Evaluating Action Thresholds for Amrasca devastans (Hemiptera: Cicadellidae) Management on Transgenic and Conventional Cotton Across Multiple Planting Dates

Estimation of direct damage to maize seedlings by the corn leafhopper, Dalbulus maidis (Hemiptera: Cicadellidae), under different watering regimes

The corn leafhopper Dalbulus maidis (Hemiptera: Cicadellidae), a specialist herbivore, is the cause of serious losses in maize yield for its capacity to transmit three important plant pathogens. They are also active phloem feeders, that insert stylets into the plant as they feed. Females place their eggs endophytically, totally inserted in the central midrib or the leaf blades, leaving conspicuous openings in the place where the ovipositor was inserted. In spite of the consequences that feeding and oviposition may have on the water status of the plant and the production of biomass, direct damage caused by the leafhopper has been only scarcely studied. In the present contribution, we measured biomass loss due to direct damage in maize plants under two watering regimes, with water supply ad libitum and with a watering restricted regime, emulating the most frequent field conditions. Moreover, we analyzed the effects of increasing densities of the vector on the biomass loss and plant mortality and the effects of females vs males. We observed that a density of 10 insects is sufficient to cause damage to 10-day-old seedlings, even in an ad libitum watering regime; however, in drought conditions, damage can be significantly greater, causing plant mortality. Also, females cause more damage than males, due to their oviposition habits.

Field evaluation of synthetic and neem-derived alternative insecticides in developing action thresholds against cauliflower pests

Synthetic chemical pesticides can enhance crop yields but also have undesired effects. Alternative 'botanical insecticides' may also have non-target effects on pollinators and biocontrol services. Employing action thresholds (ATs) can reduce pesticide (whether synthetic or botanical) use compared to fixed-interval applications. Here the azadirachtin-based botanical formulation NeemAzal and a neem seed extract (NSE) were evaluated in field spraying trials alongside commonly-used synthetics (Voliam Flexi [chlorentraniliprole plus thiamethoxam] and imidacloprid) in developing ATs for the regular and cosmopolitan cauliflower pests Brevicoryne brassicae, Plutella xylostella and Spodoptera litura. We considered the size of the S. litura larvae infesting the crop in order to derive ATs. ATs per plant were higher for NeemAzal (0.55 larvae for P. xylostella and 3 larvae for large-sized S. litura) than for Voliam Flexi (0.30 larvae for P. xylostella and 0.80 larvae for S. litura) but were similar for B. brassicae (50 individuals). Higher ATs when using azadirachtin were associated with the diverse modes of action of botanicals, for instance NeemAzal and NSE deterred oviposition of S. litura. Although the exact values of ATs are likely to have regional limits, our approach can be applied for determining ATs against common lepidopteran and aphid pests in many other vegetable crop agro-ecosystems.