Lycorma delicatus (White, 1845) (Homoptera, Fulgoridae) is a serious pest of Alianthus altissima, Toona sinensis, Melia azedarach, Robinia pseudoacacia, Populus sp., Salix sp., Vitis vinifera, and Malus sp. etc. (Xiao, 1992; Zhang, 1993). This pest distributes widely in China as an indigenous species. However, it causes no economic damage on host plant due to the control effect of native natural enemies. L. delicatula had not been harmful on agricultural crops since its introduction into Republic of Korea in 1930s. Recently, however, this pest was reported causing a serious damage in grapevine yards, arbores and fruit trees in Korea (Xing et al, 2000; Kim et al, 2011). The increased abundance is considered by reason of the climate warming and lack of native natural enemies (Han et al, 2008; Park et al, 2009; Kim et al, 2011).

Anastatus orientalis (Hymenoptera, Eupelmidae) (Yang et al., 2014) is an egg parasitoid of L. delicatula in China and considered to be an important biocontrol agent as its parasitism rates reach up to 80% in some regions (Xiao, 1992; Zhang, 1993).

This study was supported by the cooperative project between the National Academy of Agricultural Science (CAAS) and the Rural Development Administration (RDA) of Korea. We selected A. orientalis as a candidate natural enemy for introduction into Korea, and investigated its natural parasitism on the eggs of the lantern fly depending on host trees and regions in order to choose populations with high parasitism rate.

Materials and Methods

Collection of lantern-fly egg masses

Egg masses of L. delicatula were collected as many as possible from 5 regions in China (Yangling, Qinhuangdao, Yantai, Guangang, Haidian) on April 2011 from the mainly host arbores (Ailanthus altissima, Toona sinensis, Populus sp., and Salix sp.). Egg collection was made on the over- wintering eggs of the lanternfly before the eggs begin to emerge, because A. orientalis lays eggs in preceding autumn and passes only one generation a year.

Egg mass with bark beneath was cut off together in order to make sure the integrity of each mass, and then put each egg mass in small paper bag. Eggs were collected three times and grouped them as such for data analysis.

Parasitoids culturing in laboratory

The number of egg masses and individual eggs in it were recorded. Each egg mass was put in one glass test tube gagged with cotton, and then marked the date, and cultured under the conditions of temperature about 25°C , relative humidity about 65% and natural illumination.

Parasitism rates of the parasitic wasp

Parasitism rate of egg masses: if an egg was parasitized then this mass was recorded as parasitized.

Parasitism rate of eggs: One parasitoid means one egg was parasitized.

The number of parasitoid emerged were checked at 6:00 every day, from late April to December.

Data analysis

Data was analyzed with Excel 2003 and SAS (Version 9.1.3). Variance was analyzed with one-way (ANOVA) in SAS. Differences among all treatments were compared with least significant difference (LSD) tests.

Results

Parasitism rates of egg masses parasitized by A. orientalis from different regions

As shown in Fig. 1 (open bar), parasitism rates of egg masses were significantly different (F = 4.942, df = 4, 14, P = 0.0458) among the five different regions. The percentage of the egg messes that have at least one parasitized egg reached 69.0% for those collected from Yantai, whereas it was 33.3% for those from Guangang.

Parasitism rates of eggs parasitized by A. orientalis from different regions

As shown in Fig. 1 (close bar), parasitism rates of eggs were significantly different (F = 3.022, df = 4, 26, P = 0.0396) among the five different regions with the highest parasitism rate of 33.0% on the population from Haidian to the lowest of 7.8% from Yangling. A few egg masses collected from Haidian were found parasitized 100%, and 23.6% of the egg masses had eggs parasitized up to 50%.

Emergence time and sex ratio of A. orientalis parasitizing L. delicatula from different regions

Emergence time and sex ratio of A. orientalis parasitizing L. delicatula from different regions As shown in Table 1, the lanternfly eggs from Shaanxi began to hatch seven to nine days earlier than those from other four regions, and the parasitoids in it started emerging six days later. The eggs from Hebei, Shandong, Tianjin and Beijing began to hatch almost at the same date, and three to nine days later wasp emergence initiated and completed within 2 to 3 days. Both female or male wasps emerged simultaneously. The sex ratios of the wasps were various among the populations.

Parasitism rates on the egg masses of L. delicatula from different trees

Parasitism rates of A. orientalis were significantly different on the egg masses of L. delicatula depending on the host trees from which they were collected (F = 15.369, df = 3, 11; P = 0.0011). But to Populus sp., Salix sp. and Toona sinensis, the difference was insignificant (Fig. 2, open bar).

Parasitism rates of A. orientalis on the individual eggs in the egg masses from different host trees were not significantly different (F = 2.07, df = 3, 11; P = 0.1051) (Fig. 2, close bar).

Discussions

The concept “biotype” originally considered based on different populations resulted in geographic diversity, different hosts and environment variation (Walsh, 1864). Diehl and Bush (1984) classified a biotype into one or more of the following categories, including nongenetic polyphenisms, polymorphic or polygenic variation within populations, geographic races, host races, and species.

Wei et al. (2009) found that a parasitic beetle Dastarcus helophoroides has different biotypes, one biotype that parasitizing Massicus raddei is with higher parasitism rate in parasitizing Massicus raddei than in Anoplophora glabripennis or other long-horned beetles.

In Australia, different biotypes of Microctonus aethiopoides were successfully introduced for controlling Sitona discoideus (Aeschlimann, 1983). Different biotypes of Cotesis sesamian had been successfully introduced into Cameroon for controlling Busseola fusca (Ndemah et al., 2007). So, when choosing natural enemies for biological control program, the different biotypes even from the same species of parasitoid wasp need to be considered carefully.

A. orientalis is the egg parasitoid of L. delicatula, which is widely distributed in China. It has high parasitism rate in L. delicatula and is an important biocontrol agent of the pest (Xiao, 1992; Zhang, 1993). Based on our investigation, the population of A. orientalis from Beijing was promising in controlling L. delicatula. And parasitism rates were quite different among the host eggs collected from different trees and regions. Parasitism rates both on the individual eggs and the egg masses collected from T. sinensis in Shandong were found to be the highest.

Insects choose different reproduction strategies based on host situation, and this is the same with parasitic wasps (Wang et al., 2010). During the investigation, we found that A. orientalis from Shandong had two emergence periods per year: some in May and others in September. This phenomena was absent in other regions. Probably there was no other alternative hosts in Yantai. A. orientalis choose a gambling strategy in order to keep population quantity when abundant eggs of L. delicatula are found. This may be a best strategy to maintain population (Qin, 2009).

Generally, parasitic wasps need five steps to complete parasitizing process: host habitat location, host location, host acceptance, host adaption and host regulation (Wang et al., 2008). During these processes, wasps integrate semiochemicals, vision, olfaction, feeling and hearing. So in the host searching process, pest and its host plant are all involved. During the process of coevolution, plant, pest and natural enemy will form a system with mutual influence and interaction. When plant is damaged by insect pests, some semiochemicals will be released to attract their natural enemies. But insect pests will form a dynamic evolutionary relationship with the purpose of avoiding being parasitized or preyed (Wei et al., 2007a,b).

In this investigation, discrepancies were evident in the parasitism rates of A. orientalis . To Populus sp., quantity of eggs oviposited by L. delicatula was highest, but the parasitism rate of A. orientalis on the eggs was lowest, even though Populus sp. was not the favorite host tree of L. delicatula. So, the tritrophic interaction among the host plants, lantern-fly, parasitic wasp needs further research.