Learning helps tobacco hawkmoths to select a nectar source and
oviposition site more efficiently

Date:
September 27, 2021
Source:
Max Planck Institute for Chemical Ecology
Summary:
Researchers have gained new insights into the learning ability
of tobacco hawkmoths. In two recent publications, they report
that learning odors does not only play a role in foraging, but
that female moths are also influenced by previously learned odors
when choosing a host plant to lay their eggs. In this context,
a single deposited egg on a certain plant is sufficient for the
moth's choice to visit the same plant species again even after 24
hours. In contrast, the moth's second nose, the tip of the proboscis
on which olfactory sensory cells have also been identified, does
not appear to play a role in learning odors and making odor-guided
foraging decisions. The results provide clues to the adaptability
of these insects to their environment.



FULL STORY ==========================================================================
In an earlier study, scientists led by Bill Hansson and Markus Knaden
from the Department of Evolutionary Neuroethology were already able to
show that tobacco hawkmoths can learn odors as cues to a nectar source
that they had initially perceived as unpleasant. The insects had been
found to be highly adaptive with respect to food sources.


==========================================================================
In the present study, the researchers wanted to know whether learning
also affects egg-laying. In behavioral experiments, they first gave
female tobacco hawkmoths the choice of laying their eggs on a leaf of
either the wild tobacco species Nicotiana attenuata or sacred datura
Datura wrightii. Nai"ve moths, which had not previously laid an egg on a
plant, showed an innate preference for the leaves of sacred datura. In a
second set of experiments, inexperienced females were trained on either
tobacco or datura leaves, meaning that the moths had no choice but to
lay their eggs on only one of the two plant species. In a third step,
the researchers wanted to know whether this training had any effect on selecting one plant over the other. "We were very surprised to observe
that even a single egg-laying experience was sufficient to direct a
moth's interest to the very plant on which an egg had previously been
laid. Tobacco hawkmoths learned this plant even when only one leaf was available for oviposition and the experience was thus decoupled from the
flower as a nectar source," first author Nandita Nataraj summarizes the results. Apparently, successful oviposition is in itself rewarding to
the moth and influences future behavior.

Overall, the experiments revealed that the preference for tobacco
decreased more significantly after 24 hours than the preference for
datura, whose leaves they prefer naturally. Innate preference combined
with success learning appears to be an evolutionary advantage that allows
the heavy insect, which expends a lot of energy flying and hovering,
to lay its eggs more efficiently and thereby save resources. It is also
better protected from predators if it does not have to search for host
plants for a long time.

Tobacco hawkmoths learn scents with their antennae, but not with their
second nose: the tip of their proboscis Tobacco hawkmoths do not only
learn host plants for more efficient egg laying, they also remember
flower odors that lead them to a nectar source while foraging. Tobacco hawkmoths detect olfactory cues that guide them to a flower with their antennae. However, in a 2016 study, Markus Knaden's team had found that olfactory neurons on the tip of the proboscis represent a second nose in tobacco hawkmoths. Therefore, the researchers now wanted to know whether
the moths can also learn odors with this additional olfactory organ.

"The biggest challenge for our study was the design of an artificial
flower that retains the odor inside and does not emit it. If the odor
were also perceptible outside the flower, we would not have been able
to distinguish between odor learning with the antennae and with the
proboscis," says first author Elisabeth Adam, describing the special
feature of the experimental setup. In their natural environment, the crepuscular insects also follow visual cues. The scientists therefore
developed a flower made of blue acrylic that reliably attracted moths
even without emitting an odor.

The behavioral experiments in the wind tunnel revealed that tobacco
hawkmoths do not learn odors that they perceive only with their
proboscis. Previous experience with specific odors within the flower
therefore did not alter foraging behavior. "We know from previous studies
that higher brain regions are involved in learning. Maybe the role of the proboscis is more that of a tactile or gustatory organ to evaluate the
quality of a flower. It therefore presumably perceives odors differently
and does not pass odor information on to higher brain regions," Elisabeth
Adam explains the results.

The tobacco hawkmoth Manduca sexta: an ideal model to study the effects of learning on odor-guided behavior in an insect Tobacco hawkmoths exhibit
many complex behaviors even under laboratory conditions. Following
a plume indicating flower nectar, or distinguishing between host and
non-host plants to lay their eggs to ensure that they offspring can
thrive, are behaviors that are of particular ecological interest.

"We already know a lot about olfaction in this insect, in particular which brain regions are involved in the transmission and processing of olfactory cues. The moths are therefore ideal models to study odor perception and learning -- from the detection of an odor molecule via neuronal processing
to the resulting behavior," summarizes study leader Markus Knaden.

Further studies will now address the questions of whether tobacco
hawkmoths can also learn to lay their eggs on plants that do not belong
to their host range and whether they can also learn a variety of different flowers and host plants.

Additional experiments will also examine how the moth uses the olfactory neurons on its proboscis to evaluate flower odors.

========================================================================== Story Source: Materials provided by
Max_Planck_Institute_for_Chemical_Ecology. Note: Content may be edited
for style and length.


========================================================================== Journal References:
1. Nandita Nataraj, Elisabeth Adam, Bill S. Hansson, Markus
Knaden. Host
Plant Constancy in Ovipositing Manduca sexta. Journal of Chemical
Ecology, 2021; DOI: 10.1007/s10886-021-01309-3
2. Elisabeth Adam, Bill S. Hansson, Markus Knaden. Moths sense but
do not
learn flower odors with their proboscis during flower investigation.

Journal of Experimental Biology, 2021; 224 (17) DOI:
10.1242/jeb.242780 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/09/210927102602.htm

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