Two-way predation between immature stages of the hoverfly Eupeodes corollae and the invasive fall armyworm(Spodoptera frugiperda J.E.Smith)

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 2 nd or 3 rd instar larvae of E.corollae preyed on 1 st and 2 nd 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 3 rd instar,they exhibited aggressive behavior and equally preyed on syrphid larvae with a Holling type III response.Those 5 th and 6 th instar larvae of S.frugiperda consumed a respective 16.39-19.23,6.02-19.61 and 6.76-8.26 of 1 st,2 nd and 3 rd 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.

Mechanisms for flowering plants to benefit arthropod natural enemies of insect pests： Prospects for enhanced use in agriculture

Reduction of noncrop habitats, intensive use of pesticides and high levels of disturbance associated with intensive crop production simplify the farming landscape and bring about a sharp decline of biodiversity. This, in turn, weakens the biological control ecosystem service provided by arthropod natural enemies. Strategic use of flowering plants to enhance plant biodiversity in a well-targeted manner can provide natural enemies with food sources and shelter to improve biological control and reduce dependence on chemical pesticides. This article reviews the nutritional value of various types of plant-derived food for natural enemies, possible adverse effects on pest management, and the practical application of flowering plants in orchards, vegetables and field crops, agricultural systems where most research has taken place. Prospects for more effective use of flowering plants to maximize biological control of insect pests in agroecosystem are good but depend up on selection of optimal plant species based on information on the ecological mechanisms by which natural enemies are selectively favored over pest species.

Knowing your enemies： Integrating molecular and ecological methods to assess the impact of arthropod predators on crop pests

The importance of natural enemies as the foundation of integrated pest management （IPM） is widely accepted, but few studies conduct the manipulative field experiments necessary to directly quantify their impact on pest populations in this context. This is particularly true for predators. Studying arthropod predator-prey interactions is inherently difficult： prey items are often completely consumed, individual predator-prey interactions are ephemeral （rendering their detection difficult） and the typically fluid or soft-bodied meals cannot be easily identified visually within predator guts. Serological techniques have long been used in arthropod predator gut-contents analysis, and current enzyme linked immunosorbent assays （ELISA） are highly specific and sensitive. Recently, poly- merase chain reaction （PCR） methods for gut-contents analysis have developed rapidly and they now dominate the diagnostic methods used for gut-contents analysis in field-based research. This work has identified trophic linkages within food webs, determined predator diet breadth and preference, demonstrated the importance of cannibalism and intraguild predation within and between certain taxa, and confirmed the benefits （predator persis- tence） and potential disadvantages （reduced feeding on pest species） of the availability of alternative nonpest prey. Despite considerable efforts to calibrate gut-contents assays, these methods remain qualitative. Available techniques for predator gut-contents analysis can provide rapid, accurate, cost-effective identification of predation events. As such, they perfectly compliment the ecological methods developed to directly assess predator im- pacts on prey populations but which are imperfect at identifying the key predators. These diagnostic methods for gut-contents analysis are underexploited in agricultural research and they are almost never applied in unison with the critical field experiments to measure predator impact. This paper stresses the need for a combined approach and suggests a framework that would make this possible, so that appropriate natural enemies can be targeted in conservation biological control.

Assessing the short-term impact of an insecticide （Deltamethrin） on predator and herbivore abundance in soybean Glycine max using a replicated small-plot field experiment

A greater understanding of the relative impact of insecticide use on non-target species is critical for the incorporation of natural enemies into integrated pest management strategies. Here we use a small-plot field trial to examine the relative impact of an insec- ticide on herbivores and predators found in soybean （Glycine max L.）, and to highlight the issues associated with calculating impact factors from these studies. The pyrethroid insecticide （Deltamethrin） caused a significant reduction in invertebrate abundance in the treated plots, and populations did not recover to pre-treatment levels even 20 days af- ter spraying. To assess the relative impact of the spray on arthropods we first examined the mean difference in abundance in each plot before and after spraying. All herbivores decreased in abundance in the sprayed plots but increased in the control plots after spray- ing. Most predators （excluding hemipterans） showed a decrease in the control plots but a proportionally greater decrease in the sprayed plots. Next we examined the corrected per- centage population reduction calculated using Abbott＇s formula. All predators （including Araneae） experienced a greater reduction （mean 87% 4- 3.54 SE） than herbivores （mean 56% -4- 4.37 SE） and Araneae alone （mean 71% 4- 8.12 SE）. The range in values across the plots varied and made categorising overall impact subjective for some taxa. Despite the constraints associated with small-plot trials, by using a combination of impact factors and examining community-level response across time, we did get some indication of the likely impact of this insecticide if used in a commercial situation.