Phenacoccus manihoti, Matile-Ferrero, 1977

Joshi, Sunil, Pai, Sachin G., Deepthy, K. B., Ballal, Chandish R. & Watson, Gillian W., 2020, The cassava mealybug, Phenacoccus manihoti Matile-Ferrero (Hemiptera: Coccomorpha: Pseudococcidae) arrives in India, Zootaxa 4772 (1), pp. 191-194 : 191-194

Phenacoccus manihoti

has been found by Sachin G. Pai severely infesting cassava plants ( Manihot esculenta Crantz ) in INDIA, Kerala, Thrissur, Vellanikara, Vidya Nagar, in plots at 10.5454° N and 76.2720° E, 28.ii.2020 ; 10.3243° N and 76.1619° E, 7.iii.2020 ; and at 10.5494° N and 76.2833° E, 10.iii.2020 .

The infestation was observed on an experimental plot of cassava about 2,000 m 2 ( Fig. 1 A ). All developmental stages of the mealybug (eggs, nymphs and adults, Figs 1B & 1C ) were found on all aerial plant parts including leaf undersides ( Fig. 1D ) causing curling of the leaves and growing tips resulting in bunchy tops ( Fig. 1E ) and on adventitious buds at almost all the internodes ( Fig. 1F ). The heavy infestation caused drying of the leaves and defoliation ( Fig. 1G ).

Morphological study of slide-mounted adult females identified the pest as Ph. manihoti , based on the characters in Fig. 2 . Pseudococcus jackbeardsleyi was also found in the same samples. In India, Ps. jackbeardsleyi , Ferrisia virgata (Cockerell) , Paracoccus marginatus and Ph. madeirensis have all been recorded previously on cassava in Kerala and in the Andaman and Nicobar Islands (personal observations). We found Ph. manihoti reproducing on other hosts such as Alternanthera sessilis (Amaranthaceae) , and Synedrella nodiflora and Blumea lacera (Asteraceae) , which may enable it to survive in the field between cassava crops. Note that this mealybug has not been reported before from Amaranthaceae or Asteraceae ; such exploitation of all available resources increases its chances of survival and spread. Phenacoccus manihoti was preyed upon by Spalgis epeus (Westwood) ( Lepidoptera : Lycaenidae ), Scymnus coccivora Ayyar ( Coleoptera : Coccinellidae ) and an unidentified anthocorid bug ( Hemiptera : Heteroptera: Anthocoridae ). No hymenopteran parasitoids of Ph. manihoti were found in our samples.

Using the Climex distribution model, Parasa et al. 2012 estimated the climatic conditions suitable for the spread of Ph. manihoti and predicted that, in India, southern Karnataka was at most risk of infestation; however, the pest has established much further south.

Cassava is grown in about 10 states in North-East and southern India. In 2017-2018, Kerala had 54.73 thousand hectares area under cassava, second only to Tamil Nadu with 89.61 thousand hectares (according to Socio-economic Statistical Information on India at https://www.indiastat.com). In Kerala, the very large area of cassava provides very suitable conditions for further spread and establishment of the mealybug.

The main objective of the Indian scientific community at present should be prevention of further spread of this mealybug to other cassava-growing areas through complete destruction of the infested plants; avoiding transport and the planting of sets from the infested area; constant exhaustive monitoring of other cassava-growing areas for new infestations on cassava and alternate host plants and weeds; recording and augmentative use of native natural enemies; and use of organic chemical control at heavily infested sites.

Figures

FIGURE 1. Phenacoccus manihoti Matile-Ferrero in the field: (A) infested experimental plot of cassava; (B) oblong, yellow eggs enclosed in white woolly ovisacs; (C) ovoid, rose-pink nymphs and adult females; (D) heavily infested lower leaf surface; (E) infestation causing distortion of leaves into bunchy top; (F) heavily infested axiliary buds; (G) desiccation of leaves and defoliation.

FIGURE 2. Phenacoccus manihoti Matile-Ferrero: diagnostic features of a slide-mounted female: (A) Oval, membranous body; (B) Antenna 9 segmented; (C) Claw with denticle; (D) Circulus ox-yoke-shaped; (E) Anal ring with 3 pairs of setae; (F) Anal lobe cerarius with two lanceolate setae and few trilocular pores situated on raised derm; (G) Penultimate cerarius similar to anal lobe cerarius; (H) Frontal cerarius with three setae; (I) Dorsal setae of three different sizes distributed randomly on dorsum, some setae each associated with one trilocular pore; (J) Trilocular pores (dorsal and ventral); (K) Discoidal pores (dorsal and ventral); (L) Ventral setae long and flagellate; (M) Multilocular disc pores in rows across mid-regions of abdominal segments V-IX and on dorsal margin of abdomen and thorax; (N) Small oral collar tubular ducts anterior to multilocular pores on median area of abdomen; (O) Groups of larger oral collar tubular ducts on margin of abdomen, thorax and head; (P) Ventral side of head anterior to clypeus with more than 30 quinquelocular pores, a few pores adjacent to the hind and mid coxa and a few scattered on abdomen