The research continues into the kudzu bug problem in Kentucky, report Clara A. Bradley, University of Kentucky undergraduate entomology student, and Raul T. Villanueva, UK Extension entomology specialist in a year 2 update they issued this week.
The kudzu bug, Megacopta cribraria (Hemiptera: Plataspidae), is an invasive insect pest of legumes (Fabaceae) in the southeastern United States, including Kentucky. Kudzu bug originated from Asia and was first detected in the U.S. in Atlanta, Ga., in 2009, where it became a serious economic pest of legume plants (including soybean) producing high population outbreaks.
Kudzu bug overwinters as adults in plant debris and behind tree bark in areas near soybean fields and kudzu patches. They may also overwinter in buildings. In the spring (May and June), they fly to kudzu patches and early planted legume fields and lay their eggs in masses (Figure 1). Kudzu bug nymphs and adults cause damage to legumes by using their piercing-sucking mouthparts to penetrate the phloem and suck out nutrients and water. There are two generations of the kudzu bug per year; the second generation of adults are also the overwintering generation.
Researchers have found natural enemies of kudzu bug. These include tachinid flies (Phasia robertsonii and Strongygaster triangulifera), mermithid nematode, entomopathogenic fungus (Beauveria bassiana), and egg parasitoid wasps (Paratelenomus saccharalis and Ooencyrtus nezarae). None of these parasitoids was reported in the Western Hemisphere until 2013.
The goals of this study were to evaluate the oviposition period of the first-generation kudzu bugs in Kentucky and to detect the presence of parasitoids of kudzu bug egg masses. This study was conducted on two different kudzu patches in Caldwell County, Ky, (named as CC1 and CC2) and one patch in Lyon County, Ky., that had kudzu bug adults and eggs.
"We collected eggs once a week in these three locations, placed the eggs in 60 ml plastic containers, and took them to the laboratory. We examined the egg masses daily under a dissecting microscope for 20 to 30 days to evaluate egg eclosion and to search for egg parasitoids," Bradley and Villanueva explain.
Based on the samples collected in the field, egg oviposition in western Kentucky had started by mid-May and continued through mid-June. After June 22, egg clusters were not found in any of the sites. This may be an indication that oviposition of first generation kudzu bugs had ceased by the end of June in Kentucky. The number of eggs per cluster ranged from 16 to 18.3 eggs in Caldwell County CC1, 11 to 17 eggs in Caldwell County CC2, and 12.6 to 16.7 eggs in Lyon County. The mean percentage of eggs hatched ranged from 55% to 90% at CC1, 0% to 100% at CC2, and 73% to 86% at Lyon Co. These results show that kudzu bug eggs can hatch at high percentage rates in Kentucky.
For a second year, no parasitoids were found in egg clusters of kudzu bug for the first-generation of this insect. This finding coincides with a similar study conducted in Kentucky in 2021.
The absence of parasitoids of kudzu bug eggs may be due to several reasons:
(1) It is possible that our sampling size was small, as not all eggs are hatching,
(2) Kudzu bug eggs might have been parasitized by native wasp species (wasp lays eggs in the kudzu eggs), but the wasps were not successful in developing. For example, oviposition by the wasp may have injured the kudzu bug egg, but this host and wasp were incompatible, so the wasp was not able to complete its development using kudzu bug eggs as its host.
(3) Kentucky may be in a zone where the two exotic parasitoid wasps have not yet colonized. These parasitoids have become established in some areas of the southern U.S. (eastern Tennessee and Georgia); however, it is not yet known how they may survive and adapt to weather and cropping conditions in Kentucky.
Until 2019, scouting conducted in soybeans did not detect kudzu bugs in those fields. However, in 2020 and 2021, several fields showed some presence of kudzu bugs (1 to 2 specimens per field in an entire year); these low numbers are not considered a potential pest risk. However, detections of kudzu bugs were made in several commercial fields across several counties in Kentucky (including, Caldwell Lyon, Trig, Warren, and Daviess) in 2022. In some of these locations, egg clusters had been detected in late July to Early August, the researchers explained
"These latter findings may indicate that kudzu bugs (second generation) are in the process of a geographic expansion in western Kentucky, and the short winters and long summers may be favoring this expansion. However, as it occurred in Georgia and other southern states, kudzu bug might become a secondary pest. In addition, the high humidity here in Kentucky favors the presence of the entomopathogenic fungus (B. bassiana) that caused high kudzu bug mortalities in the Eastern Tennessee (90% mortality in second-generation immature kudzu bugs and 33% mortality in adult kudzu bugs)." Bradley and Villanueva add.
Categories: Kentucky, Crops