• Korean journal of applied entomology
• /
• v.59 no.4
• /
• pp.455-460
• /
• 2020

Rice grain damage caused by Paromius exiguus under various conditions in paddy fields was analyzed. One nymph of P. exiguus caused 2.7 pecky grains in brown rice in one day, and sixteen nymphs caused 132.3 pecky grains over sixteen days. The relationship between the inoculated nymphal density and the number of pecky grains was well described by a linear regression (Y = 8.8446X, r2 = 0.9622). When a pair of P. exiguus adults was inoculated in the heading stage of rice, the damage at the time of harvesting consisted of 40.2% of cracked rice and 30.5% of pecky rice among whole rice grains. Inoculation of 16 pairs resulted in 81.7% of cracked rice and 74.5% of pecky rice. The damage analysis indicated that the quantity of ripened rice decreased as the damage started earlier in the heading stage of rice. On the contrary, the proportion of cracked and pecky rice rapidly increased from the heading time until 28 days after heading of the rice grains.

• Korean journal of applied entomology
• /
• v.48 no.1
• /
• pp.37-44
• /
• 2009

This study was carried out to survey the occurrence of stink bugs and pecky rice grain caused by the stink bugs in paddy fields in six districts of Gyeonggi-do. In the levee of the paddy fields, 30 species of the stink bugs were collected, and the dominant species were Paromius exiguus in Hwaseong and Siheung, and Stenotus rubrovittatus in Pyeongtaek, Icheon and Paju. In the paddy fields, 23 species were collected, and the dominant species were Paromius exiguus in Siheung, and Stenotus rubrovittatus in Pyeongtaek, Icheon and Paju. P. exiguus overwintered and proliferated mainly in the west coastal region, where its host plants, Imperata cylindrica and Calamagrostis epigeois, were abundant, and then moved to paddy fields later in the season, resulting in the peak density in September in paddy area. Stenotus rubrovittatus and Cletus punctiger were abundant in paddy area in August and September, and Eysarcoris aeneus was abundant in June and July. When the stink bugs were inoculated on the rice, the rate of pecky rice caused by E. aeneus and P. exiguus at milk ripe stage was 10.2% and 4.8%, respectively, and the rate by S. rubrovittatus and P. exiguus at dough ripe stage was 4.3% and 2.7%, respectively. The damage shape of pecky rice was distinctive according to the species. The surface of pecky rice by P. exiguus was very smooth but the surface of pecky rice by E. aeneus was rough and caved. In the pecky rice by S. rubrovittatus, the spot occurred at the topside of the grain.

• Korean journal of applied entomology
• /
• v.46 no.1 s.145
• /
• pp.51-56
• /
• 2007

The two species of rice bugs causing pecky rice, Cletus punctiger and Cletus schmidti are often observed coexisting in the rice fields of nearby fallow land. Direct feeding damage to rice by C. punctiger and C. schmidti can lead to a reduction in grain quality and quantity. These studies were carried out to investigate the development of C. punctiger and C. schmidti at various constant temperatures ranging from 20 to $30^{\circ}C$, 65% RH, and a photoperiod of 16L:8D. Egg hatchability of C. punctiger/C. schmidti at the temperatures of 20, 25 and $30^{\circ}C$ were 80.6/88.0, 91.7/96.3, 96.4/96.2%, respectively. The development periods of eggs of C. punctiger/C. schmidti at the temperatures of 20, 25, and $30^{\circ}C$ were 16.4/18.4, 9.4/10.2 and 6.4/7.3 days, respectively. Mean developmental periods of 1 st, 2nd, 3rd, 4th and 5th nymphs of C. punctiger/c. schmidti at $30^{\circ}C$ were 2.1/2.0, 3.5/4.0, 3.3/5.6, 3.2/4.8 and 5.8/6.9 days, respectively. Oviposition began 8.1 days after emergence at $25^{\circ}C$, and the longevity of female and male were 120.0 and 117.3 days, respectively. Total number of eggs through the life of female were 245.5 laying 2.2 eggs a day in average at $25^{\circ}C$. The development periods of egg and nymphs of C. punctiger were relatively shorter than those of C. schmidti. Availability of male had affected the egg hatchability greatly that laid at 30th day after 60 days period of oviposition in the presence of adult male of C. punctiger. The fertile eggs laid by the female together with male was 92.1% but those without male was only 9.6%.

• Korean journal of applied entomology
• /
• v.48 no.1
• /
• pp.21-27
• /
• 2009

Paromius exiguus (Distant) has caused serious damage by pecky grains around Gimpo paddy fields in 2001. We conducted field and laboratory studies to determine the seasonal occurrence and age distribution of P. exiguus on the three major host plants. The overwintering P. exiguus was found mainly on the basal part of gramineae weeds in various localities. After overwintering, in mid-May, the adults aggregated on the grain parts of Imperata cylindrica, laid their eggs and nymphs developed into adults on the same host plants. By the time, the Calamagrostis epigeios colony had newly occupied I. cylindrica areas, the nymphs and adults of first generation had already moved to the second host. The second generation of P. exiguus, after having completed its life cycle on C. epigeios, the newly emerged adults migrated to the rice plants and other gramineae weeds in early August. Afterwards, they complete its third generation cycle where they can move to the overwintering site again. P. exiguus has the five nymphal stages and each nymphal stage could be determined by head or prothoracic width. On the I. cylindrica and O. sativa hosts, the age distribution of P. exiguus showed a simple structure as each stage ratio increased stepwise with time. But in case of C. epigeios, as the newly emerged adults and immature nymphs continuously migrate after a month from the I. cylindrica, the age structure became remarkably complex. The peak nymphal density was observed when the ratio of third and forth instar was the highest in the population. The finding about the specific age structure on each generation of the insect would be very useful in control decision making on the major host plants. It is also important to consider the host's specificity to pesticide sensitivity in relation to various nymphal stages.

• Korean journal of applied entomology
• /
• v.56 no.4
• /
• pp.387-394
• /
• 2017

Temperature-dependent oviposition model and life table parameters of Paromius exiguus (Distant), the causal agent of 'pecky' rice grain were examined at eight constant temperatures (17.5, 20, 22.5, 25, 27.5, 30, 32.5, and $35{\pm}^{\circ}C$) and a photoperiod of 14:10 (L:D) h. Unit functions of the oviposition model were developed and life table parameters were estimated. The longevity of P. exiguus adults decreased with increasing temperature (123.8 days at $17.5^{\circ}C$ and 23.6 days at $32.5^{\circ}C$). Total fecundity was highest at $30^{\circ}C$ (585.2 eggs/female) and lowest at $17.5^{\circ}C$ (21.5 eggs/female). In order to develop a temperature-dependent oviposition model, adult aging-rate, temperature-dependent fecundity, age-specific survival rate, and age-specific cumulative oviposition rate equations were estimated. All unit equations ($r^2=0.92{\sim}0.98$) except for the temperature-dependent fecundity equation ($r^2=0.83{\sim}0.85$), described oviposition characteristics of P. exiguus adequately. Life table parameters of P. exiguus were estimated at various constant temperatures. Net reproduction rate ($R_0$) was highest at $30^{\circ}C$ (118.21). Mean generation time (T) was shortest at $32.5^{\circ}C$ (32.99 days) and doubling time (Dt) was shortest at $30^{\circ}C$ (5.69 days). The highest values of intrinsic rate of increase ($r_m$) and finite rate of increase (${\lambda}$) were 0.122 and 1.129 at $30^{\circ}C$, respectively.