New Horizons in Insect Science Towards Sustainable Pest Management

Nanomaterials: A Review of Their Action and Application in Pest Management ... 123

The purpose of this work was to evaluate
whether this specific hormone analog RH-5992
has potential effect in insect hormonal alteration,
which then can be introduced as ecofriendly in-
secticide. The long-term effect of the above-said
product might alter the hormone feedback
mechanisms in the physiology of H. armigera.
The tebufenozide RH-5992, a nonsteroid agonist,
exhibited an effective disruption in the insect de-
velopment, which included moulting and meta-
morphosis controlled by the steroid hormone
20-hydroxyecdysone (20E).
Naturally, it may be assumed that tebufeno-
zide RH-5992 can bind ecdysterone receptors
to cause a precocious and incomplete moulting
that is lethal to larvae. RH-5992 has the ability
to bind with lepidopteran ecdysterone receptor
(Retnakaran et al. 2001 ; Hu et al. 2004 ). H. ar-
migera undergoes six larval instars and it is from
the third instar that active feeding on tomato
fruits begin. The life cycle is completed in 30 to
35 days on tomato crop, depending on the con-
ditions (David and Ramamurthy 2011 ). Tomato
fruit loss can be prevented in early instar larvae
are prevented from feeding on fruits without any
adverse effects on environment, human health,
and other nontarget species.
The biochemical alterations lead to death of
the larvae. It has already been reported that in-
sect chitinases were found in the integument,
gut, and fat bodies but were absent in the hae-
mocytes which belong to glycosylhydrolases.
These glycosylhydrolases have been observed
in moulting fluid and midgut tissues. Moreover,
these chitinases can synthesize chitin through
peritrophic membrane (PM) of the midgut.
Genes and cDNAs encoding insect chitinases

have been identified and characterized from sev-

eral lepidopteran insects (Zhu et al. 2008 ). Fur-

ther observations have established that certain

endotoxins may bind with the midgut epithelial

cells and can inhibit the synthesis of proteases

and aminopeptidases causing lysis of the midgut

epithelial cells (Sanjay et al. 2001 ).

Cross section of the midgut of the newly born

and fourth instar treated larvae revealed morpho-

logical differences in the treated compared to un-

treated larvae. In newly born larvae, the epider-

mal cells were dearranged and the imaginal buds

failed to show any growth and development. The

cement, epicuticle, and exocuticle layers were

dearranged. In the fourth instar larvae, the epicu-

ticle was partially detached from the exocuticle

and cells were dearranged. The cells showed

damage to varying degrees. Vacuolation of epi-

thelial cells, destructured cytoplasmic, and pro-

toplasmic organelles were evident from the cross

section of the midgut.

Tebufenozide (RH-5992) at 10 to 20 ppm dis-

rupted growth and development of H. armigera

larvae in a week. Limited knowledge on the mode

of action of this IGR in the physiology of neonate

larvae of H. armigera will of value in the future.

Tebufenozide (RH-5992) showed consistent ef-

fects in disrupting the gene functions. Thus, the

study revealed that tebufenozide potentially can

be used as ecofriendly biopesticide.

Acknowledgment The investigators are thankful to the

Director of Research, University of Agricultural Sciences,

GKVK, Bangalore 650 065. Tebufenozide [RH-5992]

was gifted from Dr. Daniel Doucet of Canada. This study

was also facilitated by the National Bureau of Agricultur-

ally important Insects (NBAII) and IIHR, Bangalore.

Tebufenozide

(conc. ppm)

Average single

larval weight

after 7 days

(mg) (X ± SE)

Average larval

weight (mg)

(X ± SE)

Day 100 %

larval mortality

occurred

Average single

pupal weight

(mg) (X ± SE)

Control 1 13.51 ± 0.21 568.45 ± 21.4a – 209.53 ± 1 1.9a

1.00 109.46 ± 0.60 468.55 ± 19.6b – 188.45 ± 15.4b

2.50 1 10.57 ± 0.74 428.37 ± 14.3b – 178.55 ± 13.8b

5.00 1 12.35 ± 0.29 220.51 ± 18.5c – 162.35 ± 17.5c

10.00 1 11.53 ± 0.35 145.57 ± 1 1.3d 6 –

20.00 112.57 ± 0.31 138.41 ± 20.4d 6 –

Experiment terminated 48 h after treatment; means followed by the same letter are not

significantly different ( p < 0.01; one-way ANOVA followed by Tukey–Kramer test)

Table 5 Effect of feeding
on tebufenozide (RH-
5992) treated diet on
growth and development
of IV instar larvae of H.
armigera for 48 h