Proteome of urticating setae of Ochrogaster lunifer, a processionary caterpillar of medical and veterinary importance, including primary structures of putative toxins.

Ochrogaster lunifer (Lepidoptera: Notodontidae) is an Australian processionary caterpillar with detachable urticating setae that have a defensive function. These true setae induce inflammation when they contact human skin, and equine foetal loss syndrome if they are accidentally ingested by gravid horses. We used transcriptomics and proteomics to identify proteins and peptides present in and on urticating setae, which may include toxins that contribute to inflammation and/or foetal loss syndromes. This process identified 37 putative toxins, including multiple homologues of the honeybee venom peptide secapin, and proteins with similarity to odorant binding proteins, arylphorins, and the insect immune modulator Diedel. This work identifies candidate molecules that may contribute to the adverse effects of processionary caterpillar setae on human and animal health.

Movement behaviour of two social urticating caterpillars in opposite hemispheres.

BACKGROUND: Investigating movement ecology of organisms has economic, societal, and conservation benefits. Larval movement of insects for example, plays many significant ecological roles, and with the expansion of the human population and development, encounters and conflicts with insects have increased. Urticating caterpillars are a health concern to people and animals, especially when they disperse in a gregarious and synchronised manner in areas frequented by humans. Ochrogaster lunifer and Thaumetopoea pityocampa from the southern and northern hemispheres respectively, are two geographically-isolated species of moth with similar gregarious urticating caterpillars that can outbreak causing defoliation and medical issues. METHODS: Each year from March to May, O. lunifer and T. pityocampa caterpillars leave their nesting sites and form head-to-tail processions on the ground in search of pupation sites. This pre-pupation procession behaviour and its associated risk of human contact with O. lunifer and T. pityocampa caterpillars were studied and compared in Australia and Italy, respectively. The distance, duration, orientation and response to visible light of the pre-pupation processions were studied in both species to determine general patterns. RESULTS: In the morning, O. lunifer and T. pityocampa processions travelled on average 40 and 16 m per day from the nest in 153 and 223 min respectively, in search for potential pupation sites. Ochrogaster lunifer pre-pupation processions travelled generally to the north or south when leaving the nest, as was their final orientation to the bivouac/pupation site. Whereas T. pityocampa processions had no preference in orientation. Ochrogaster lunifer and T. pityocampa pre-pupation processions travelled towards the darker and the lighter areas of the environment, respectively. During our observations, 27% of O. lunifer and 44% of T. pityocampa processions had contact with humans driving, cycling or walking. CONCLUSIONS: The amount of human contact is surprising and alarming, because of the serious health implications they cause to humans and animals. The processionary dispersal on the ground risks further spread of urticating hairs that can be easily detached, and particular during inadvertent contact. Our limited sample size of T. pityocampa processions may benefit from more observations to make conclusive remarks on their pre-pupation behaviour. Understanding the movement behaviour of O. lunifer and T. pityocampa pre-pupation processions around populated areas is crucial for predicting exposure risk and application of management strategies.

Variation in Morphology and Airborne Dispersal of the Urticating Apparatus of Ochrogaster lunifer (Lepidoptera: Notodontidae), an Australian Processionary Caterpillar, and Implications for Livestock and Humans.

True setae borne on the abdominal tergites of Ochrogaster lunifer Herrich-Schӓffer caterpillars are the agents of an irritating contact dermatitis, osteomyelitis, ophthalmia, and severe allergic reactions in humans, and are the cause of Equine Amnionitis and Fetal Loss in Australia. The setae are detached and readily dislodge from the integument whereby they disperse throughout the environment. To better understand the true setae of O. lunifer as agents of medical and veterinary concern, we studied their characteristics and distance dispersed. Whereas members of the European Thaumetopoeinae have been widely studied, their southern-hemisphere counterparts such as O. lunifer are not well known despite their harmfulness and known medical and veterinary importance. The caterpillar's investment in true setae increased with age and size, and two distinct size classes co-occurred in setae fields. A previously undescribed morphological type of true seta was found on the first abdominal segment. All true setae were calculated to travel long distances in the air even under light breeze conditions. Our results show there is a high risk of exposure to airborne urticating setae within 100 m of elevated caterpillar activity, and a likely risk of exposure for some kilometers in the direction of the prevailing breeze. This information should be used to inform management strategies in areas where urticating processionary caterpillars are active, and especially during periods of an outbreak.

Generalist insects behave in a jasmonate-dependent manner on their host plants, leaving induced areas quickly and staying longer on distant parts.

Plants are sessile, so have evolved sensitive ways to detect attacking herbivores and sophisticated strategies to effectively defend themselves. Insect herbivory induces synthesis of the phytohormone jasmonic acid which activates downstream metabolic pathways for various chemical defences such as toxins and digestion inhibitors. Insects are also sophisticated animals, and many have coevolved physiological adaptations that negate this induced plant defence. Insect behaviour has rarely been studied in the context of induced plant defence, although behavioural adaptation to induced plant chemistry may allow insects to bypass the host's defence system. By visualizing jasmonate-responsive gene expression within whole plants, we uncovered spatial and temporal limits to the systemic spread of plant chemical defence following herbivory. By carefully tracking insect movement, we found induced changes in plant chemistry were detected by generalist Helicoverpa armigera insects which then modified their behaviour in response, moving away from induced parts and staying longer on uninduced parts of the same plant. This study reveals that there are plant-wide signals rapidly generated following herbivory that allow insects to detect the heterogeneity of plant chemical defences. Some insects use these signals to move around the plant, avoiding localized sites of induction and staying ahead of induced toxic metabolites.