e c o l o g i c a l e n g i n e e r i n g 3 4 ( 2 0 0 8 ) 328–331
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Comparison of biological and conventional insecticide treatments for the management of the pineapple fruit borer, Strymon megarus (Lepidoptera: Lycaenidae) in Costa Rica Diego J. Inclán a , Felipe J. Bermúdez a , Edgar Alvarado a , Mike Ellis b , Roger N. Williams b,∗ , Nuris Acosta b a b
EARTH University, P.O. Box 4442-1000, San José, Costa Rica The Ohio State University, OARDC, 1680 Madison Avenue, Wooster, OH 44691, United States
a r t i c l e
i n f o
a b s t r a c t
Article history:
Carbaryl is currently one of the most commonly used insecticides for the control of the
Received 20 May 2008
pineapple fruit borer, Strymon megarus (Godart), in commercial pineapple production. To
Received in revised form 2 July 2008
evaluate more sustainable biological alternatives to conventional insecticides, three micro-
Accepted 3 July 2008
bial and one botanical insecticide were studied. Beauveria bassiana, Metarhizium anisopliae, Bacillus thuringiensis (Bt) and a plant extract from Quassia amara were compared with carbaryl in replicated field trials in Costa Rica during 2005 and 2006. In both years of testing,
Keywords:
the untreated control received over 50% fruit damage from S. megarus. Bt and carbaryl pro-
Pineapple
vided the highest level of control and the lowest level of fruit damage compared to all other
Thecla
treatments. Based on the results of this study, Bt appears to be an acceptable biological alter-
Fruit borer
native to the conventional insecticide (carbaryl) for control of S. megarus on pineapple. In
Strymon megarus
addition, Bt was the least expensive treatment used in this study.
Natural insecticides
© 2008 Elsevier B.V. All rights reserved.
Carbaryl Economics
1.
Introduction
The pineapple fruit borer, Strymon megarus (Godart) (Lepidoptera: Lycaenidae), is one of the most economically important pests of pineapple, Ananas comosus (L.) Merr. (Coto and Saunders, 2004; Picado and Vásquez, 1997; EMBRAPA, 2005). Reports show that S. megarus can cause up to 80% damage in pineapple plantations in Brazil (EMBRAPA, 2005). In addition to pineapple, this pest has been reported on several other cultivated and wild plants, including Aphelandra deppeana; Brugmansia arborea; Capsicum spp.; Capsicum annuum var. annuum; Cordia sebestena; Hyptis sp.; Lantana sp.; Lan-
tana camara; Mangifera indica; Solanum americanum; Solanum sanitwongsei; Solanum tuberosum; Stigmaphyllon emarginatum; Solanum melongena; Clerodendrum chinense; Hibiscus furcellatus (DAFF, 2002); Aechmea bracteata (Coto and Saunders, 2004). The fruit borer is widely distributed from Mexico throughout South America wherever pineapples are grown (DAFF, 2002; Coto and Saunders, 2004; Bérmudez, 2005). According to The Department of Agriculture, Fisheries and Forestry of Australia (DAFF, 2002) and Picado and Vásquez (1997), S. megarus primarily affects flowers and fruits. Damage caused by the larval stage is initiated at floral induction and continues until the last flowers emerge (Jiménez, 1999).
∗ Corresponding author at: The Ohio State University, Department of Entomology, 1680 Madison Avenue, Wooster, OH 44691, United States. Tel.: +1 330 263 3731; fax: +1 330 263 3686. E-mail address:
[email protected] (R.N. Williams). 0925-8574/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.ecoleng.2008.07.005
e c o l o g i c a l e n g i n e e r i n g 3 4 ( 2 0 0 8 ) 328–331
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with concerns over the intensive use of synthetic insecticides and human health is forcing pineapple producers to evaluate biological alternatives for controlling this serious pest. In order to evaluate several biological alternatives for control of pineapple borer in Costa Rica, this research was initiated at EARTH University in 2005. The primary objective of these studies was to find effective biological treatments that could potentially replace the intensive use of conventional insecticides.
2.
Fig. 1 – Pineapple fruit exposing damage of the pineapple fruit borer, Strymon megarus (Godart).
When the larva feeds, it opens galleries in the fruit (Fig. 1) causing gelatinous exudates known as “resinosis” or “gummosis” (Rodríguez and Jordán, 1993; Picado and Vásquez, 1997; DAFF, 2002; Coto and Saunders, 2004; EMBRAPA, 2005). During floral induction, the fruit is highly susceptible and some level of chemical control is usually applied in commercial plantings. The Brazilian Agricultural Corporation (EMBRAPA) (2005) recommends monitoring 200 plants per hectare in plantations with less than 5 ha. To accomplish this, examine 20 consecutive inflorescences at 10 random locations across the field in a zigzag pattern. If the plantation is larger than 5 ha, then increase the sample size to 20 locations per hectare for a total of 400 hundred plants per hectare. Weekly monitoring should start when the first inflorescences open up, about 6 weeks after floral induction, and continue monitoring 6 more weeks, as the rest of the inflorescences open up. Application of insecticide is recommended when the economic threshold of one adult or one egg is observed per two inflorescences. Control practices for this pest have generally been limited to the use of conventional synthetic insecticides, such as carbaryl, diazinon, or dimethoate (Rodríguez and Jordán, 1993; Maldonado, 1997). Pineapple production is increasing rapidly in Costa Rica (CIMS, 2005; PROCOMER, 2006). Costa Rica used to be known principally as a producer of bananas and coffee, but pineapples have surpassed coffee to become the number two agricultural export. At present, 26,000 ha of pineapple are being produced annually. This represents an increase of 179% over the last 7 years (PROCOMER, 2006). Increased interest in the introduction of organic production systems combined
Materials and methods
Field studies were conducted on the experimental farm of EARTH University in Guácimo, Limón, Costa Rica, from April to September in 2005 and were repeated during the same period in 2006. Six treatments were evaluated in a completely randomized block design with 6 replications for a total of 36 experimental units. Treatments consisted of three microbial insecticides: Beauveria bassiana (Balsamo) Vuillemin (1 × 108 conidia/g: 6 kg/ha), Metarhizium anisopliae (Metschnikoff) Sorokin (1 × 108 conidia/g: 6 kg/ha), Bacillus thuringiensis (Berliner) subspecies kurstaki (Javelin 6.4 WG: 1 kg/ha), and one botanical insecticide consisting of the extract from the tree Amargo, Quassia amara L. (Quassinon 40 SL: 8.5 L/ha). These insecticides were compared to the standard synthetic insecticide, carbaryl (Sevin 50 WP: 240 kg/ha) and an untreated control. Experimental units consisted of 48 pineapple plants of the cultivar MD2 at a density of 60,000 plants per hectare. Plants were arranged in two beds with 70 cm between beds. Each bed had two rows of plants with 27 cm between rows and 12 plants with 30 cm between plants in each row for a total of 48 plants. Treatments were initiated in May, 45 days after floral induction (DAFI) in 2005, and 39 days after floral induction in 2006. Microbial and botanical treatments were repeated on a 7-day interval for 7 weeks (7 applications) in 2005 and for 6 weeks (6 applications) in 2006. Carbaryl was only applied twice on the first day of application and 10 days later. Based on the results from 2005, the two fungi did not control pineapple borer adequately and hence the concentration (1 × 108 conidia/g) of the fungi and the rate of (6 kg/ha) were increased for use in the 2006 trials. The concentration of B. bassiana was increased to 2.0 × 109 conidia/g and for M. anisopliae was increased to 2.5 × 109 conidia/g. The new rate for 2006 was increased to 8 kg/ha. The botanical extract did not provide good control in 2005; therefore, the rate was increased from 6 to 8 L/ha in 2006. Control plants were sprayed with water only. The pH of the water used in all treatments was between 6.0 and 6.5. All treatments were also mixed with the adjuvant NP-7 (Alquil Aril Polimer) at a rate of 150 mL/100 L of water. Applications were conducted with a 15-L backpack sprayer. Treatments were delivered at a rate of 500 L/ha. This rate resulted in approximately 8 mL of treatment solution per inflorescence. A destructive sample was conducted on 12 plants in 2005 at 94 DAFI and 8 plants in 2006 at 120 DAFI. Plants were taken from the center of the two middle rows of each experimental unit. The percentage of damaged fruits and the number of
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Table 1 – Evaluation of S. megarus damage to pineapple fruit (mean ± S.E.); EARTH University, Guácimo, Costa Rica, 2005 Treatments
Fruit % Damagea
Beauveria bassiana Metarhizium anisopliae Untreated control Quassia amara Carbaryl Bacillus thuringiensis a
72.11 64.97 58.71 52.57 16.12 15.29
± ± ± ± ± ±
No. of galleries
8.43 a 7.95 a 5.49 a 7.02 a 4.28 b 3.92 b
3.24 3.30 2.71 2.44 0.25 0.21
± ± ± ± ± ±
0.70 a 0.67 a 0.39 a 0.65 a 0.07 b 0.08 b
Means followed by the same letter are not statistically different (P > 0.05; Duncan).
galleries per fruit were recorded at each sampling date. The exterior of the fruit was evaluated for galleries, and then the outer layer of the pineapple was removed, exposing the galleries created by the larvae of the pineapple borer. The galleries were in turn counted and recorded. An economic analysis was conducted on the cost per hectare for manually applied treatments during one season; these include two applications for carbaryl and seven applications for biological and microbial insecticides. The estimated costs included the cost of the products, the adjuvant, labor, protective gear, and the rental cost of the backpack sprayer. Since the carbaryl treatment is a granular formulation, it needs to be applied by hand directly to the whorl. Data from each experiment (percentage of damage and number of galleries per fruit) were analyzed by ANOVA using the GLM procedures of SAS and means were separated using Duncan’s multiple range test.
3.
Results and discussion
In both years of testing, populations of S. megarus were very high with more than 50% of the fruit damaged in the untreated controls (Tables 1 and 2). In 2005, B. bassiana, M. anisopliae, and Q. amara were not statistically different from the untreated control in the level of fruit damage. The B. bassiana treatment had the highest percentage of fruit damage and number of galleries per fruit (72% and 3.2) followed by M. anisopliae (64%
Table 2 – Evaluation of S. megarus damage to pineapple fruit (mean ± S.E.); EARTH University, Guácimo, Costa Rica, 2006 Treatments
Untreated control Beauveria bassiana Quassia amara Metarhizium anisopliae Carbaryl Bacillus thuringiensis a
Acknowledgements
Fruit % Damagea 54.18 33.33 25.00 16.67 4.17 0.00
± ± ± ± ± ±
8.33 a 9.50 b 9.68 b 4.17 bc 2.64 c 0.00 c
and 3.3), the untreated control (58% and 2.7), and Q. amara (52% and 2.4) (Table 1). Bt and carbaryl provided significantly better control of fruit damage (about 16% fruit damage and 0.2 galleries per fruit) than all other treatments and there was no significant difference between Bt and carbaryl. In 2006, populations of S. megarus and percentage of damaged fruit in the untreated control were very similar to 2005. However, all treatments in 2006 provided a significantly lower percentage of damaged fruit and number of galleries per fruit than the untreated control. They were 33% and 1.5 for B. bassiana, 25% and 0.9 for Q. amara, and 16% and 0.4 for M. anisopliae (Table 2). As in 2005, Bt and carbaryl provided significantly better control than all other treatments, with the exception of M. anisopliae. There were no significant differences between these treatments for percentage fruit with damage and number of galleries per fruit. The percentage of damaged fruit and number of galleries per fruit for Bt was 0 for both variables and 4.2% and 0 for carbaryl (Table 2). The improved level of control by B. bassiana, M. anisopliae and Q. amara, in 2006, was probably due to the increase in concentration and rate of the fungi (Inclán, 2006). The most noticeable impact of these changes was shown by M. anisopliae, which reduced the insect damage by 48% over 2005. The economic analysis of the seven manual applications of the biological and microbial insecticide treatments per hectare of pineapple showed that the most expensive treatment was the botanical extract Q. amara ($723 ha−1 , US) and the least expensive was Bt ($602 ha−1 , US). Application costs for B. bassiana and M. anisopliae were very similar, at about $624 ha−1 , US. Two manual applications of the conventional insecticide, carbaryl, cost approximately $812 ha−1 . Our results suggest that the biological fungicides B. bassiana and M. anisopliae have good potential for providing an acceptable level of control of S. megarus in pineapple plantations. However, further research and evaluations are required to determine the most efficacious formulations and rates, including their effect on pollinating insects. The most efficacious compounds observed in this study were the biological product B. thuringiensis subspecies kurstaki and the standard conventional insecticide carbaryl. Both products provided an excellent level of control and there were no significant differences in efficacy between them. At present, Bt provides an effective biological alternative to the conventional insecticide carbaryl. These results are of great significance for growers who are attempting organic pineapple production. In addition, our results suggest that Bt is much more economical to use per hectare than carbaryl, $602 versus $812.
No. of galleries 2.00 1.52 0.92 0.44 0.04 0.00
± ± ± ± ± ±
0.30 a 0.48 b 0.43 c 0.17 cd 0.03 d 0.00 d
Means followed by the same letter are not statistically different (P > 0.05; Duncan).
This research was partially supported by the U.S. Department of Energy under Award Number DE FG02-04ER 63856, EARTH University and The Ohio State University.
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