Haibo Wen

Biological assessment of Tetrastichus brontispae, a pupal parasitoid of coconut leaf beetle Brontispa longissima

Abstract To control coconut leaf beetle, Brontispa longissima (Gestro), the pupal parasitoid Tetrastichus brontispae Ferrière was imported from Taiwan and its biology was studied in quarantine in Hainan, China. The parasitoid development includes an egg, three larval instars and three pupal stages. Its developmental time from egg to adult was 19.5±0.5 days under conditions of 24±2°C and 75±5% relative humidity (RH). Temperature had no effect on the sex ratio of offspring, but significantly affected the parasitism rate and reproduction. The parasitism rates were 98.07, 97.97 and 95.03% at 28, 24 and 20°C, respectively, whereas the parasitism rate was 52.18% at 18°C and 69.48% at 30°C, respectively. Furthermore, the parasitoids reared at 18 and 30°C produced fewer offspring than those at 20, 24 and 28°C, respectively. With the increase in temperature, developmental time decreased linearly from 46.19 days at 18°C to 17.10 days at 28°C. RH significantly influenced development, parasitism rate and the reproduction of T. brontispa. With the decrease of RH, developmental time increased from 22.94 days at 20% RH to 18.84 days at 95% RH. In contrast, parasitism rate and the number of offspring per female increased with the increase of RH. Though emergence rates between 50 and 95% RH were much higher than those between 20 and 35% RH, the sex ratios between 20 and 95% RH were not different. Photoperiod had no effect on parasitism, the number of offspring per female, emergence and the sex ratio of T. brontispae, but developmental time was significantly different for different photoperiods. Sucrose, honey and glucose significantly enhanced adult longevity, parasitism and the number of offspring per female of T. brontispae, but had no effect on the sex ratio and survival. Females of T. brontispae only parasitized fourth to fifth larval instars and 1–5-day-old pupae, but there was a significant difference in the number of offspring per female, development time, emergence and the sex ratio of offspring in different instars. These results showed that 1-day-old pupae, a temperature of 24–28°C and 65–95% RH were optimal for T. brontispae. These findings should be helpful in developing a production system to rear and release T. brontispae in large enough quantities to effectively control coconut leaf beetle.

Population Susceptibility to Insecticides and the Development of Resistance in Bactrocera cucurbitae (Diptera: Tephritidae)

Abstract Excessive insecticide applications are commonly used to manage Bactrocera cucurbitae Coquillett in China. Resistance status, resistance development trends, and patterns of cross-resistance to insecticides in B. cucurbitae were investigated. Among 21 populations from Hainan Island, two populations expressed high resistance to beta-cypermethrin; seven, eight, and ten populations expressed intermediate resistance to spinosad, avermectin, and beta-cypermethrin, respectively; four, six, one, five, and four populations expressed low resistance to spinosad, avermectin, trichlorfon, beta-cypermethrin, and fipronil, respectively; and the remaining populations exhibited either minor resistance or remained susceptible. Analysis of the development of resistance showed that resistance levels to spinosad and avermectin were readily developed at 40.68- and 18.42-fold, respectively, and a spinosad-resistant strain also showed relative positive cross-resistance to beta-cypermethrin and avermectin, but relative negative cross-resistance to trichlorfon and fipronil. These data represent the most extensive survey of insecticide resistance conducted in B. cucurbitae to date, and the level of insecticide resistance in populations should be considered when designing control measures and pest management strategies.

Age-Stage, Two-Sex Life Table of Brontispa longissima (Gestro) (Coleoptera: Hispidae) Feeding on Four Palm Plant Varieties

ABSTRACT The life history of Brontispa longissima (Gestro) (Coleoptera: Hispidae), reared under laboratory conditions on leaves of coconut (Cocos nucifera L.), royal palm [Roystonea regia (Kunth) O.F.Cook], bottle palm [Hyophorbe lagenicaulis (L. Bailey) H.E.Moore], and fishtail palm (Caryota ochlandra Hance) was analyzed using age-stage, two-sex life table. Means and standard errors of population growth parameters were calculated using the jackknife method. Moreover, survival rate and fecundity data were applied to project the population for revealing the different stage structure. The mean intrinsic rates of population growth when reared on each respective leaf type were 0.032, 0.031, 0.019, and 0.044. Individuals reared on C. nucifera achieved the highest net reproduction rate at 114.5 offspring per female. The mean generation times of B. longissima ranged from 93.2 d (reared on C. ochlandrai) to 161.5 d (reared on H. lagenicaulis). Projections from survival rate and fecundity data indicated that B. longissima populations can row considerably faster on C. ochlandra than on the other three host plants. The results validate the two-stage life history approach taken, providing an essential tool for developing and testing future control strategies.

Differential Susceptibilities of Brontispa longissima (Coleoptera: Hispidae) to Insecticides in Southeast Asia

ABSTRACT To present the susceptibility of Brontispa longissima (Gestro) (Coleoptera: Hispidae) to insecticides, 22 populations were collected in Southeast Asia from 2007 to 2010. Moreover, the laboratory susceptible strain was maintained. The results demonstrated that the lethal concentration50 value of the susceptible strain to avermectin, &bgr;-cypermethrin, and acetamiprid was 0.034, 0.024, and 1.843 mg liter-1, respectively. Compared with the susceptible strain, 10 populations developed a medium level of resistance to avermectin (10.8-fold < resistance ratio [RR] < 34.7-fold) and 11 populations had low or minor resistance (3.6-fold<RR<9.6-fold), only one population from Qionghai still remained susceptible (RR = 2.04-fold). The Zhangjiang population expressed high resistance (RR = 46.1-fold), five populations expressed medium resistance (10.6-fold <RR<18.1-fold), and 12 populations had low resistance (5.36-fold<RR<9.66-fold) for &bgr;-cypermethrin, only four populations maintained low resistance or susceptibility (2.08-fold < RR< 3.49-fold). All populations were susceptible to acetamiprid (1.65-fold<RR<2.89-fold), except for the Jakarta population that developed minor resistance (4.33-fold). This study shows that the resistance to &bgr;-cypermethrin and avermectin in B. longissima is widespread. However, most populations remain susceptible to acetamiprid. Acetamiprid may be considered an available option for the control of B. longissima and should be considered when designing pest management programs.

Factors affecting the parasitism rate and the number and sex ratio of offspring of Asecodes hispinarum Bouček (Hymenoptera: Eulophidae), a biological control agent of Brontispa longissima (Gestro) (Coleoptera: Chrysomelidae)

To optimise the production of Asecodes hispinarum Bouček (Hymenoptera: Eulophidae), a parasitoid of coconut leaf beetle, Brontispa longissima (Gestro) (Coleoptera: Chrysomelidae), some of the factors affecting rates of parasitism, number of offspring produced per host and sex ratio of A. hispinarum were investigated. The numbers and sex ratio of A. hispinarum offspring per host reduced significantly at extreme low humidity (30% relative humidity [RH]), but there was no significant effect on parasitism. Photoperiod had no significant effects on any of the life traits tested. A. hispinarum was able to reproduce via arrhenotoky, and while increasing the proportion of female parents increased the number of parasitoids produced, the proportion of female offspring decreased. Older females showed a lower rate of parasitism than young females, however, maternal age did not affect the number or the sex ratio of offspring. Increasing the number of hosts offered to a pair of parasitoids significantly increased the number of parasitised hosts but decreased the parasitism rate while the sex ratio of progeny was not affected. Present work showed that to maximise the production of female parasitoids, a parasitoid/host ratio of 1:1, using one-day old A. hispinarum at a female/male ratio of 3:1 and RH of at least 55% is recommended.

Life table analysis under constant temperature for Opisina arenosella (Lepidoptera: Xyloryctidae), an invasive moth of palm plants

The coconut black‐headed caterpillar Opisina arenosella Walker, which is spreading in Southeast Asia and southern China, is a significant pest of palm trees. All life stages of this species were reared at 20, 23, 26, 29, 32 and 35 °C to understand the effect of temperature on the biology of O. arenosella. Total developmental time egg to adult generally was longest (≈114 days) at 20 °C, declined significantly with increasing temperature, and shortest (≈47 days) at 32 °C. Estimated lower developmental threshold temperature was 11.5 °C, and estimated effective accumulated temperature was 996.93°days. A third‐order polynomial model estimated an optimal temperature of 32 °C for development. The predicted number of generations per year was calculated as 4–5 under average climatic conditions experienced in Hainan, China. The oviposition period ranged from 2 to 4 days and was longest at 26 °C while fecundity ranged from 30 to 180 total eggs laid per female and was greatest at 32 °C. The highest reproductive values were found at 32 °C. At this temperature, net reproductive rate (R0), generation time (T), intrinsic rate of increase (rm), finite rate of increase (λ) and doubling time (DT) were 64, 45 days, 0.09, 1.1 and 7.6 days, respectively. Knowledge of the effect of temperature on the life history characteristics of Opisina arenosella can be used to predict population growth, develop pest management strategies and mass produce insects for production of biocontrol agents.