Yield loss in coconut variety East Coast Tall (ECT) owing to rugose spiralling whitefly (RSW), Aleurodicus rugioperculatus M. infestation

Nut yield reduction in East Coast Tall (ECT) variety of coconut palms with exotic and invasive rugose spiralling whitefly (RSW) infestation @ low (<10 spirals per leaflet), medium (10–20 spirals per leaflet) and high (> 20 spirals per leaflet) incidence was studied out at two experimental locations viz., Dr. YSR HU - Horticultural Research Station (HRS), Ambajipeta and Kalavalapalli. Yield loss was estimated to be 6.61% and 22.45% in ECT palms with low and medium RSW incidence, while comparatively greater yield loss of 27.59% was recorded in palms with high incidence at Ambajipeta. Likewise, at Kalavalapalli village, yield loss in ECT palms with low, medium and high RSW incidence was recorded to be 6.49%, 25.65% and 30.38%, respectively. Further, a declining trend of button setting was noticed for the last 2 years (2019 to 2021) at Ambajipeta with 45.04% during 2018 (highest before RSW infestation), while the least setting was recorded in 2021 with 28.39%. Button setting during the years 2019 and 2020 was 33.41% and 31.19%, respectively.


Background
Coconut, Cocos nucifera L., belongs to the family Arecaceae, regarded as the "Tree of Life", "Kalpavriksha" and "Tree of Abundance" providing livelihoods to billions of people across the world (Ahuja et al., 2014).It is grown for oil, coconut meat, coconut water and raw ingredients for the coir industry.In India it is grown over an area of 2.18 million ha, with production and productivity of 21,206.74 million nuts and 9687 nuts/ha in 2020-21 (Nair & Pramod, 2021).In the present scenario of climatic change this valuable palm is devastated by several pests and diseases that not only reduced the quality of nuts but also reduced the vigour and yield of palms (Chowdappa et al., 2018;Neeraja et al., 2020).
In this modern era, invasion of exotic insect pests, particularly whiteflies, are responsible for damage of coconut palms.Among different invasive whiteflies, rugose spiralling whitefly (RSW), Aleurodicus rugioperculatus Martin (Hemiptera: Aleyrodidae) is highly polyphagous and invasive pest, originally described from Belize in year 2004 on coconut trees (Martin, 2004) has entered into India and reported initially during 2016 in Tamil Nadu on coconut palms (Sundararaj & Selvaraj, 2017).Later on, the pest was documented from different Vol:.( 1234567890) coconut growing areas of India viz., Kerala, Karnataka, Andhra Pradesh, Assam, Goa, West Bengal, Maharashtra, Telangana, Meghalaya and Gujarat on oil palm, banana, sapota, maize, mango, cashew and many other ornamental plants (Chalapathi et al., 2018).The pest is also reported in a high incidence on Oil Palm plantations in coastal Andhra Pradesh (Kalidas, 2019).The invasive RSW feeds and reproduces prolifically on the undersides of coconut palm leaves where they secrete honeydew.This honeydew facilitates the growth of sooty mould on leaves, which further degrades photosynthetic activity and vigour, resulting in yield loss. Very recently, studies of Raghuteja et al. (2023) for the first time reported that East Coast Tall (ECT) variety of coconut palms infested with low, medium and high incidence of invasive A. rugioperculatus resulted in nut dropping of 4.06, 22.33 and 28.51% at Ambajipeta, while it was 4.68, 23.49 and 30.58% at Kalavalapalli coconut plantations.Though literature pertaining to yield loss particulars in ECT coconut palms due to RSW is meagre, the similar study by Kalidas (2019) in oil palm revealed that fresh fruit bunch (FFB) yield losses were in the range of 20 to 45% and 30 to 42% in farmer's fields at village and mandal levels after one year of the RSW infestation.Selvaraj et al. (2019) also reported that there was a reduction in bunch yield of oil palm by 20 to 25% due to RSW infestation.Nut yield reduction caused by other pests has been studied in coconut palms.Chandrika et al. (2010) estimated nut yield reduction of 45.4% due to Opisinia arenosella W. (Coconut black headed caterpillar) and Rajan et al. (2011) reported that slug caterpillar (Macroplecta nararia M.) inflicted yield losses of up to 90 to 95%.Studies of Rezende et al. (2016) reported that higher the invasive perianth mite, Aceria gurerronis incidence on coconut palms resulted in a 60% decrease in the mean number of nuts harvested per bunch.Nut yield reduction must be estimated to plan realistically for research and development policies.As a result, the study was undertaken to evaluate yield loss in terms of nut production of ECT palms due to A. rugioperculatus infestation at different intensities.Nut yield reduction must be estimated so as to plan realistically for research and development policies.This study was undertaken to evaluate yield loss in terms of nut production of ECT palms due to A. rugioperculatus infestation at different intensities.
The invasive RSW oviposits its eggs in distinctive spiral patterns on the adaxial surface of coconut leaflets, as the name suggests.The white spiral pattern of eggs and waxy material, which covers the immature nymphal, pupal and adult stages on the lower surface of the leaves, is conspicuous and distinctive.In each ECT palm, 40% of leaflets were examined to decide whether the infestation was low, medium or high grade.The entire coconut plantation of ECT variety at Ambajipeta and Kalavalapalli was found to be infested with invasive RSW.Henceforth, the coconut trees were categorized into low (< 10 spirals), medium (10 to 20 spirals) and high (> 20 spirals) incidence palms to record the observations on nut yield aspects and no chance of control palm (without RSW infestation) could be involved in this experimentation.
The data pertaining to number of harvested nuts per palm were recorded at monthly intervals during the year 2020-21 at Ambajipeta and Kalavalapalli village.Additional observations were also recorded on button setting (%) in ECT palms selected for hybridization at Ambajipeta only.
The impact of RSW infestation on nut yield of ECT palms was validated at Ambajipeta and Kalavalapalli.Fifteen different palms carrying developing nuts after fertilization i.e., three months and more were identified and marked by using a simple random sampling method.The number of harvested nuts per palm was recorded at monthly intervals during the year 2020-21.Data on number of harvested nuts per palm was noted when harvesting was carried out in each of the five selected palms of local ECT variety under varied RSW intensities in which Vol.: (0123456789) number of nuts/palm recorded separately for each infestation level.
The data on harvested nut yield of those five selected palms in local ECT variety for preceding three years (2018-20) was also obtained from yield record registers maintained in the research station as to compare the yield and to calculate the yield loss (%) at Ambajipeta and Kalavalapalli by using the following formula.
The data on button setting (%) was collected in 15 selected and marked ECT variety palms (5 for low, medium and high RSW infestation each) meant for hybridization in 7 different blocks at Ambajipeta for 4 consecutive years (2018 to 2021).The means are tabulated and finally expressed as mean button setting (%) per year.

Statistical analysis
The nut yield of all 15 coconut palms under low, medium and high RSW incidence (5 palms each) was quantified and tabulated with means for the years 2018, 2019, 2020 and 2021 at Ambajipeta and Kalavalapalli.Further, the data on mean yield of nuts per ECT palm was analysed by comparing statistically between the years using paired t-test [SPSS 17.0 version] pioneered by Gosset (1908) and later developed and extended by Fisher (1954).

Results and discussion
An average nut yield of 121.00 nuts per palm was recorded in 2018 and this was reduced by 6.61% in the year 2021 in ECT palms with low RSW incidence (Table 1).The results given in Table 2, depicted that there was a reduction in nut yield of 22.45% in ECT palms with medium RSW incidence, while comparatively higher yield loss of 27.59% was observed in ECT palms with high RSW incidence at Ambajipeta (Table 3).At Kalavalapalli, the percentage yield loss from 2018 to 2021 was 6.49% in ECT palms with low RSW incidence (Table 4), whereas in medium and high RSW incidence the nut yield reduction was 25.65% and 30.38%, respectively (Tables 5 and 6).
The mean nut yield per ECT palm with all levels of RSW infestation differed significantly at Ambajipeta and Kalavapalli between the years 2018 and 2019 as per the paired t-statistical value (t cal = 6.78* and 7.71*) depicted in the Table 7.Similarly, the data presented in Table 8 also reveal significant differences in The reduction in harvested nut yield was least in ECT palms with low RSW incidence in comparison to that of medium and high incidence ECT palms which signifies that variable infestation of RSW caused high or low yield loss (Tables 1, 2, 3,   4, 5 and 6).The pest infestation on coconut palms was variable which could be due to the preference in migratory behaviour of RSW from one palm to other in which the palms were separated by blocks, natural and artificial barriers.The RSW incidence was ascertained initially on ECT palms in the year 2019 and its continuous incidence all through the years up to 2021 resulted in significant nut yield reduction at HRS, Ambajipeta and Kalavalapalli.
No literature is available on yield loss studies due to RSW infestation at different intensities in coconut palms.The percentage yield reduction in coconut is similar to fruit yield reduction of oil palm due to RSW infestation.The study conducted by Kalidas (2019) in oil palm revealed that fresh fruit bunch (FFB) yield losses were in the range of 20 to 45% due to RSW incidence.In the same year, Selvaraj et al. also estimated bunch yield reduction of oil palm (20 to 25%) due to RSW infestation.The percentage yield loss recorded was higher in Kalavalapalli plantations than that of Ambajipeta.It could be due to the multi cropping system of coconut and oil palms in which both the host crops being highly attractive to RSW, thereby enhancing the oviposition, colonization and RSW infestation against ECT palms resulting in more nut yield reduction.Similar observations on combined high incidence of RSW on coconut and oil palm in West Godavari district was also reported by Kalidas (2019).
The current yield loss estimation studies are contrary to Chandrika et al. (2017) and Subramanian et al. (2018) who reported that heavy RSW incidence may not result in any economic crop loss in coconut.The present study showed that it is only under low incidence of RSW that there may not be any economic crop loss in coconut.Taylor (1937) recorded the mean reduction in coconut production by 50% with Fiji coconut hispid, Promecotheca coeruleipennis infestation.Voegele (1989) estimated 50 to 70% nut yield loss due to the coconut hispid beetle, Brontispa longissima in Samoa.Perera (1993) reported 40% damage to the coconut leaves during O. arenosella outbreak.
Studies of Chandrika et al. (2010) recorded comparatively more yield loss of 45.4% from O. arenosella infested coconut palms than that of invasive RSW in the succeeding year of severe pest incidence.Subramanian et al. (2018) reported that red palm weevil (RPW) causing loss to negligible extent of 1 to 3% in young coconut plantations.Button setting of 45.05% recorded in 2018, before RSW infestation, compares well with setting of 48.24% reported by Niral et al. (2009).The button setting during the years 2019 and 2020 was also on a lower scale i.e., 33.41 and 31.19%respectively.

Conclusion
The study revealed that yield loss was minimal (6.61% and 6.49%) in ECT palms with low RSW incidence (< 10 spirals per leaflet), whereas greater losses of 22.45% and 25.65% were estimated in palms with medium RSW incidence (10 to 20 spirals per leaflet), and 27.59% and 30.38% in palms with high  RSW incidence (> 20 spirals per leaflet) at Ambajipeta and Kalavalapalli, respectively.Button setting in ECT hybridized palms at HRS, Ambajipeta declined from 2018 to 2021 after the infestation of coconut palms by RSW.Thus, considering all aspects in the present study management operations should be undertaken at low incidence of RSW instead of medium and high incidence for effective control and to overcome the problem of yield loss in coconut palms due to invasive RSW menace.The aim is to reduce the number of spirals per leaflet below 10 (low) since there will be a negligible yield loss (%) at this level of infestation in coconut palms.

Fig. 1
Fig. 1 Redundant -shows same as means in Table 10

Table 10
Impact of RSW infestation on button setting (%) in ECT coconut palms meant for hybridization at HRS, Ambajipeta Mean values are captured in bold