these Cynipidae. Eliason and Potter (2000) evaluated the effect of spraying bifenthrin or chlorpyrifos at different concentrations on the canopy of Q. palustris Münchh. individuals during the emergence of C. cornigera adults on branch galls. They also evaluated the injection of concentrated solutions of Abamectin, Imidacloprid, or Bidrin to the trunk and the foliar spraying of pesticides Dimethoate, Acephate, Abamectin, or Imidacloprid against larvae in leaf galls. The spraying of the canopy reduced the number of leaves with galls and the number of galls on the leaves; the injection on the trunk caused the death of the habitants of the galls, although it did not reduce the number of new branch galls; foliar spraying caused high mortality of the inhabitants of the galls; in all cases there was mortality of the parasitoids. Johnson and Sloughfy (1996) found that Imidacloprid injected on the ground does not have any effect on the development of branch galls. The European and Mediterranean Plant Protection Organization mentions that infestations of the Cynipidae D. kuriphilus in small chestnut orchards can be reduced through the pruning and destruction of infested branches, and that persistent pesticides can be effective against females and young larvae, but with sever environmental effects (Anonymous, 2005).
Due to the havoc wreaked by A. quercuslaurinus on the Q. affinis population and to the lack of studies on chemical combat against Cynipidae in Mexico, this study was developed with the objective of evaluating the effect of the pesticides Imidacloprid, Acephate, Abamectin, and Spirotetramat on adults, eggs, and first larval stages of A. quercuslaurinus on Q. affinis leaf galls. Acephate, Imidacloprid, and Abamectin were selected based on information regarding their effect on the control of Cynipidae; Spirotetramat was chosen because it is a systemic pesticide that affects immature insects, unlike other pesticides that mainly affect adults, and also due to the fact that no information was found regarding its use in the control of Cynipidae.
Materials and methods
Field of Study
The experiment was established on the property La Victoria, Acaxochitlán, Hidalgo, located between coordinates 98º 11’ 54” and 98º 11’ 20” west longitude and 20º 11’ 07” and 20º 10’ 22” north latitude, at a height between 2,100 and 2,194 m. Acaxochitlán is adjoined to the north and the east by the state of Veracruz, to the south by the state of Veracruz and the Hidalguense municipality of Cuautepec de Hinojosa, and to the west by the municipalities of Cuautepec de Hinojosa, Tulancingo de Bravo, Metepec, and the state of Veracruz (Anonymous, 2009). The municipality of Acaxochitlán is located in the Trans-Mexican Volcanic Belt and the Sierra Madre Oriental, between 1,200 to 2,800 m; it has a humid temperate climate with rain in the summer or all year round, or sub-humid with rain in the summer (Anonymous, 2009).
Determination of the moment of pesticide application
The presence of new growths of Q. affinis was the most important factor in order to determine the date of the first pesticide application, given that the A. quercuslaurinus females that emerge from the branch galls oviposit in the youngest leaves found in the new growths.
On January 17, 2012, various sites of the property were inspected without detecting Q. affinis plants with new growths in the undergrowth or in the tree stratum. One week later, another inspection was carried out finding new growths only in the tree stratum. On these dates, branch galls were collected in order to determine the development of the individuals; the majority were in a pupa state with little pigmentation and others completely pigmented but with incomplete wing development, as well as some adult females. One part of the collected branches was placed in emergence chambers of 41.8 cm in length by 41.5 cm in width by 96 cm in height, situated in a greenhouse at the División de Ciencias Forestales (DICIFO) of the Universidad Autónoma Chapingo (UACh). The first females began to emerge on February 2, thus a new collection of plant material was carried out on February 7. Some larval chambers collected on February 7 were dissected in order to examine them; the majority of the A. quercuslaurinus individuals were not very active females and in a lesser quantity there were completely pigmented pupas with incomplete wing development; thus it was estimated that the in-field date of emergence would be between February 12 and 20, 2012.
Pesticide application on Quercus affinis
Table 1 shows the four pesticides applied and the doses: Imidacloprid, Spirotetramat, Acephate and Abamectin. The treatments were evaluated in a completely random experimental design; water was used as the control.
|Treatment||Toxicological group||Active ingredient (%)||Dose|
|Spirotetramat||Derived from tetramic acid||15.30||0.75 L·ha-1|
The pesticides were applied by foliar spraying, given that this method is simple to implement in wide expanses of forest. The experimental units were 100 m2 squares with at least 20 m between each square, with Q. affinis plants of less than 2 m in height and with a good quantity of foliage. Each treatment was assigned at random to five trees with similar heights and quantities of foliage; a number from one to five was assigned at random. The first pesticide application was done on February 16, 2012, during the massive emergence of adults, oviposition, and initial development of the foliar galls in order to evaluate the effect of the pesticides on the adults and on the oviposition. The second application was carried out on March 11 of the same year in order to evaluate the effect of the pesticides on the larvae. In both cases, a motorized sprayer was used (FORZA25 TURBO®, model KP, Mexico).
Evaluation of the effect of the pesticides on A. quercuslaurinus in Quercus affinis
The foliage of the Q. affinis individuals previously selected was collected on March 3, 2012 in order to evaluate the first pesticide application. Subsequently, on March 27 of the same year a collection on the same individuals was carried out in order to evaluate the second application. The plant material was collected from the marked trees of each treatment. From each tree, five or more new growths were cut from at least four points alongside the external border of the canopy. The collected growths were placed in resealable plastic bags labeled with the corresponding treatment and tree number, and were maintained in refrigeration for eight days until their review.
The effect of the pesticides was evaluated with the following process. From each tree, five growths of the plant material collected were selected at random; the leaves were taken from each growth. Each leaf was checked in order to look for new eggs or galls. The eggs are mainly found inserted on the epidermis of the underside of the leaf, and thus the body of the egg is visible, whereas the galls have the appearance of light deformities when they have little development and cause a light or severe deformity of the foliar layer when they are completely developed. Each egg was checked in order to determine if it was alive or dead and if it showed signs of gall formation. The galls were dissected in order to determine the development of the individuals inside and if these were alive or dead. All the individuals found were preserved in 70 % alcohol. The evaluated variables were: number of eggs, larvae, pupas and adults, alive or dead in the different states, and galls with or without development.
The data of the evaluations were submitted to an analysis of variance and comparison of means Tukey test for each of the variables (P = 0.05) using the SAS program (Statistical Analysis System, 2002) for Windows 9.0.
Results and discussion
The results are shown according to the development of the insect during the two evaluations.
Effect of the pesticides on the oviposition of A. quercuslaurinus
Given that the first pesticide application was done on one of the days of massive emergence, it was considered that the asexual A. quercuslaurinus females came into contact with the applied pesticides, which reduced the number of eggs deposited. Table 2 shows the egg averages per growth and leaves with eggs found on Q. affinis. The egg average per growth was less on the trees treated with Acephate; the effects with Spirotetramat and Imidacloprid were similar. In the case of Abamectin, the egg mortality was less than the control. Regarding the leaves with eggs, Acephate produced the best result, whereas with Abamectin the leaf average was the greatest, even greater than the control.
|Treatment||Eggs per growth||Leaves with eggs|
|Acephate||0.00 a||0.0 a|
|Spirotetramat||1.68 ab||1.08 ab|
|Imidacloprid||1.96 ab||1.20 b|
|Control||3.36 bc||1.76 bc|
|Abamectin||5.12 c||2.80 c|
Effect of the pesticides on the eggs of A. quercuslaurinus and the formation of galls
According to Table 3, on all treatments the averages of leaves with galls and galls per growth increased between the first and second pesticide application, which could be due to the ovipositing of asexual females after the first evaluation. The results of the variable “leaves with galls” after the first application represent the population of eggs that managed to survive from oviposition until the first evaluation; the same variable on the second evaluation includes those eggs that survived the two applications and that managed to develop a gall. The least presence of galls was recorded on individuals treated with Acephate. In the treatments with Spirotetramat and Imidacloprid, a similar reduction was recorded on the quantity of galls, whereas with Abamectin the reduction was statistically similar (P = 0.05) to the control.
|Treatment||Leaves with galls||Treatment||Galls per growth|
|Evaluation 1||Evaluation 2||Evaluation 1||Evaluation 2|
|Acephate||0.0 a||0.04 a||Acephate||0.0 a||0.04 a|
|Spirotetramat||0.6 bc||1.12 a||Spirotetramat||0.76 ab||1.44 ab|
|Imidacloprid||1.04 bc||1.6 ab||Imidacloprid||1.16 bc||2.2 ab|
|Control||1.44 c||3.36 bc||Abamectin||2.28 bc||3.96 bc|
|Abamectin||1.52 c||4.72 c||Control||3.04 c||6.32 c|
In the variable “eggs in developed galls” (Table 4), it was found that all the pesticides caused a significant mortality of the eggs with regard to the control. The lesser result of Abamectin on the variables “eggs per growth”, “leaves with eggs”, and “leaves with galls” is not due to a lesser effect of the pesticide, rather to the greater quantity of eggs with regard to those found on the other treatments.
|Treatment||Eggs on developed galls|
Effect of the pesticides on the A. quercuslaurinus larvae
Table 5 shows the average of the A. quercuslaurinus larvae on Q. affinis trees. The trees treated with Acephate did not have larvae. The trees treated with the pesticides Spirotetramat and Imidacloprid had similar averages of live larvae, whereas Abamectin had the largest quantity of live larvae after the control. On the other hand, treatments in which dead larvae were found were Imidacloprid, the control and Abamectin.
|Acephate||0.00 a||0.00 a||0.00 a|
|Spirotetramat||0.60 ab||0.00 a||0.60 a|
|Imidacloprid||0.60 ab||0.16 ab||0.76 ab|
|Abamectin||1.88 bc||0.60 b||2.48 bc|
|Control||3.04 c||0.12 ab||3.16 c|
By comparing the obtained results with those reported by Eliason and Potter (2000), it was found that the effect of the two applications on the reduction of the live larvae of A. quercuslaurinus was greater with Acephate, Spirotetramat and Imidacloprid, whereas on C. cornigera, Acephate, Spirotetramat and Abamectin were the effective pesticides. Acephate prevented oviposition, whereas Spirotetramat and Imidacloprid reduced the survival rate of the larvae on the second application. From the obtained results, any of the products can be recommended as an alternative to the control of the larval stage, if applied during the first stages. It can also be assumed that the first application had a greater effect on the eggs, whereas the second had a greater effect on the larvae, with Acephate having the best control. It is important to stress that no dead eggs or larvae were found on the samples treated with Acephate.
Eliason and Potter (2000) indicate that the growth of the galls depends on the number of C. cornigera larvae that develop there. According to the aforementioned and with the results of this study, it could be expected that on the treated areas the reduction in the number of eggs and larvae decreases the number and size of the galls, although the reduction could be less than what is expected due to the fact that A. quercuslaurinus individuals can arrive from bordering areas.
The application of combat measures against A. quercuslaurinus can be carried out with systemic pesticides on sexual reproduction. The spraying of Q. affinis foliage with pesticides Acephate, Spirotetramat and Imidacloprid are options to be considered. Acephate prevented oviposition on the treated foliage. On the other hand, Spirotetramat had not been evaluated for the control of Cynipidae, and alongside Imidacloprid resulted to be effective in reducing the survival rate of eggs and larvae.