This long-awaited book would seem to mark the end of classical tropical botany and phytogeography as subjects for scholarly pursuits. Since the middle of the century, when the first edition of The Tropical Rain Forest appeared, the wet tropical lowlands of the world have become an industrial battleground and, today at the end of the "Second Millennium", the future of the remaining rainforests that have evolved over millions of years looks bleak. Indeed, the book may well become "a record of what the rainforest was like in the twentieth century", as stated on its first page. This elegiac declaration not only reflects world concern about its pending extinction, but also Professor Richards' increasingly personal involvement with rainforest conservation in his later years.

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The Tropical Rain Forest: An Ecological Study

The biology and behaviour of the psyllid Diaphorina citri Kuwayama (Hemiptera: Sternorrhyncha: Liviidae), the major insect vector of bacteria associated with huanglongbing, have been extensively studied with respect to host preferences, thermal requirements, and responses to visual and chemical volatile stimuli. However, development of the psyllid in relation to the ontogeny of immature citrus flush growth has not been clearly defined or illustrated. Such information is important for determining the timing and frequency of measures used to minimize populations of the psyllid in orchards and spread of HLB. Our objective was to study how flush ontogeny influences the biotic potential of the psyllid. We divided citrus flush growth into six stages within four developmental phases: emergence (V1), development (V2 and V3), maturation (V4 and V5), and dormancy (V6). Diaphorina citri oviposition and nymph development were assessed on all flush stages in a temperature controlled room, and in a screen-house in which ambient temperatures varied. Our results show that biotic potential of Diaphorina citri is not a matter of the size or the age of the flushes (days after budbreak), but the developmental stage within its ontogeny. Females laid eggs on flush V1 to V5 only, with the time needed to commence oviposition increasing with the increasing in flush age. Stages V1, V2 and V3 were most suitable for oviposition, nymph survival and development, and adult emergence, which showed evidence of protandry. Flush shoots at emerging and developmental phases should be the focus of any chemical or biological control strategy to reduce the biotic potential of D. citri, to protect citrus tree from Liberibacter infection and to minimize HLB dissemination.

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Citrus flush shoot ontogeny modulates biotic potential of Diaphorina citri.

Although many studies have been conducted on the development and reproductive potential of Diaphorina citri Kuwayama, 1908 (Hemiptera: Liviidae) in different host species, few have evaluated these parameters on different varieties of the same host species. This study evaluated the influence of five commercial varieties of citrus (Citrus spp. L.)--Hamlin, Natal, Pera, Ponkan, and Valencia-and orange jasmine [Murraya exotica (L.) Jack] on the development of D. citri. Survival rates for the egg stage were highest on orange jasmine (85.7%) and on Valencia (83.3%). The lowest viability of the nymphal stage was also observed on Hamlin, averaging 57.4%. Values for total viability ranged from 65.9 to 32.6%, and were highest on Valencia. The longest egg-adult development time was on Natal, with a mean of 18.4 d; the shortest total development time was on orange jasmine, with a mean of 17.3 d. Based on the fertility life table, the net reproductive rate (Ro) of D. citri was 2.5 times higher when reared on Valencia than on Hamlin. The other parameters (duration of each generation [T], finite rate of increase [lambda], and innate capacity to increase in number [r(m)]) also demonstrated that Valencia is best suited to this insect. The results obtained for the biological parameters and the fertility life table indicate that Valencia and orange jasmine were the most suitable hosts, whereas Hamlin was least suitable for the development of D. citri. These results provide information for the installation of new citrus groves, especially in the choice of varieties to be planted and the location of different varieties within the groves, with a view toward the management of Huanglongbing or HLB.

https://bioone.org/journals/journal-of-economic-entomology/volume-107/issue-2/EC13339/Biology-of-the-Huanglongbing-Vector-Diaphorina-citri-Hemiptera--Liviidae/10.1603/EC13339.pdf

Biology of the Huanglongbing Vector Diaphorina citri (Hemiptera: Liviidae) on Different Host Plants

Since its discovery in 2008, the pestiferous Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), has become widely established in residential citrus trees throughout southern California. In 2011, Tamarixia radiata (Waterston) (Hymenoptera: Eulophidae), a host-specific parasitoid of D. citri , sourced from Punjab Pakistan, was introduced into California as part of a classical biological program aimed at suppressing D. citri populations in urban areas. Despite these release efforts, little is known about the population dynamics of D. citri in urban citrus or the efficacy of T. radiata in controlling psyllid populations in urban-grown citrus. To address this shortcoming, the population phenology of D. citri was monitored biweekly for 2–3 yr on five different host plants (Rutaceae) at 11 residential sites across Riverside and Los Angeles Counties in southern California. Citrus flush growth patterns and parasitoid activity levels were also assessed. Urban D. citri populations were present year round at each site, with highest densities occurring over July through November. Temperature was an important indicator of overall D. citri densities with positive correlations across all life stages. Regularly flushing lime trees consistently supported the highest densities of psyllid eggs and nymphs, while equally vigorous flushing curry leaf plants supported the highest adult densities. While T. radiata activity was detected at all sites, average year-round percent parasitism was low throughout the study, averaging <5% in 2012, 2013, and 2014.

Phenology of Asian Citrus Psyllid (Hemiptera: Liviidae), With Special Reference to Biological Control by Tamarixia radiata , in the Residential Landscape of Southern California.

Novel, suitable and sustainable alternative control tactics that have the potential to reduce migration of Diaphorina citri into commercial citrus orchards are essential to improve management of huanglongbing (HLB). In this study, the effect of orange jasmine (Murraya paniculata) as a border trap crop on psyllid settlement and dispersal was assessed in citrus orchards. Furthermore, volatile emission profiles and relative attractiveness of both orange jasmine and sweet orange (Citrus × aurantium L., syn. Citrus sinensis (L.) Osbeck) nursery flushes to D. citri were investigated. In newly established citrus orchards, the trap crop reduced the capture of psyllids in yellow sticky traps and the number of psyllids that settled on citrus trees compared to fallow mowed grass fields by 40% and 83%, respectively. Psyllids were attracted and killed by thiamethoxam-treated orange jasmine suggesting that the trap crop could act as a ‘sink’ for D. citri. Additionally, the presence of the trap crop reduced HLB incidence by 43%. Olfactometer experiments showed that orange jasmine plays an attractive role on psyllid behavior and that this attractiveness may be associated with differences in the volatile profiles emitted by orange jasmine in comparison with sweet orange. Results indicated that insecticide-treated M. paniculata may act as a trap crop to attract and kill D. citri before they settled on the edges of citrus orchards, which significantly contributes to the reduction of HLB primary spread.

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Orange jasmine as a trap crop to control Diaphorina citri

Air pollution monitoring and tree and forest decline in East Asia: A review.

Problem statement: In order to establish the important host range of D. citri, the performance of this psyllid on different rutacous host plants was assessed. Apparent regional differences in host preferences of D. citri as noted above and the need for empirical knowledge of its host preferences in Malaysia where it is lacking. Approach: Experiments on host plant preference between citrus, jasmine orange and curry leaf were conducted over a period of 14 days in the field cage in October 1998 at the agricultural research centre, Semonggok, 15 km from Kuching, Kuching Division, Sarawak in Malaysia. Results: A comparative life cycle study of the Asian Citrus Psyllid Diaphorina citri Kuwayama on three different Rutaceous plant hosts namely citrus, jasmine orange and curry leaf plants was conducted inside the temperature controlled growth chamber maintain at 26 ± 1°C temperature, 75-80% relative humidity with artificial illumination intensity of 10,000 lux equipped with a photoperiod of 14:10 h light: dark regime to permit normal growth. Conclusion: The screenhouse studies confirmed that D. citri can colonise and breed on citrus, jasmine orange and curry leaf plant and that jasmine orange is the preferred host. It is also confirmed that females prefer to oviposit on immature flush 3-10 mm in length. In growth chamber experiments the life cycle of the psyllid was 18.5 days on jasmine orange, 19.0 days on citrus and 23.0 days on curry leaf.

Influence of host plant species and flush growth stage on the Asian citrus psyllid, Diaphorina citri Kuwayama.

Problem statement: Effective control of phytophagous pests requires a thorough understanding of their seasonal population dynamics, dispersion behavior, natural enemy activity and climate To date, although very little detail information had been published on the ecology of Diaphorina citri The objective of this investigation was to test through field experiment the hypothesis that the major factors influencing local D citri populations particularly their seasonal population dynamics in Sarawak are (a) flushing cycles, (b) climate and (c) the impact of the primary parasitoids namely Tamarixia radiata and Diaphorencyrtus aligarhensis Approach: Seasonal abundance D citri was studied weekly from March 1998 to December 2000 in the 1-ha citrus honey mandarin (Citrus aurantium L) commercial orchard at Jemukan (1° 33'N, 110° 41'E), Kota Samarahan Division, Southwest Sarawak, in Malaysia Results: Field studies on citrus trees showed that the D citri population fluctuates throughout the year on citrus honey mandarin in Sarawak Generations overlapped but adult and egg population peaks for a short period generally coincided with three annual flushing cycles, in August-September, February-March and June-July between March 1998 and December 2000 Conclusion: Psyllid population levels are positively related to the availability of new shoot flushes Psyllid populations are adversely affected by weather conditions and parasitoids Adult psyllid populations increased exponentially during periods of flush growth and migration and dispersal of the adults was also related to flushing cycles Dispersal and colonization of new trees is greatest in September-October, at the onset of the rainy season

Seasonal population dynamics of the Asian citrus psyllid, Diaphorina citri Kuwayama in Sarawak

Problem Statement: Forest structure assessment provides information on forest succession, dynamics, biodiversity and health which are important but only few information is available on rehabilitated forest. The objective of this study was to assess the forest structure of selected age stands at a rehabilitated forest situated in Universiti Putra Malaysia Bintulu Sarawak Campus, Sarawak, Malaysia. Approach: Four 20A20) m plots were established in stands planted in
1991, 1999, 2008 and an adjacent natural regenerating secondary forest (Â±22years) and all stands were measured for Diameter Breast Height (DBH) and height and identified. Results: Forest structural analysis showed better performance in the structural characteristics mainly the mean basal area (61%), mean Dbh (56%) and mean height (60%) of the trees as compared to the adjacent natural regenerating secondary forest. Conclusion: It can be concluded that after 18 years, rehabilitated forest using accelerating natural regeneration technique showed better structural dimension. This can help to promote the reforestation and restoration activities on degraded forest. Overall, rehabilitated forest areas have yet recovered in terms of size and height.

Forest Structure Assessment of a Rehabilitated Forest

Inappropriate drainage and agricultural development on tropical peatland may lead to an increase in methane (CH4) emission, thus expediting the rate of global warming and climate change. It was hypothesized that water table fluctuation affects CH4 emission in pineapple cultivation on tropical peat soils. The objectives of this study were to: (i) quantify CH4 emission from a tropical peat soil cultivated with pineapple and (ii) determine the effects of water table depth on CH4 emission from a peat soil under simulated water table fluctuation. Soil CH4 emissions from an open field pineapple cultivation system and field lysimeters were determined using the closed chamber method. High-density polyethylene field lysimeters were set up to simulate the natural condition of cultivated drained peat soils under different water table fluctuations. The soil CH4 flux was measured at five time intervals to obtain a 24 h CH4 emission in the dry and wet seasons during low- and high-water tables. Soil CH4 emissions from open field pineapple cultivation were significantly lower compared with field lysimeters under simulated water table fluctuation. Soil CH4 emissions throughout the dry and wet seasons irrespective of water table fluctuation were not affected by soil temperature but emissions were influenced by the balance between methanogenic and methanotrophic microorganisms controlling CH4 production and consumption, CH4 transportation through molecular diffusion via peat pore spaces, and non-microbial CH4 production in peat soils. Findings from the study suggest that water table fluctuation at the soil–water interface relatively controls the soil CH4 emission from lysimeters under simulated low- and high-water table fluctuation. The findings of this study provide an understanding of the effects of water table fluctuation on CH4 emission in a tropical peatland cultivated with pineapple.

Roland Kueh Jui Heng

Papers

Air pollution monitoring and tree and forest decline in East Asia: A review.

Influence of host plant species and flush growth stage on the Asian citrus psyllid, Diaphorina citri Kuwayama.

Seasonal population dynamics of the Asian citrus psyllid, Diaphorina citri Kuwayama in Sarawak

Forest Structure Assessment of a Rehabilitated Forest

Water Table Fluctuation and Methane Emission in Pineapples (Ananas comosus (L.) Merr.) Cultivated on a Tropical Peatland