Vestaron (United States)

The twolined spittlebug, Prosapia bicincta (Say), is a pest of forage and turfgrasses causing economic and ecological damage to rangelands in Hawai'i. First detected in 2016, this pest now infests >143,000 ha on Hawai'i Island. Host plant resistance is a key strategy for management of grass-feeding spittlebugs in pastures. The susceptibility of 12 different grass species and cultivars to adult P. bicincta feeding was evaluated in greenhouse trials. Grasses were arranged in a randomized complete block design and after 12 d of adult feeding, damage to the foliage was quantified and above- and below-ground dry biomass were measured. Three species/cultivars were moderately susceptible (foliar damage 28 to 41%) and 2 were extremely susceptible (foliar damage ≥80%). Kikuyu (Cenchrus clandestinus (Hochst. ex Chiov.) Morrone), a key pasture grass used for livestock forage in Hawai'i, exhibited the highest level of susceptibility (≥85% mean foliar damage) and significant reductions in above- (38 to 50%) and below-ground (51 to 71%) biomass compared to non-infested control plants. Seven grasses demonstrated resistance, with ≤15% mean foliar damage. Among the resistant grasses, 5 were Urochloa (P. Beauv.) cultivars (Cayana, Cayman, Marandú, Mulato II, Sabiá) and the remaining 2 were Bahia T9 (Paspalum notatum (Flugge) var. saurae (Parodi) cv. 'Tifton-9') and fountain grass (Cenchrus setaceus (Forssk.) Morrone). This study is the first to identify resistance in these grasses to P. bicincta. The underlying mechanisms of resistance were not identified and necessitates further research. Hawai'i's existing Kikuyu grass pastures are severely threatened, but the incorporation of resistant grasses is a promising management strategy.

The western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), poses a serious threat to maize (Zea mays L.) growers in the U.S. Corn Belt. Transgenic corn expressing Bacillus thuringiensis (Bt) Berliner is the major management tactic along with crop rotation. Bt crops targeting WCR populations have been widely planted throughout the Corn Belt. Rootworms have developed resistance to nearly all management strategies including Bt corn. Therefore, there is a need for new products that are not cross-resistant with the current Bt proteins. In this study, we evaluated the susceptibility of WCR strains resistant and susceptible to Cry3Bb1 to the biological insecticide Spear-T (GS-omega/kappa-Hexatoxin-Hv1a) alone and combined with Cry3Bb1 protein. The activity of Hv1a alone was similar between Cry3Bb1-resistant and susceptible strains (LC50s = 0.95 mg/cm2 and 1.50 mg/cm2, respectively), suggesting that there is no cross-resistance with Cry3Bb1 protein. Effective concentration (EC50), molt inhibition concentration (MIC50), and inhibition concentration (IC50) values of Hv1a alone were also similar between both strains, based on non-overlapping confidence intervals. Increased mortality (64%) was observed on resistant larvae exposed to Hv1a (0.6 mg/cm2) + Cry3Bb1 protein (170.8 µg/cm2) compared to 0% mortality when exposed to Cry3Bb1 alone and 34% mortality to Hv1a alone (0.3 mg/cm2). The time of larval death was not significantly different between Hv1a alone (3.79 mg/cm2) and Hv1a (0.6 mg/cm2) + Cry3Bb1 (170.8 µg/cm2). New control strategies that are not cross-resistant with current insecticides and Bt proteins are needed to better manage the WCR, and Hv1a together with Cry3Bb1 may fit this role.