Aphid Parasitism: A Sustainable BioControl Option Against Aphid Pests of Pecans in the Southeastern U.S.

View the project final report

Commodities

• Nuts: pecans

Practices

• Pest Management: biological control, integrated pest management

In Georgia, pecan is one of the top agricultural commodities producing an average yield of 599.4 kg per hectare over 52,204 hectares in 2019 (NASS 2020). The farm gate value for pecan production in 2018 was $218,477,486 (Wolfe and Stubbs 2019). Pecan, like many other agricultural commodities, is susceptible to damage by an assemblage of pest whose life histories and management tactics vary (Wells et al. 2007). Three species of aphid feed on pecan in the southeast including yellow pecan aphid, Monelliopsis pecanis Bissell, blackmargined aphid, Monellia caryella (Fitch), and black pecan aphid, Melanocallis caryaefoliae (Davis), (Hemiptera: Aphididae) (Wood et al. 1987, Mizell III and Schiffhauer 1990, Wells and Conner 2007, Shapiro–Ilan et al. 2013). The yellow pecan aphid and blackmargined aphid are collectively referred to as the ‘yellow aphid’ complex. All three species of aphid feed on the leaves of the tree causing both direct and indirect damage. Feeding on the leaf removes valuable nutrients from the leaf which are valuable for vital functions. In addition, as pecan aphids feed they secrete honeydew as a byproduct. Honeydew coats the leaf and overtime promotes the growth of sooty mold which can hinder the photosynthetic capabilities of the plant (Tedders 1978, Cottrell et al. 2009, Paulsen et al. 2013).

While insecticides are the primary method of control for these pests, the threat of insecticide resistance and non-target effects is a growing issue for aphid management in many different systems (Kandil et al. 2017, Tang et al. 2017, Mingeot et al. 2020). Therefore, alternative methods are needed in order to address pecan aphid issues in the field. One method is the use of natural enemies that can keep aphid populations in check.  An example of a natural enemy that can be implemented for aphid management is Aphelinus perpallidus, a primary parasitoid of pecan aphids (Tedders 1978, Bueno Jr and Stone 1983, Bueno Jr and Stone 1985, Bueno Jr and Stone 1987). Despite previous research on the effects of intraguild predation and lab-based insecticide exposure studies, there is still much information that needs to be acquired including the effects of seasonality and vertical stratification (a.k.a canopy height)(Tedders 1978, Bueno Jr and Stone 1983, Bueno Jr and Stone 1985, Bueno Jr and Stone 1987).

The objectives of this research was to assess environmental factors on pecan aphids and A. perpallidus. In our first objective, we assessed the effects of seasonality on pecan aphids and A. perpallidus in four commercial orchards with different pest management regimes. In our second objective, we assessed the abundance of pecan aphids and A. perpallidus  at different canopy heights in pecan trees at an experimental orchard. A third objective, which was a lab-based study devoted to assessing pecan aphid and A. perpallidus interactions, was canceled due to the covid-19 pandemic.

We conclude from this research that while management regimes can change between orchards, aphid phenology often remains similar as we saw few consistent differences between orchards throughout the two years of study on objective 1. Aphids followed similar seasonal patterns as demonstrated in previous studies in experimental orchards despite being present in lower population numbers. A. perpallidus populations typically followed that of their hosts. In objective 2, we found that when significant differences were detected between canopy heights, aphid and A. perpallidus were more abundant in the lower half of the pecan trees.

What these conclusions show is that growers may be able to rely on natural enemies and other factors to manage aphid populations in their orchards. In objective 1, we found that growers were applying insecticides for aphids despite having numbers below threshold. This opens the possibility for growers to reduce or eliminate spraying as a tool for aphid management saving growers time and money. In objective 2, we showed that when pecan aphids and A. perpallidus were present in higher numbers, they were typically more abundant in the lower parts of the tree. This is beneficial information for growers as they can be confident that their insecticide applications are appropriately covering areas of the tree with the highest amount of aphids. A more detailed explanations of the results and discussion can be found below.  

Literature Cited

• Bueno Jr, R., and J. Stone. 1983. Phenology of a Parasite of the Blackmargined Aphid in West Texas [Aphelinus Perpallidus, Monellia Caryella]. Southwest. Entomol.
• Bueno Jr, R., and J. D. Stone. 1985. Aphelinus Perpallidus Parasitism of Monellia Caryella Populations in Far West Texas. J. Entomol. Sci. 20: 325-330.
• Bueno Jr, R., and J. Stone. 1987. Reproductive Response of Aphelinus perpallidus (Hymenoptera: Aphelinidae) to Age of Its Parent and Density of Its Host, Monellia Caryella (Homoptera: Aphidae). Environ. Entomol. 16: 877-880.
• Bueno Jr, R., and H. Van Cleve. 1997. The Effect of Temperature and Host Density on the Reproduction of Aphelinus Perpallidus. Southwest. Entomol.
• Cottrell, T. E., B. W. Wood, and X. Ni. 2009. Chlorotic Feeding Injury by the Black Pecan Aphid (Hemiptera: Aphididae) to Pecan Foliage Promotes Aphid Settling and Nymphal Development. Environ. Entomol. 38: 411-416
• Kandil, M.A.; Abdallah, I.S.; Abou-Yousef, H.M.; Abdallah, N.A.; Fouad, E.A. 2017. Mechanism of Resistance to Pirimicarb in the Cowpea Aphid Aphis craccivora. Crop Prot. 94: 173-177.
• Mingeot, D.; Hautier, L.; Jansen, J.P. 2020. Structuration of Multilocus Genotypes Associated with Insecticide Resistance of the Peach Potato Aphid, Myzus persicae (Sulzer), in Potato Fields in Southern Belgium. Pest Manag. Sci. 
• Mizell III, R. F., and D. E. Schiffhauer. 1990. Effects of Pesticides on Pecan Aphid Predators Chrysoperla rufilabris (Neuroptera: Chrysopidae), Hippodamia convergens, Cycloneda sanguinea (L.), Olla v-nigrum (Coleoptera: Coccinellidae), and Aphelinus perpallidus (Hymenoptera: Encyrtidae). J Econ Entomol 83: 1806-1812.
• NASS, U. 2020. United States Department of Agriculture National Agricultural Statistics Service. 2017. Quick stats database.
• Paulsen, C., T. Cottrell, and J. Ruberson. 2013. Distribution of the Black Pecan Aphid, Melanocallis caryaefoliae, On the Upper and Lower Surface of Pecan Foliage. Entomol. Exp. Appl. 146: 252-260.
• Shapiro–Ilan, D. I., T. E. Cottrell, M. A. Jackson, and B. W. Wood. 2013. Control of Key Pecan Insect Pests Using Biorational Pesticides. J Econ Entomol 106: 257-266.
• Tang, Q.-L.; Ma, K.-S.; Hou, Y.-M.; Gao, X.-W. 2017. Monitoring Insecticide Resistance and Diagnostics of Resistance Mechanisms in the Green Peach Aphid, Myzus persicae (Sulzer)(Hemiptera: Aphididae) in China. Pestic. Biochem. Phys., 143, 39-47.
• Tedders, W. L. 1978. Important Biological and Morphological Characteristics of the Foliar-feeding Aphids of Pecan, vol. 1578-1587, Department of Agriculture, Science and Education Administration, 1978.
• Watterson, G. P., and J. D. Stone. 1982. Parasites of Blackmargined Aphids and their Effect on Aphid Populations in Far-West Texas. Environ. Entomol. 11: 667-669.
• Wells, L. 2017. Pecan: America's Native Nut Tree,  University of Alabama Press.
• Wells, L., and P. Conner. 2007. Southeastern Pecan Growers' Handbook.

Our objectives include:

1. Identifying the parasitoid species attacking pecan aphids in Georgia and quantifying their parasitism rates. We have updated this objective to include a seasonal phenology of all threes aphid species and A. perpallidus (the primary aphid parasitoid in Georgia).

2. Assessing parasitism rates on pecan aphids in the laboratory (Canceled)

3. Examining the relationship between canopy height and parasitism rates. We also included the effects of canopy height on aphid and parasitoid numbers.