A Monograph on Whiteflies

N.S. Butter, A.K. Dhawan

• Publisher: CRC Press
• Year: 2021
• ISBN:
  9781000469325
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Agronomy
• Index: Technology & Engineering

In all, 1550 species of whiteflies have been identified. The rapid spread of Bemisia tabaci has occurred throughout the globe and it is regarded as the most notorious species. It is a complex species known to contain many biotypes namely, New World (Biotype -A), B-biotype MEAM1 (Biotype-B or Bemisia argentifolii, and MED (Biotype-Q) depending upon the geographical location. The complete information on the bio-ecology of important species along with the feeding mechanism has been presented in this book. The use of modern techniques of identification has added more biotypes considering the variations in host range, species of endosymbionts, virus transmission efficiency, and resistance to pesticides. The resistance and resurgence due to pesticides has been discussed in the monograph. The information on economic thresholds for judicious use of pesticides or release of natural enemies against whiteflies has been quoted in this compilation The pest control methods, namely chemical, cultural measures, biocontrol agents, resistant varieties, and mechanical devices have been elaborated on. Based on the availability of information the integrated model has been suggested to contain the whitefly menace under different situations. Considering the key factors responsible for the outbreak of whiteflies, a sound system of IPM has been formulated. The book also contains the use of semiochemicals and biotechnological tools likely to gain momentum in the future.

CHAPTER 2

Bioecology and the Extent of Damage

The bioecology of whiteflies and the damage inflicted by them are almost similar for most species of whiteflies. The important species are greenhouse whitefly, Trialeurodes vaporariorum, tobacco whitefly, Bemisia tabaci, spirally whitefly, Aleurothrixus dispersus, citrus whitefly, Aleurothrixus floccosus and cabbage whitefly, Aleyrodes proletella. For the purpose of discussion, the most common and agriculturally important species have been taken for exploring various aspects.

2.1 Bioecology

The whiteflies are poikilothermic insect pests affecting field and greenhouse crops throughout the globe. The selection of the host plant is done taking into account the color of the substratum as these insects have a strong attraction to yellow color and a lesser attraction towards other colors (green > dark green > red > purple ones). There are of course some variations within different species but broadly, they follow the same pattern. To cite an instance, the Trialeurodes species and Bemisia tabaci have an attraction to blue ultraviolet rays (shorter wavelength) and yellow color rays (longer wavelength) of light. Similarly, Aleyrodes proletella has altogether different preferences based on odor (Trehan 1944). After landing, further changes in the insects’ behavior are apparent. The feeding is initiated and the penetration of stylet inside the plant is generally through stomatal openings. Initially, the stylets follow the intercellular path in non-vascular tissues like the cuticle/mesophyll/parenchyma. At this stage, the stylet is withdrawn in case the host is incompatible, otherwise it continues to withdraw and penetrate the plant. Once the stylet touches the phloem tissues, it follows the intercellular path and commences the feeding. The penetration of the stylet continues until the adult’s hunger is fully satisfied. The penetration time taken by stylet to reach the phloem is between 15–30 minutes. However, the stylet penetration continues to be generally intercellular once the entry into the phloem has taken place. After the feeding, the development of the pest is an important parameter to be looked into. Both Bemisia tabaci and Trialeurodes vaporariorum prefer young glabrous leaves for egg-laying (Mound 1984). The development of two whiteflies (Bemisia tabaci and Trialeurodes vaporariorum) was studied and the ideal temperature range determined was 30–33°C. With the increase in temperature, the increase in fecundity and decrease in generation period was recorded. This resulted in the production of more generations (Hilje and Morales 2008). The changes in the behavior of whitefly adults were conspicuous with respect to different host plants under various conditions. In this context, eggplant, cucumber, tomato, and pepper were selected as hosts to study the biology of whiteflies. Out of these four host plants; cucumber was the most preferred host plant for oviposition and feeding while pepper was the least preference for Bemisia tabaci (Sharma and Budha 2015). The influence of temperature on the biology of two important species was also examined. The biological parameters include adult longevity, fecundity and mortality of immatures. The females of both the species were more tolerant to high temperature (39°C). Bemisia tabaci was more tolerant to high temperature than Trialeurodes vaporariorum as the former was able to withstand high temperature of 41°C or beyond while the latter perished at this temperature (Cui et al. 2008). The fecundity of Trialeurodes vaporariorum declined with the increase in temperature with the result that it was nil at 43°C. Similarly, the development of the offspring towards adult formation of both the species declined as the temperature rose (Cui et al. 2008). The influence of temperature on immature stages is more pronounced and the immature development is completed in about 18 days at 21°C. The generation from egg to adult takes about 27days (CABI 2020). While analysing the development of these two species of whiteflies on different hosts, the short development period of these insects on brinjal (eggplant) versus the much longer period on sweet pepper were recorded. The generation is completed in much shorter time as the eggplant is much preferred host of this species (CABI 2020). It was further demonstrated that stylet of Bemisia tabaci while feeding on a lower surface of the leaf remained within the leaf, whereas it could reach up to the upper surface of the leaf in Trialeurodes vaporariorum (Pollard 1955). Due to the proximity to the phloem on the lower surface, the Bemisia tabaci concentrates on the lower side of the leaf. However, as the gap from the phloem to upper cuticle is more, the length of the stylet can manage to reach the phloem from the upper surface, thus the species of the whitefly, Trialeurodes vaporariorum concentrates on the upper surface of the leaf. However, both species avoid rain and thus tend to localize themselves on the lower leaf surface in such weather.

The response of both the species of whiteflies to low temperatures was evaluated to clarify the interspecific differentiation in adaptation. It was found that the cold-tolerant ability of all developmental stages of Trialeurodes vaporariorum was much higher than that of Bemisia tabaci (B-Biotype) on exposure to a temperature of 2°C for 1–12 days. When the species were kept at a cold temperature (5°C for 48 h), the survival of Trialeurodes vaporariorum was 78% (at −8°C for 10 h), that is, greater than that of the Bemisia tabaci B-biotype. It was further indicated that the optimal temperature required for the development of Trialeurodes vaporariorum was lower than that for the B-Biotype. On account of this, the development period from egg to adult stage of the B-biotype was demonstrated to be 1.5 times longer than that of the Trialeurodes vaporariorum (at 18° and 15°C, respectively). These findings further indicated the faster development of B-Biotype over Trialeurodes vaporariorum at a constant temperature of 24°C. It was found that the ability of the latter species of whitefly to tolerate lower temperature was also greater than B-Biotype in a detailed study that was carried out (Cui et al. 2010).

After emergence, the adults soon feed and mate within one to two days through arrhenotokous mode of reproduction in which the unmated females produce male progeny. After 1 to 2 days (of the pre-oviposition period), eggs are laid one by one on the underside of the leaf in summer. The developmental rates vary, depending upon the temperature (Butler and Henneberry 1986) and host plants (Coudriet et al. 1985). In a study by Gameel (1978), the hatching of eggs took 21 and 5 days at 15°C and 40°C, respectively. The total time of development from egg to adult at 27°C was 16 days when the insect was attached to a sweet potato and 38 days on carrots (Coudriet et al. 1985). Depending upon the temperature, the longevity was between 2 to 34 days for males and 8 to 60 days for females (Butler and Henneberry 1986). The population build-up and development of Trialeurodes was lower than that of Bemisia tabaci (B-biotype) at 2°C for 1–12 days/5°C for 48 h. The survival of the former was greater (78%) at 8°C for 10 h than B-biotype. The species Bemisia tabaci possessed wider adaptability than the other species.

2.1.1 Bemisia tabaci

The genus Bemisia contains thirty-seven species and is thought to have originated from Asia (Mound and Halsey 1978). Bemisia tabaci, being possibly of Indian origin (Fishpool and Burban 1994), was described by numerous...