MSc

The study entitled “Natural history of the curry leaf tortoise beetle Silana
farinosa (Boheman, 1856) (Coleoptera, Chrysomelidae, Cassidinae, Cassidini) in
Kerala” was carried out at the College of Agriculture, Vellayani during 2022-2023.
The main objectives were to study the external morphology, genitalia, immature
stages, life history, seasonality and natural enemies of the curry leaf tortoise beetle
Silana farinosa.
The curry leaf tortoise beetle, S. farinosa is a major defoliating pest of Bergera
koenigii (L.) (= Murraya koenigii (L.) Spreng.) (Sapindales, Rutaceae). Originally
described from Sri Lanka, Premila et al. (2003) reported its occurrence in India from
Kerala. External morphology of all life stages of the pest were studied, illustrated and
detailed descriptions were prepared using light microscopy as well as scanning
electron microscopy. A laboratory culture was established and the life history,
behaviour, nature and intensity of damage, seasonality and natural enemies were
studied.
Adults are 6.39–7.85 mm long and can be separated from other Cassidini by
the second antennomere subequal to third; pronotum with explanate margin separated
from disc by a deep, longitudinal groove on either side; pronotum basally with a
shallow transverse depression in front of scutellum; pronotum and elytra with short
setae, especially towards lateral sides; and the dorsum of adult in life is covered with
white, powdery, waxy coating. Other salient characters of the species include
aedeagus in ventral view with broadly truncate apex; spermatheca is long, hookshaped;
fully everted endophallus has several lobes and a long sclerite apically.
Genitalia in S. farinosa has been studied and illustrated for the first time. Sexual
dimorphism in S. farinosa was observed for the first time. The last female ventrite has
curved, minute ridges and a window, visible in macerated specimens.
Final instar larvae measured 4.26–7.24 mm long and 1.42–2.8 mm wide.
Stemmata 6; four in a curved line, equidistant; 5, 6 ventral. Mandible palmate with 6
sharp denticles. Pronotum pigmented, overlapping head, margin with three pairs of
scoli, two anterolateral, fused basally, one posterolateral. Mesonotum with three pairs
of lateral scoli – one anterolateral, one medio-lateral and one posteriolateral,
mediolateral being shortest. Spiracle uniforus, rounded, raised, white on black socket.
Pronotum with short, seta bearing, dark, raised randomly distributed pinnacles.
Metanotum with two pairs of scoli, anterior pair shorter than posterior. Abdomen 10
segmented, 1 – 8 with a pair of scoli laterally. Segments 9, 10 without scoli. Tergum 8
modified with a pair of long caudal processes, reaching beyond apex of anal tube.
First instar 2.24 – 2.69 mm long, 0.76 – 0.78 mm wide. Spiracles 8, elevated,
annular biforous. Body with 16 pairs of lateral scoli, and a pair of supraanal
processes. All scoli unbranched, tapering towards apex, armed apically with a seta
longer than half length of scolus.
Pupa 6.66 – 7.03 mm long, 5.35− 6.25 mm wide. Colour creamy white with
brown patches. Pronotum widest anteriorly, anterolateral corners slightly produced
laterally. Posterolateral corners with a postero-mesally directed, finger-like process.
Abdominal tergum VI or VII and beyond covered with exuvia, fecal shield not
retained.
Eggs are enclosed in ootheca, 3.31 – 3.61 mm long, 4.0 – 4.47 mm wide.
Single egg measures 1.08– 1.46 mm long and 0.54 – 0.77 mm wide. Total longevity
ranged from 105 – 128 days, with egg period of 6-7 days, larval period of 15–22 days
and pupal period of 4–7 days. Five larval instars with duration as follows: I 2 to 3, II 3
to 4; III 3 to 4; IV 3 to 4 and V 4 to 7 days. The lifecycle was completed in about 32 –
41 days (mean 35.6 days). The adults lived for 80-92 days under laboratory
conditions. Cycloalexy, a characteristic subsocial defensive behaviour, performed by
the larvae of cassidinae, was observed. Mating lasted for about 2–3 hours and mostly
occured at night. Female laid about 24 oothecae within a month. Feeding behaviour of
all larval instars and adult were recorded. The white powdery coating on the dorsum
of adult was fully formed within 6 – 8 days of emergence. Formation of fecal shield
and moulting were recorded. Adults exhibited thanatosis, a defensive tactic by
feigning death, for about one minute, when they were kept upside down.
The population of S. farinosa was directly dependent on the rain. The highest
population was observed from 3 July to 2 September 2023. The population declined
from 14 March and disappeared by 14 April 2023 and reappeared in May following
premonsoon showers. Of the 50 plants observed, 22 (44%) were infested. On the
infested plants, 6.7 – 93.8 % of branches were affected (mean 36 %). Proportion of
damaged leaves varied from 6.6 – 82.7% (mean 40.5%).
The natural enemies of S. farinosa such as predators, Oecophylla smaragdina
on larvae, unidentified ants on eggs, a pupal parasitoid Brachymeria apicicornis and
native isolates of fungal pathogens Fusarium longifundum and Cordyceps javanica,
were reported for the first time.
The red ant Oecophylla smaragdina collected and fed on the white powder on
the dorsum of the adult. The chemical composition of both white powder and fecal
shield was analysed. The white powder contained tetratetracontane and the fecal
shield has decanoic acid, both the compounds having anti-microbial property as per
literature. Males of Bactrocera cucurbitae and Bactrocera caudatus were found
attracted to fecal shield. The male fruit flies are usually attracted to kairomones and
feed on them to attain sexual maturity. Hence, we suspect that some attractant
chemicals are present in the fecal shield. Hong and Nishida (2005) reported that
various species of Bactrocera were attracted to the flowers of Bulbophyllum apertum
due to the release of raspberry ketone by the plant. The fecal shield also contains a
ketone compound and the possibility of it being an attractant needs to be further explored