Determining Potential Hosts of Melanaphis sacchari (Hemiptera: Aphididae) in the Louisiana Agroecoscape

Belowground Herbivory to Sweetpotato by Sweetpotato Weevil (Coleoptera: Brentidae) Alters Population Dynamics and Probing Behavior of Aboveground Herbivores

Aboveground and belowground herbivory can alter host quality and trophic interactions. However, little research has explored the impacts of belowground herbivory on plant virus epidemiology. To understand this interaction in sweetpotato, Ipomoea batatas L. (Lam), we studied the impact of herbivory by sweetpotato weevil, Cylas formicarius elegantulus (Summers), to storage roots on vector herbivore, Myzus persicae (Sulzer), the green peach aphid, and Aphis gossypii Glover, the cotton aphid, feeding behavior (M. persicae and A. gossypii) and population dynamics (M. persicae only as A. gossypii does not colonize sweetpotato). In addition, a nonvector herbivore, Chrysodeixis includens (Walker), the soybean looper, weight gain was included for comparison. Infestations of sweetpotato weevil in storage roots reduced C. includens weight gain and M. persicae intrinsic rate of increase (rm), net reproductive rate (Ro), and finite rate of increase (λ) on aboveground portions of the plant. In probing behaviors related to nonpersistent virus spread (30 min trials), M. persicae probed less often, took longer to reach the first pd (potential drop), had shorter II-3 (intracellular subphase sap ingestion) durations, and had fewer archlets on plants infested with C. formicarius elegantulus. Total phloem duration did not differ between treatments, indicating that the lowered performance of M. persicae on infested plants was not due to discrepancies in probing duration. Results were less clear for A. gossypii. Thus, in sweetpotato, belowground herbivory can alter plant virus vector abundance and behavior. Understanding the mechanisms underlying these changes in behavior could improve plant virus vector integrated pest management.

Resistance of sorghum hybrids to sorghum aphid

Abstract The aphid Melanaphis sorghi (Theobald) (Hemiptera: Aphididae), which infest the sorghum crop, has been an economically important pest which have been causing severe damage to sorghum crops in Brazil since 2019. These species have been observed mainly at the end of vegetative stage and beginning of reproductive stage of plants. Their high reproductive rate on sorghum raises concerns about these pests. Therefore, the present study aimed to estimate the life expectancy and fertility tables of Melanaphis sorghi fed on 15 hybrids of grain sorghum, in order to know the resistance characteristics of these materials and understand how plant resistance can help manage this insect. This study was carried out in a laboratory at 26±2 ºC and 60±10% R.H (relative humidity). Fifty insects were kept in each hybrid, each insect was considered one repetition. According to biological parameters and fertility life table, hybrids BRS373, DKB590 and 50A10 were less suitable for the sugarcane aphid multiplication. Thus, these hybrids could be useful to manage this pest, since the population growth speed is one of the worst problems for the implementation of cropping systems. Genotypes AG1090, MSK327 and XGN1305 favored the development of this pest and, when chosen within a cropping system, other management strategies should be considered.

Host Acceptance and Plant Resistance: A Comparative Behavioral Study of Myzus persicae and Acyrthosiphon pisum

Simple Summary

Aphids are one of the most destructive insect pests worldwide. The green peach aphid (Myzus persicae) feeds on a broad range of plants, whereas the pea aphid (Acyrthosiphon pisum) only feeds on legumes. In this study, these two aphid species were used to investigate host acceptance and plant resistance to aphid feeding. Experiments on host plant preference and aphid performance (with regard to survival, development, and fecundity) confirmed that rape (Brassica rapa) is a suitable host and that faba bean (Vicia faba) is a poor host for the green peach aphid; for the pea aphid, faba bean is a suitable host, whereas rape is a nonhost. The probing and feeding behavior of these two aphid species on rape and faba bean was examined, and the results demonstrated the feeding preferences of these two aphid species. The green peach aphid had difficulty ingesting the phloem sap of faba bean. For the nonhost, the pea aphid spent relatively little time on mesophyll probing and did not achieve phloem sap ingestion. Furthermore, the effects of the probing and feeding behavior of specialist and generalist aphids on the spread of plant diseases caused by viruses were discussed.

Abstract

Aphids are prominent phloem-feeding insect pests. Myzus persicae and Acyrthosiphon pisum are generalist and specialist species, respectively. In this study, these two aphid species were used to investigate host acceptance and plant resistance to aphid feeding. M.persicae survived and reproduced on rape (Brassica rapa), but few individuals (9%) survived on faba bean (Vicia faba). A.pisum survived and reproduced on faba bean, but no A.pisum survived on rape. The probing and feeding behavior of M. persicae and A. pisum on rape and faba bean was examined using an electrical penetration graph (EPG) technique. The results demonstrated the feeding preferences of these two aphid species. The EPG results suggest that the resistance of faba bean to M. persicae and that of rape to A. pisum are likely residing in the phloem and mesophyll tissues, respectively. Due to the distinct probing and feeding behaviors, specialist and generalist aphids would have different impacts on the epidemiology of plant viral diseases. The findings can be applied to the management of viral diseases transmitted by specialist or generalist aphids in crop production.

Influence of Sorghum Cultivar, Nitrogen Fertilization, and Insecticides on Infestations of the Sugarcane Aphid (Hemiptera: Aphididae) in the Southern United States

The sugarcane aphid, Melanaphis sacchari Zehntner, is an economically damaging pest of sorghum, Sorghum bicolor (L.), across the southern United States. Field experiments investigated impacts of sorghum cultivar, nitrogen fertilization, and insecticides on M. sacchari infestations and sorghum yields in Louisiana and South Carolina in 2017 and 2018. In South Carolina, M. sacchari densities in unprotected plots peaked on 30-31 July of both years before declining by early- to mid-August. In Louisiana, infestations peaked on 26 and 12 July for 2017 and 2018, respectively, and declined by mid-August. Nitrogen fertilization influenced M. sacchari densities in Louisiana in 2018 with the highest-level infestations recorded from plots that received high N rates. Densities of M. sacchari on susceptible sorghum cultivar, DKS 38-88, were 1.5- to 2.3-fold greater than on DKS 37-07 in both years in Louisiana and in 2018 in South Carolina. Nitrogen fertilization was associated with improved sorghum yields in Louisiana experiments. Sorghum yields across experiments were 2- to 4-fold greater in plots protected with multiple insecticide applications than in unprotected plots. Yield from plots with insecticides sprayed once at currently used action thresholds differed from unprotected plots only in the 2018 Louisiana experiment. Results from these experiments indicate insecticidal protection of susceptible sorghum cultivars remains critical throughout much of the southern United States. Further research is needed to develop integrated management programs that incorporate fertilization manipulation, cultivar resistance, and insecticidal control.

Detailed Characterization of Melanaphis sacchari (Hemiptera: Aphididae) Feeding Behavior on Different Host Plants

Worldwide, Melanaphis sacchari Zehntner is reported on several plants in the family Poaceae, including important crops. In the United States, M. sacchari has been present primarily on sugarcane (Saccharum officinarum L.), but recently sorghum (Sorghum bicolor (L.) Moench) has become a main host. It is not clear how M. sacchari exploits sorghum or other plant species present in the Louisiana agro-ecoscape, but there is potential for these plants to be bridging hosts. Thus, this study determined the feeding behavior of M. sacchari on sorghum, rice, Oryza sativa (L.), sweetpotato, Ipomea batatas (L.), maize, Zea mays (L.), Johnsongrass, S. halepense (L.), and wheat Triticum aestivum (L.) using electrical penetration graphs. Melanaphis sacchari established sustained feeding on sorghum, Johnsongrass, wheat, and rice, only a negligent percentage on maize and no aphid fed on sweetpotato. Differences in Electrical Penetration Graph parameters among the plants in nonpenetrating total time and the lower number of probes, time to penetration initiation, proportion of individuals probing, number of probes shorter than 30 s, number of probes longer than 30 s but shorter than 3 min, pathway phase duration, and number of cell punctures during pathway phase, suggest epidermis and mesophyll factors affecting aphid feeding behavior. While the lack of differences in number of feeding occurrences, total time feeding, and number of sustained feeding occurrences shows that M. sacchari is able to feed on those plants, sieve element factors such as resistance or low nutritional quality prevent the growth of this population in field.