Since its 2018 invasion of eastern Asia, the fall armyworm Spodoptera frugiperda (Lepidoptera: Noctuidae) has become a key pest in local maize production.  Though pesticides have been widely used to mitigate the initial S. frugiperda attack, biological control is receiving ample attention as a desirable, environmentally-sound alternative to chemical control.  Hoverflies (Diptera: Syrphidae) are abundant natural enemies in Chinese maize fields and have been observed to consume S. frugiperda larvae.  In this study, we use laboratory assays to study the two-way interaction between immature stages of S. frugiperda and the endemic syrphid Eupeodes corollae.  To mimic natural conditions, assays were performed in the presence of fresh maize leaves.  Those 2nd or 3rd instar larvae of E. corollae preyed on 1st and 2nd instar S. frugiperda larvae with a Holling type III response, consuming a respective theoretical maximum of 43.48 and 83.33 larvae over a 24-h period.  Conversely, once S. frugiperda larvae reached 3rd instar, they exhibited aggressive behavior and equally preyed on syrphid larvae with a Holling type III response.  Those 5th and 6th instar larvae of S. frugiperda consumed a respective 16.39–19.23, 6.02–19.61 and 6.76–8.26 of 1st, 2nd and 3rd instar E. corollae larvae per day.  Though our results await field-level validation, S. frugiperda agonistic (i.e., defensive) and consumptive behavior towards resident natural enemies such as E. corollae possibly degrades biotic resistance and raises its invasion potential.  Our findings shine new light on the interaction between lepidopteran herbivores and their natural enemies, and can help advance the development of conservation biological control and other integrated pest management (IPM) strategies against S. frugiperda in China and abroad.  

 

Floral resources, such as carbohydrate-rich nectar or pollen, can bolster fitness and raise reproductive output of adult lepidopterans.  Here, we used laboratory experiments to assess how those plant-derived foods impact adult fecundity, reproductive physiology and flight performance of an invasive strain of the fall armyworm, Spodoptera frugiperda (FAW; Lepidoptera: Noctuidae) in China.  More specifically, supplementary feeding on bee pollen and honey enhanced FAW flight duration, testis size, ovarian development, longevity and adult fecundity.  FAW adults attained the longest pre-oviposition (10.8 days) and oviposition period (6.8 days) and longevity (19.2 days) on 5% acacia honey.  Upon access to 2.5% acacia honey and 2.5‰ pine pollen, S. frugiperda attained the highest mating rate (79.7%), fecundity (644.9 eggs/female) and egg hatching rate (82.3%).  Feeding on honey further delayed decay of male testes, while ovarian development was enhanced when female moths were allowed access to 2.5% honey and 2.5‰ pine pollen.  Upon feeding on 5% honey solution, S. frugiperda engaged in flight over the longest duration (9.5 h), distance (29.9 km) and speed (3.1 km h^–1).  Honey had a comparatively greater effect on the above parameters than pollen.  Our findings help decipher FAW invasion patterns and population dynamics, facilitate the development of nutritional attractants, and contribute to integrated pest management of this newly-invasive pest in eastern Asia.