Preoverwintering Copulation and Female Ratio Bias: Life History Characteristics Contributing to the Invasiveness and Rapid Spread of Megacopta cribraria (Heteroptera: Plataspidae)by J. R. Golec, X. P. Hu

Environmental Entomology

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Year
2015
DOI
10.1093/ee/nvv014
Subject
Ecology, Evolution, Behavior and Systematics / Insect Science / Ecology

Text

PHYSIOLOGICAL ECOLOGY

Preoverwintering Copulation and Female Ratio Bias: Life

History Characteristics Contributing to the Invasiveness and

Rapid Spread of Megacopta cribraria (Heteroptera: Plataspidae)

J. R. GOLEC AND X. P. HU1

Department of Entomology & Plant Pathology, Auburn University, 301 Funchess Hall, Auburn, AL 36849.

Environ. Entomol. 44(2): 411–417 (2015); DOI: 10.1093/ee/nvv014

ABSTRACT Prewinter copulation, sperm storage, and oocyte development in overwintering adultMegacopta cribraria (F.) was examined in Alabama (Lee Co.). Microscopic examinations of the spermathecae and ovaries were made in females and of the testes in males that were collected approximately weekly from September 2013 through March 2014. The results indicated that approximately 15% of females mated before entering winter dormancy and sperm was stored in their spermatheca for up to seven months, oocytes in mated overwintering females proceeded to postblastoderm stage before the onset of spring feeding and mating in March, all of the overwintering males had sperm in their testes, and the ratio of females gradually increased in populations during overwintering. This study indicates that both males and females are capable of reproductive dormancy. The biological significance of these life cycle aspects is discussed from the viewpoints of invasiveness and adaptation.

KEY WORDS kudzu bug, invasive pest, overwinter biology and ecology, reproductive trait

The kudzu bug, Megacopta cribraria (F.) (Heteroptera:

Plataspidae), is native to Asia and India (review by

Eger et al. 2010). Many authors indicate that the kudzu bug is an occasional to serious pest of many leguminous crops and vegetables in its native distribution (Takasu and Hirose 1985, Chen et al. 2009). It is commonly reported as a key pest of the soybean (Glycine max L.

Merrill) in China and Japan (Takasu and Hirose 1985,

Wu and Xu 2002, Xing et al. 2006), as feeding by this insect significantly reduces crop yield (Chen et al. 1996).

The kudzu bug was first discovered in the United

States in Georgia in October 2009, when adults were found aggregating on residential homes in abundance apparently seeking overwintering sites (Eger et al. 2010, Suiter et al. 2010). At that time it was defined only as a nuisance pest, yet the following year kudzu bugs were subsequently discovered infesting vegetative soybean fields in Georgia and South Carolina (Seiter et al. 2013). This quickly elevated its status from an invasive urban nuisance to that of a serious economic pest of the soybean in the United States (Greene et al. 2012), and a concern for international trade (Ruberson et al. 2013). The distribution of the kudzu bug has rapidly expanded since its initial detection, and can now be found in 13 southeastern states as well as Washington D.C. (http://www.kudzubug.org/distribution_map. cfm).

In its temperate Oriental distribution, the kudzu bug completes one to three generations a year (Hibino and

Itoˆ 1983, Tayutivutikul and Kusigemati 1992, Wu et al. 2006), whereas in more tropical areas it may be active year round (Thippeswamy and Rajagopal 1998). In its

U.S. range, the kudzu bug undergoes two generations per year (Zhang et al. 2012). It has a hemimetabolous life cycle that consists of an egg stage, five nymphal stages, and adult stage (Ramakrishna Ayyar 1913,

Ahmad and Moizuddin 1977, Tayutivutikul and Yano 1990). When temperatures increase in spring, overwintering adults become active and colonize kudzu (Pueraria montana (Lour.) Merr. variety lobata (Willd.)

Maesen and S. Almeid), where they aggregate, feed, mate, and lay eggs. The first generation nymphs develop on kudzu, and adults may switch to additional host plants such as soybean, or remain on kudzu to develop the second generation (Zhang et al. 2012). The first-instar stage ingests bacterial symbionts from capsules deposited beneath the egg mass by their mother before dispersing to obtain plant food (Fukatsu and

Hosokawa 2008). Kudzu bug nymphs and adults feed on plant phloem by inserting their stylet into stems, leaves, petioles, pods, and possibly flowers of host plants (Zhang et al. 2012, Seiter et al. 2013). In the fall, adults prepare for overwintering by migrating to areas where they aggregate and shelter from adverse environmental conditions. Reported overwintering shelters include cavities under tree bark, on or in structures, and in or under ground litter adjacent to kudzu patches, or near soybean fields. At this time they often become a nuisance pest, as they commonly invade residential structures and home gardens (Eger et al. 2010,

Waldvogel and Alder 2012). Although many legume and nonlegume species are reported as host plants to this insect, only kudzu, soybean, pigeon pea (Cajanus cajan L.), black eye pea (Vigna sinensis L.), lima bean 1 Corresponding author, e-mail: huxingp@auburn.edu.

VC The Authors 2015. Published by Oxford University Press on behalf of Entomological Society of America.

All rights reserved. For Permissions, please email: journals.permissions@oup.com (Phaseolus lunatas L.), and pinto bean (Phaseolus vulgaris L.) are confirmed as being the primary reproductive hosts in the southeastern United States (Zhang et al. 2012, Del Pozo-Valdivia and Reisig 2013, Ruberson et al. 2013, Medal et al. 2013).

Despite the studies and reports on various aspects of its biology and control methods in the United States, kudzu bug overwintering biology has not been studied in detail. To date, there is limited knowledge of ecological and behavioral information during this life history period. This includes adult insect overwintering locations as well as habitat use and aggregation behaviors of overwintering adults (Eger et al. 2010, Zhang et al. 2012). Zhang et al. (2012) reported a small peak of egglaying that occurred in October in Georgia; the eggs hatched but the nymphs (possibly a 3rd generation or part of the 2nd generation) did not complete development. We also observed oviposition on 21 November 2013 by females collected on 05 November 2013 from a residential area when kept in screen-capped glass jars and held in the laboratory (a photoperiod of 10:14 [L:D] h; 22–24C). However, a separate collection of females restricted to identical screen-capped jars, but kept outside did not lay eggs (a photoperiod of 10:20–10:45: 13:40–13:15 [L:D] h; 13.5 [11.6–26]C). These observations suggested that adults may be capable of prewinter mating, and that adults do not enter deep winter dormancy, but rather a reproductive quiescence or dormancy that can be terminated with comparatively high temperatures, changes in photoperiod, or both. Thus, environmental stimuli that induce winter quiescence or dormancy may prevent fertilization and subsequent embryogenesis in females, allowing the insect to stay reproductively inactive until spring.