Validation of the sampling methodology for Opsiphanes invirae caterpillars on oil palm plantations in the Brazilian Amazon

Validação da metodologia de amostragem para lagartas de Opsiphanes invirae em plantios de palma de óleo na Amazônia brasileira

ABSTRACT:

This study validated the use of leaf 17 on the sampling of Opsiphanes invirae Hübner (Lepidoptera: Nymphalidae) through the quantification of caterpillar abundance on the different spirals leaves, in comparison to leaf 17, and, on the apical, intermediate and basal leaf regions. This study was performed in the state of Pará, between March-2014 and March-2015. Results confirmed that leaf 17 is the most adequate method for monitoring this defoliator pest.

Key words:
Defoliator insects; Elaeis guineensis Jacquin (Arecaceae); monitoring; oil palm

RESUMO:

Esta pesquisa validou a utilização da folha 17, nas amostragens de Opsiphanes invirae Hübner )Lepidoptera: Nymphalidae), através da quantificação da abundância de lagartas nas diferentes folhas que compõem os espirais em comparação com a folha 17, e, em diferentes regiões da folha (apical, intermediária e basal). O estudo foi realizado no Pará entre março de 2014 e março de 2015. Os resultados confirmam que a folha 17 é a mais adequada para ser utilizada no monitoramento desse desfolhador.

Palavras-chave:
Desfolhadores; Elaeis guineensis Jacquin (Arecaceae); monitoramento; palma de óleo d

The state of Pará is the largest producer of oil palm (Elaeis guineensis Jacquin, Arecaceae) in Brazil (IBGE-SIDRA, 2017). Phytosanitary problems are still issues to be resolved, such as lepidopteran defoliating pests Opsiphanes invirae Hübner and Brassolis sophorae L. (Lepidoptera: Nymphalidae). Monitoring of O. invirae is a strategic tool for the Integrated Pest Management (IPM) of this insect and, due to common outbreaks, control measures are adopted based on the economic threshold (ET) of the caterpillars on leaf 17, i.e., 10 caterpillars/leaf.

Use of palm leaves in the monitoring of defoliating pests is a recurrent practice (GENTY et al., 1978; GONZÁLEZ et al., 2011). In oil palm, leaf emergence is regular and constant, in a spiral arrangement, with 8 leaves in a specific direction and 13 leaves in the opposite direction. In this way, it is possible to locate and classify the oil palm leaves, numbering them sequentially. For this, the youngest leaf, with recently opened leaflets, is located; the next leaf, in the next spiral, is the leaf 9 and the next, in the other spiral, the leaf 17 (Figure 1) (MÜLLER & ANDRADE, 2010).

Figure 1
Phyllotaxy of the palm tree, Elaeis guineenses. Source: FAIRHURST & HADFTER (2003).

Although the use of leaf 17 in the monitoring of O. invirae is a recurrent practice, there is no scientific evidence of the efficiency of this method since it was implemented, based on empiric use, on the monitoring of O. cassina (L.) (Lepidoptera: Nymphalidae) in Colombia. Thus, the current study proposed to validate the use of leaf 17 in the sampling of O. invirae in Brazil. We hypothesized that the abundance of O. invirae are higher in leaves located in the medium spiral - leaves 9-17 (Figure 1), independently of the leaf sampled. Abundance of caterpillars on the leaves and on the apical, intermediate and basal regions was compared to leaf 17.

Our study was performed using a methodology similar to that used in Colombia, to select the lines and quantity of plants sampled, but with small adaptations used by the technicians of the studied plantations. The study was carried out between March 2014 and March 2015 in commercial plantations in the municipality of Tailândia-PA. Samplings were done in the months of pest incidence: 1^st sampling 03/2014, 2^nd 04/2014, 3^rd 06/2014, 4^th 07/2014, 5^th 09/2014, 6^th 11/2014, 7^th 01/2015 and 8^th 03/2015.

Oil palm trees were randomly selected, with the Excel^® 97-2003 software, always excluding the first and last palms. Twenty-five leaves (leaves 1-25) were cut from each palm and the number of caterpillars on them was counted. The choice for such leaves occurred because the technicians reported the occurrence of O. invirae on all these leaves. After locating the “leaf arrow”, all the other leaves were counted, following the phyllotaxy of the palm tree (Figure 1). Leaves were divided in three regions: apical (leaflet pairs from 1 to 50), intermediate (from 51 to 101), and basal (from 102 and onward) (RHAINDS et al., 1996).

Data was submitted to a variance analysis with the Scott & Knott test (p<0.05). Initially, all data was analyzed (whole sampling period) to determine the leaf with highest caterpillar abundance. Finally, caterpillar abundance was compared within leaf regions (apical, intermediate and basal). All analyses were run on the statistical program AgroEstat.

Opsiphanes invirae caterpillars varied on the different leaves (F=38.17; df=24; P<0.0001), from 2.48±1.70 caterpillars on leaf 01, to 32.44±1.59 on leaf 17. The highest numbers of caterpillars were reported in leaves located in the middle and upper spirals (leaves 9-25), disagreeing with the hypothesis that the highest numbers would occur only in leaves located in the median spiral (leaves 9-17). It was also verified that the caterpillars were not abundant in the new leaves from the inferior spiral (1-8) (Figure 1 and Table 1).

Table 1
Number of O. invirae (Lepidoptera: Nymphalidae) caterpillars per leaf of Elaeis guineenses, between March 2014 and March 2015, in commercial plantations of Pará state.

Leaves	Mean	Variance	SD	MSE
L1	2.48	926.72	30.44	1.70	g
L2	7.67	506.29	22.50	1.26	f
L3	11.74	370.89	19.26	1.08	e
L4	12.47	339.24	18.42	1.03	e
L5	14.39	283.85	16.85	0.94	e
L6	15.96	237.27	15.40	0.86	d
L7	17.77	418.39	20.45	1.14	d
L8	20.38	430.07	20.74	1.16	c
L9	21.49	250.23	15.82	0.88	c
L10	22.96	176.01	13.27	0.74	c
L23	23.26	414.13	20.35	1.14	c
L24	23.46	330.78	18.19	1.02	c
L25	24.16	275.81	16.61	0.93	c
L21	24.88	467.69	21.63	1.21	c
L12	25.70	330.44	18.18	1.02	b
L18	26.23	313.44	17.70	0.99	b
L22	26.49	356.03	18.87	1.05	b
L20	26.73	270.31	16.44	0.92	b
L11	27.02	542.48	23.29	1.30	b
L19	27.27	368.63	19.20	1.07	b
L13	27.48	618.89	24.88	1.39	b
L14	27.99	413.74	20.34	1.14	b
L16	30.93	821.87	28.67	1.60	a
L15	31.17	1304.92	36.12	2.02	a
L17	32.44	807.21	28.41	1.59	a

• Means followed by the same letter do not differ from each other by the Scott-Knott test at 5% probability. Where, SD= standard deviation; MSE= mean standard error.

Caterpillars of Acharia spp. showed a preference for leaves 1-12 (youngest, upper layer), while Euprosterna eleasa Dyar and Euclea sp. (Lepidoptera: Limacodidae) preferred leaves 13-26 (VERA, 2000). The preference of oil palm defoliators for old leaves has been reported in other studies (HOWARD, 2001). Low abundance of caterpillars in young leaves is likely related to the nutritional variation between young and old palm leaves (RODRIGUES et al., 2006). In addition, it is believed that younger leaves are less attractive to the caterpillars due to the synthesis of defensive secondary metabolites. These metabolites can be produced in higher amounts in younger leaves, preventing the attack of these herbivores (HARTMANN, 1996). Since the current study did not aim to evaluate the production of primary and secondary metabolites by oil palm trees, we suggested that further studies be carried out to test the above hypothesis.

Although, different leaves (leaves 9-25) harbor high abundance of caterpillars, the efficiency of leaf 17 in monitoring O. invirae was confirmed since that leaf showed the highest abundance of caterpillars (Table 1). Use of different leaves to monitor palm tree defoliators is a recurring practice. There are recommendations for using leaves 9, 17, and 25 for monitoring O. cassina (GENTY et al., 1978; GONZÁLEZ et al., 2011); leaf 25 for Euclea diversa Druce, and Talima straminea Schaus (Lepidoptera: Limacodidae); and leaves 17 and 33 for Acharia spp. Hübner and E. elaeasa (Lepidoptera: Limacodidae) (GENTY et al., 1978).

Our results showed that the abundance of O. invirae caterpillars varied depending on the leaf region sampled (F=24.28; df=959; P<0.0001), from 4.52 caterpillars on the apical region of leaf 9 to 15.74 on the intermediate region of leaf 16. The highest abundance was on leaflets 51 to 101, which corresponds to the intermediate region of the leaves. However, starting from leaf 21, the presence of caterpillars on the apical region was similar to what was observed on the intermediate region (Table 2), revealing that, as the leaves grow older, the caterpillars migrate from the intermediate region of the leaf towards the apical region, and then, both regions start to hold high numbers of caterpillars. Automeris liberia Cramer (Lepidoptera: Saturniidae), another defoliator observed in the plantations studied, was detected in higher abundance in leaflets closer to the leaf apex (ALDANA et al., 2010). The highest number of caterpillars of O. cassina has been reported for leaflet pairs 41 to 80, due to the lower levels of tanines and high levels of nitrogen in these leaflets (GONZÁLEZ et al., 2011). This difference in the number of O. invirae caterpillars between the different regions of the leaf reinforces the need to evaluate the primary and secondary metabolites produced in the palm trees in different phenological stages.

Table 2
Mean number of O. invirae (Lepidoptera: Nymphalidae) caterpillars in different regions of the oil palm leaves (Elaeis guineenses), in commercial plantations.

Leaflet regions

Leaves

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

Apical

4.52b

5.39b

6.74b

7.07b

7.63b

7.8b

0.60b

9.02b

10.41b

9.23b

9.50b

9.59b

9.11a

10.19a

9.63a

9.82a

9.66b

Intermediate

11.83a

12.14a

14.13a

12.54a

13.61a

13.42a

15.33a

15.74a

15.63a

11.66a

13.23a

12.50a

11.43a

11.74a

10.12a

10.17a

11.23a

Basal

5.48b

5.36b

6.16b

5.87b

6.17b

6.80b

6.61b

5.98b

6.34c

4.89c

4.80c

4.71c

4.41b

4.55b

3.51b

3.53b

3.65c

• Means followed by the same letter, in the column, do not differ from each other by the Scott-Knott test at 5% probability.

In conclusion, leaf 17 is an acceptable methodology for the sampling of O. invirae caterpillars, which occur in higher numbers in the intermediate region of the leaf. Although, other leaves present similar numbers of caterpillars, we recommend that leaf 17 continues to be used for monitoring this pest, due to the expertise of the field technicians (pest monitors) in locating this leaf on site.

ACKNOWLEDGEMENTS

To the Agropalma S/A company and the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq/MCTI/Brazil). To the anonymous reviewers who contributed to improve the final version of this manuscript, and Dr Moacyr Bernardino Dias-Filho, Embrapa Amazônia Oriental, for the critical review of manuscript

REFERENCES:

• ALDANA, R.C. et al. Manual de plagas de la palma aceite em Colômbia. CENILPA, 4ed, 2010. 198p.
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• GONZÁLEZ, G.R. et al. Metodología para muestrear las fases inmaduras del defoliador Opsiphanes cassina Felder (1862) (Lepidoptera: Nymphalidae) en palma aceitera. Revista Científica UDO Agrícola, v. 11, n. 1, p. 104-108, 2011.
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• RHAINDS, M. et al. Development of a sampling method for first instar Oiketicus kirbyi (Lepidoptera: Psichidae) in oil palm plantations. Journal of Economic Entomology, v.89, n 2, p.396-401, 1996. Available from: http://dx.doi.org/10.1093/jee/89.2.396>. Accessed: Jun. 01, 2016. doi: 10.1093/jee/89.2.396.
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• RODRIGUES, M.R.L. et al. Avaliação do estado nutricional do dendezeiro: análise foliar. Manaus, AM, 2006. 12p. (Circular técnica, 26).
• VERA, J. Avances preliminares sobre el establecimiento de un programa de Manejo Integrado de Plagas en Palmas del Espino S.A. - Perú. Palmas, v. 21, n. especial, Tomo 1, p. 227 - 233, 2000.

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  CR-2017-0742.R1

Publication Dates

• Publication in this collection
  2018

History

• Received
  16 Oct 2017
• Accepted
  18 Apr 2018
• Reviewed
  09 June 2018