Progress 10/15/01 to 10/31/04
Outputs
We found that Japanese beetles paired more frequently in the morning and evening and at lower temperatures. The sex ratio on the food plants, although male-biased, did not change consistently over the course of a day and unpaired females and males existed throughout the day. Copulation in this species is quite short (a few minutes) but males may remain mounted on females for more than three hours. The duration, and likely the effectiveness, of this mate guarding behavior is affected by local density and by temperature and foraging history. Males pay a cost while mate guarding due to thermoregulatory concerns and the average water levels of individuals collected in the field was related to time of day (higher in morning) and whether they were paired (paired males often had lower water levels than single males in the morning and evening). Paired females are larger than unpaired females throughout the day; this pattern seems to be a result of a male preference for mating
with large females and a tendency for males to guard larger females for a longer period of time. Males also mount other males; this homosexual behavior occurs at a low but consistent frequency in the field and, in contrast to heterosexual mating behavior, is most frequent in the afternoon and least frequent in the morning. Laboratory studies indicated that the frequency of this homosexual behavior is affected by sex ratio, density, and temperature. The basis for this homosexual behavior appears to be a limited ability by male Japanese beetles to distinguish other males from nonvirgin females. Nonvirgin females do not emit a sex pheromone and thus one of the only ways males may have of distinguishing sex is size, because females tend to be larger than males. Although males attempt to pair with other males regardless of the potential mates size, males remain paired longer, and are more likely to attempt to copulate with, males that are larger than they are. This limited ability to
distinguish sexes may be responsible for the lack of sex ratio to influence mate guarding behavior. Direct male competition for females, in the form of males physically attempting to takeover females from other males, occurs in the field. Field observations determined that fights are most common in the afternoon and at higher temperatures, and tend to be won by the male initially guarding the female. When takeover attempts are successful, it tends to because the intruder was larger than the resident male. In summary, our studies yielded some important, general patterns: (1) Japanese beetle behavior has a strong temporal component (2) Individual male Japanese beetles vary greatly in their behavior, and this variation may be explained by differences in their characteristics (e.g. size, condition, foraging history); (3) social environment and affect many aspects of Japanese beetle mating behavior; and (4) imprecise cues used for sex identification may lead males to make mounting
mistakes.
Impacts
In summary, our studies yielded some important, general patterns: Japanese beetle behavior has a strong temporal component both daily and seasonally (2) Individual male Japanese beetles vary greatly in their behavior, and this variation may be explained by differences in their characteristics (e.g. size, condition, foraging history); (3) social environment and affect many aspects of Japanese beetle mating behavior; and (4) imprecise cues used for sex identification may lead males to make mounting mistakes. Results from this study are some of the first quantitative, behavioral observations on individual Japanese beetle mating behavior. These findings help us better understand their breeding biology and should provide a starting point for further studies that will hopefully help control this important pest species. Dr. Paul Switzer will very soon (November 2004) submit a Strengthening, Standard USDA Research Project Award proposal to further elucidate the
behavior/ecology of the Japanese beetle. His proposal is based on the patterns we found with this seed grant and will have a direct impact on improved management of Japanese beetle infestations.
Publications
- Switzer, P.V., K. Escajeda*, and K. Kruse. (2001). Pairing patterns in Japanese beetles (Popillia japonica Newman): effects of sex ratio and time of day. Journal of Insect Behavior 14(6): 713-724.
- Switzer, P.V., P.S. Forsythe*, K. Escajeda*, and K.C. Kruse. (2004). Effects of Environmental and social conditions on homosexual pairing in the Japanese beetle (Popillia japonica Newman). Journal of Insect Behavior 17:1-16.
- Saeki, Y.*, K. C. Kruse, and P. V. Switzer. (2005-In Press). Physiological costs of mate guarding in the Japanese beetle (Popillia japonica Newman). Ethology
- Saeki, Y,* K.C. Kruse and P.V. Switzer (2005-In Press). Male preference for large females in the Japanense beetle (Popillia japonica) (Coleoptera:Scarabaeidae). J. Kansas Entomol. Soc.
- Kruse, K.C. and P.V. Switzer. (2005-In Review). Male fighting behavior in the Japanese Beetle (Popillia japonica Newman). Journal of Insect Behavior.
- Saeki, Y.*, K. C. Kruse, and P. V. Switzer. (2005-In Review). Social environment affects mate guarding behavior in Japanese beetles, Popillia japonica Newman (Coleoptera: Scarabaeidae). Journal of Insect Science.
- Switzer, P.V., P.S. Forsythe*, and K.C. Kruse. (2005-In Review). Homosexual behavior and the (un)reliability of body size as a cue for mate choice in the Japanese beetle (Popillia japonica Newman). Behav. Ecol. Sociobiol.
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Progress 10/01/02 to 09/30/03
Outputs
Two field seasons and laboratory experiments revealed that Japanese Beetle (Popillia japonica) same sex pairings (male-male pairs) are rare but regularly occurring. Our studies are the first to look in detail at this pairing behavior; we have found that it is largely size dependent and likely relates to the unreliability of size as a cue for mate choice. Male competition is present in the field and, like much of their mating behavior, appears to be dependent on the time of day. Our initial physiological studies suggest that mate guarding is costly in this species and guarding duration will be at least partially determined by energy reserves.
Impacts
Research involving the costs of mate guarding, male-male pairing and other reproductive decisions in the Japanese Beetle (Popillia japonica) were conducted in east-central Illinois in 2002 and 2003. Mating activity is temperature related; beetles are the most active during the warmest parts of the days but extreme temperatures reduce mating activity. Copulation takes 2 minutes (in the laboratory) but males "guard" females for an extended period of time (3-4 hrs). Laboratory results suggest that male guard time is reduced with increased temperature and beetles that have low metabolic reserves do not guard females as long as those that are well fed. We are developing assays to directly compare the physiological reserves (lipids and glycogen) between paired and unpaired beetles and among beetles that guarded for different lengths of time. Data from the field also indicate that guarding males may pay a cost in terms of higher body temperature. Direct competition exists
between males for females in the field, although at a relatively low frequency. The prevalence of this competition varies with time of day, with more fighting in the middle of the day. Although rare (4 percent of all pairs), same sex pairings (male-male) do occur in the field. We found that although males of all sizes mount other males, smaller males attempt to copulate with larger males more frequently than do large males with smaller males and small males stay on the backs of large males significantly longer than when large males mount small males; in some cases, these homosexual mounts may last for hours.
Publications
- Switzer, P.V., P.S. Forsythe*, K. Escajeda*, and K.C. Kruse. 2004 (IN PRESS). Effects of Environmental and social conditions on homosexual pairing in the Japanese beetle (Popillia japonica Newman). Journal of Insect Behavior.
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