Several herbivorous insects utilize plant chemical cues to identify hosts for feeding. The role of smell in host plant detection by
Mahanarva spectabilis
(Distant) remains largely unknown. In this study, assays were applied to assess
M
.
spectabilis
olfactory responses to forage grasses (
Pennisetum purpureum
cvs. Roxo Botucatu and Pioneiro;
Panicum maximum
cvs. Makueni and Tanzânia;
Hyparrhenia rufa
cv. Jaraguá;
Melinis minutiflora
;
Cynodon dactylon
cv. Tifton;
Brachiaria brizantha
cv. Marandú; and
Brachiaria decumbens
cv. Basilisk). Bioassays were performed using a Y-olfactometer to evaluate the behavior of adult
M
.
spectabilis
to forage damaged and undamaged by insects.
M
.
spectabilis
preferred volatiles of undamaged Basilisk and Pioneiro. Repellent behavior by
M
.
spectabilis
to cospecifics was recorded for plant volatiles from damaged Marandú. The mixture of volatiles from undamaged forage grasses differed from that of forage grasses damaged by insects. Forage grasses showed a greater diversity of compounds after damage, including menthone, eucalyptol and camphor, which are compounds likely to cause loss of attractiveness or repellence. Our results demonstrate that
M
.
spectabilis
employs plant chemical cues in its choice of hosts. This fact may contribute to strategies of integrated management against this pest.
The damage caused by spittlebugs varies according to the species of grass, and the losses can reach alarming levels. Measures for population control are currently restricted to the use of resistant grasses and the diversification of pastures. Therefore, alternative control measures are necessary, such as the use of botanical insecticides. The aim of this study was to evaluate the insecticidal activities of thymol, carvacrol, eugenol, cinnamaldehyde, and trans-anethole on Mahanarva spectabilis eggs, nymphs, and adults under laboratory conditions. In the egg tests, treatments with eugenol, carvacrol, and thymol showed the highest mortalities, presenting efficiencies higher than 85% after 48 h of application. In the nymph tests, the treatments with thymol and carvacrol at 2.5% and eugenol at 2.0% and 2.5% showed intermediate efficiencies, with values above 61%. The highest mortality was observed in the treatment with trans-anethole at 2.5%, with an efficiency of 95%. In the tests with adults, only treatment with trans-anethole at 2.5% obtained an efficiency reaching 90%; in the other treatments, the efficiency did not exceed 51%. These results showed that, at these concentrations, trans-anethole presents a high rate of insecticidal activity on M. spectabilis nymphs and adults and, therefore, is recommended as a potential natural insecticide for the control of this pest.
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